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  • 1. Aviation Maintenance Technician Handbook—Airframe Volume 1 2012 U.S. Department of Transportation FEDERAL AVIATION ADMINISTRATION Flight Standards Service
  • 2. ii
  • 3. Volume ContentsVolume 1 Volume 2Preface.....................................................................v Chapter 10 Aircraft Instrument ............................................10-1Acknowledgments. ...............................................vii . Chapter 11Table of Contents.................................................xiii Communication and Navigation.......................11-1 .Chapter 1 Chapter 12Aircraft Structures. ..............................................1-1 . Hydraulic and Pneumatic .................................12-1Chapter 2 Chapter 13Aerodynamics, Aircraft Assembly, and Aircraft Landing . ...............................................13-1Rigging..................................................................2-1 Chapter 14Chapter 3 Aircraft Fuel System..........................................14-1Aircraft Fabric Covering......................................3-1 Chapter 15Chapter 4 Ice and Rain Protection.....................................15-1Aircraft Metal Structural Repair..........................4-1 Chapter 16Chapter 5 Cabin Environmental ........................................16-1Aircraft Welding. ..................................................5-1 . Chapter 17Chapter 6 Fire Protection Systems....................................17-1Aircraft Wood . .....................................................6-1 Glossary...............................................................G-1Chapter 7Advanced Composite Materials..........................7-1 Index.......................................................................I-1Chapter 8Aircraft Painting and Finishing...........................8-1Chapter 9Aircraft Electrical System....................................9-1Glossary...............................................................G-1Index.......................................................................I-1 iii
  • 4. iv
  • 5. PrefaceThe Aviation Maintenance Technician Handbook—Airframe (FAA-H-8083-31) is one of a series of three handbooks forpersons preparing for certification as an airframe or powerplant mechanic. It is intended that this handbook provide thebasic information on principles, fundamentals, and technical procedures in the subject matter areas relating to the airframerating. It is designed to aid students enrolled in a formal course of instruction, as well as the individual who is studying onhis or her own. Since the knowledge requirements for the airframe and powerplant ratings closely parallel each other insome subject areas, the chapters which discuss fire protection systems and electrical systems contain some material whichis also duplicated in the Aviation Maintenance Technician Handbook—Powerplant (FAA-H-8083-32).This volume contains information on airframe construction features, assembly and rigging, fabric covering, structural repairs,and aircraft welding. The handbook also contains an explanation of the units that make up the various airframe systems.Because there are so many different types of aircraft in use today, it is reasonable to expect that differences exist in airframecomponents and systems. To avoid undue repetition, the practice of using representative systems and units is carried outthroughout the handbook. Subject matter treatment is from a generalized point of view and should be supplemented byreference to manufacturers manuals or other textbooks if more detail is desired. This handbook is not intended to replace,substitute for, or supersede official regulations or the manufacturer’s instructions. Occasionally the word “must” or similarlanguage is used where the desired action is deemed critical. The use of such language is not intended to add to, interpret,or relieve a duty imposed by Title 14 of the Code of Federal Regulations (14 CFR).This handbook is available for download, in PDF format, from www.faa.gov.The subject of Human Factors is contained in the Aviation Maintenance Technician Handbook—General (FAA-H-8083-30).This handbook is published by the United States Department of Transportation, Federal Aviation Administration, AirmanTesting Standards Branch, AFS-630, P.O. Box 25082, Oklahoma City, OK 73125.Comments regarding this publication should be sent, in email form, to the following address:AFS630comments@faa.gov v
  • 6. vi
  • 7. AcknowledgmentsThe Aviation Maintenance Technician Handbook—Airframe (FAA-H-8083-31) was produced by the Federal AviationAdministration (FAA) with the assistance of Safety Research Corporation of America (SRCA). The FAA wishes toacknowledge the following contributors: Mr. Chris Brady (www.b737.org.uk) for images used throughout this handbook Captain Karl Eiríksson for image used in Chapter 1 Cessna Aircraft Company for image used in Chapter 1 Mr. Andy Dawson (www.mossie.org) for images used throughout Chapter 1 Mr. Bill Shemley for image used in Chapter 1 Mr. Bruce R. Swanson for image used in Chapter 1 Mr. Burkhard Domke (www.b-domke.de) for images used throughout Chapter 1 and 2 Mr. Chris Wonnacott (www.fromtheflightdeck.com) for image used in Chapter 1 Mr. Christian Tremblay (www.zodiac640.com) for image used in Chapter 1 Mr. John Bailey (www.knots2u.com) for image used in Chapter 1 Mr. Rich Guerra (www.rguerra.com) for image used in Chapter 1 Mr. Ronald Lane for image used in Chapter 1 Mr. Tom Allensworth (www.avsim.com) for image used in Chapter 1 Navion Pilots Association’s Tech Note 001 (www.navionpilots.org) for image used in Chapter 1 U.S. Coast Guard for image used in Chapter 1 Mr. Tony Bingelis and the Experimental Aircraft Association (EAA) for images used throughout Chapter 2 Mr. Benoit Viellefon (www.johnjohn.co.uk/compare-tigermothflights/html/tigermoth_bio_aozh.html) for image used in Chapter 3 Mr. Paul Harding of Safari Seaplanes–Bahamas (www.safariseaplanes.com) for image used in Chapter 3 Polyfiber/Consolidated Aircraft Coatings for images used throughout Chapter 3 Stewart Systems for images used throughout Chapter 3 Superflite for images used throughout Chapter 3 Cherry Aerospace (www.cherryaerospace.com) for images used in Chapters 4 and 7 Raytheon Aircraft (Structural Inspection and Repair Manual) for information used in Chapter 4 Mr. Scott Allen of Kalamazoo Industries, Inc. (www.kalamazooind.com) for image used in Chapter 4 Miller Electric Mfg. Co. (www.millerwelds.com) for images used in Chapter 5 Mr. Aaron Novak, contributing engineer, for charts used in Chapter 5 Mr. Bob Hall (www.pro-fusiononline.com) for image used in Chapter 5 vii
  • 8. Mr. Kent White of TM Technologies, Inc. for image used in Chapter 5 Safety Supplies Canada (www.safetysuppliescanada.com) for image used in Chapter 5 Smith Equipment (www.smithequipment.com) for images used in Chapter 5 Alcoa (www.alcoa.com) for images used in Chapter 7 Mr. Chuck Scott (www.itwif.com) for images used throughout Chapter 8 Mr. John Lagerlof of Paasche Airbrush Co. (paascheairbrush.com) for image used in Chapter 8 Mr. Philip Love of Turbine Products, LLC (www.turbineproducts.com) for image used in Chapter 8 Consolidated Aircraft Coatings for image used in Chapter 8 Tianjin Yonglida Material Testing Machine Co., Ltd for image used in Chapter 8 Mr. Jim Irwin of Aircraft Spruce & Specialty Co. (www.aircraftspruce.com) for images used in Chapters 9, 10, 11, 13, 14, 15 Mr. Kevan Hashemi for image used in Chapter 9 Mr. Michael Leasure, Aviation Multimedia Library (www2.tech.purdue.edu/at/courses/aeml) for images used in Chapters 9, 13, 14 Cobra Systems Inc. (www.cobrasys.com) for image used in Chapter 10 www.free-online-private-pilot-ground-school.com for image used in Chapters 10, 16 DAC International (www.dacint.com) for image used in Chapter 10 Dawson Aircraft Inc. (www.aircraftpartsandsalvage.com) for images used throughout Chapter 10 Mr. Kent Clingaman for image used in Chapter 10 TGH Aviation-FAA Instrument Repair Station (www.tghaviation.com) for image used in Chapter 10 The Vintage Aviator Ltd. (www.thevintageaviator.co.nz) for image used in Chapter 10 ACK Technologies Inc. (www.ackavionics.com) for image used in Chapter 11 ADS-B Technologies, LLC (www.ads-b.com) for images used in Chapter 11 Aviation Glossary (www.aviationglossary.com) for image used in Chapter 11 AT&T Archives and History Center for image used in Chapter 11 Electronics International Inc. (www.buy-ei.com) for image used in Chapter 11 Excelitas Technologies (www.excelitas.com) for image used in Chapter 11 Freestate Electronics, Inc. (www.fse-inc.com) for image used in Chapter 11 AirTrafficAtlanta.com for image used in Chapter 11 Western Historic Radio Museum, Virginia City, Nevada (www.radioblvd.com) for image used in Chapter 11 Avidyne Corporation (www.avidyne.com) for image used in Chapter 11 Kintronic Laboratories (www.kintronic.com) for image used in Chapter 11 Mr. Dan Wolfe (www.flyboysalvage.com) for image used in Chapter 11 Mr. Ken Shuck (www.cessna150.net) for image used in Chapter 11 Mr. Paul Tocknell (www.askacfi.com) for image used in Chapter 11 Mr. Stephen McGreevy (www.auroralchorus.com) for image used in Chapter 11 Mr. Todd Bennett (www.bennettavionics.com) for image used in Chapter 11 National Oceanic and Atmospheric Administration, U.S. Department of Commerce for image used in Chapter 11 RAMI (www.rami.com) for image used in Chapter 11 Rockwell Collins (www.rockwellcollins.com) for image used in Chapter 11viii
  • 9. Sarasota Avionics International (www.sarasotaavionics.com) for images used in Chapter 11 Southeast Aerospace, Inc. (www.seaerospace.com) for image used in Chapter 11 Sporty’s Pilot Shop (www.sportys.com) for image used in Chapter 11 Watts Antenna Company (www.wattsantenna.com) for image used in Chapter 11 Wings and Wheels (www.wingsandwheels.com) for image used in Chapter 11 Aeropin, Inc. (www.aeropin.com) for image used in Chapter 13 Airplane Mart Publishing (www.airplanemart.com) for image used in Chapter 13 Alberth Aviation (www.alberthaviation.com) for image used in Chapter 13 AVweb (www.avweb.com) for image used in Chapter 13 Belle Aire Aviation, Inc. (www.belleaireaviation.com) for image used in Chapter 13 Cold War Air Museum (www.coldwarairmuseum.org) for image used in Chapter 13 Comanche Gear (www.comanchegear.com) for image used in Chapter 13 CSOBeech (www.csobeech.com) for image used in Chapter 13 Desser Tire & Rubber Co., Inc. (www.desser.com) for image used in Chapter 13 DG Flugzeugbau GmbH (www.dg-flugzeugbau.de) for image used in Chapter 13 Expedition Exchange Inc. (www.expeditionexchange.com) for image used in Chapter 13 Fiddlers Green (www.fiddlersgreen.net) for image used in Chapter 13 Hitchcock Aviation (hitchcockaviation.com) for image used in Chapter 13 KUNZ GmbH aircraft equipment (www.kunz-aircraft.com) for images used in Chapter 13 Little Flyers (www.littleflyers.com) for images used in Chapter 13 Maple Leaf Aviation Ltd. (www.aircraftspeedmods.ca) for image used in Chapter 13 Mr. Budd Davisson (Airbum.com) for image used in Chapter 13 Mr. C. Jeff Dyrek (www.yellowairplane.com) for images used in Chapter 13 Mr. Jason Schappert (www.m0a.com) for image used in Chapter 13 Mr. John Baker (www.hangar9aeroworks.com) for image used in Chapter 13 Mr. Mike Schantz (www.trailer411.com) for image used in Chapter 13 Mr. Robert Hughes (www.escapadebuild.co.uk) for image used in Chapter 13 Mr. Ron Blachut for image used in Chapter 13 Owls Head Transportation Museum (www.owlshead.org) for image used in Chapter 13 PPI Aerospace (www.ppiaerospace.com) for image used in Chapter 13 Protective Packaging Corp. (www.protectivepackaging.net, 1-800-945-2247) for image used in Chapter 13 Ravenware Industries, LLC (www.ravenware.com) for image used in Chapter 13 Renold (www.renold.com) for image used in Chapter 13 Rotor F/X, LLC (www.rotorfx.com) for image used in Chapter 13 SkyGeek (www.skygeek.com) for image used in Chapter 13 Taigh Ramey (www.twinbeech.com) for image used in Chapter 13 Texas Air Salvage (www.texasairsalvage.com) for image used in Chapter 13 The Bogert Group (www.bogert-av.com) for image used in Chapter 13 W. B. Graham, Welded Tube Pros LLC (www.thefabricator.com) for image used in Chapter 13 ix
  • 10. Zinko Hydraulic Jack (www.zinkojack.com) for image used in Chapter 13 Aviation Institute of Maintenance (www.aimschool.com) for image used in Chapter 14 Aviation Laboratories (www.avlab.com) for image used in Chapter 14 AVSIM (www.avsim.com) for image used in Chapter 14 Eggenfellner (www.eggenfellneraircraft.com) for image used in Chapter 14 FlightSim.Com, Inc. (www.flightsim.com) for image used in Chapter 14 Fluid Components International LLC (www.fluidcomponents.com) for image used in Chapter 14 Fuel Quality Services, Inc. (www.fqsinc.com) for image used in Chapter 14 Hammonds Fuel Additives, Inc. (www.biobor.com) for image used in Chapter 14 Jeppesen (www.jeppesen.com) for image used in Chapter 14 MGL Avionics (www.mglavionics.com) for image used in Chapter 14 Mid-Atlantic Air Museum (www.maam.org) for image used in Chapter 14 MISCO Refractometer (www.misco.com) for image used in Chapter 14 Mr. Gary Brossett via the Aircraft Engine Historical Society (www.enginehistory.org) for image used in Chapter 14 Mr. Jeff McCombs (www.heyeng.com) for image used in Chapter 14 NASA for image used in Chapter 14 On-Track Aviation Limited (www.ontrackaviation.com) for image used in Chapter 14 Stewart Systems for image used in Chapter 14 Prist Aerospace Products (www.pristaerospace.com) for image used in Chapter 14 The Sundowners, Inc. (www.sdpleecounty.org) for image used in Chapter 14 Velcon Filters, LLC (www.velcon.com) for image used in Chapter 14 Aerox Aviation Oxygen Systems, Inc. (www.aerox.com) for image used in Chapter 16 Biggles Software (www.biggles-software.com) for image used in Chapter 16 C&D Associates, Inc. (www.aircraftheater.com) for image used in Chapter 16 Cobham (Carleton Technologies Inc.) (www.cobham.com) for image used in Chapter 16 Cool Africa (www.coolafrica.co.za) for image used in Chapter 16 Cumulus Soaring, Inc. (www.cumulus-soaring.com) for image used in Chapter 16 Essex Cryogenics of Missouri, Inc. (www.essexind.com) for image used in Chapter 16 Flightline AC, Inc. (www.flightlineac.com) for image used in Chapter 16 IDQ Holdings (www.idqusa.com) for image used in Chapter 16 Manchester Tank & Equipment (www.mantank.com) for image used in Chapter 16 Mountain High E&S Co. (www.MHoxygen.com) for images used throughout Chapter 16 Mr. Bill Sherwood (www.billzilla.org) for image used in Chapter 16 Mr. Boris Comazzi (www.flightgear.ch) for image used in Chapter 16 Mr. Chris Rudge (www.warbirdsite.com) for image used in Chapter 16 Mr. Richard Pfiffner (www.craggyaero.com) for image used in Chapter 16 Mr. Stephen Sweet (www.stephensweet.com) for image used in Chapter 16 Precise Flight, Inc. (www.preciseflight.com) for image used in Chapter 16 SPX Service Solutions (www.spx.com) for image used in Chapter 16x
  • 11. SuperFlash Compressed Gas Equipment (www.oxyfuelsafety.com) Mr. Tim Mara (www.wingsandwheels.com) for images used in Chapter 16 Mr. Bill Abbott for image used in Chapter 17Additional appreciation is extended to Dr. Ronald Sterkenburg, Purdue University; Mr. Bryan Rahm, Dr. Thomas K. Eismain,Purdue University; Mr. George McNeill, Mr. Thomas Forenz, Mr. Peng Wang, and the National Oceanic and AtmosphericAdministration (NOAA) for their technical support and input. xi
  • 12. xii
  • 13. Table of ContentsVolume Contents....................................................iii Tail Wheel Gear Configuration.................................1-37 Tricycle Gear.............................................................1-38Preface.....................................................................v Maintaining the Aircraft...............................................1-38 Location Numbering Systems...................................1-39Acknowledgments. ...............................................vii . Access and Inspection Panels. ..................................1-40 . Helicopter Structures....................................................1-40Table of Contents.................................................xiii Airframe....................................................................1-40 Fuselage. ...................................................................1-42 .Chapter 1 Landing Gear or Skids..............................................1-42 .Aircraft Structures. ..............................................1-1 . Powerplant and Transmission...................................1-42A Brief History of Aircraft Structures............................1-1 Turbine Engines.....................................................1-42General............................................................................1-5 Transmission..........................................................1-43Major Structural Stresses................................................1-6 Main Rotor System...................................................1-43 .Fixed-Wing Aircraft.......................................................1-8 . Rigid Rotor System...............................................1-44 . Fuselage. .....................................................................1-8 . Semirigid Rotor System. .......................................1-44 . Truss Type...............................................................1-8 Fully Articulated Rotor System................................1-44 . Monocoque Type.....................................................1-9 Antitorque System.....................................................1-45 Semimonocoque Type.............................................1-9 Controls.....................................................................1-46 Pressurization ...........................................................1-10Wings............................................................................1-10 Chapter 2 Wing Configurations.................................................1-10 Aerodynamics, Aircraft Assembly, and Wing Structure..........................................................1-11 Rigging..................................................................2-1 Wing Spars................................................................1-13 Introduction.....................................................................2-1 Wing Ribs. ................................................................1-15 . Basic Aerodynamics ......................................................2-2 Wing Skin. ................................................................1-17 . The Atmosphere..............................................................2-2 Nacelles.....................................................................1-19 Pressure.......................................................................2-2Empennage ..................................................................1-22 Density........................................................................2-3Flight Control Surfaces.................................................1-24 Humidity.....................................................................2-3 . Primary Flight Control Surfaces...............................1-24 Aerodynamics and the Laws of Physics.........................2-3 Ailerons.................................................................1-26 . Velocity and Acceleration...........................................2-3 Elevator..................................................................1-27 Newton’s Laws of Motion..........................................2-4 . Rudder ..................................................................1-27 Bernoulli’s Principle and Subsonic Flow....................2-4 Dual Purpose Flight Control Surfaces. .....................1-27 . Airfoil.............................................................................2-5 . Secondary or Auxiliary Control Surfaces ................1-28 Shape of the Airfoil.....................................................2-5 Flaps. .....................................................................1-28 . Angle of Incidence......................................................2-6 Slats ......................................................................1-30 Angle of Attack (AOA)...............................................2-6 Spoilers and Speed Brakes....................................1-30 . Boundary Layer...........................................................2-7 Thrust and Drag..............................................................2-7 Tabs ......................................................................1-31 Center of Gravity (CG)...................................................2-9 Other Wing Features.................................................1-34 The Axes of an Aircraft .................................................2-9Landing Gear................................................................1-35 xiii
  • 14. Stability and Control ......................................................2-9 Offset Flapping Hinge...............................................2-32 Static Stability.............................................................2-9 Stability Augmentation Systems (SAS)....................2-32 Dynamic Stability. ....................................................2-11 . Helicopter Vibration. ................................................2-32 . Longitudinal Stability. ..............................................2-11 . Extreme Low Frequency Vibration.......................2-32 Directional Stability..................................................2-11 Low Frequency Vibration......................................2-32 Lateral Stability.........................................................2-11 Medium Frequency Vibration...............................2-32 . Dutch Roll.................................................................2-11 High Frequency Vibration.....................................2-32Primary Flight Controls................................................2-12 Rotor Blade Tracking................................................2-32Trim Controls................................................................2-12 Flag and Pole.........................................................2-32Auxiliary Lift Devices..................................................2-13 Electronic Blade Tracker.......................................2-33 Winglets....................................................................2-14 Tail Rotor Tracking...................................................2-34 Canard Wings............................................................2-14 Marking Method....................................................2-34 Wing Fences .............................................................2-14 Electronic Method.................................................2-34Control Systems for Large Aircraft..............................2-14 Rotor Blade Preservation and Storage......................2-35 Mechanical Control...................................................2-14 Helicopter Power Systems............................................2-35 Hydromechanical Control.........................................2-15 Powerplant. ...............................................................2-35 . Fly-By-Wire Control ................................................2-15 Reciprocating Engine................................................2-35High-Speed Aerodynamics...........................................2-15 Turbine Engine..........................................................2-36Rotary-Wing Aircraft Assembly and Rigging..............2-16 Transmission System....................................................2-36Configurations of Rotary-Wing Aircraft. .....................2-18 . Main Rotor Transmission..........................................2-36 Autogyro...................................................................2-18 . Clutch........................................................................2-37 Single Rotor Helicopter. ...........................................2-18 . Centrifugal Clutch.................................................2-37 Dual Rotor Helicopter...............................................2-18Types of Rotor Systems................................................2-18 Belt Drive Clutch...................................................2-37 Fully Articulated Rotor.............................................2-18 Freewheeling Unit.....................................................2-38 Semirigid Rotor.........................................................2-19 Airplane Assembly and Rigging...............................2-38 Rigid Rotor................................................................2-19 Rebalancing of Control Surfaces..............................2-38 .Forces Acting on the Helicopter...................................2-19 Static Balance........................................................2-38 Torque Compensation...............................................2-19 Dynamic Balance...................................................2-38 Gyroscopic Forces.....................................................2-20 Rebalancing Procedures ...........................................2-39Helicopter Flight Conditions .......................................2-22 Rebalancing Methods................................................2-40 Hovering Flight.........................................................2-22 Aircraft Rigging............................................................2-41 Translating Tendency or Drift...............................2-22 Rigging Specifications..............................................2-41 . Ground Effect........................................................2-23 Type Certificate Data Sheet...................................2-41 Coriolis Effect (Law of Conservation of Maintenance Manual.............................................2-41 Angular Momentum) ............................................2-23 Structural Repair Manual (SRM)..........................2-41 . Vertical Flight...........................................................2-24 Manufacturer’s Service Information.....................2-41 . Forward Flight...........................................................2-24 Airplane Assembly ...................................................2-41 Translational Lift...................................................2-24 Aileron Installation ...............................................2-41 Effective Translational Lift (ETL)........................2-25 . Flap Installation.....................................................2-41 Dissymmetry of Lift..............................................2-26 Empennage Installation.........................................2-41 Autorotation..............................................................2-28 Control Operating Systems.......................................2-41Rotorcraft Controls.......................................................2-29 Cable Systems. ......................................................2-41 . Swash Plate Assembly..............................................2-29 Cable Inspection....................................................2-44 Collective Pitch Control............................................2-29 Cable System Installation......................................2-44 Throttle Control.........................................................2-30 Push Rods (Control Rods).....................................2-47 Governor/Correlator .................................................2-30 Torque Tubes.........................................................2-48 Cyclic Pitch Control..................................................2-30 Cable Drums..........................................................2-48 Antitorque Pedals......................................................2-31 Rigging Checks.........................................................2-48Stabilizer Systems.........................................................2-31 Structural Alignment.............................................2-48 Bell Stabilizer Bar System........................................2-31xiv
  • 15. Cable Tension........................................................2-52 Fabric Cement. ........................................................3-7 . Control Surface Travel..........................................2-53 Fabric Sealer............................................................3-8 Checking and Safetying the System......................2-55 Fillers.......................................................................3-8 Biplane Assembly and Rigging.................................2-58 Topcoats. .................................................................3-8 .Aircraft Inspection........................................................2-60 Available Covering Processes........................................3-8 . Purpose of Inspection Programs . .............................2-60 Determining Fabric Condition—Repair or Recover?.....3-9 Perform an Airframe Conformity and Fabric Strength................................................................3-9 Airworthiness Inspection..........................................2-61 . How Fabric Breaking Strength is Determined..........3-10 Required Inspections.................................................2-61 Fabric Testing Devices..............................................3-11 Preflight.................................................................2-61 . General Fabric Covering Process.................................3-11 . Periodic Maintenance Inspections:........................2-61 Blanket Method vs. Envelope Method .....................3-12 Altimeter and Static System Inspections...............2-63 Preparation for Fabric Covering Work.....................3-12 . Air Traffic Control (ATC) Transponder Removal of Old Fabric Coverings............................3-13 Inspections.............................................................2-63 Preparation of the Airframe Before Covering...........3-14 Emergency Locator Transmitter (ELT) Attaching Polyester Fabric to the Airframe..............3-15 Seams.....................................................................3-16 Operational and Maintenance Practices Fabric Cement. ......................................................3-16 . in Accordance With Advisory Circular (AC) Fabric Heat Shrinking............................................3-17 91-44 .....................................................................2-64 Attaching Fabric to the Wing Ribs........................3-18 Annual and 100-Hour Inspections............................2-64 . Preparation.............................................................2-64 Rib Lacing.............................................................3-18 Other Aircraft Inspection and Maintenance Rings, Grommets, and Gussets . ...........................3-21 Programs...................................................................2-66 . Finishing Tapes. ....................................................3-21 . Continuous Airworthiness Maintenance Coating the Fabric.................................................3-22 . Program (CAMP)..................................................2-68 . Polyester Fabric Repairs ..............................................3-23 Title 14 CFR part 125, section 125.247, Applicable Instructions.............................................3-23 Inspection Programs and Maintenance..................2-68 Repair Considerations...............................................3-23 Cotton-Covered Aircraft...............................................3-23 Helicopter Inspections, Piston-Engine and Fiberglass Coverings....................................................3-24 . Turbine-Powered...................................................2-69 Light-Sport Aircraft, Powered Parachute, and Chapter 4 Weight-Shift Control Aircraft ..............................2-69 Aircraft Metal Structural Repair..........................4-1 Aircraft Metal Structural Repair.....................................4-1Chapter 3 Stresses in Structural Members...................................4-2Aircraft Fabric Covering......................................3-1 Tension....................................................................4-2General History...............................................................3-1 Compression............................................................4-3Fabric Terms...................................................................3-3 Shear........................................................................4-3Legal Aspects of Fabric Covering..................................3-3 Bearing. ...................................................................4-3 .Approved Materials .......................................................3-4 Torsion . ..................................................................4-3 Fabric . ........................................................................3-4 Other Fabric Covering Materials................................3-5 . Bending . .................................................................4-4 Anti-Chafe Tape......................................................3-5 Tools for Sheet Metal Construction and Repair.............4-4 Reinforcing Tape.....................................................3-5 Layout Tools...............................................................4-4 Scales.......................................................................4-4 Rib Bracing..............................................................3-5 Combination Square................................................4-4 Surface Tape............................................................3-5 Dividers...................................................................4-4 . Rib Lacing Cord......................................................3-5 Rivet Spacers...........................................................4-4 Sewing Thread.........................................................3-6 Marking Tools.............................................................4-4 Special Fabric Fasteners..........................................3-6 Pens..........................................................................4-4 Grommets................................................................3-6 Scribes.....................................................................4-5 . Inspection Rings......................................................3-6 Punches.......................................................................4-5 . Primer......................................................................3-7 Prick Punch..............................................................4-6 xv
  • 16. Center Punch. ..........................................................4-6 . Reamers.....................................................................4-19 Automatic Center Punch..........................................4-6 Drill Stops.................................................................4-19 Transfer Punch.........................................................4-6 Drill Bushings and Guides........................................4-19 Drive Punch.............................................................4-6 Drill Bushing Holder Types......................................4-19 Pin Punch.................................................................4-7 Hole Drilling Techniques..........................................4-20 Drilling Large Holes..............................................4-20 Chassis Punch..........................................................4-7 Chip Chasers.............................................................4-20 Awl..........................................................................4-7 Forming Tools..............................................................4-21 . Hole Duplicator...........................................................4-8 Bar Folding Machine. ...............................................4-21 . Cutting Tools...............................................................4-8 Cornice Brake. ..........................................................4-22 . Circular-Cutting Saws.............................................4-8 Box and Pan Brake (Finger Brake)...........................4-22 Kett Saw .................................................................4-8 Press Brake................................................................4-22 Pneumatic Circular Cutting Saw.............................4-8 Slip Roll Former........................................................4-23 Reciprocating Saw...................................................4-9 Rotary Machine.........................................................4-24 Cut-off Wheel..........................................................4-9 Stretch Forming.........................................................4-24 Nibblers...................................................................4-9 . Drop Hammer. ..........................................................4-24 . Shop Tools..................................................................4-9 . Hydropress Forming. ................................................4-24 . Squaring Shear.........................................................4-9 Spin Forming.............................................................4-25 Throatless Shear ...................................................4-10 Forming With an English Wheel. .............................4-26 . Scroll Shears..........................................................4-10 Piccolo Former..........................................................4-26 Rotary Punch Press................................................4-10 Shrinking and Stretching Tools.................................4-26 Band Saw...............................................................4-11 Shrinking Tools.....................................................4-26 Disk Sander. ..........................................................4-11 . Stretching Tools.....................................................4-27 Belt Sander............................................................4-11 . Manual Foot-Operated Sheet Metal Shrinker........4-27 Notcher..................................................................4-12 Hand-Operated Shrinker and Stretcher. ................4-27. Grinding Wheels....................................................4-13 Hardwood Form Blocks. .......................................4-27 . Hand Cutting Tools...................................................4-13 V-Blocks................................................................4-27 Straight Snips.........................................................4-13 Shrinking Blocks...................................................4-28 Aviation Snips.......................................................4-13 Sandbags................................................................4-28 Files.......................................................................4-13 . Sheet Metal Hammers and Mallets........................4-28 Die Grinder............................................................4-14 Sheet Metal Holding Devices.......................................4-28 Burring Tool..........................................................4-14 Clamps and Vises .....................................................4-28Hole Drilling.................................................................4-14 C-Clamps...............................................................4-28 Portable Power Drills................................................4-15 Vises......................................................................4-29 Pneumatic Drill Motors.........................................4-15 Reusable Sheet Metal Fasteners................................4-29 Right Angle and 45° Drill Motors.........................4-15 Cleco Fasteners......................................................4-29 Two Hole ..............................................................4-15 Hex Nut and Wing Nut Temporary Sheet Drill Press..................................................................4-15 Fasteners................................................................4-30 Drill Extensions and Adapters .................................4-16 Aluminum Alloys.........................................................4-30 Extension Drill Bits...............................................4-16 Structural Fasteners . ....................................................4-31 Straight Extension. ................................................4-16 . Solid Shank Rivet . ...................................................4-31 Angle Adapters .....................................................4-16 Description. ...........................................................4-31 . Snake Attachment..................................................4-16 Installation of Rivets..............................................4-32 Types of Drill Bits . ..................................................4-17 Rivet Installation Tools.........................................4-36 . Step Drill Bits........................................................4-17 Riveting Procedure ...............................................4-40 Cobalt Alloy Drill Bits..........................................4-17 . Countersunk Rivets. ..............................................4-41 . Twist Drill Bits......................................................4-17 Evaluating the Rivet..............................................4-44 Drill Bit Sizes............................................................4-18 Removal of Rivets.................................................4-45 Drill Lubrication. ......................................................4-18 . Replacing Rivets....................................................4-46xvi
  • 17. National Advisory Committee for Aeronautics Description of Titanium. .......................................4-85 . (NACA) Method of Double Flush Riveting..........4-46 Basic Principles of Sheet Metal Repair........................4-86 Special Purpose Fasteners.........................................4-47 Maintaining Original Strength..................................4-87 Blind Rivets...........................................................4-47 Shear Strength and Bearing Strength........................4-88 Pin Fastening Systems (High-Shear Fasteners) . ..4-50 Maintaining Original Contour...................................4-89 Lockbolt Fastening Systems .................................4-52 Keeping Weight to a Minimum. ...............................4-89 . Blind Bolts.............................................................4-54 Flutter and Vibration Precautions.............................4-89 Rivet Nut. ..............................................................4-56 . Inspection of Damage ..............................................4-90 Blind Fasteners (Nonstructural). ...........................4-57 . Types of Damage and Defects..................................4-90Forming Process...........................................................4-57 Classification of Damage..........................................4-91Forming Operations and Terms....................................4-58 Negligible Damage................................................4-91 Stretching..................................................................4-58 Damage Repairable by Patching. ..........................4-91 . Shrinking...................................................................4-58 Damage Repairable by Insertion...........................4-92 Bumping....................................................................4-59 Damage Necessitating Replacement of Parts........4-92 Crimping...................................................................4-59 . Repairability of Sheet Metal Structure.........................4-92 Folding Sheet Metal..................................................4-59 Structural Support During Repair.............................4-92Layout and Forming.....................................................4-59 . Assessment of Damage.............................................4-92 Terminology .............................................................4-59 Inspection of Riveted Joints......................................4-92 Layout or Flat Pattern Development.........................4-60 Inspection for Corrosion...........................................4-93 . Making Straight Line Bends.....................................4-61 Damage Removal......................................................4-93 Bending a U-Channel............................................4-62 Repair Material Selection......................................4-93 Using a J-Chart To Calculate Total Developed Repair Parts Layout ..............................................4-93 Width.....................................................................4-67 Rivet Selection . ....................................................4-94 How To Find the Total Developed Width Using Rivet Spacing and Edge Distance..........................4-94 a J-Chart.................................................................4-67 Corrosion Treatment . ...........................................4-94 Using a Sheet Metal Brake to Fold Metal.................4-68 Approval of Repair....................................................4-94 Step 1: Adjustment of Bend Radius......................4-68 . Repair of Stressed Skin Structure ............................4-95 Step 2: Adjusting Clamping Pressure....................4-70 Patches ..................................................................4-95 Step 3: Adjusting the Nose Gap............................4-71 . Typical Repairs for Aircraft Structures ....................4-97 Folding a Box............................................................4-71 Floats.....................................................................4-97 . Relief Hole Location.............................................4-73 . Corrugated Skin Repair.........................................4-97 Layout Method......................................................4-73 . Replacement of a Panel.........................................4-97 Open and Closed Bends............................................4-74 Outside the Member .............................................4-97 Open End Bend (Less Than 90°)...........................4-74 Inside the Member.................................................4-97 Closed End Bend (More Than 90°).......................4-74 Edges of the Panel ................................................4-97 Hand Forming...........................................................4-74 Repair of Lightening Holes.................................4-100 Straight Line Bends...............................................4-75 Repairs to a Pressurized Area..............................4-100 Formed or Extruded Angles..................................4-75 . Stringer Repair.....................................................4-100 Flanged Angles......................................................4-76 Former or Bulkhead Repair.................................4-102 Shrinking...............................................................4-76 . Longeron Repair..................................................4-103 Stretching...............................................................4-77 Spar Repair..........................................................4-103 Curved Flanged Parts. ...........................................4-77 . Rib and Web Repair............................................4-104 . Forming by Bumping. ...........................................4-80 . Leading Edge Repair...........................................4-105 Joggling.................................................................4-81 . Trailing Edge Repair...........................................4-105 . Lightening Holes...................................................4-82 Specialized Repairs. ............................................4-108 . Working Stainless Steel............................................4-83 Inspection Openings............................................4-108 Working Inconel® Alloys 625 and 718.....................4-83 Working Magnesium.................................................4-84 Working Titanium.....................................................4-85 xvii
  • 18. Chapter 5 Correct Forming of a Weld.......................................5-16Aircraft Welding. ..................................................5-1 . Characteristics of a Good Weld................................5-16Introduction.....................................................................5-1 Oxy-Acetylene Welding of Ferrous Metals . ...............5-16Types of Welding...........................................................5-2 . Steel (Including SAE 4130)......................................5-16 Gas Welding................................................................5-2 Chrome Molybdenum...............................................5-17 Electric Arc Welding. .................................................5-2 . Stainless Steel. ..........................................................5-17 . Shielded Metal Arc Welding (SMAW)...................5-2 Oxy-Acetylene Welding of Nonferrous Metals............5-18 Gas Metal Arc Welding (GMAW)..........................5-3 Aluminum Welding...................................................5-18 Gas Tungsten Arc Welding (GTAW)......................5-3 Magnesium Welding ................................................5-19 Electric Resistance Welding ......................................5-5 Brazing and Soldering..................................................5-20 . Spot Welding...........................................................5-6 Torch Brazing of Steel..............................................5-20 Seam Welding. ........................................................5-6 . Torch Brazing of Aluminum.....................................5-21 Soldering...................................................................5-21 Plasma Arc Welding (PAW).......................................5-6 Aluminum Soldering.............................................5-21 Plasma Arc Cutting ....................................................5-7 Silver Soldering.....................................................5-22Gas Welding and Cutting Equipment.............................5-7 Welding Gases ...........................................................5-7 Gas Metal Arc Welding (TIG Welding).......................5-22 Acetylene.................................................................5-7 TIG Welding 4130 Steel Tubing...................................... ...................................................................................5-23 Argon.......................................................................5-7 TIG Welding Stainless Steel.....................................5-23 Helium.....................................................................5-7 TIG Welding Aluminum...........................................5-24 Hydrogen.................................................................5-7 TIG Welding Magnesium.........................................5-24 . Oxygen. ...................................................................5-7 . TIG Welding Titanium..............................................5-24 Pressure Regulators.....................................................5-7 Arc Welding Procedures, Techniques, and Welding Welding Hose..............................................................5-8 Safety Equipment..........................................................5-25 Check Valves and Flashback Arrestors. .....................5-8 . Multiple Pass Welding..............................................5-27 Torches........................................................................5-9 Techniques of Position Welding...............................5-28 Equal Pressure Torch...............................................5-9 Flat Position Welding................................................5-28 Injector Torch..........................................................5-9 Bead Weld.............................................................5-28 Cutting Torch...........................................................5-9 Groove Weld. ........................................................5-28 . Torch Tips...................................................................5-9 Fillet Weld.............................................................5-28 Welding Eyewear........................................................5-9 Lap Joint Weld. .....................................................5-29 . Filler Rod...............................................................5-10 Vertical Position Welding ........................................5-29 Equipment Setup.......................................................5-10 Overhead Position Welding......................................5-29 Gas Cylinders........................................................5-10 . Expansion and Contraction of Metals...........................5-30 Regulators..............................................................5-11 Welded Joints Using Oxy-Acetylene Torch.................5-31 Hoses.....................................................................5-11 . Butt Joints. ................................................................5-31 . Connecting Torch..................................................5-11 Tee Joints..................................................................5-31 . Select the Tip Size.................................................5-11 Edge Joints................................................................5-31 Adjusting the Regulator Working Pressure...........5-13 Corner Joints.............................................................5-32 Lighting and Adjusting the Torch ............................5-13 Lap Joints..................................................................5-32 Different Flames. ......................................................5-13 . Repair of Steel Tubing Aircraft Structure by Neutral Flame........................................................5-13 Welding.........................................................................5-32 Carburizing Flame.................................................5-13 Dents at a Cluster Weld. ...........................................5-32 . Oxidizing Flame....................................................5-13 Dents Between Clusters............................................5-32 Tube Splicing with Inside Sleeve Reinforcement.....5-33 Soft or Harsh Flames.............................................5-13 Tube Splicing with Outer Split Sleeve Handling of the Torch. ..........................................5-14 . Reinforcement...........................................................5-34Oxy-acetylene Cutting..................................................5-14 Landing Gear Repairs...............................................5-35 . Shutting Down the Gas Welding Equipment............5-15 Engine Mount Repairs. .............................................5-36 .Gas Welding Procedures and Techniques....................5-15 . Rosette Welding........................................................5-37xviii
  • 19. Chapter 6 Fiberglass.................................................................7-4Aircraft Wood and Structural Repair..................6-1 Kevlar®....................................................................7-4Aircraft Wood and Structural Repair..............................6-1 Carbon/Graphite......................................................7-6Wood Aircraft Construction and Repairs.......................6-2 Boron.......................................................................7-6 Inspection of Wood Structures....................................6-3 Ceramic Fibers.........................................................7-6 External and Internal Inspection..............................6-3 Lightning Protection Fibers.....................................7-6 Glued Joint Inspection.............................................6-4 Matrix Materials..........................................................7-7 Wood Condition .....................................................6-5 Thermosetting Resins..............................................7-7Repair of Wood Aircraft Structures................................6-7 Curing Stages of Resins..............................................7-8 Materials......................................................................6-7 Pre-Impregnated Products (Prepregs).........................7-8 Suitable Wood.............................................................6-7 Dry Fiber Material. .....................................................7-9 . Defects Permitted....................................................6-9 . Thixotropic Agents. ....................................................7-9 . Defects Not Permitted.............................................6-9 . Adhesives....................................................................7-9 Glues (Adhesives). ................................................6-10 . Film Adhesives........................................................7-9 Definition of Terms Used in the Glue Process......6-10 Paste Adhesives.......................................................7-9 Preparation of Wood for Gluing...............................6-11 . Foaming Adhesives...............................................7-10 Preparing Glues for Use........................................6-12 . Description of Sandwich Structures.............................7-10 . Applying the Glue/Adhesive ................................6-12 Properties. .................................................................7-11 . Pressure on the Joint..............................................6-12 Facing Materials........................................................7-11 Testing Glued Joints .............................................6-13 Core Materials...........................................................7-11 Repair of Wood Aircraft Components......................6-13 Honeycomb............................................................7-11 Wing Rib Repairs .................................................6-13 Foam......................................................................7-12 Wing Spar Repairs . ..............................................6-15 Balsa Wood. ..........................................................7-13 . Bolt and Bushing Holes.........................................6-20 Manufacturing and In-Service Damage........................7-13 Plywood Skin Repairs...............................................6-20 Manufacturing Defects..............................................7-13 Fabric patch .........................................................6-20 Fiber Breakage.......................................................7-13 Splayed Patch........................................................6-20 . Matrix Imperfections ............................................7-13 Surface Patch.........................................................6-20 Delamination and Debonds...................................7-14 . Plug Patch..............................................................6-21 Combinations of Damages. ...................................7-14 . Scarf Patch.............................................................6-24 Flawed Fastener Holes. .........................................7-14 . The Back of the Skin is Accessible for Repair .....6-25 In-Service Defects.....................................................7-14 The Back of the Skin Is Not Accessible Corrosion...................................................................7-15 for Repair...............................................................6-25 Nondestructive Inspection (NDI) of Composites.........7-15 Visual Inspection.......................................................7-15Chapter 7 Audible Sonic Testing (Coin Tapping) ....................7-16Advanced Composite Materials..........................7-1 Automated Tap Test..............................................7-16Description of Composite Structures..............................7-1 Ultrasonic Inspection................................................7-17 . Introduction.................................................................7-1 Through Transmission Ultrasonic Inspection. ......7-17 . Laminated Structures..................................................7-2 . Pulse Echo Ultrasonic Inspection..........................7-18 Major Components of a Laminate...........................7-2 Ultrasonic Bondtester Inspection. .........................7-18 . Strength Characteristics...........................................7-2 Phased Array Inspection........................................7-18 Fiber Orientation. ....................................................7-2 . Radiography..............................................................7-19 Warp Clock..............................................................7-3 Thermography...........................................................7-19 Fiber Forms.................................................................7-3 Neutron Radiography................................................7-19 Roving.....................................................................7-3 . Moisture Detector . ...................................................7-19 Unidirectional (Tape) .............................................7-3 Composite Repairs........................................................7-19 Bidirectional (Fabric)..............................................7-3 . Layup Materials........................................................7-19 . Hand Tools............................................................7-19 . Nonwoven (Knitted or Stitched). ............................7-4 . Air Tools................................................................7-20 Types of Fiber.............................................................7-4 xix
  • 20. Caul Plate . ............................................................7-20 Damage Requiring Core Replacement and Support Tooling and Molds...................................7-20 Repair to One or Both Faceplates..........................7-34 Vacuum Bag Materials . ...........................................7-21 Solid Laminates.........................................................7-37 Release Agents......................................................7-21 . Bonded Flush Patch Repairs..................................7-37 Bleeder Ply............................................................7-21 . Trailing Edge and Transition Area Patch Peel Ply..................................................................7-21 Repairs...................................................................7-40 Layup Tapes..........................................................7-21 . Resin Injection Repairs..........................................7-40 Perforated Release Film. .......................................7-21 . Composite Patch Bonded to Aluminum Solid Release Film.................................................7-21 Structure. ...............................................................7-40 . Breather Material...................................................7-21 Fiberglass Molded Mat Repairs.............................7-41 Vacuum Bag .........................................................7-21 Radome Repairs.....................................................7-41 Vacuum Equipment...................................................7-22 External Bonded Patch Repairs.............................7-41 Vacuum Compaction Table...................................7-22 Bolted Repairs.......................................................7-44 Heat Sources . ...........................................................7-22 Fasteners Used with Composite Laminates..............7-46 Oven. .....................................................................7-22 . Corrosion Precautions. ..........................................7-46 . Autoclave...............................................................7-23 Fastener Materials . ...............................................7-46 Heat Bonder and Heat Lamps................................7-23 Fastener System for Sandwich Honeycomb Thermocouples......................................................7-25 Structures (SPS Technologies Comp Tite)............7-46 Types of Layups........................................................7-26 Hi-Lok® and Huck-Spin® Lockbolt Fasteners.....7-46 Wet Layups . .........................................................7-26 Eddie-Bolt® Fasteners..........................................7-46 . Prepreg...................................................................7-27 Cherry’s E-Z Buck ® (CSR90433) Hollow Rivet. .7-47 . Co-curing...............................................................7-28 Blind Fasteners......................................................7-47 Secondary Bonding. ..............................................7-28 . Blind Bolts ............................................................7-48 Co-bonding............................................................7-28 Fiberlite..................................................................7-48 Layup Process (Typical Laminated Wet Layup)......7-28 . Screws and Nutplates in Composite Structures.....7-48 Layup Techniques. ................................................7-28 . Machining Processes and Equipment. ......................7-49 . Bleedout Technique...............................................7-29 Drilling. .................................................................7-49 . No Bleedout...........................................................7-29 Countersinking. .....................................................7-52 . Ply Orientation Warp Clock..................................7-29 Cutting Processes and Precautions........................7-52 Mixing Resins ..........................................................7-30 Cutting Equipment.................................................7-52 Saturation Techniques...............................................7-30 Repair Safety.............................................................7-53 Fabric Impregnation With a Brush or Eye Protection. ......................................................7-53 . Squeegee................................................................7-30 Respiratory Protection...........................................7-53 Fabric Impregnation Using a Vacuum Bag...........7-30 Skin Protection......................................................7-53 . Vacuum Bagging Techniques...................................7-31 Fire Protection.......................................................7-53 Single Side Vacuum Bagging................................7-31 Transparent Plastics......................................................7-54 Envelope Bagging. ................................................7-31 . Optical Considerations..............................................7-54 Alternate Pressure Application.................................7-32 . Identification.............................................................7-54 . Shrink Tape. ..........................................................7-32 . Storage and Handling............................................7-54 C-Clamps...............................................................7-32 Forming Procedures and Techniques........................7-54 Shotbags and Weights...........................................7-32 . Heating. .................................................................7-54 . Curing of Composite Materials.................................7-32 Forms.....................................................................7-55 Room Temperature Curing....................................7-32 Forming Methods..................................................7-55 . Elevated Temperature Curing................................7-32 Sawing and Drilling..................................................7-55Composite Honeycomb Sandwich Repairs. .................7-33 . Sawing...................................................................7-55 Damage Classification...............................................7-34 Drilling. .................................................................7-55 . Sandwich Structures..................................................7-34 Cementing.................................................................7-56 Minor Core Damage (Filler and Potting Application of Cement. .........................................7-56 . Repairs)..................................................................7-34xx
  • 21. Repairs. .....................................................................7-56 . Mixing Equipment...................................................8-9 Cleaning....................................................................7-57 Preparation ...................................................................8-10 Polishing....................................................................7-57 Surfaces.....................................................................8-10 Windshield Installation.............................................7-57 Primer and Paint........................................................8-10 Installation Procedures..............................................7-57 Spray Gun Operation....................................................8-11 Adjusting the Spray Pattern......................................8-11 .Chapter 8 Applying the Finish...................................................8-11Aircraft Painting and Finishing...........................8-1 Common Spray Gun Problems. ................................8-12 .Introduction . ..................................................................8-1 Sequence for Painting a Single-Engine or LightFinishing Materials ........................................................8-2 Twin Airplane...............................................................8-13 Acetone.......................................................................8-2 . Common Paint Troubles...............................................8-13 Alcohol........................................................................8-2 Poor Adhesion...........................................................8-13 Benzene.......................................................................8-2 Blushing....................................................................8-13 Methyl Ethyl Ketone (MEK)......................................8-2 . Pinholes.....................................................................8-14 Methylene Chloride.....................................................8-2 Sags and Runs...........................................................8-14 Toluene........................................................................8-2 Orange Peel...............................................................8-14 Turpentine...................................................................8-3 Fisheyes.....................................................................8-15 Mineral Spirits.............................................................8-3 Sanding Scratches.....................................................8-15 Naphtha.......................................................................8-3 Wrinkling..................................................................8-15 Linseed Oil..................................................................8-3 Spray Dust.................................................................8-16 Thinners. .....................................................................8-3 . Painting Trim and Identification Marks........................8-16 Varnish........................................................................8-3 Masking and Applying the Trim...............................8-16Primers............................................................................8-3 Masking Materials.................................................8-16 Wash Primers..............................................................8-3 Masking for the Trim.............................................8-16 Red Iron Oxide............................................................8-3 Display of Nationality and Registration Marks .......8-17 Gray Enamel Undercoat..............................................8-4 Display of Marks...................................................8-17 Urethane .....................................................................8-4 Location and Placement of Marks.........................8-17 Epoxy..........................................................................8-4 Size Requirements for Different Aircraft..............8-18 Zinc Chromate.............................................................8-4 Decals...........................................................................8-18 .Identification of Paints....................................................8-4 Paper Decals..............................................................8-18 Dope............................................................................8-4 Metal Decals with Cellophane Backing....................8-18 Synthetic Enamel........................................................8-4 . Metal Decals With Paper Backing............................8-18 Lacquers......................................................................8-4 Metal Decals with No Adhesive...............................8-18 . Polyurethane................................................................8-5 Vinyl Film Decals.....................................................8-18 Urethane Coating........................................................8-5 . Removal of Decals ...................................................8-19 Acrylic Urethanes. ......................................................8-5 . Paint System Compatibility..........................................8-19Methods of Applying Finish...........................................8-5 Paint Touchup...........................................................8-19 Dipping........................................................................8-5 Identification of Paint Finishes..............................8-19 Brushing......................................................................8-5 Surface Preparation for Touchup...........................8-20 Spraying......................................................................8-5Finishing Equipment.......................................................8-6 Stripping the Finish...................................................8-20 Paint Booth..................................................................8-6 Chemical Stripping................................................8-21 Air Supply...................................................................8-6 Plastic Media Blasting (PMB)...............................8-21 Spray Equipment.........................................................8-6 New Stripping Methods.........................................8-21 Air Compressors......................................................8-6 Safety in the Paint Shop................................................8-21 Large Coating Containers........................................8-7 Storage of Finishing Materials..................................8-21 System Air Filters....................................................8-7 Protective Equipment for Personnel.............................8-22 Miscellaneous Painting Tools and Equipment............8-7 Spray Guns..............................................................8-7 . Fresh Air Breathing Systems...................................8-8 Viscosity Measuring Cup........................................8-9 xxi
  • 22. Chapter 9 Generator Controls for High OutputAircraft Electrical System....................................9-1 Generators..............................................................9-35Introduction.....................................................................9-1 Generator Controls for Low-Output Ohm’s Law..................................................................9-2 Generators..............................................................9-36 Current. .......................................................................9-2 . DC Alternators and Controls.....................................9-38 Conventional Current Theory and Electron DC Alternators . ....................................................9-39 Theory . ...................................................................9-3 Alternator Voltage Regulators . ............................9-40 Electromotive Force (Voltage)....................................9-4 Solid-State Regulators...........................................9-40 Resistance....................................................................9-4 Power Systems..........................................................9-41 Factors Affecting Resistance...................................9-4 AC Alternators .........................................................9-41 Electromagnetic Generation of Power........................9-5 Alternator Drive .......................................................9-42 Alternating Current (AC) Introduction ......................9-9 AC Alternators Control Systems . ............................9-45 Definitions...............................................................9-9 . Aircraft Electrical Systems...........................................9-47 Opposition to Current Flow of AC. ..........................9-12 . Small Single-Engine Aircraft....................................9-47 Resistance..............................................................9-12 Battery Circuit.......................................................9-47 Inductive Reactance...............................................9-12 Generator Circuit...................................................9-48 Capacitive Reactance.............................................9-14 Alternator Circuit...................................................9-48 Impedance . ...........................................................9-15 External Power Circuit..........................................9-50 Parallel AC Circuits...............................................9-18 Starter Circuit........................................................9-50 . Power in AC Circuits.............................................9-20 Avionics Power Circuit.........................................9-51 . True Power............................................................9-20 . Landing Gear Circuit.............................................9-52 Apparent Power ....................................................9-20 AC Supply.............................................................9-55 Power Factor ............................................................9-20 Light Multiengine Aircraft........................................9-57Aircraft Batteries. .........................................................9-21 . Paralleling Alternators or Generators....................9-57 Type of Batteries.......................................................9-21 Power Distribution on Multiengine Aircraft ........9-58 Lead-Acid Batteries...............................................9-21 Large Multiengine Aircraft.......................................9-60 NiCd Batteries.......................................................9-22 AC Power Systems................................................9-60 Capacity.................................................................9-22 Wiring Installation........................................................9-65 Aircraft Battery Ratings by Specification..............9-23 Wiring Diagrams ......................................................9-65 Storing and Servicing Facilities.............................9-23 Block Diagrams.....................................................9-65 Battery Freezing....................................................9-23 . Pictorial Diagrams.................................................9-65 Temperature Correction.........................................9-23 Schematic Diagrams..............................................9-65 Battery Charging . .................................................9-24 Wire Types................................................................9-65 Battery Maintenance..............................................9-24 Conductor..............................................................9-67 Battery and Charger Characteristics......................9-25 Plating....................................................................9-68 Aircraft Battery Inspection....................................9-26 Insulation...............................................................9-68 Ventilation Systems...............................................9-26 Wire Shielding.......................................................9-68 Installation Practices..............................................9-26 Wire Substitutions.................................................9-69 Troubleshooting.....................................................9-27 Areas Designated as Severe Wind and DC Generators and Controls.....................................9-27 Moisture Problem (SWAMP) ...............................9-69 Generators..............................................................9-27 Wire Size Selection...................................................9-69 Construction Features of DC Generators. .............9-29 . Current Carrying Capacity. ...................................9-71 . Types of DC Generators........................................9-32 Allowable Voltage Drop........................................9-75 Generator Ratings..................................................9-33 Wire Identification....................................................9-77 . DC Generator Maintenance...................................9-33 Placement of Identification Markings. ..................9-77 . Generator Controls....................................................9-34 Types of Wire Markings . .....................................9-77 Theory of Generator Control.................................9-34 Wire Installation and Routing...................................9-78 Functions of Generator Control Systems. .............9-35 . Open Wiring..........................................................9-78xxii
  • 23. Wire Groups and Bundles and Routing.................9-78 Conduit..................................................................9-83 Wire Shielding.......................................................9-85 Lacing and Tying Wire Bundles...............................9-88 Tying......................................................................9-89 Wire Termination......................................................9-90 Stripping Wire ......................................................9-90 Terminal Strips......................................................9-91 Terminal Lugs. ......................................................9-91 . Emergency Splicing Repairs.................................9-92 . Junction Boxes . ....................................................9-92 AN/MS Connectors...............................................9-93 Coaxial Cable........................................................9-96 . Wire Inspection.........................................................9-96Electrical System Components.....................................9-96 Switches....................................................................9-96 Type of Switches...................................................9-98 Toggle and Rocker Switches.................................9-98 Rotary Switches.....................................................9-99 Precision (Micro) Switches...................................9-99 . Relays and Solenoids (Electromagnetic Switches)...................................................................9-99 Solenoids...............................................................9-99 . Relays....................................................................9-99 Current Limiting Devices........................................9-100 Fuses....................................................................9-100 Circuit Breakers...................................................9-100Aircraft Lighting Systems...........................................9-101 Exterior Lights........................................................9-101 . Position Lights.....................................................9-101 Anticollision Lights.............................................9-102 Landing and Taxi Lights. ....................................9-103 . Wing Inspection Lights.......................................9-104 . Interior Lights. ........................................................9-104 . Maintenance and Inspection of Lighting Systems...................................................................9-105 .Glossary...............................................................G-1Index.......................................................................I-1 xxiii
  • 24. xxiv
  • 25. Chapter 1Aircraft Structures A Brief History of Aircraft Structures The history of aircraft structures underlies the history of aviation in general. Advances in materials and processes used to construct aircraft have led to their evolution from simple wood truss structures to the sleek aerodynamic flying machines of today. Combined with continuous powerplant development, the structures of “flying machines” have changed significantly. The key discovery that “lift” could be created by passing air over the top of a curved surface set the development of fixed and rotary-wing aircraft in motion. George Cayley developed an efficient cambered airfoil in the early 1800s, as well as successful manned gliders later in that century. He established the principles of flight, including the existence of lift, weight, thrust, and drag. It was Cayley who first stacked wings and created a tri-wing glider that flew a man in 1853. 1-1
  • 26. Earlier, Cayley studied the center of gravity of flyingmachines, as well as the effects of wing dihedral. Furthermore,he pioneered directional control of aircraft by including theearliest form of a rudder on his gliders. [Figure 1-1]In the late 1800s, Otto Lilienthal built upon Cayley’sdiscoveries. He manufactured and flew his own gliderson over 2,000 flights. His willow and cloth aircraft hadwings designed from extensive study of the wings of birds.Lilienthal also made standard use of vertical and horizontalfins behind the wings and pilot station. Above all, Lilienthalproved that man could fly. [Figure 1-2]Octave Chanute, a retired railroad and bridge engineer,was active in aviation during the 1890s. [Figure 1-3] Hisinterest was so great that, among other things, he publisheda definitive work called “Progress in Flying Machines.” Thiswas the culmination of his effort to gather and study all the Figure 1-2. Master of gliding and wing study, Otto Lilienthal (top) and one of his more than 2,000 glider flights (bottom). information available on aviation. With the assistance of others, he built gliders similar to Lilienthal’s and then his own. In addition to his publication, Chanute advanced aircraft structure development by building a glider with stacked wings incorporating the use of wires as wing supports. The work of all of these men was known to the Wright Brothers when they built their successful, powered airplane in 1903. The first of its kind to carry a man aloft, the Wright Flyer had thin, cloth-covered wings attached to what was primarily truss structures made of wood. The wings contained forward and rear spars and were supported with both strutsFigure 1-1. George Cayley, the father of aeronautics (top) and a and wires. Stacked wings (two sets) were also part of theflying replica of his 1853 glider (bottom). Wright Flyer. [Figure 1-4]1-2
  • 27. still supported by wires, but a mast extending above the fuselage enabled the wings to be supported from above, as well as underneath. This made possible the extended wing length needed to lift an aircraft with a single set of wings. Bleriot used a Pratt truss-type fuselage frame. [Figure 1-5] Figure 1-5. The world’s first mono-wing by Louis Bleriot.Figure 1-3. Octave Chanute gathered and published all of the More powerful engines were developed and airframeaeronautical knowledge known to date in the late 1890s. Many structures changed to take advantage of the benefits. Asearly aviators benefited from this knowledge. early as 1910, German Hugo Junkers was able to build an aircraft with metal truss construction and metal skin due toPowered heavier-than-air aviation grew from the Wright the availability of stronger powerplants to thrust the planedesign. Inventors and fledgling aviators began building their forward and into the sky. The use of metal instead of woodown aircraft. Early on, many were similar to that constructed for the primary structure eliminated the need for externalby the Wrights using wood and fabric with wires and struts wing braces and wires. His J-1 also had a single set of wingsto support the wing structure. In 1909, Frenchman Louis (a monoplane) instead of a stacked set. [Figure 1-6]Bleriot produced an aircraft with notable design differences.He built a successful mono-wing aircraft. The wings wereFigure 1-4. The Wright Flyer was the first successful powered aircraft. It was made primarily of wood and fabric. 1-3
  • 28. Figure 1-6. The Junker J-1 all metal construction in 1910.Leading up to World War I (WWI), stronger engines alsoallowed designers to develop thicker wings with strongerspars. Wire wing bracing was no longer needed. Flatter, lowerwing surfaces on high-camber wings created more lift. WWIexpanded the need for large quantities of reliable aircraft.Used mostly for reconnaissance, stacked-wing tail draggerswith wood and metal truss frames with mostly fabric skindominated the wartime sky. [Figure 1-7] The Red Baron’sFokker DR-1 was typical.Figure 1-7. World War I aircraft were typically stacked-wing fabric-covered aircraft like this Breguet 14 (circa 1917). Figure 1-8. The flying boat hull was an early semimonocoque designIn the 1920s, the use of metal in aircraft construction like this Curtiss HS-2L.increased. Fuselages able to carry cargo and passengerswere developed. The early flying boats with their hull-type construction of the fuselage. [Figure 1-9] The fiberglassconstruction from the shipbuilding industry provided the radome was also developed during this period.blueprints for semimonocoque construction of fuselages.[Figure 1-8] Truss-type designs faded. A tendency toward After WWII, the development of turbine engines led tocleaner monowing designs prevailed. higher altitude flight. The need for pressurized aircraft pervaded aviation. Semimonocoque construction neededInto the 1930s, all-metal aircraft accompanied new lighter and to be made even stronger as a result. Refinements to themore powerful engines. Larger semimonocoque fuselages all-metal semimonocoque fuselage structure were made towere complimented with stress-skin wing designs. Fewer increase strength and combat metal fatigue caused by thetruss and fabric aircraft were built. World War II (WWII) pressurization-depressurization cycle. Rounded windowsbrought about a myriad of aircraft designs using all metal and door openings were developed to avoid weak areastechnology. Deep fuel-carrying wings were the norm, but the where cracks could form. Integrally machined copperdesire for higher flight speeds prompted the development of alloy aluminum skin resisted cracking and allowed thickerthin-winged aircraft in which fuel was carried in the fuselage. skin and controlled tapering. Chemical milling of wingThe first composite structure aircraft, the De Havilland skin structures provided great strength and smooth highMosquito, used a balsa wood sandwich material in the performance surfaces. Variable contour wings became easier1-4
  • 29. Figure 1-9. The DeHavilland Mosquito, the first aircraft with foamcore honeycomb in the fuselage. Figure 1-10. The nearly all composite Cessna Citation Mustangto construct. Increases in flight speed accompanying jet travel very light jet (VLJ).brought about the need for thinner wings. Wing loading also Generalincreased greatly. Multispar and box beam wing designs weredeveloped in response. An aircraft is a device that is used for, or is intended to be used for, flight in the air. Major categories of aircraft are airplane,In the 1960s, ever larger aircraft were developed to carry rotorcraft, glider, and lighter-than-air vehicles. [Figure 1-11]passengers. As engine technology improved, the jumbo jet Each of these may be divided further by major distinguishingwas engineered and built. Still primarily aluminum with a features of the aircraft, such as airships and balloons. Bothsemimonocoque fuselage, the sheer size of the airliners of are lighter-than-air aircraft but have differentiating featuresthe day initiated a search for lighter and stronger materials and are operated differently.from which to build them. The use of honeycomb constructedpanels in Boeing’s airline series saved weight while not The concentration of this handbook is on the airframe ofcompromising strength. Initially, aluminum core with aircraft; specifically, the fuselage, booms, nacelles, cowlings,aluminum or fiberglass skin sandwich panels were used on fairings, airfoil surfaces, and landing gear. Also included arewing panels, flight control surfaces, cabin floor boards, and the various accessories and controls that accompany theseother applications. structures. Note that the rotors of a helicopter are considered part of the airframe since they are actually rotating wings.A steady increase in the use of honeycomb and foam core By contrast, propellers and rotating airfoils of an engine onsandwich components and a wide variety of composite an airplane are not considered part of the airframe.materials characterizes the state of aviation structures fromthe 1970s to the present. Advanced techniques and material The most common aircraft is the fixed-wing aircraft. Ascombinations have resulted in a gradual shift from aluminum the name implies, the wings on this type of flying machineto carbon fiber and other strong, lightweight materials. These are attached to the fuselage and are not intended to movenew materials are engineered to meet specific performance independently in a fashion that results in the creation of lift.requirements for various components on the aircraft. Many One, two, or three sets of wings have all been successfullyairframe structures are made of more than 50 percent utilized. [Figure 1-12] Rotary-wing aircraft such asadvanced composites, with some airframes approaching helicopters are also widespread. This handbook discusses100 percent. The term “very light jet” (VLJ) has come to features and maintenance aspects common to both fixed-describe a new generation of jet aircraft made almost entirely wing and rotary-wing categories of aircraft. Also, in certainof advanced composite materials. [Figure 1-10] It is possible cases, explanations focus on information specific to onlythat noncomposite aluminum aircraft structures will become one or the other. Glider airframes are very similar to fixed-obsolete as did the methods and materials of construction wing aircraft. Unless otherwise noted, maintenance practicesused by Cayley, Lilienthal, and the Wright Brothers. described for fixed-wing aircraft also apply to gliders. The same is true for lighter-than-air aircraft, although thorough 1-5
  • 30. Figure 1-11. Examples of different categories of aircraft, clockwise from top left: lighter-than-air, glider, rotorcraft, and airplane. coverage of the unique airframe structures and maintenance practices for lighter-than-air flying machines is not included in this handbook. The airframe of a fixed-wing aircraft consists of five principal units: the fuselage, wings, stabilizers, flight control surfaces, and landing gear. [Figure 1-13] Helicopter airframes consist of the fuselage, main rotor and related gearbox, tail rotor (on helicopters with a single main rotor), and the landing gear. Airframe structural components are constructed from a wide variety of materials. The earliest aircraft were constructed primarily of wood. Steel tubing and the most common material, aluminum, followed. Many newly certified aircraft are built from molded composite materials, such as carbon fiber. Structural members of an aircraft’s fuselage include stringers, longerons, ribs, bulkheads, and more. The main structural member in a wing is called the wing spar. The skin of aircraft can also be made from a variety of materials, ranging from impregnated fabric to plywood, aluminum, or composites. Under the skin and attached to the structural fuselage are the many components that support airframe function. The entire airframe and its components are joined by rivets, bolts, screws, and other fasteners. Welding, adhesives, and special bonding techniques are also used. Major Structural Stresses Aircraft structural members are designed to carry a load or to resist stress. In designing an aircraft, every square inch of wing and fuselage, every rib, spar, and even each metal fitting must be considered in relation to the physical characteristicsFigure 1-12. A monoplane (top), biplane (middle), and tri-wing of the material of which it is made. Every part of the aircraftaircraft (bottom). must be planned to carry the load to be imposed upon it.1-6
  • 31. Wings Flight controls Powerplant Stabilizers Fuselage Flight controls Landing gearFigure 1-13. Principal airframe units.The determi­ ation of such loads is called stress analysis. Al­ n tension, which stretches the aircraft. The tensile strength ofthough planning the design is not the function of the aircraft a material is measured in pounds per square inch (psi) and istechnician, it is, nevertheless, important that the technician calculated by dividing the load (in pounds) re­ uired to pull the qunderstand and appreciate the stresses in­ olved in order to v material apart by its cross-sec­ional area (in square inches). tavoid changes in the original design through improper repairs. Compression is the stress that res­ sts a crushing force. iThe term “stress” is often used interchangeably with the [Figure 1-14B] The compressive strength of a material isword “strain.” While related, they are not the same thing. also measured in psi. Compression is the stress that tends toExternal loads or forces cause stress. Stress is a material’s shorten or squeeze aircraft parts.internal resistance, or counterforce, that opposes deformation.The degree of deformation of a material is strain. When Torsion is the stress that produces twisting. [Figure 1-14C]a material is subjected to a load or force, that material is While moving the aircraft forward, the en­ ine also tends to gdeformed, regardless of how strong the material is or how twist it to one side, but other aircraft components hold it onlight the load is. course. Thus, torsion is created. The torsion strength of a material is its resistance to twisting or torque.There are five major stresses [Figure 1-14] to which allaircraft are subjected: Shear is the stress that resists the force tending to cause • Tension one layer of a material to slide over an adjacent layer. [Figure 1-14D] Two riveted plates in tension subject the • Compression rivets to a shearing force. Usually, the shearing strength • Torsion of a material is either equal to or less than its tensile or compressive strength. Aircraft parts, especially screws, bolts, • Shear and rivets, are often subject to a shearing force. • Bending Bending stress is a combination of compression and tension.Tension is the stress that resists a force that tends to pull The rod in Figure 1-14E has been short­ ned (compressed) on esomething apart. [Figure 1-14A] The engine pulls the aircraft the inside of the bend and stretched on the outside of the bend.forward, but air resistance tries to hold it back. The result is 1-7
  • 32. A. Tension B. Compression C. Torsional D. Shear Tension outside of bend Bent structural member Shear along imaginary line (dotted) Compression inside of bend E. Bending (the combination stress)Figure 1-14. The five stresses that may act on an aircraft and its parts.A single member of the structure may be subjected to Fixed-Wing Aircrafta combination of stresses. In most cases, the struc­ ural t Fuselagemembers are designed to carry end loads rather than side The fuselage is the main structure or body of the fixed-wingloads. They are designed to be subjected to tension or aircraft. It provides space for cargo, controls, acces­ ories, scompression rather than bending. passengers, and other equipment. In single-engine aircraft, the fuselage houses the powerplant. In multiengine aircraft,Strength or resistance to the external loads imposed during the engines may be either in the fuselage, attached to theoperation may be the principal requirement in cer­ ain t fuselage, or suspended from the wing structure. There are twostructures. However, there are numerous other characteristics general types of fuselage construc­ion: truss and monocoque. tin addition to designing to control the five major stresses thatengineers must consider. For example, cowling, fairings, and Truss Typesimi­ar parts may not be subject to significant loads requiring la high degree of strength. However, these parts must have A truss is a rigid framework made up of members, such asstreamlined shapes to meet aerodynamic requirements, such beams, struts, and bars to resist deforma­ion by applied loads. tas reducing drag or directing airflow. The truss-framed fuselage is generally covered with fabric.1-8
  • 33. The truss-type fuselage frame is usually constructed of steeltubing welded together in such a manner that all members Skin Formerof the truss can carry both tension and compression loads.[Figure 1-15] In some aircraft, principally the light, single-engine models, truss fuselage frames may be constructed ofaluminum alloy and may be riveted or bolted into one piece,with cross-bracing achieved by using solid rods or tubes. Longeron Diagonal web members Bulkhead Figure 1-16. An airframe using monocoque construction. design but, additionally, the skin is reinforced by longitudinal Vertical web members members called longerons. Longerons usually extend across several frame members and help the skin support primary bending loads. They are typically made of aluminum alloyFigure 1-15. A truss-type fuselage. A Warren truss uses mostly Figure 1-2. The Warren truss. either of a single piece or a built-up construction.diagonal bracing.Monocoque Type Stringers are also used in the semimonocoque fuselage. These longitudinal members are typically more numerous and lighterThe monocoque (single shell) fuselage relies largely on the in weight than the longerons. They come in a variety of shapesstrength of the skin or covering to carry the primary loads. and are usually made from single piece aluminum alloyThe design may be di­ ided into two classes: v extrusions or formed aluminum. Stringers have some rigidity 1. Monocoque but are chiefly used for giving shape and for attachment of 2. Semi­ onocoque m the skin. Stringers and longerons together prevent tension and compression from bending the fuselage. [Figure 1-17]Different por­ions of the same fuselage may belong to either tof the two classes, but most modern aircraft are consideredto be of semimonocoque type construction. Longeron SkinThe true monocoque construction uses formers, frameassemblies, and bulkheads to give shape to the fuselage.[Figure 1-16] The heaviest of these structural members arelocated at intervals to carry concentrated loads and at pointswhere fittings are used to attach other units such as wings,powerplants, and stabilizers. Since no other bracing membersare present, the skin must carry the primary stresses andkeep the fuselage rigid. Thus, the biggest problem involvedin mono­ oque construction is maintaining enough strength cwhile keeping the weight within allowable limits. StringerSemimonocoque TypeTo overcome the strength/weight problem of monocoque Bulkheadconstruction, a modification called semi­ onocoque mconstruction was devel­ ped. It also consists of frame o Figure 1-17. The most common airframe construction isassemblies, bulkheads, and formers as used in the monocoque semimonocoque. 1-9
  • 34. Other bracing between the longerons and stringers can also construction, may with­ tand considerable damage and still sbe used. Often referred to as web members, these additional be strong enough to hold together.support pieces may be installed vertically or diagonally. Itmust be noted that manufacturers use different nomenclature Fuselages are generally constructed in two or more sections.to describe structural members. For example, there is often On small aircraft, they are generally made in two or threelittle difference between some rings, frames, and formers. sections, while larger aircraft may be made up of as many asOne manufacturer may call the same type of brace a ring or six sections or more before being assembled.a frame. Manufacturer instructions and specifications for aspecific aircraft are the best guides. Pressurization Many aircraft are pressurized. This means that air is pumpedThe semimonocoque fuselage is constructed primarily of into the cabin after takeoff and a difference in pressurealloys of aluminum and magnesium, although steel and between the air inside the cabin and the air outside the cabin istitanium are sometimes found in areas of high temperatures. established. This differential is regulated and maintained. InIndividually, no one of the aforementioned components is this manner, enough oxygen is made available for passengersstrong enough to carry the loads imposed during flight and to breathe normally and move around the cabin withoutlanding. But, when combined, those components form a special equipment at high altitudes.strong, rigid framework. This is accomplished with gussets,rivets, nuts and bolts, screws, and even friction stir welding. Pressurization causes significant stress on the fuselageA gusset is a type of connection bracket that adds strength. structure and adds to the complexity of design. In addition[Figure 1-18] to withstanding the difference in pressure between the air inside and outside the cabin, cycling from unpressurized to pressurized and back again each flight causes metal fatigue. To deal with these impacts and the other stresses of flight, nearly all pressurized aircraft are semimonocoque in design. Pressurized fuselage structures undergo extensive periodic inspections to ensure that any damage is discovered and repaired. Repeated weakness or failure in an area of structure may require that section of the fuselage be modified or redesigned. Wings Wing Configurations Wings are airfoils that, when moved rapidly through the air, create lift. They are built in many shapes and sizes. Wing design can vary to provide certain desirable flightFigure 1-18. Gussets are used to increase strength. characteristics. Control at various operating speeds, the amount of lift generated, balance, and stability all change as the shape of the wing is altered. Both the leading edge andTo summarize, in semimonocoque fuselages, the strong, the trailing edge of the wing may be straight or curved, orheavy longerons hold the bulkheads and formers, and these, one edge may be straight and the other curved. One or bothin turn, hold the stringers, braces, web members, etc. All are edges may be tapered so that the wing is narrower at the tipdesigned to be attached together and to the skin to achieve than at the root where it joins the fuselage. The wing tip maythe full strength benefits of semimonocoque design. It is be square, rounded, or even pointed. Figure 1-19 shows aimportant to recognize that the metal skin or covering carries number of typical wing leading and trailing edge shapes.part of the load. The fuselage skin thickness can vary with theload carried and the stresses sustained at a particular location. The wings of an aircraft can be attached to the fuselage at the top, mid-fuselage, or at the bottom. They may extendThe advantages of the semimonocoque fuselage are many. perpendicular to the horizontal plain of the fuselage or canThe bulkheads, frames, stringers, and longerons facilitate the angle up or down slightly. This angle is known as the wingde­ ign and construction of a streamlined fuselage that is both s dihedral. The dihedral angle affects the lateral stability ofrigid and strong. Spreading loads among these structures and the aircraft. Figure 1-20 shows some common wing attachthe skin means no single piece is failure critical. This means points and dihedral angle.that a semimonocoque fuselage, because of its stressed-skin1-10
  • 35. Tapered leading edge, Tapered leading and Delta wing straight trailing edge trailing edges Straight leading and Straight leading edge, Sweptback wings trailing edges tapered trailing edgeFigure 1-19. Various wing design shapes yield different performance. Wing Structure The wings of an aircraft are designed to lift it into the air. Their particular design for any given aircraft depends on a number of factors, such as size, weight, use of the aircraft, Low wing Dihedral desired speed in flight and at landing, and desired rate of climb. The wings of aircraft are designated left and right, corresponding to the left and right sides of the operator when seated in the cockpit. [Figure 1-21] High wing Mid wing Often wings are of full cantilever design. This means they are built so that no external bracing is needed. They are supported internally by structural members assisted by the skin of the aircraft. Other aircraft wings use external struts Gull wing Inverted gull or wires to assist in supporting the wing and carrying the aerodynamic and landing loads. Wing support cables andFigure 1-20. Wing attach points and wing dihedrals. struts are generally made from steel. Many struts and their 1-11
  • 36. Left wing Right wingFigure 1-21. “Left” and “right” on an aircraft are oriented to the perspective of a pilot sitting in the cockpit.attach fittings have fairings to reduce drag. Short, nearly bulkheads running chordwise (leading edge to trailing edge).vertical supports called jury struts are found on struts that The spars are the principle structural members of a wing.attach to the wings a great distance from the fuselage. This They support all distributed loads, as well as concentratedserves to subdue strut movement and oscillation caused by weights such as the fuselage, landing gear, and engines. Thethe air flowing around the strut in flight. Figure 1-22 shows skin, which is attached to the wing structure, carries part ofsamples of wings using external bracing, also known as the loads imposed during flight. It also transfers the stressessemicantilever wings. Cantilever wings built with no external to the wing ribs. The ribs, in turn, transfer the loads to thebracing are also shown. wing spars. [Figure 1-23]Aluminum is the most common material from which In general, wing construction is based on one of threeto construct wings, but they can be wood covered with fundamental designs:fabric, and occasionally a magnesium alloy has been used. 1. MonosparMoreover, modern aircraft are tending toward lighter andstronger materials throughout the airframe and in wing 2. Multisparconstruction. Wings made entirely of carbon fiber or other 3. Box beamcomposite materials exist, as well as wings made of acombination of materials for maximum strength to weight Modification of these basic designs may be adopted byperformance. various manufacturers.The internal structures of most wings are made up of spars The monospar wing incorporates only one main spanwise orand stringers running spanwise and ribs and formers or longitudinal member in its construction. Ribs or bulkheads Wire braced biplane Full cantilever Semicantilever Long struts braced with jury strutsFigure 1-22. Externally braced wings, also called semicantilever wings, have wires or struts to support the wing. Full cantilever wingshave no external bracing and are supported internally.1-12
  • 37. Ribs Rear spar Stringer Nose rib Ribs Front spar SkinFigure 1-23. Wing structure nomenclature.supply the necessary contour or shape to the airfoil. Although the upper surface of the wing and stiffeners on the lowerthe strict monospar wing is not common, this type of design surface is sometimes used. Air transport category aircraftmodified by the addition of false spars or light shear webs often utilize box beam wing construction.along the trailing edge for support of control surfaces issometimes used. Wing Spars Spars are the principal structural members of the wing. TheyThe multispar wing incorporates more than one main correspond to the longerons of the fuse­age. They run parallel llongitudinal member in its construction. To give the wing to the lateral axis of the aircraft, from the fuselage towardcontour, ribs or bulkheads are often included. the tip of the wing, and are usually attached to the fuselage by wing fittings, plain beams, or a truss.The box beam type of wing construction uses two mainlongitudinal members with connecting bulkheads to Spars may be made of metal, wood, or composite materialsfurnish additional strength and to give contour to the wing. depending on the design criteria of a specific aircraft.[Figure 1-24] A corrugated sheet may be placed between Wooden spars are usually made from spruce. They can bethe bulkheads and the smooth outer skin so that the wing generally classified into four different types by their cross-can better carry tension and compression loads. In some sectional configu­ ation. As shown in Figure 1-25, they may rcases, heavy longitudinal stiffeners are substituted for the be (A) solid, (B) box shaped, (C) partly hollow, or (D) incorrugated sheets. A combination of corrugated sheets on the form of an I-beam. Lamination of solid wood spars isFigure 1-24. Box beam construction. 1-13
  • 38. A B C D EFigure 1-25. Typical wooden wing spar cross-sections.often used to increase strength. Laminated wood can also be foundation for attaching the skin. Although the spar shapesfound in box shaped spars. The spar in Figure 1-25E has had in Figure 1-26 are typi­ al, actual wing spar configura­ions c tmaterial removed to reduce weight but retains the strength assume many forms. For example, the web of a spar may beof a rectangular spar. As can be seen, most wing spars are a plate or a truss as shown in Figure 1-27. It could be built upbasically rectangular in shape with the long dimension of the from light weight materials with vertical stiffeners employedcross-section oriented up and down in the wing. for strength. [Figure 1-28]Currently, most manufactured aircraft have wing sparsmade of solid extruded aluminum or aluminum extrusions Upper cap memberriveted together to form the spar. The increased use of Diagonal tubecomposites and the combining of materials should makeairmen vigilant for wings spars made from a variety of Vertical tubematerials. Figure 1-26 shows examples of metal wing sparcross-sections.In an I–beam spar, the top and bottom of the I–beam arecalled the caps and the vertical section is called the web.The entire spar can be extruded from one piece of metalbut often it is built up from multiple extrusions or formed Lower cap memberangles. The web forms the principal depth portion of thespar and the cap strips (extrusions, formed angles, or milledsections) are attached to it. Together, these members carry Figure 1-27. A truss wing spar.the loads caused by wing bending, with the caps providing aFigure 1-26. Examples of metal wing spar shapes.1-14
  • 39. Upper spar cap Upper spar cap Stiffener Rivets Splice Up pe rs pa rw Lo eb we rs Rib attach angle pa rw eb Lower spar cap Lower spar capFigure 1-28. A plate web wing spar with vertical stiffeners. Figure 1-30. A fail-safe spar with a riveted spar web.It could also have no stiffeners but might contain flanged False spars are commonly used in wing design. They areholes for reducing weight but maintaining strength. Some longitudinal members like spars but do not extend the entiremetal and composite wing spars retain the I-beam concept spanwise length of the wing. Often, they are used as hingebut use a sine wave web. [Figure 1-29] attach points for control surfaces, such as an aileron spar. Wing Ribs Sine wave web Ribs are the structural crosspieces that combine with spars and stringers to make up the framework of the wing. They Caps usually extend from the wing leading edge to the rear spar or to the trailing edge of the wing. The ribs give the wing its cambered shape and transmit the load from the skin and stringers to the spars. Similar ribs are also used in ailerons, elevators, rudders, and stabilizers. Wing ribs are usually manufactured from either wood or metal. Aircraft with wood wing spars may have wood orFigure 1-29. A sine wave wing spar can be made from aluminum metal ribs while most aircraft with metal spars have metalor composite materials. ribs. Wood ribs are usually manufactured from spruce. The three most common types of wooden ribs are the plywoodAdditionally, fail-safe spar web design exists. Fail-safe web, the lightened plywood web, and the truss types. Of thesemeans that should one member of a complex structure fail, three, the truss type is the most efficient because it is strongsome other part of the structure assumes the load of the failed and lightweight, but it is also the most complex to construct.member and permits continued operation. A spar with fail-safe construction is shown in Figure 1-30. This spar is made Figure 1-31 shows wood truss web ribs and a lightenedin two sections. The top section consists of a cap riveted to plywood web rib. Wood ribs have a rib cap or cap stripthe upper web plate. The lower section is a single extrusion fastened around the entire perimeter of the rib. It is usuallyconsisting of the lower cap and web plate. These two sections made of the same material as the rib itself. The rib cap stiffensare spliced together to form the spar. If either section of this and strengthens the rib and provides an attaching surfacetype of spar breaks, the other section can still carry the load. for the wing covering. In Figure 1-31A, the cross-sectionThis is the fail-safe feature. of a wing rib with a truss-type web is illustrated. The dark rectangular sections are the front and rear wing spars. Note thatAs a rule, a wing has two spars. One spar is usually located to reinforce the truss, gussets are used. In Figure 1-31B, a trussnear the front of the wing, and the other about two-thirds of web rib is shown with a continuous gusset. It provides greaterthe distance toward the wing’s trailing edge. Regardless of support throughout the entire rib with very little additionaltype, the spar is the most important part of the wing. When weight. A continuous gusset stiffens the cap strip in the planeother structural members of the wing are placed under load, of the rib. This aids in preventing buckling and helps to obtainmost of the resulting stress is passed on to the wing spar. better rib/skin joints where nail-gluing is used. Such a rib can resist the driving force of nails better than the other types. 1-15
  • 40. the trailing edge of the wing. Wing butt ribs may be found at the inboard edge of the wing where the wing attaches A to the fuselage. Depending on its location and method of attachment, a butt rib may also be called a bulkhead rib or a compression rib if it is designed to receive compression loads that tend to force the wing spars together. B Since the ribs are laterally weak, they are strengthened in some wings by tapes that are woven above and below rib sections to prevent sidewise bending of the ribs. Drag and anti-drag C wires may also be found in a wing. In Figure 1-32, they are shown criss­ rossed between the spars to form a truss to resist c forces acting on the wing in the direction of the wing chord. These tension wires are also referred to as tie rods. The wireFigure 1-31. Examples of wing ribs constructed of wood. designed to resist the back­ ard forces is called a drag wire; wContinuous gussets are also more easily handled than the many the anti-drag wire resists the forward forces in the chordsmall separate gussets otherwise required. Figure 1-31C shows direction. Figure 1-32 illustrates the structural componentsa rib with a lighten plywood web. It also contains gussets to of a basic wood wing.support the web/cap strip interface. The cap strip is usuallylaminated to the web, especially at the leading edge. At the inboard end of the wing spars is some form of wing attach fitting as illustrated in Figure 1-32. These provideA wing rib may also be referred to as a plain rib or a main rib. a strong and secure method for attaching the wing to theWing ribs with specialized locations or functions are given fuselage. The interface between the wing and fuselage isnames that reflect their uniqueness. For example, ribs that often covered with a fairing to achieve smooth airflow in thisare located entirely forward of the front spar that are used to area. The fairing(s) can be removed for access to the wingshape and strengthen the wing leading edge are called nose attach fittings. [Figure 1-33]ribs or false ribs. False ribs are ribs that do not span the entirewing chord, which is the distance from the leading edge to Leading edge strip Nose rib or false rib Wing tip Front spar Anti-drag wire or tire rod Drag wire or tire rod Wing attach fittings False spar or aileron spar Rear spar Wing rib or plain rib Aileron Aileron hinge Wing butt rib (or compression rib or bulkhead rib)Figure 1-32. Basic wood wing structure and components.1-16
  • 41. to the tip with countersunk screws and is secured to the interspar structure at four points with ¼-inch diameter bolts. To prevent ice from forming on the leading edge of the wings of large aircraft, hot air from an engine is often channeled through the leading edge from wing root to wing tip. A louver on the top surface of the wingtip allows this warm air to be exhausted overboard. Wing position lights are located at the center of the tip and are not directly visible from the cockpit. As an indication that the wing tip light is operating, some wing tips are equipped with a Lucite rod to transmit the light to the leading edge. Wing Skin Often, the skin on a wing is designed to carry part of theFigure 1-33. Wing root fairings smooth airflow and hide wing flight and ground loads in combination with the spars andattach fittings. ribs. This is known as a stressed-skin design. The all-metal, full cantilever wing section illustrated in Figure 1-35 showsThe wing tip is often a removable unit, bolted to the outboard the structure of one such design. The lack of extra internalend of the wing panel. One reason for this is the vulnerability or external bracing requires that the skin share some of theof the wing tips to damage, especially during ground handling load. Notice the skin is stiffened to aid with this function.and taxiing. Figure 1-34 shows a removable wing tip for alarge aircraft wing. Others are different. The wing tip assemblyis of aluminum alloy construction. The wing tip cap is secured Access panel Upper skin Points of attachment to front and rear spar fittings (2 upper, 2 lower) Louver Wing tip navigation light Leading edge outer skin Corrugated inner skin Reflector rod Heat duct Wing capFigure 1-34. A removable metal wing tip. 1-17
  • 42. Fuel is often carried inside the wings of a stressed-skin On aircraft with stressed-skin wing design, honeycombaircraft. The joints in the wing can be sealed with a special structured wing panels are often used as skin. A honeycombfuel resistant sealant enabling fuel to be stored directly inside structure is built up from a core material resembling a beethe structure. This is known as wet wing design. Alternately, hive’s honeycomb which is laminated or sandwiched betweena fuel-carrying bladder or tank can be fitted inside a wing. thin outer skin sheets. Figure 1-37 illustrates honeycombFigure 1-36 shows a wing section with a box beam structural panes and their components. Panels formed like this aredesign such as one that might be found in a transport category lightweight and very strong. They have a variety of usesaircraft. This structure increases strength while reducing on the aircraft, such as floor panels, bulkheads, and controlweight. Proper sealing of the structure allows fuel to be stored surfaces, as well as wing skin panels. Figure 1-38 shows thein the box sections of the wing. locations of honeycomb construction wing panels on a jet transport aircraft.The wing skin on an aircraft may be made from a wide varietyof materials such as fabric, wood, or aluminum. But a single A honeycomb panel can be made from a wide variety ofthin sheet of material is not always employed. Chemically materials. Aluminum core honeycomb with an outer skin ofmilled aluminum skin can provide skin of varied thicknesses. aluminum is common. But honeycomb in which the core isFigure 1-35. The skin is an integral load carrying part of a stressed skin design. Sealed structure fuel tank—wet wingFigure 1-36. Fuel is often carried in the wings.1-18
  • 43. an Arimid® fiber and the outer sheets are coated Phenolic® nacelles are built into the wings or attached to the fuselageis common as well. In fact, a myriad of other material at the empennage (tail section). Occasionally, a multienginecombinations such as those using fiberglass, plastic, Nomex®, aircraft is designed with a nacelle in line with the fuselage aftKevlar ®, and carbon fiber all exist. Each honeycomb of the passenger compartment. Regardless of its location, astructure possesses unique characteristics depending upon nacelle contains the engine and accessories, engine mounts,the materials, dimensions, and manufacturing techniques structural members, a firewall, and skin and cowling on theemployed. Figure 1-39 shows an entire wing leading edge exterior to fare the nacelle to the wind.formed from honeycomb structure. Some aircraft have nacelles that are designed to house theNacelles landing gear when retracted. Retracting the gear to reduceNacelles (sometimes called “pods”) are streamlined wind resistance is standard procedure on high-performance/enclosures used primarily to house the engine and its high-speed aircraft. The wheel well is the area where thecomponents. They usually present a round or elliptical landing gear is attached and stowed when retracted. Wheelprofile to the wind thus reducing aerodynamic drag. On wells can be located in the wings and/or fuselage when notmost single-engine aircraft, the engine and nacelle are at the part of the nacelle. Figure 1-40 shows an engine nacelleforward end of the fuselage. On multiengine aircraft, engine incorporating the landing gear with the wheel well extending into the wing root. Core Skin A Skin Constant thickness Core Skin B Skin Tapered coreFigure 1-37. The honeycomb panel is a staple in aircraft construction. Cores can be either constant thickness (A) or tapered (B). Taperedcore honeycomb panels are frequently used as flight control surfaces and wing trailing edges. 1-19
  • 44. Trailing edge sandwich panels constant-thickness core Wing leading edge Spoiler sandwich panel tapered core, solid wedge Trailing edge sandwich panels constant-thickness core Inboard flap Spoiler sandwich panel Outboard flap tapered core, solid wedge Aileron tab sandwich panel Aileron tab sandwich panel tapered core, Phenolic wedge constant-thickness core Trailing edge wedge sandwich panel tapered core, cord wedgeFigure 1-38. Honeycomb wing construction on a large jet transport aircraft.The framework of a nacelle usually consists of structural components inside. Both are usually made of sheet aluminummembers similar to those of the fuselage. Lengthwise or magnesium alloy with stainless steel or titanium alloysmembers, such as longerons and stringers, combine with being used in high-temperature areas, such as around thehorizontal/vertical members, such as rings, formers, and exhaust exit. Regardless of the material used, the skin isbulkheads, to give the nacelle its shape and structural typically attached to the framework with rivets.integrity. A firewall is incorporated to isolate the enginecompartment from the rest of the aircraft. This is basically a Cowling refers to the detachable panels covering those areasstainless steel or titanium bulkhead that contains a fire in the into which access must be gained regularly, such as the engineconfines of the nacelle rather than letting it spread throughout and its accessories. It is designed to provide a smooth airflowthe airframe. [Figure 1-41] over the nacelle and to protect the engine from damage. Cowl panels are generally made of aluminum alloy construction.Engine mounts are also found in the nacelle. These are However, stainless steel is often used as the inner skin aftthe structural assemblies to which the engine is fastened. of the power section and for cowl flaps and near cowl flapThey are usually constructed from chrome/molybdenum openings. It is also used for oil cooler ducts. Cowl flaps aresteel tubing in light aircraft and forged chrome/nickel/ moveable parts of the nacelle cowling that open and closemolybdenum assemblies in larger aircraft. [Figure 1-42] to regulate engine temperature.The exterior of a nacelle is covered with a skin or fitted with There are many engine cowl designs. Figure 1-43 shows ana cowling which can be opened to access the engine and exploded view of the pieces of cowling for a horizontally1-20
  • 45. Metal wing spar Metal member bonded to sandwich Honeycomb sandwich core Wooden members spanwise and chordwise Glass reinforced plastics sandwich the coreFigure 1-39. A wing leading edge formed from honeycomb material bonded to the aluminum spar structure.Figure 1-40. Wheel wells in a wing engine nacelle with gear coming down (inset). 1-21
  • 46. Figure 1-41. An engine nacelle firewall.opposed engine on a light aircraft. It is attached to the nacelle Figure 1-42. Various aircraft engine mounts.by means of screws and/or quick release fasteners. Somelarge reciprocating engines are enclosed by “orange peel”cowlings which provide excellent access to componentsinside the nacelle. [Figure 1-44] These cowl panels areattached to the forward firewall by mounts which also serveas hinges for opening the cowl. The lower cowl mounts aresecured to the hinge brackets by quick release pins. The sideand top panels are held open by rods and the lower panel isretained in the open position by a spring and a cable. All ofthe cowling panels are locked in the closed position by over-center steel latches which are secured in the closed positionby spring-loaded safety catches.An example of a turbojet engine nacelle can be seen inFigure 1-45. The cowl panels are a combination of fixed andeasily removable panels which can be opened and closedduring maintenance. A nose cowl is also a feature on a jet Figure 1-43. Typical cowling for a horizontally opposedengine nacelle. It guides air into the engine. reciprocating engine. The tail cone serves to close and streamline the aft end ofEmpennage most fuselages. The cone is made up of structural membersThe empennage of an aircraft is also known as the tail like those of the fuselage; however, cones are usually ofsection. Most empennage designs consist of a tail cone, lighter con­ truction since they receive less stress than the sfixed aerodynamic surfaces or stabilizers, and movable fuselage. [Figure 1-46]aerodynamic surfaces.1-22
  • 47. Figure 1-44. Orange peel cowling for large radial reciprocating engine.Figure 1-45. Cowling on a transport category turbine engine nacelle. 1-23
  • 48. Frame Longeron Skin Stringer Rib Stringer Bulkhead Spars SkinFigure 1-46. The fuselage terminates at the tail cone with similarbut more lightweight construction. Figure 1-48. Vertical stabilizer.The other components of the typical empennage are of any overloads to the fuselage. A horizontal stabilizer is builtheavier construction than the tail cone. These members the same way.include fixed surfaces that help stabilize the aircraft andmovable surfaces that help to direct an aircraft during flight. The rudder and elevator are flight control surfaces that areThe fixed surfaces are the horizon­al stabilizer and vertical t also part of the empennage discussed in the next section ofstabilizer. The movable surfaces are usually a rudder located this chapter.at the aft edge of the vertical stabilizer and an elevator locatedat the aft edge the horizontal stabilizer. [Figure 1-47] Flight Control Surfaces The directional control of a fixed-wing aircraft takes place Vertical stabilizer around the lateral, longitudinal, and vertical axes by means of flight control surfaces designed to create movement about these axes. These control devices are hinged or movable Horizontal stabilizer Rudder surfaces through which the attitude of an aircraft is controlled during takeoff, flight, and landing. They are usually divided into two major groups: 1) pri­ ary or main flight control m Trim tabs surfaces and 2) secondary or auxiliary control surfaces. Primary Flight Control Surfaces The primary flight control surfaces on a fixed-wing aircraft include: ailerons, elevators, and the rudder. The ailerons are attached to the trailing edge of both wings and when moved, Elevator rotate the aircraft around the longitudinal axis. The elevator is attached to the trailing edge of the horizontal stabilizer.Figure 1-47. Components of a typical empennage. When it is moved, it alters aircraft pitch, which is the attitude about the horizontal or lateral axis. The rudder is hinged toThe structure of the stabilizers is very similar to that which the trailing edge of the vertical stabilizer. When the rudderis used in wing construction. Figure 1-48 shows a typical changes position, the aircraft rotates about the vertical axisvertical stabilizer. Notice the use of spars, ribs, stringers, (yaw). Figure 1-49 shows the primary flight controls of aand skin like those found in a wing. They perform the light aircraft and the movement they create relative to thesame functions shaping and supporting the stabilizer and three axes of flight.transferring stresses. Bending, torsion, and shear createdby air loads in flight pass from one structural member to Primary control surfaces are usually similar in construc­ion tanother. Each member absorbs some of the stress and passes to one another and vary only in size, shape, and methods ofthe remainder on to the others. Ultimately, the spar transmits1-24
  • 49. Primary control surfaces constructed from composite El Rudder—Yaw ev materials are also commonly used. These are found on many at La or— Vertical axis heavy and high-performance aircraft, as well as gliders, te (lo ra Pit (directional stangi l ax ch stability) home-built, and light-sport aircraft. The weight and strength bil tud is Roll ity ina on— advantages over traditional construction can be significant. ) l Ailer al itudin A wide variety of materials and construction techniques are Long(lateral axis ity) employed. Figure 1-51 shows examples of aircraft that use stabil composite technology on primary flight control surfaces. Note that the control surfaces of fabric-covered aircraft often have fabric-covered surfaces just as aluminum-skinned (light) aircraft typically have all-aluminum control surfaces. There is a critical need for primary control surfaces to be balanced so they do not vibrate or flutter in the wind. Primary Control Airplane Axes of Type of Surface Movement Rotation Stability Aileron Roll Longitudinal Lateral Elevator/ Pitch Lateral Longitudinal Stabilator Rudder Yaw Vertical DirectionalFigure 1-49. Flight control surfaces move the aircraft around thethree axes of flight.attachment. On aluminum light aircraft, their structure isoften similar to an all-metal wing. This is appropriate becausethe primary control surfaces are simply smaller aerodynamicdevices. They are typically made from an aluminum alloystructure built around a sin­ le spar member or torque tube to gwhich ribs are fitted and a skin is attached. The lightweightribs are, in many cases, stamped out from flat aluminum sheetstock. Holes in the ribs lighten the assembly. An aluminumskin is attached with rivets. Figure 1-50 illustrates this type ofstructure, which can be found on the primary control surfacesof light aircraft as well as on medium and heavy aircraft. Aileron hinge-pin fitting Actuating horn Spar Lightning hole Figure 1-51. Composite control surfaces and some of the manyFigure 1-50. Typical structure of an aluminum flight control surface. aircraft that utilize them. 1-25
  • 50. Performed to manufacturer’s instructions, balancing usuallyconsists of assuring that the center of gravity of a particular Up ailerondevice is at or forward of the hinge point. Failure to properlybalance a control surface could lead to catastrophic failure.Figure 1-52 illustrates several aileron configurations with Down ailerontheir hinge points well aft of the leading edge. This is acommon design feature used to prevent flutter. Figure 1-54. Differential aileron control movement. When one aileron is moved down, the aileron on the opposite wing is deflected upward.Figure 1-52. Aileron hinge locations are very close to but aft of the The pilot’s request for aileron movement and roll arecenter of gravity to prevent flutter. transmitted from the cockpit to the actual control surface in a variety of ways depending on the aircraft. A system of controlAilerons cables and pulleys, push-pull tubes, hydraulics, electric, or aAilerons are the primary flight control surfaces that move the combination of these can be employed. [Figure 1-55]aircraft about the longitudinal axis. In other words, movementof the ailerons in flight causes the aircraft to roll. Ailerons Stopare usually located on the outboard trailing edge of each ofthe wings. They are built into the wing and are calculated as Elevator cablespart of the wing’s surface area. Figure 1-53 shows aileronlocations on various wing tip designs. Tether stop Stop To ailerons Note pivots not on center of shaft Figure 1-55. Transferring control surface inputs from the cockpit.Figure 1-53. Aileron location on various wings. Simple, light aircraft usually do not have hydraulic or electric fly-by-wire aileron control. These are found on heavy andAilerons are controlled by a side-to-side motion of the control high-performance aircraft. Large aircraft and some high-stick in the cockpit or a rotation of the control yoke. When performance aircraft may also have a second set of aileronsthe aileron on one wing deflects down, the aileron on the located inboard on the trailing edge of the wings. These areopposite wing deflects upward. This amplifies the movement part of a complex system of primary and secondary controlof the aircraft around the longitudinal axis. On the wing on surfaces used to provide lateral control and stability in flight.which the aileron trailing edge moves downward, camber is At low speeds, the ailerons may be augmented by the useincreased and lift is increased. Conversely, on the other wing, of flaps and spoilers. At high speeds, only inboard aileronthe raised aileron decreases lift. [Figure 1-54] The result is deflection is required to roll the aircraft while the other controla sensitive response to the control input to roll the aircraft. surfaces are locked out or remain stationary. Figure 1-561-26
  • 51. illustrates the location of the typical flight control surfaces to the right. The left pedal is rigged to simultaneously movefound on a transport category aircraft. aft. When the left pedal is pushed forward, the nose of the aircraft moves to the left.ElevatorThe elevator is the primary flight control surface that moves As with the other primary flight controls, the transfer of thethe aircraft around the horizontal or lateral axis. This causes movement of the cockpit controls to the rudder varies withthe nose of the aircraft to pitch up or down. The elevator is the complexity of the aircraft. Many aircraft incorporate thehinged to the trailing edge of the horizontal stabilizer and directional movement of the nose or tail wheel into the ruddertypically spans most or all of its width. It is controlled in the control system for ground operation. This allows the operatorcockpit by pushing or pulling the control yoke forward or aft. to steer the aircraft with the rudder pedals during taxi when the airspeed is not high enough for the control surfaces to beLight aircraft use a system of control cables and pulleys or effective. Some large aircraft have a split rudder arrangement.push pull tubes to transfer cockpit inputs to the movement This is actually two rudders, one above the other. At lowof the elevator. High performance and large aircraft speeds, both rudders deflect in the same direction when thetypically employ more complex systems. Hydraulic power pedals are pushed. At higher speeds, one of the ruddersis commonly used to move the elevator on these aircraft. On becomes inoperative as the deflection of a single rudder isaircraft equipped with fly-by-wire controls, a combination aerodynamically sufficient to maneuver the aircraft.of electrical and hydraulic power is used. Dual Purpose Flight Control SurfacesRudder The ailerons, elevators, and rudder are consideredThe rudder is the primary control surface that causes an conventional primary control surfaces. However, someaircraft to yaw or move about the vertical axis. This provides aircraft are designed with a control surface that may serve adirectional control and thus points the nose of the aircraft dual purpose. For example, elevons perform the combinedin the direction desired. Most aircraft have a single rudder functions of the ailerons and the elevator. [Figure 1-57]hinged to the trailing edge of the vertical stabilizer. It iscontrolled by a pair of foot-operated rudder pedals in the A movable horizontal tail section, called a stabilator, is acockpit. When the right pedal is pushed forward, it deflects control surface that combines the action of both the horizontalthe rudder to the right which moves the nose of the aircraft stabilizer and the elevator. [Figure 1-58] Basically, a Flight spoilers Outboard aileron Inboard aileronFigure 1-56. Typical flight control surfaces on a transport category aircraft. 1-27
  • 52. edge. Movement of the ruddervators can alter the movement Elevons of the aircraft around the horizontal and/or vertical axis. Additionally, some aircraft are equipped with flaperons. [Figure 1-60] Flaperons are ailerons which can also act as flaps. Flaps are secondary control surfaces on most wings, discussed in the next section of this chapter. FlaperonsFigure 1-57. Elevons. Figure 1-60. Flaperons. Secondary or Auxiliary Control Surfaces There are several secondary or auxiliary flight control surfaces. Their names, locations, and functions of those for most large aircraft are listed in Figure 1-61. FlapsFigure 1-58. A stabilizer and index marks on a transport categoryaircraft. Flaps are found on most aircraft. They are usually inboard on the wings’ trailing edges adjacent to the fuselage. Leadingstabilator is a horizontal stabilizer that can also be rotated edge flaps are also common. They extend forward and downabout the horizontal axis to affect the pitch of the aircraft. from the inboard wing leading edge. The flaps are loweredA ruddervator combines the action of the rudder and elevator. to increase the camber of the wings and provide greater lift[Figure 1-59] This is possible on aircraft with V–tail and control at slow speeds. They enable landing at slowerempennages where the traditional horizontal and vertical speeds and shorten the amount of runway required for takeoffstabilizers do not exist. Instead, two stabilizers angle upward and landing. The amount that the flaps extend and the angleand outward from the aft fuselage in a “V” configuration. they form with the wing can be selected from the cockpit.Each contains a movable ruddervator built into the trailing Typically, flaps can extend up to 45–50°. Figure 1-62 shows various aircraft with flaps in the extended position. Flaps are usually constructed of materials and with techniques used on the other airfoils and control surfaces of a particular aircraft. Aluminum skin and structure flaps are the norm on Ruddervator light aircraft. Heavy and high-performance aircraft flaps may also be aluminum, but the use of composite structures is also common. There are various kinds of flaps. Plain flaps form the trailing edge of the wing when the flap is in the retracted position. [Figure 1-63A] The airflow over the wing continues over the upper and lower surfaces of the flap, making the trailing edge of the flap essentially the trailing edge of the wing. The plainFigure 1-59. Ruddervator.1-28
  • 53. Secondary/Auxiliary Flight Control Surfaces Name Location Function Extends the camber of the wing for greater lift and slower flight. Flaps Inboard trailing edge of wings Allows control at low speeds for short field takeoffs and landings. Trailing edge of primary Trim tabs flight control surfaces Reduces the force needed to move a primary control surface. Trailing edge of primary Balance tabs Reduces the force needed to move a primary control surface. flight control surfaces Trailing edge of primary Anti-balance tabs Increases feel and effectiveness of primary control surface. flight control surfaces Trailing edge of primary Servo tabs Assists or provides the force for moving a primary flight control. flight control surfaces Spoilers Upper and/or trailing edge of wing Decreases (spoils) lift. Can augment aileron function. Extends the camber of the wing for greater lift and slower flight. Slats Mid to outboard leading edge of wing Allows control at low speeds for short field takeoffs and landings. Outer leading edge of wing Directs air over upper surface of wing during high angle of attack. Slots forward of ailerons Lowers stall speed and provides control during slow flight. Extends the camber of the wing for greater lift and slower flight. Leading edge flap Inboard leading edge of wing Allows control at low speeds for short field takeoffs and landings. NOTE: An aircraft may possess none, one, or a combination of the above control surfaces.Figure 1-61. Secondary or auxiliary control surfaces and respective locations for larger aircraft.Figure 1-62. Various aircraft with flaps in the extended position. A B Plain flap Split flap p C Fowler flapFigure 1-63. Various types of flaps. 1-29
  • 54. flap is hinged so that the trailing edge can be lowered. Thisincreases wing camber and provides greater lift.A split flap is normally housed under the trailing edge of the Hinge pointwing. [Figure 1-63B] It is usually just a braced flat metalplate hinged at several places along its leading edge. The Actuatorupper surface of the wing extends to the trailing edge of theflap. When deployed, the split flap trailing edge lowers awayfrom the trailing edge of the wing. Airflow over the top of thewing remains the same. Airflow under the wing now followsthe camber created by the lowered split flap, increasing lift. Flap extendedFowler flaps not only lower the trailing edge of the wing when Flap retracteddeployed but also slide aft, effectively increasing the area of thewing. [Figure 1-63C] This creates more lift via the increased Retractable nosesurface area, as well as the wing camber. When stowed, thefowler flap typically retracts up under the wing trailing edge Figure 1-65. Leading edge flaps.similar to a split flap. The sliding motion of a fowler flap canbe accomplished with a worm drive and flap tracks. The differing designs of leading edge flaps essentially provide the same effect. Activation of the trailing edgeAn enhanced version of the fowler flap is a set of flaps flaps automatically deploys the leading edge flaps, whichthat actually contains more than one aerodynamic surface. are driven out of the leading edge and downward, extendingFigure 1-64 shows a triple-slotted flap. In this configuration, the camber of the wing. Figure 1-66 shows a Krueger flap,the flap consists of a fore flap, a mid flap, and an aft flap. recognizable by its flat mid-section.When deployed, each flap section slides aft on tracks as itlowers. The flap sections also separate leaving an open slot Slatsbetween the wing and the fore flap, as well as between each Another leading-edge device which extends wing camber isof the flap sections. Air from the underside of the wing flows a slat. Slats can be operated independently of the flaps withthrough these slots. The result is that the laminar flow on the their own switch in the cockpit. Slats not only extend outupper surfaces is enhanced. The greater camber and effective of the leading edge of the wing increasing camber and lift,wing area increase overall lift. but most often, when fully deployed leave a slot between their trailing edges and the leading edge of the wing. [Figure 1-67] This increases the angle of attack at which Retracted the wing will maintain its laminar airflow, resulting in the ability to fly the aircraft slower and still maintain control. Spoilers and Speed Brakes A spoiler is a device found on the upper surface of many Fore flap heavy and high-performance aircraft. It is stowed flush to Mid flap the wing’s upper surface. When deployed, it raises up into the airstream and disrupts the laminar airflow of the wing, Aft flap thus reducing lift.Figure 1-64. Triple slotted flap. Spoilers are made with similar construction materials and techniques as the other flight control surfaces on the aircraft. Often, they are honeycomb-core flat panels. At low speeds,Heavy aircraft often have leading edge flaps that are used spoilers are rigged to operate when the ailerons operate toin conjunction with the trailing edge flaps. [Figure 1-65] assist with the lateral movement and stability of the aircraft.They can be made of machined magnesium or can have an On the wing where the aileron is moved up, the spoilersaluminum or composite structure. While they are not installed also raise thus amplifying the reduction of lift on that wing.or operate independently, their use with trailing edge flaps [Figure 1-68] On the wing with downward aileron deflection,can greatly increase wing camber and lift. When stowed, the spoilers remain stowed. As the speed of the aircraftleading edge flaps retract into the leading edge of the wing.1-30
  • 55. Figure 1-66. Side view (left) and front view (right) of a Krueger flap on a Boeing 737. Figure 1-68. Spoilers deployed upon landing on a transport categoryFigure 1-67. Air passing through the slot aft of the slat promotes aircraft.boundary layer airflow on the upper surface at high angles of attack. The speed brake control in the cockpit can deploy all spoilerincreases, the ailerons become more effective and the spoiler and speed brake surfaces fully when operated. Often, theseinterconnect disengages. surfaces are also rigged to deploy on the ground automatically when engine thrust reversers are activated.Spoilers are unique in that they may also be fully deployedon both wings to act as speed brakes. The reduced lift and Tabsincreased drag can quickly reduce the speed of the aircraft in The force of the air against a control surface during the highflight. Dedicated speed brake panels similar to flight spoilers speed of flight can make it difficult to move and hold thatin construction can also be found on the upper surface of control surface in the deflected position. A control surfacethe wings of heavy and high-performance aircraft. They are might also be too sensitive for similar reasons. Severaldesigned specifically to increase drag and reduce the speed different tabs are used to aid with these types of problems.of the aircraft when deployed. These speed brake panels The table in Figure 1-69 summarizes the various tabs anddo not operate differentially with the ailerons at low speed. their uses. 1-31
  • 56. Flight Control Tabs Direction of Motion Type Activation Effect (in relation to control surface) Statically balances the aircraft Trim Opposite Set by pilot from cockpit. in flight. Allows “hands off” Uses independent linkage. maintenance of flight condition. Moves when pilot moves control surface. Aids pilot in overcoming the force Balance Opposite Coupled to control surface linkage. needed to move the control surface. Directly linked to flight control Aerodynamically positions control Servo Opposite input device. Can be primary surfaces that require too much or back-up means of control. force to move manually. Increases force needed by pilot Anti-balance Same Directly linked to flight to change flight control position. or Anti-servo control input device. De-sensitizes flight controls. Located in line of direct linkage to servo Enables moving control surface Spring Opposite tab. Spring assists when control forces when forces are high. become too high in high-speed flight. Inactive during slow flight.Figure 1-69. Various tabs and their uses.While in flight, it is desirable for the pilot to be able to take hisor her hands and feet off of the controls and have the aircraftmaintain its flight condition. Trims tabs are designed to allowthis. Most trim tabs are small movable surfaces located onthe trailing edge of a primary flight control surface. A smallmovement of the tab in the direction opposite of the directionthe flight control surface is deflected, causing air to strike thetab, in turn producing a force that aids in maintaining the flightcontrol surface in the desired position. Through linkage setfrom the cockpit, the tab can be positioned so that it is actuallyholding the control surface in position rather than the pilot.Therefore, elevator tabs are used to maintain the speed of theaircraft since they assist in maintaining the selected pitch.Rudder tabs can be set to hold yaw in check and maintainheading. Aileron tabs can help keep the wings level. Ground adjustable rudder trimOccasionally, a simple light aircraft may have a stationarymetal plate attached to the trailing edge of a primary flightcontrol, usually the rudder. This is also a trim tab as shown in Figure 1-70. Example of a trim tab.Figure 1-70. It can be bent slightly on the ground to trim the direction of the desired control surface movement causesaircraft in flight to a hands-off condition when flying straight a force to position the surface in the proper direction withand level. The correct amount of bend can be determined only reduced force to do so. Balance tabs are usually linked directlyby flying the aircraft after an adjustment. Note that a small to the control surface linkage so that they move automaticallyamount of bending is usually sufficient. when there is an input for control surface movement. They also can double as trim tabs, if adjustable in the flight deck.The aerodynamic phenomenon of moving a trim tab in onedirection to cause the control surface to experience a force A servo tab is similar to a balance tab in location and effect,moving in the opposite direction is exactly what occurs with but it is designed to operate the primary flight control surface,the use of balance tabs. [Figure 1-71] Often, it is difficult to not just reduce the force needed to do so. It is usually used asmove a primary control surface due to its surface area and a means to back up the primary control of the flight controlthe speed of the air rushing over it. Deflecting a balance tab surfaces. [Figure 1-72]hinged at the trailing edge of the control surface in the opposite1-32
  • 57. surfaces are signaled by electric input. In the case of hydraulic Tab geared to deflect proportionally to the system failure(s), manual linkage to a servo tab can be used Lift control deflection, but in the opposite direction to deflect it. This, in turn, provides an aerodynamic force that moves the primary control surface. A control surface may require excessive force to move only in the final stages of travel. When this is the case, a spring Fixed surface Con trol tab can be used. This is essentially a servo tab that does not activate until an effort is made to move the control surface beyond a certain point. When reached, a spring in line of the tab control linkage aids in moving the control surface through the remainder of its travel. [Figure 1-73]Figure 1-71. Balance tabs assist with forces needed to positioncontrol surfaces. Control stick Spring Free link Control stick Free link Figure 1-73. Many tab linkages have a spring tab that kicks in as the forces needed to deflect a control increase with speed and the angle of desired deflection. Control surface hinge line Figure 1-74 shows another way of assisting the movement of an aileron on a large aircraft. It is called an aileron balanceFigure 1-72. Servo tabs can be used to position flight control panel. Not visible when approaching the aircraft, it issurfaces in case of hydraulic failure. positioned in the linkage that hinges the aileron to the wing.On heavy aircraft, large control surfaces require too muchforce to be moved manually and are usually deflected out Balance panels have been constructed typically of aluminumof the neutral position by hydraulic actuators. These power skin-covered frame assemblies or aluminum honeycombcontrol units are signaled via a system of hydraulic valves structures. The trailing edge of the wing just forward of theconnected to the yoke and rudder pedals. On fly-by-wire leading edge of the aileron is sealed to allow controlled airflowaircraft, the hydraulic actuators that move the flight control in and out of the hinge area where the balance panel is located. Hinge Balance panel Vent gap Control tab AILERON WING Lower pressure Vent gapFigure 1-74. An aileron balance panel and linkage uses varying air pressure to assist in control surface positioning. 1-33
  • 58. [Figure 1-75] When the aileron is moved from the neutralposition, differential pressure builds up on one side of thebalance panel. This differential pressure acts on the balancepanel in a direction that assists the aileron movement. Forslight movements, deflecting the control tab at the trailingedge of the aileron is easy enough to not require significant Antiservo tabassistance from the balance tab. (Moving the control tab movesthe ailerons as desired.) But, as greater deflection is requested,the force resisting control tab and aileron movement becomes Stabilator pivot pointgreater and augmentation from the balance tab is needed. Theseals and mounting geometry allow the differential pressureof airflow on the balance panel to increase as deflection ofthe ailerons is increased. This makes the resistance felt whenmoving the aileron controls relatively constant. Figure 1-76. An antiservo tab moves in the same direction as the control tab. Shown here on a stabilator, it desensitizes the pitch control. Balance panelFigure 1-75. The trailing edge of the wing just forward of the leadingedge of the aileron is sealed to allow controlled airflow in and outof the hinge area where the balance panel is located.Antiservo tabs, as the name suggests, are like servo tabs butmove in the same direction as the primary control surface.On some aircraft, especially those with a movable horizontalstabilizer, the input to the control surface can be too sensitive.An antiservo tab tied through the control linkage creates an Figure 1-77. A winglet reduces aerodynamic drag caused by airaerodynamic force that increases the effort needed to move spilling off of the wing tip.the control surface. This makes flying the aircraft morestable for the pilot. Figure 1-76 shows an antiservo tab in Vortex generators are small airfoil sections usually attachedthe near neutral position. Deflected in the same direction as to the upper surface of a wing. [Figure 1-78] They arethe desired stabilator movement, it increases the required designed to promote positive laminar airflow over thecontrol surface input. wing and control surfaces. Usually made of aluminum and installed in a spanwise line or lines, the vortices created byOther Wing Features these devices swirl downward assisting maintenance of theThere may be other structures visible on the wings of an boundary layer of air flowing over the wing. They can alsoaircraft that contribute to performance. Winglets, vortex be found on the fuselage and empennage. Figure 1-79 showsgenerators, stall fences, and gap seals are all common wing the unique vortex generators on a Symphony SA-160 wing.features. Introductory descriptions of each are given in thefollowing paragraphs. A chordwise barrier on the upper surface of the wing, called a stall fence, is used to halt the spanwise flow of air. DuringA winglet is an obvious vertical upturn of the wing’s tip low speed flight, this can maintain proper chordwise airflowresembling a vertical stabilizer. It is an aerodynamic device reducing the tendency for the wing to stall. Usually madedesigned to reduce the drag created by wing tip vortices in of aluminum, the fence is a fixed structure most commonflight. Usually made from aluminum or composite materials, on swept wings, which have a natural spanwise tendingwinglets can be designed to optimize performance at a desired boundary air flow. [Figure 1-80]speed. [Figure 1-77]1-34
  • 59. Stall fenceFigure 1-78. Vortex generators. Figure 1-80. A stall fence aids in maintaining chordwise airflow over the wing. and disrupt the upper wing surface airflow, which in turn reduces lift and control surface responsiveness. The use of gap seals is common to promote smooth airflow in these gap areas. Gap seals can be made of a wide variety of materials ranging from aluminum and impregnated fabric to foam and plastic. Figure 1-81 shows some gap seals installed on various aircraft. Landing Gear The landing gear supports the aircraft during landing andFigure 1-79. The Symphony SA-160 has two unique vortex while it is on the ground. Simple aircraft that fly at low speedsgenerators on its wing to ensure aileron effectiveness through the generally have fixed gear. This means the gear is stationarystall. and does not retract for flight. Faster, more complex aircraftOften, a gap can exist between the stationary trailing edge have retractable landing gear. After takeoff, the landingof a wing or stabilizer and the movable control surface(s). gear is retracted into the fuselage or wings and out of theAt high angles of attack, high pressure air from the lower airstream. This is important because extended gear createwing surface can be disrupted at this gap. The result can significant parasite drag which reduces performance. Parasitebe turbulent airflow, which increases drag. There is also a drag is caused by the friction of the air flowing over the gear.tendency for some lower wing boundary air to enter the gap It increases with speed. On very light, slow aircraft, the Aileron gap seal Tab gap sealFigure 1-81. Gap seals promote the smooth flow of air over gaps between fixed and movable surfaces. 1-35
  • 60. extra weight that accompanies a retractable landing gear ismore of a detriment than the drag caused by the fixed gear.Lightweight fairings and wheel pants can be used to keepdrag to a minimum. Figure 1-82 shows examples of fixedand retractable gear.Landing gear must be strong enough to withstand the forcesof landing when the aircraft is fully loaded. In addition tostrength, a major design goal is to have the gear assembly beas light as possible. To accomplish this, landing gear are madefrom a wide range of materials including steel, aluminum,and magnesium. Wheels and tires are designed specificallyfor aviation use and have unique operating characteristics.Main wheel assemblies usually have a braking system. Toaid with the potentially high impact of landing, most landinggear have a means of either absorbing shock or acceptingshock and distributing it so that the structure is not damaged.Not all aircraft landing gear are configured with wheels.Helicopters, for example, have such high maneuverabilityand low landing speeds that a set of fixed skids is commonand quite functional with lower maintenance. The same is truefor free balloons which fly slowly and land on wood skidsaffixed to the floor of the gondola. Other aircraft landing gearare equipped with pontoons or floats for operation on water.A large amount of drag accompanies this type of gear, but anaircraft that can land and take off on water can be very useful Figure 1-82. Landing gear can be fixed (top) or retractable (bottom).in certain environments. Even skis can be found under someaircraft for operation on snow and ice. Figure 1-83 shows Amphibious aircraft are aircraft than can land either on landsome of these alternative landing gear, the majority of which or on water. On some aircraft designed for such dual usage,are the fixed gear type. the bottom half of the fuselage acts as a hull. Usually, it is accompanied by outriggers on the underside of the wings near the tips to aid in water landing and taxi. Main gear that retract into the fuselage are only extended when landing onFigure 1-83. Aircraft landing gear without wheels.1-36
  • 61. the ground or a runway. This type of amphibious aircraft is by rigging cables attached to the rudder pedals. Othersometimes called a flying boat. [Figure 1-84] conventional gear have no tail wheel at all using just a steel skid plate under the aft fuselage instead. The small tail wheel or skid plate allows the fuselage to incline, thus giving clearance for the long propellers that prevailed in aviation through WWII. It also gives greater clearance between the propeller and loose debris when operating on an unpaved runway. But the inclined fuselage blocks the straight ahead vision of the pilot during ground operations. Until up to speed where the elevator becomes effective to lift the tail wheel off the ground, the pilot must lean his head out the side of the cockpit to see directly ahead of the aircraft.Figure 1-84. An amphibious aircraft is sometimes called a flyingboat because the fuselage doubles as a hull.Many aircraft originally designed for land use can be fittedwith floats with retractable wheels for amphibious use.[Figure 1-85] Typically, the gear retracts into the floatwhen not needed. Sometimes a dorsal fin is added to the aftunderside of the fuselage for longitudinal stability duringwater operations. It is even possible on some aircraft to directthis type of fin by tying its control into the aircraft’s rudderpedals. Skis can also be fitted with wheels that retract to allow Figure 1-86. An aircraft with tail wheel gear.landing on solid ground or on snow and ice. The use of tail wheel gear can pose another difficulty. When landing, tail wheel aircraft can easily ground loop. A ground loop is when the tail of the aircraft swings around and comes forward of the nose of the aircraft. The reason this happens is due to the two main wheels being forward of the aircraft’s center of gravity. The tail wheel is aft of the center of gravity. If the aircraft swerves upon landing, the tail wheel can swing out to the side of the intended path of travel. If far enough to the side, the tail can pull the center of gravity out from its desired location slightly aft of but between the main gear. Once the center of gravity is no longer trailing the mains, the tail of the aircraft freely pivots around the main wheels causing the ground loop.Figure 1-85. Retractable wheels make this aircraft amphibious. Conventional gear is useful and is still found on certain models of aircraft manufactured today, particularly aerobatic aircraft,Tail Wheel Gear Configuration crop dusters, and aircraft designed for unpaved runway use.There are two basic configurations of airplane landing gear: It is typically lighter than tricycle gear which requires a stout,conventional gear or tail wheel gear and the tricycle gear. fully shock absorbing nose wheel assembly. The tail wheelTail wheel gear dominated early aviation and therefore configuration excels when operating out of unpaved runways.has become known as conventional gear. In addition to its With the two strong main gear forward providing stabilitytwo main wheels which are positioned under most of the and directional control during takeoff roll, the lightweight tailweight of the aircraft, the conventional gear aircraft also wheel does little more than keep the aft end of the fuselagehas a smaller wheel located at the aft end of the fuselage. from striking the ground. As mentioned, at a certain speed,[Figure 1-86] Often this tail wheel is able to be steered the air flowing over the elevator is sufficient for it to raise the 1-37
  • 62. tail off the ground. As speed increases further, the two main used information required to maintain the aircraft properly.wheels under the center of gravity are very stable. The Type Certificate Data Sheet (TCDS) for an aircraft also contains critical information. Complex and large aircraftTricycle Gear require several manuals to convey correct maintenanceTricycle gear is the most prevalent landing gear configuration procedures adequately. In addition to the maintenancein aviation. In addition to the main wheels, a shock absorbing manual, manufacturers may produce such volumes asnose wheel is at the forward end of the fuselage. Thus, the structural repair manuals, overhaul manuals, wiring diagramcenter of gravity is then forward of the main wheels. The tail manuals, component manuals, and more.of the aircraft is suspended off the ground and clear viewstraight ahead from the cockpit is given. Ground looping Note that the use of the word “manual” is meant to includeis nearly eliminated since the center of gravity follows the electronic as well as printed information. Also, properdirectional nose wheel and remains between the mains. maintenance extends to the use of designated tools and fixtures called out in the manufacturer’s maintenanceLight aircraft use tricycle gear, as well as heavy aircraft. Twin documents. In the past, not using the proper tooling hasnose wheels on the single forward strut and massive multistrut/ caused damage to critical components, which subsequentlymultiwheel main gear may be found supporting the world’s failed and led to aircraft crashes and the loss of humanlargest aircraft, but the basic configuration is still tricycle. life. The technician is responsible for sourcing the correctThe nose wheel may be steered with the rudder pedals on information, procedures, and tools needed to performsmall aircraft. Larger aircraft often have a nose wheel steering airworthy maintenance or repairs.wheel located off to the side of the cockpit. Figure 1-87 showsaircraft with tricycle gear. Chapter 13, Aircraft Landing Gear Standard aircraft maintenance procedures do exist and canSystems, discusses landing gear in detail. be used by the technician when performing maintenance or a repair. These are found in the Federal Aviation AdministrationMaintaining the Aircraft (FAA) approved advisory circulars (AC) 43.13-2 and ACMaintenance of an aircraft is of the utmost importance for safe 43.13-1. If not addressed by the manufacturer’s literature,flight. Licensed technicians are committed to perform timely the technician may use the procedures outlined in thesemaintenance functions in accordance with the manufacturer’s manuals to complete the work in an acceptable manner.instructions and under the 14 CFR. At no time is an act These procedures are not specific to any aircraft or componentof aircraft maintenance taken lightly or improvised. The and typically cover methods used during maintenance of allconsequences of such action could be fatal and the technician aircraft. Note that the manufacturer’s instructions supersedecould lose his or her license and face criminal charges. the general procedures found in AC 43.13-2 and AC 43.13-1.Airframe, engine, and aircraft component manufacturers are All maintenance related actions on an aircraft or componentresponsible for documenting the maintenance procedures that are required to be documented by the performing technicianguide managers and technicians on when and how to perform in the aircraft or component logbook. Light aircraft may havemaintenance on their products. A small aircraft may only only one logbook for all work performed. Some aircraft mayrequire a few manuals, including the aircraft maintenance have a separate engine logbook for any work performed onmanual. This volume usually contains the most frequently the engine(s). Other aircraft have separate propeller logbooks.Figure 1-87. Tricycle landing gear is the most predominant landing gear configuration in aviation.1-38
  • 63. Large aircraft require volumes of maintenance documentation the aircraft from which all fore and aft dis­ances are tcomprised of thousands of procedures performed by hundreds measured. The distance to a given point is measuredof technicians. Electronic dispatch and recordkeeping of in inches paral­el to a center line extending through lmaintenance performed on large aircraft such as airliners the aircraft from the nose through the center of theis common. The importance of correct maintenance tail cone. Some manufacturers may call the fuselagerecordkeeping should not be overlooked. station a body sta­ion, abbreviated BS. t • Buttock line or butt line (BL) is a vertical referenceLocation Numbering Systems plane down the center of the aircraft from whichEven on small, light aircraft, a method of precisely locating measurements left or right can be made. [Figure 1-89]each structural component is required. Various numberingsystems are used to facilitate the location of specific wing • Water line (WL) is the measurement of height inframes, fuselage bulkheads, or any other structural members inches perpendicular from a horizontal plane usuallyon an aircraft. Most manufacturers use some system of located at the ground, cabin floor, or some other easilystation marking. For example, the nose of the air­ raft may be c referenced location. [Figure 1-90]designated “zero station,” and all other stations are located at • Aileron station (AS) is measured out­ oard from, bmeasured distances in inches behind the zero station. Thus, and parallel to, the inboard edge of the aileron,when a blueprint reads “fuselage frame station 137,” that perpendicular to the rear beam of the wing.particular frame station can be located 137 inches behind • Flap station (KS) is measured perpendicular to the rearthe nose of the aircraft. beam of the wing and parallel to, and outboard from, the in­ oard edge of the flap. bTo locate structures to the right or left of the center line of anaircraft, a similar method is employed. Many manufacturers • Nacelle station (NC or Nac. Sta.) is measured eithercon­ ider the center line of the aircraft to be a zero station s forward of or behind the front spar of the wing andfrom which measurements can be taken to the right or left perpendic­ lar to a designated water line. uto locate an airframe member. This is often used on thehorizontal stabilizer and wings. In addition to the location stations listed above, other measurements are used, especially on large aircraft. Thus,The applicable manufacturer’s numbering system and there may be horizontal stabilizer stations (HSS), verticalabbreviated designations or symbols should al­ ays be w stabilizer stations (VSS) or powerplant stations (PPS).reviewed before attempting to locate a structural member. [Figure 1-91] In every case, the manufacturer’s terminologyThey are not always the same. The following list includes and station lo­ ation system should be consulted before cloca­ ion designations typical of those used by many t locating a point on a particular aircraft.manufacturers. Another method is used to facilitate the location of aircraft • Fuselage stations (Fus. Sta. or FS) are numbered in components on air transport aircraft. This involves dividing inches from a reference or zero point known as the the aircraft into zones. These large areas or major zones reference datum. [Figure 1-88] The reference datum are further divided into sequentially numbered zones and is an imaginary ver­ical plane at or near the nose of t subzones. The digits of the zone number are reserved and WL 0.00 FS −97.0 FS −85.20 FS 273.52 FS −80.00 FS 234.00 FS −59.06 FS 224.00 FS −48.50 FS 214.00 FS −31.00 FS 200.70 FS −16.25 FS 189.10 FS 0.00 FS 177.50 FS 20.20 FS 154.75 FS 37.50 FS 132.00 FS 58.75 FS 109.375 FS 69.203 FS 89.25Figure 1-88. The various body stations relative to a single point of origin illustrated in inches or some other measurement (if of foreigndevelopment). 1-39
  • 64. better laminar airflow, which causes lift. On large aircraft, BL 21.50 BL 21.50 walkways are sometimes designated on the wing upper BL 47.50 BL 47.50 surface to permit safe navigation by mechanics and inspectors BL 96.50 BL 96.50 to critical structures and components located along the wing’s leading and trailing edges. Wheel wells and special component bays are places where numerous components and accessories are grouped together for easy maintenance access. Panels and doors on aircraft are numbered for positive identification. On large aircraft, panels are usually numbered sequentially containing zone and subzone information in the BL 96.62 BL 86.56 BL 86.56 BL 96.62 panel number. Designation for a left or right side location on BL 76.50 BL 76.50 the aircraft is often indicated in the panel number. This could BL 61.50 BL 61.50 BL 47.27 BL 47.27 be with an “L” or “R,” or panels on one side of the aircraft BL 34.5 BL 34.5 BL 23.25 could be odd numbered and the other side even numbered. BL 16.00 The manufacturer’s maintenance manual explains the panel numbering system and often has numerous diagrams andFigure 1-89. Butt line diagram of a horizontal stabilizer. tables showing the location of various components and underindexed to indicate the location and type of system of which which panel they may be found. Each manufacturer is entitledthe component is a part. Figure 1-92 illustrates these zones to develop its own panel numbering system.and subzones on a transport category aircraft. Helicopter StructuresAccess and Inspection Panels The structures of the helicopter are designed to give theKnowing where a particular structure or component is located helicopter its unique flight characteristics. A simplifiedon an aircraft needs to be combined with gaining access to explanation of how a helicopter flies is that the rotors arethat area to perform the required inspections or maintenance. rotating airfoils that provide lift similar to the way wingsTo facilitate this, access and inspection panels are located on provide lift on a fixed-wing aircraft. Air flows faster over themost surfaces of the aircraft. Small panels that are hinged or curved upper surface of the rotors, causing a negative pressureremovable allow inspection and servicing. Large panels and and thus, lifting the aircraft. Changing the angle of attack ofdoors allow components to be removed and installed, as well the rotating blades increases or decreases lift, respectivelyas human entry for maintenance purposes. raising or lowering the helicopter. Tilting the rotor plane of rotation causes the aircraft to move horizontally. Figure 1-93The underside of a wing, for example, sometimes contains shows the major components of a typical helicopter.dozens of small panels through which control cablecomponents can be monitored and fittings greased. Various Airframedrains and jack points may also be on the underside of The airframe, or fundamental structure, of a helicopter can bethe wing. The upper surface of the wings typically have made of either metal or wood composite materials, or somefewer access panels because a smooth surface promotes combination of the two. Typically, a composite component WL 123.483 WL 97.5 WL 79.5 WL 73.5 WL 7.55 Ground line WL 9.55Figure 1-90. Water line diagram.1-40
  • 65. 652.264 511.21 568.5 843.8 379 411 437 536 585 863 886 903 943 C FUS-WING STA 0 L 16.5 15.2 25.7 41.3 56.9 65.7 NAC C L 76.5 72.5 85.5 BL 86.179 88.1 2° 106.4 104.1 111 122 127.2 FS 652.264 FS 674.737 177.0 FS 625.30 148 15° 163 178 199 FUS C L 220 WGLTS 49.89 242 258 264 NAC C L 274 WGLTS 0.00 282 BL 86.179 294.5 2° 315.5 353 371 329.5 100.72 135.845 151.14 155.315 177 185 200 218.17 230.131 343.5 353 371 4°Figure 1-91. Wing stations are often referenced off the butt line, which bisects the center of the fuselage longitudinally. Horizontalstabilizer stations referenced to the butt line and engine nacelle stations are also shown. ZONE 300—Empennage E 326 324 ZONE 300—Empennage 344 343 342 345 341 335 334 325 323 322 321 333 351 312 332 331 311 Zone 600—Right wing Zone 400—Engine nacelles ZONE 800 Doors 800—Doors 825 824 Zone 200—Upper half of fuselage 822 823 82 821 811 Zone 700—Landing gear and landing gear doors ZONE 100—Lower half of fuselage 146 144 142 143 Zone 500—Left wing 132 123 133 145 141 122 131 Z Zones 135 Su Subzones 134 111 112 121Figure 1-92. Large aircraft are divided into zones and subzones for identifying the location of various components. 1-41
  • 66. consists of many layers of fiber-impregnated resins, bonded Landing Gear or Skidsto form a smooth panel. Tubular and sheet metal substructures As mentioned, a helicopter’s landing gear can be simply aare usually made of aluminum, though stainless steel or set of tubular metal skids. Many helicopters do have landingtitanium are sometimes used in areas subject to higher gear with wheels, some retractable.stress or heat. Airframe design encompasses engineering,aerodynamics, materials technology, and manufacturing Powerplant and Transmissionmethods to achieve favorable balances of performance, The two most common types of engine used in helicopters arereliability, and cost. the reciprocating engine and the turbine engine. Reciprocating engines, also called piston engines, are generally usedFuselage in smaller helicopters. Most training helicopters useAs with fixed-wing aircraft, helicopter fuselages and tail reciprocating engines because they are relatively simplebooms are often truss-type or semimonocoque structures and inexpensive to operate. Refer to the Pilot’s Handbookof stress-skin design. Steel and aluminum tubing, formed of Aeronautical Knowledge for a detailed explanation andaluminum, and aluminum skin are commonly used. Modern illustrations of the piston engine.helicopter fuselage design includes an increasing utilizationof advanced composites as well. Firewalls and engine Turbine Enginesdecks are usually stainless steel. Helicopter fuselages vary Turbine engines are more powerful and are used in a widewidely from those with a truss frame, two seats, no doors, variety of helicopters. They produce a tremendous amountand a monocoque shell flight compartment to those with of power for their size but are generally more expensivefully enclosed airplane-style cabins as found on larger to operate. The turbine engine used in helicopters operatestwin-engine helicopters. The multidirectional nature of differently than those used in airplane applications. In mosthelicopter flight makes wide-range visibility from the applications, the exhaust outlets simply release expendedcockpit essential. Large, formed polycarbonate, glass, or gases and do not contribute to the forward motion of theplexiglass windscreens are common. helicopter. Because the airflow is not a straight line pass through as in jet engines and is not used for propulsion, the Tail rotor Tail boom Main rotor hub assembly Stabilizer Main rotor blades Pylon Tail skid Powerplant Airframe Fuselage Transmission Landing gear or skidFigure 1-93. The major components of a helicopter are the airframe, fuselage, landing gear, powerplant/transmission, main rotor system,and antitorque system.1-42
  • 67. cooling effect of the air is limited. Approximately 75 percent Transmissionof the incoming airflow is used to cool the engine. The transmission system transfers power from the engine to the main rotor, tail rotor, and other accessories during normalThe gas turbine engine mounted on most helicopters is flight conditions. The main components of the transmissionmade up of a compressor, combustion chamber, turbine, system are the main rotor transmission, tail rotor driveand accessory gearbox assembly. The compressor draws system, clutch, and freewheeling unit. The freewheeling unit,filtered air into the plenum chamber and compresses it. or autorotative clutch, allows the main rotor transmission toCommon type filters are centrifugal swirl tubes where debris drive the tail rotor drive shaft during autorotation. Helicopteris ejected outward and blown overboard prior to entering transmissions are normally lubricated and cooled with theirthe compressor, or engine barrier filters (EBF), similar to own oil supply. A sight gauge is provided to check the oilthe K&N filter element used in automotive applications. level. Some transmissions have chip detectors located in theThis design significantly reduces the ingestion of foreign sump. These detectors are wired to warning lights locatedobject debris (FOD). The compressed air is directed to the on the pilot’s instrument panel that illuminate in the eventcombustion section through discharge tubes where atomized of an internal problem. Some chip detectors on modernfuel is injected into it. The fuel/air mixture is ignited and helicopters have a “burn off” capability and attempt to correctallowed to expand. This combustion gas is then forced the situation without pilot action. If the problem cannot bethrough a series of turbine wheels causing them to turn. corrected on its own, the pilot must refer to the emergencyThese turbine wheels provide power to both the engine procedures for that particular helicopter.compressor and the accessory gearbox. Depending on modeland manufacturer, the rpm range can vary from a range low Main Rotor Systemof 20,000 to a range high of 51,600. The rotor system is the rotating part of a helicopter which generates lift. The rotor consists of a mast, hub, and rotorPower is provided to the main rotor and tail rotor systems blades. The mast is a cylindrical metal shaft that extendsthrough the freewheeling unit which is attached to the upwards from and is driven, and sometimes supported, byaccessory gearbox power output gear shaft. The combustion the transmission. At the top of the mast is the attachmentgas is finally expelled through an exhaust outlet. The point for the rotor blades called the hub. The rotor blades aretemperature of gas is measured at different locations and is then attached to the hub by any number of different methods.referenced differently by each manufacturer. Some common Main rotor systems are classified according to how the mainterms are: inter-turbine temperature (ITT), exhaust gas rotor blades are attached and move relative to the main rotortemperature (EGT), or turbine outlet temperature (TOT). hub. There are three basic classifications: rigid, semirigid,TOT is used throughout this discussion for simplicity or fully articulated.purposes. [Figure 1-94] Gearbox Compression Section Turbine Section Combustion Section Section Exhaust air outlet N2 Rotor Stator N1 Rotor Compressor rotor Igniter plug Air inlet Fuel nozzle Gear Inlet air Compressor discharge air Output Shaft Combustion liner Combustion gases Exhaust gasesFigure 1-94. Many helicopters use a turboshaft engine to drive the main transmission and rotor systems. The main difference betweena turboshaft and a turbojet engine is that most of the energy produced by the expanding gases is used to drive a turbine rather thanproducing thrust through the expulsion of exhaust gases. 1-43
  • 68. Rigid Rotor System the blades to flap up and down. With this hinge, when oneThe simplest is the rigid rotor system. In this system, the blade flaps up, the other flaps down.rotor blades are rigidly attached to the main rotor hub and arenot free to slide back and forth (drag) or move up and down Flapping is caused by a phenomenon known as dissymmetry(flap). The forces tending to make the rotor blades do so are of lift. As the plane of rotation of the rotor blades is tilted andabsorbed by the flexible properties of the blade. The pitch the helicopter begins to move forward, an advancing bladeof the blades, however, can be adjusted by rotation about and a retreating blade become established (on two-bladedthe spanwise axis via the feathering hinges. [Figure 1-95] systems). The relative windspeed is greater on an advancing blade than it is on a retreating blade. This causes greater lift to be developed on the advancing blade, causing it to rise Static stops up or flap. When blade rotation reaches the point where the blade becomes the retreating blade, the extra lift is lost and the blade flaps downward. [Figure 1-97] Teetering hinge Direction of Flight Retreating Side Advancing Side a tion rot de a Bl Blade tip Blade tip Relative wind Relative wind speed speed Pitch horn minus plus helicopter helicopter speed speed Feathering hinge Feathering hinge (200 knots) (400 knots) io n at rotFigure 1-95. The teetering hinge allows the main rotor hub to tilt, and Bladethe feathering hinge enables the pitch angle of the blades to change. Forward Flight 100 knotsSemirigid Rotor System Figure 1-97. The blade tip speed of this helicopter is approximatelyThe semirigid rotor system in Figure 1-96 makes use of a 300 knots. If the helicopter is moving forward at 100 knots, theteetering hinge at the blade attach point. While held in check relative windspeed on the advancing side is 400 knots. On thefrom sliding back and forth, the teetering hinge does allow retreating side, it is only 200 knots. This difference in speed causes a dissymetry of lift. Coning hinge Teetering hinge Fully Articulated Rotor System Blade grip Blade grip Fully articulated rotor blade systems provide hinges that allow the rotors to move fore and aft, as well as up and down. This lead-lag, drag, or hunting movement as it is called is in response to the Coriolis effect during rotational Blade pitch change horn speed changes. When first starting to spin, the blades lag until centrifugal force is fully developed. Once rotating, a Pitch link Coning hinge reduction in speed causes the blades to lead the main rotor hub until forces come into balance. Constant fluctuations in rotor blade speeds cause the blades to “hunt.” They are free Swash plate to do so in a fully articulating system due to being mounted on the vertical drag hinge. One or more horizontal hinges provide for flapping on a fully articulated rotor system. Also, the feathering hinge allows blade pitch changes by permitting rotation about the spanwise axis. Various dampers and stops can be found onFigure 1-96. The semirigid rotor system of the Robinson R22. different designs to reduce shock and limit travel in certain1-44
  • 69. directions. Figure 1-98 shows a fully articulated main rotorsystem with the features discussed. Pitch change axis (feathering) Pitch horn Flap hinge Drag hinge Figure 1-99. Five-blade articulated main rotor with elastomeric bearings. Damper by changing the pitch of the tail rotor blades. This, in turn, changes the amount of countertorque, and the aircraft can be rotated about its vertical axis, allowing the pilot to control the direction the helicopter is facing.Figure 1-98. Fully articulated rotor system. ation Tor d e rot quNumerous designs and variations on the three types of main Bla erotor systems exist. Engineers continually search for ways toreduce vibration and noise caused by the rotating parts of thehelicopter. Toward that end, the use of elastomeric bearingsin main rotor systems is increasing. These polymer bearingshave the ability to deform and return to their original shape.As such, they can absorb vibration that would normally betransferred by steel bearings. They also do not require regular elubrication, which reduces maintenance. Tor qu tion Blade rota ResultantSome modern helicopter main rotors have been designed with torque from Tail rotor thrustflextures. These are hubs and hub components that are made main rotor bladesout of advanced composite materials. They are designed totake up the forces of blade hunting and dissymmetry of lift by Figure 1-100. A tail rotor is designed to produce thrust in a directionflexing. As such, many hinges and bearings can be eliminatedfrom the tradition main rotor system. The result is a simpler opposite to that of the torque produced by the rotation of the mainrotor mast with lower maintenance due to fewer moving rotor blades. It is sometimes called an antitorque rotor.parts. Often designs using flextures incorporate elastomericbearings. [Figure 1-99] Similar to a vertical stabilizer on the empennage of an airplane, a fin or pylon is also a common feature on rotorcraft.Antitorque System Normally, it supports the tail rotor assembly, althoughOrdinarily, helicopters have between two and seven main some tail rotors are mounted on the tail cone of the boom.rotor blades. These rotors are usually made of a composite Additionally, a horizontal member called a stabilizer is oftenstructure. The large rotating mass of the main rotor blades constructed at the tail cone or on the pylon.of a helicopter produce torque. This torque increases withengine power and tries to spin the fuselage in the opposite A Fenestron® is a unique tail rotor design which is actually adirection. The tail boom and tail rotor, or antitorque rotor, multiblade ducted fan mounted in the vertical pylon. It workscounteract this torque effect. [Figure 1-100] Controlled the same way as an ordinary tail rotor, providing sidewayswith foot pedals, the countertorque of the tail rotor must be thrust to counter the torque produced by the main rotors.modulated as engine power levels are changed. This is done [Figure 1-101] 1-45
  • 70. Controls The controls of a helicopter differ slightly from those found in an aircraft. The collective, operated by the pilot with the left hand, is pulled up or pushed down to increase or decrease the angle of attack on all of the rotor blades simultaneously. This increases or decreases lift and moves the aircraft up or down. The engine throttle control is located on the hand grip at the end of the collective. The cyclic is the control “stick” located between the pilot’s legs. It can be moved in any direction to tilt the plane of rotation of the rotor blades. This causes the helicopter to move in the direction that the cyclic is moved. As stated, the foot pedals control the pitch of the tail rotor blades thereby balancing main rotor torque. Figures 1-103 and 1-104 illustrate the controls found in aFigure 1-101. A Fenestron or “fan-in-tail” antitorque system. typical helicopter.This design provides an improved margin of safety during groundoperations.A NOTAR® antitorque system has no visible rotor mountedon the tail boom. Instead, an engine-driven adjustable fanis located inside the tail boom. NOTAR® is an acronymthat stands for “no tail rotor.” As the speed of the mainrotor changes, the speed of the NOTAR® fan changes. Air Throttle controlis vented out of two long slots on the right side of the tailboom, entraining main rotor wash to hug the right side of thetail boom, in turn causing laminar flow and a low pressure(Coanda Effect). This low pressure causes a force counterto the torque produced by the main rotor. Additionally, theremainder of the air from the fan is sent through the tailboom to a vent on the aft left side of the boom where it isexpelled. This action to the left causes an opposite reaction Collectiveto the right, which is the direction needed to counter the mainrotor torque. [Figures 1-102] Figure 1-103. The collective changes the pitch of all of the rotor blades simultaneously and by the same amount, thereby increasing or decreasing lift. Downwash Air jet Main rotor wake Lift Air intake Rotating nozzleFigure 1-102. While in a hover, Coanda Effect suppliesapproximately two-thirds of the lift necessary to maintaindirectional control. The rest is created by directing the thrust fromthe controllable rotating nozzle.1-46
  • 71. Swash plate Sideware flight Forward flight Cyclic control stick moved sideways Cyclic control stick moved forwardFigure 1-104. The cyclic changes the angle of the swash plate whichchanges the plane of rotation of the rotor blades. This moves theaircraft horizontally in any direction depending on the positioningof the cyclic. 1-47
  • 72. 1-48
  • 73. Chapter 2Aerodynamics, AircraftAssembly, and RiggingIntroductionThree topics that are directly related to the manufacture,operation, and repair of aircraft are: aerodynamics, aircraftassembly, and rigging. Each of these subject areas, thoughstudied separately, eventually connect to provide a scientificand physical understanding of how an aircraft is prepared forflight. A logical place to start with these three topics is the studyof basic aerodynamics. By studying aerodynamics, a personbecomes familiar with the fundamentals of aircraft flight. 2-1
  • 74. Basic Aerodynamics the definition of a substance that has the ability to flow or assume the shape of the container in which it is enclosed.Aerodynamics is the study of the dynamics of gases, the If the container is heated, pressure increases; if cooled, theinteraction between a moving object and the atmosphere pressure decreases. The weight of air is heaviest at sea levelbeing of primary interest for this handbook. The movement of where it has been compressed by all of the air above. Thisan object and its reaction to the air flow around it can be seen compression of air is called atmospheric pressure.when watching water passing the bow of a ship. The majordifference between water and air is that air is compressible Pressureand water is incompressible. The action of the airflow over Atmospheric pressure is usually defined as the force exerteda body is a large part of the study of aerodynamics. Some against the earth’s surface by the weight of the air abovecommon aircraft terms, such as rudder, hull, water line, and that surface. Weight is force applied to an area that resultskeel beam, were borrowed from nautical terms. in pressure. Force (F) equals area (A) times pressure (P), or F = AP. Therefore, to find the amount of pressure, divideMany textbooks have been written about the aerodynamics area into force (P = F/A). A column of air (one square inch)of aircraft flight. It is not necessary for an airframe and extending from sea level to the top of the atmosphere weighspowerplant (A&P) mechanic to be as knowledgeable as an approximately 14.7 pounds; therefore, atmospheric pressureaeronautical engineer about aerodynamics. The mechanic is stated in pounds per square inch (psi). Thus, atmosphericmust be able to understand the relationships between pressure at sea level is 14.7 psi.how an aircraft performs in flight and its reaction to theforces acting on its structural parts. Understanding why Atmospheric pressure is measured with an instrumentaircraft are designed with particular types of primary and called a barometer, composed of mercury in a tube thatsecondary control systems and why the surfaces must be records atmospheric pressure in inches of mercury ("Hg).aerodynamically smooth becomes essential when maintaining [Figure 2-1] The standard measurement in aviation altimeterstoday’s complex aircraft. and U.S. weather reports has been "Hg. However, world-wide weather maps and some non-U.S. manufactured aircraftThe theory of flight should be described in terms of the laws instruments indicate pressure in millibars (mb), a metric unit.of flight because what happens to an aircraft when it fliesis not based upon assumptions, but upon a series of facts.Aerodynamics is a study of laws which have been provento be the physical reasons why an airplane flies. The term Vacuum Inches ofaerodynamics is derived from the combination of two Greek Standard Mercury Millibars Standard Sea Level Sea Levelwords: “aero,” meaning air, and “dyne,” meaning force of Pressure 30 1016 Pressurepower. Thus, when “aero” joins “dynamics” the result is 29.92"Hg 25 847 1013 mb“aerodynamics”—the study of objects in motion through 20 677the air and the forces that produce or change such motion. 15 508 10 339Aerodynamically, an aircraft can be defined as an object 5 170traveling through space that is affected by the changes Atmospheric Pressure 0 0in atmospheric conditions. To state it another way,aerodynamics covers the relationships between the aircraft,relative wind, and atmosphere. 1"The Atmosphere 1"Before examining the fundamental laws of flight, severalbasic facts must be considered, namely that an aircraft 1"operates in the air. Therefore, those properties of air that 0.491 lb Mercuryaffect the control and performance of an aircraft must beunderstood. Figure 2-1. Barometer used to measure atmospheric pressure.The air in the earth’s atmosphere is composed mostly ofnitrogen and oxygen. Air is considered a fluid because it fits2-2
  • 75. At sea level, when the average atmospheric pressure is Assuming that the temperature and pressure remain the same,14.7 psi, the barometric pressure is 29.92 "Hg, and the metric the density of the air varies inversely with the humidity. Onmeasurement is 1013.25 mb. damp days, the air density is less than on dry days. For this reason, an aircraft requires a longer runway for takeoff onAn important consideration is that atmospheric pressure damp days than it does on dry days.varies with altitude. As an aircraft ascends, atmosphericpressure drops, oxygen content of the air decreases, and By itself, water vapor weighs approximately five-eighthstemperature drops. The changes in altitude affect an aircraft’s as much as an equal amount of perfectly dry air. Therefore,performance in such areas as lift and engine horsepower. The when air contains water vapor, it is not as heavy as dry aireffects of temperature, altitude, and density of air on aircraft containing no moisture.performance are covered in the following paragraphs. Aerodynamics and the Laws of PhysicsDensity The law of conservation of energy states that energy mayDensity is weight per unit of volume. Since air is a mixture neither be created nor destroyed.of gases, it can be compressed. If the air in one container isunder half as much pressure as an equal amount of air in an Motion is the act or process of changing place or position.identical container, the air under the greater pressure weighs An object may be in motion with respect to one object andtwice as much as that in the container under lower pressure. motionless with respect to another. For example, a personThe air under greater pressure is twice as dense as that in sitting quietly in an aircraft flying at 200 knots is at rest orthe other container. For the equal weight of air, that which motionless with respect to the aircraft; however, the personis under the greater pressure occupies only half the volume and the aircraft are in motion with respect to the air and toof that under half the pressure. the earth.The density of gases is governed by the following rules: Air has no force or power, except pressure, unless it is in 1. Density varies in direct proportion with the motion. When it is moving, however, its force becomes pressure. apparent. A moving object in motionless air has a force exerted on it as a result of its own motion. It makes no 2. Density varies inversely with the temperature. difference in the effect then, whether an object is moving with respect to the air or the air is moving with respect toThus, air at high altitudes is less dense than air at low the object. The flow of air around an object caused by thealtitudes, and a mass of hot air is less dense than a mass of movement of either the air or the object, or both, is calledcool air. the relative wind.Changes in density affect the aerodynamic performance of Velocity and Accelerationaircraft with the same horsepower. An aircraft can fly faster at The terms “speed” and “velocity” are often useda high altitude where the density is low than at a low altitude interchangeably, but they do not have the same meaning.where the density is greater. This is because air offers less Speed is the rate of motion in relation to time, and velocity isresistance to the aircraft when it contains a smaller number the rate of motion in a particular direction in relation to time.of air particles per unit of volume. An aircraft starts from New York City and flies 10 hours atHumidity an average speed of 260 miles per hour (mph). At the end ofHumidity is the amount of water vapor in the air. The this time, the aircraft may be over the Atlantic Ocean, Pacificmaximum amount of water vapor that air can hold varies Ocean, Gulf of Mexico, or, if its flight were in a circular path,with the temperature. The higher the temperature of the air, it may even be back over New York City. If this same aircraftthe more water vapor it can absorb. flew at a velocity of 260 mph in a southwestward direction, 1. Absolute humidity is the weight of water vapor in a it would arrive in Los Angeles in about 10 hours. Only the unit volume of air. rate of motion is indicated in the first example and denotes the speed of the aircraft. In the last example, the particular 2. Relative humidity is the ratio, in percent, of the direction is included with the rate of motion, thus, denoting moisture actually in the air to the moisture it would the velocity of the aircraft. hold if it were saturated at the same temperature and pressure. 2-3
  • 76. Acceleration is defined as the rate of change of velocity. If an aircraft is flying against a headwind, it is slowed down.An aircraft increasing in velocity is an example of positive If the wind is coming from either side of the aircraft’sacceleration, while another aircraft reducing its velocity is an heading, the aircraft is pushed off course unless the pilotexample of negative acceleration, or deceleration. takes corrective action against the wind direction.Newton’s Laws of Motion Newton’s third law is the law of action and reaction. ThisThe fundamental laws governing the action of air about a law states that for every action (force) there is an equalwing are known as Newton’s laws of motion. and opposite reaction (force). This law can be illustrated by the example of firing a gun. The action is the forwardNewton’s first law is normally referred to as the law of movement of the bullet while the reaction is the backwardinertia. It simply means that a body at rest does not move recoil of the gun.unless force is applied to it. If a body is moving at uniformspeed in a straight line, force must be applied to increase or The three laws of motion that have been discussed apply todecrease the speed. the theory of flight. In many cases, all three laws may be operating on an aircraft at the same time.According to Newton’s law, since air has mass, it is a body.When an aircraft is on the ground with its engines off, inertia Bernoulli’s Principle and Subsonic Flowkeeps the aircraft at rest. An aircraft is moved from its state Bernoulli’s principle states that when a fluid (air) flowingof rest by the thrust force created by a propeller, or by the through a tube reaches a constriction, or narrowing, of theexpanding exhaust, or both. When an aircraft is flying at tube, the speed of the fluid flowing through that constrictionuniform speed in a straight line, inertia tends to keep the is increased and its pressure is decreased. The camberedaircraft moving. Some external force is required to change (curved) surface of an airfoil (wing) affects the airflowthe aircraft from its path of flight. exactly as a constriction in a tube affects airflow. [Figure 2-2] Diagram A of Figure 2-2 illustrates the effect of air passingNewton’s second law states that if a body moving with through a constriction in a tube. In B, air is flowing past auniform speed is acted upon by an external force, the change cambered surface, such as an airfoil, and the effect is similarof motion is proportional to the amount of the force, and to that of air passing through a restriction.motion takes place in the direction in which the force acts.This law may be stated mathematically as follows: Force = mass × acceleration (F = ma) A Mass of air Same mass of air Velocity increased Normal pressure Pressure decreased Normal pressure (Compared to original) B Normal flow Increased flow Normal flowFigure 2-2. Bernoulli’s Principle.2-4
  • 77. As the air flows over the upper surface of an airfoil, its Shape of the Airfoilvelocity increases and its pressure decreases; an area of low Individual airfoil section properties differ from thosepressure is formed. There is an area of greater pressure on properties of the wing or aircraft as a whole because of thethe lower surface of the airfoil, and this greater pressure effect of the wing planform. A wing may have various airfoiltends to move the wing upward. The difference in pressure sections from root to tip, with taper, twist, and sweepback.between the upper and lower surfaces of the wing is called The resulting aerodynamic properties of the wing arelift. Three-fourths of the total lift of an airfoil is the result of determined by the action of each section along the span.the decrease in pressure over the upper surface. The impactof air on the under surface of an airfoil produces the other The shape of the airfoil determines the amount of turbulenceone-fourth of the total lift. or skin friction that it produces, consequently affecting the efficiency of the wing. Turbulence and skin friction areAirfoil controlled mainly by the fineness ratio, which is defined asAn airfoil is a surface designed to obtain lift from the air the ratio of the chord of the airfoil to the maximum thickness.through which it moves. Thus, it can be stated that any part If the wing has a high fineness ratio, it is a very thin wing.of the aircraft that converts air resistance into lift is an airfoil. A thick wing has a low fineness ratio. A wing with a highThe profile of a conventional wing is an excellent example fineness ratio produces a large amount of skin friction. Aof an airfoil. [Figure 2-3] Notice that the top surface of the wing with a low fineness ratio produces a large amount ofwing profile has greater curvature than the lower surface. turbulence. The best wing is a compromise between these two extremes to hold both turbulence and skin friction to a minimum. 115 mph 14.54 lb/in2 The efficiency of a wing is measured in terms of the lift to drag ratio (L/D). This ratio varies with the AOA but reaches a definite maximum value for a particular AOA. At this angle, the wing has reached its maximum efficiency. The shape of the airfoil is the factor that determines the AOA at which 100 mph 14.7 lb/in2 105 mph 14.67 lb/in2 the wing is most efficient; it also determines the degree of efficiency. Research has shown that the most efficient airfoilsFigure 2-3. Airflow over a wing section. for general use have the maximum thickness occurring about one-third of the way back from the leading edge of the wing.The difference in curvature of the upper and lower surfacesof the wing builds up the lift force. Air flowing over the top High-lift wings and high-lift devices for wings have beensurface of the wing must reach the trailing edge of the wing developed by shaping the airfoils to produce the desiredin the same amount of time as the air flowing under the wing. effect. The amount of lift produced by an airfoil increasesTo do this, the air passing over the top surface moves at a with an increase in wing camber. Camber refers to thegreater velocity than the air passing below the wing because curvature of an airfoil above and below the chord line surface.of the greater distance it must travel along the top surface. Upper camber refers to the upper surface, lower camber toThis increased velocity, according to Bernoulli’s Principle, the lower surface, and mean camber to the mean line of themeans a corresponding decrease in pressure on the surface. section. Camber is positive when departure from the chordThus, a pressure differential is created between the upper line is outward and negative when it is inward. Thus, high-liftand lower surfaces of the wing, forcing the wing upward in wings have a large positive camber on the upper surface andthe direction of the lower pressure. a slightly negative camber on the lower surface. Wing flaps cause an ordinary wing to approximate this same conditionWithin limits, lift can be increased by increasing the angle by increasing the upper camber and by creating a negativeof attack (AOA), wing area, velocity, density of the air, or lower camber.by changing the shape of the airfoil. When the force of lifton an aircraft’s wing equals the force of gravity, the aircraftmaintains level flight. 2-5
  • 78. It is also known that the larger the wingspan, as comparedto the chord, the greater the lift obtained. This comparison Angle of attackis called aspect ratio. The higher the aspect ratio, the greater Resultant lift Chothe lift. In spite of the benefits from an increase in aspect rd li ne Liftratio, it was found that definite limitations were defined bystructural and drag considerations. Relative airstream DragOn the other hand, an airfoil that is perfectly streamlined Center of pressureand offers little wind resistance sometimes does not haveenough lifting power to take the aircraft off the ground. Thus, Figure 2-5. Airflow over a wing section.modern aircraft have airfoils which strike a medium betweenextremes, the shape depending on the purposes of the aircraft On each part of an airfoil or wing surface, a small force isfor which it is designed. present. This force is of a different magnitude and direction from any forces acting on other areas forward or rearwardAngle of Incidence from this point. It is possible to add all of these small forcesThe acute angle the wing chord makes with the longitudinal mathematically. That sum is called the “resultant force”axis of the aircraft is called the angle of incidence, or the angle (lift). This resultant force has magnitude, direction, andof wing setting. [Figure 2-4] The angle of incidence in most location, and can be represented as a vector, as shown incases is a fixed, built-in angle. When the leading edge of the Figure 2-5. The point of intersection of the resultant forcewing is higher than the trailing edge, the angle of incidence is line with the chord line of the airfoil is called the center ofsaid to be positive. The angle of incidence is negative when pressure (CP). The CP moves along the airfoil chord as thethe leading edge is lower than the trailing edge of the wing. AOA changes. Throughout most of the flight range, the CP moves forward with increasing AOA and rearward as the AOA decreases. The effect of increasing AOA on the CP is Angle of incidence shown in Figure 2-6. Longitudinal axis The AOA changes as the aircraft’s attitude changes. Since the AOA has a great deal to do with determining lift, it is given Chord line primary consideration when designing airfoils. In a properly of wing designed airfoil, the lift increases as the AOA is increased. When the AOA is increased gradually toward a positiveFigure 2-4. Angle of incidence. AOA, the lift component increases rapidly up to a certain point and then suddenly begins to drop off. During this action the drag component increases slowly at first, then rapidly asAngle of Attack (AOA) lift begins to drop off.Before beginning the discussion on AOA and its effect onairfoils, first consider the terms chord and center of pressure When the AOA increases to the angle of maximum lift, the(CP) as illustrated in Figure 2-5. burble point is reached. This is known as the critical angle. When the critical angle is reached, the air ceases to flowThe chord of an airfoil or wing section is an imaginary smoothly over the top surface of the airfoil and begins tostraight line that passes through the section from the leading burble or eddy. This means that air breaks away from theedge to the trailing edge, as shown in Figure 2-5. The chord upper camber line of the wing. What was formerly the arealine provides one side of an angle that ultimately forms of decreased pressure is now filled by this burbling air.the AOA. The other side of the angle is formed by a line When this occurs, the amount of lift drops and drag becomesindicating the direction of the relative airstream. Thus, AOA excessive. The force of gravity exerts itself, and the nose ofis defined as the angle between the chord line of the wing and the aircraft drops. This is a stall. Thus, the burble point isthe direction of the relative wind. This is not to be confused the stalling angle.with the angle of incidence, illustrated in Figure 2-4, whichis the angle between the chord line of the wing and thelongitudinal axis of the aircraft.2-6
  • 79. A Angle of attack = 0° Thrust and Drag Resultant An aircraft in flight is the center of a continuous battle of Negative pressure pattern forces. Actually, this conflict is not as violent as it sounds, Relative airstream but it is the key to all maneuvers performed in the air. There is nothing mysterious about these forces; they are definite and known. The directions in which they act can be calculated, and the aircraft itself is designed to take advantage of each Positive pressure Center of pressure of them. In all types of flying, flight calculations are based on the magnitude and direction of four forces: weight, lift, B Angle of attack = 6° drag, and thrust. [Figure 2-7] Resultant Negative pressure pattern moves forward Lift Relative airstream Positive pressure Drag Thrust C Angle of attack = 12° Resultant Center of pressure moves forward Weight Relative airstream Positive pressure u Figure 2-7. Forces in action during flight. D Angle of attack = 18° An aircraft in flight is acted upon by four forces: Wing completely stalled 1. Gravity or weight—the force that pulls the aircraft toward the earth. Weight is the force of gravity acting downward upon everything that goes into the aircraft, such as the aircraft itself, crew, fuel, and cargo. Positive pressure 2. Lift—the force that pushes the aircraft upward. Lift acts vertically and counteracts the effects of weight.Figure 2-6. Effect on increasing angle of attack. 3. Thrust—the force that moves the aircraft forward. Thrust is the forward force produced by the powerplantAs previously seen, the distribution of the pressure forces that overcomes the force of drag.over the airfoil varies with the AOA. The application of theresultant force, or CP, varies correspondingly. As this angle 3. Drag—the force that exerts a braking action to holdincreases, the CP moves forward; as the angle decreases, the the aircraft back. Drag is a backward deterrent forceCP moves back. The unstable travel of the CP is characteristic and is caused by the disruption of the airflow by theof almost all airfoils. wings, fuselage, and protruding objects.Boundary Layer These four forces are in perfect balance only when the aircraftIn the study of physics and fluid mechanics, a boundary layer is in straight-and-level unaccelerated flight.is that layer of fluid in the immediate vicinity of a boundingsurface. In relation to an aircraft, the boundary layer is the The forces of lift and drag are the direct result of thepart of the airflow closest to the surface of the aircraft. In relationship between the relative wind and the aircraft. Thedesigning high-performance aircraft, considerable attention force of lift always acts perpendicular to the relative wind,is paid to controlling the behavior of the boundary layer to and the force of drag always acts parallel to and in the sameminimize pressure drag and skin friction drag. direction as the relative wind. These forces are actually the components that produce a resultant lift force on the wing. [Figure 2-8] 2-7
  • 80. drag are equal. In order to maintain a steady speed, thrust and Resultant drag must remain equal, just as lift and weight must be equal for steady, horizontal flight. Increasing the lift means that the Lift aircraft moves upward, whereas decreasing the lift so that it is less than the weight causes the aircraft to lose altitude. A similar rule applies to the two forces of thrust and drag. If the revolutions per minute (rpm) of the engine is reduced, the Drag thrust is lessened, and the aircraft slows down. As long as the thrust is less than the drag, the aircraft travels more and more slowly until its speed is insufficient to support it in the air.Figure 2-8. Resultant of lift and drag. Likewise, if the rpm of the engine is increased, thrust becomesWeight has a definite relationship with lift, and thrust with greater than drag, and the speed of the aircraft increases. Asdrag. These relationships are quite simple, but very important long as the thrust continues to be greater than the drag, thein understanding the aerodynamics of flying. As stated aircraft continues to accelerate. When drag equals thrust, thepreviously, lift is the upward force on the wing perpendicular aircraft flies at a steady speed.to the relative wind. Lift is required to counteract the aircraft’sweight, caused by the force of gravity acting on the mass of The relative motion of the air over an object that producesthe aircraft. This weight force acts downward through a point lift also produces drag. Drag is the resistance of the air tocalled the center of gravity (CG). The CG is the point at which objects moving through it. If an aircraft is flying on a levelall the weight of the aircraft is considered to be concentrated. course, the lift force acts vertically to support it while theWhen the lift force is in equilibrium with the weight force, drag force acts horizontally to hold it back. The total amountthe aircraft neither gains nor loses altitude. If lift becomes of drag on an aircraft is made up of many drag forces, butless than weight, the aircraft loses altitude. When the lift is this handbook considers three: parasite drag, profile drag,greater than the weight, the aircraft gains altitude. and induced drag.Wing area is measured in square feet and includes the Parasite drag is made up of a combination of many differentpart blanked out by the fuselage. Wing area is adequately drag forces. Any exposed object on an aircraft offers somedescribed as the area of the shadow cast by the wing at high resistance to the air, and the more objects in the airstream,noon. Tests show that lift and drag forces acting on a wing the more parasite drag. While parasite drag can be reducedare roughly proportional to the wing area. This means that by reducing the number of exposed parts to as few asif the wing area is doubled, all other variables remaining the practical and streamlining their shape, skin friction is thesame, the lift and drag created by the wing is doubled. If the type of parasite drag most difficult to reduce. No surface isarea is tripled, lift and drag are tripled. perfectly smooth. Even machined surfaces have a ragged uneven appearance when inspected under magnification.Drag must be overcome for the aircraft to move, and These ragged surfaces deflect the air near the surface causingmovement is essential to obtain lift. To overcome drag and resistance to smooth airflow. Skin friction can be reduced bymove the aircraft forward, another force is essential. This using glossy smooth finishes and eliminating protruding rivetforce is thrust. Thrust is derived from jet propulsion or from heads, roughness, and other irregularities.a propeller and engine combination. Jet propulsion theoryis based on Newton’s third law of motion (page 2-4). The Profile drag may be considered the parasite drag of the airfoil.turbine engine causes a mass of air to be moved backward The various components of parasite drag are all of the sameat high velocity causing a reaction that moves the aircraft nature as profile drag.forward. The action of the airfoil that creates lift also causes inducedIn a propeller/engine combination, the propeller is actually drag. Remember, the pressure above the wing is less thantwo or more revolving airfoils mounted on a horizontal shaft. atmospheric pressure, and the pressure below the wing isThe motion of the blades through the air produces lift similar equal to or greater than atmospheric pressure. Since fluidsto the lift on the wing, but acts in a horizontal direction, always move from high pressure toward low pressure, therepulling the aircraft forward. is a spanwise movement of air from the bottom of the wing outward from the fuselage and upward around the wing tip.Before the aircraft begins to move, thrust must be exerted. This flow of air results in spillage over the wing tip, therebyThe aircraft continues to move and gain speed until thrust and setting up a whirlpool of air called a “vortex.” [Figure 2-9]2-8
  • 81. The axes of an aircraft can be considered as imaginary axles around which the aircraft turns like a wheel. At the center, where all three axes intersect, each is perpendicular to the other two. The axis that extends lengthwise through the fuselage from the nose to the tail is called the longitudinal axis. The axis that extends crosswise from wing tip to wing tip is the lateral, or pitch, axis. The axis that passes through the center, from top to bottom, is called the vertical, or yaw, axis. Roll, pitch, and yaw are controlled by three control tex Vor surfaces. Roll is produced by the ailerons, which are located at the trailing edges of the wings. Pitch is affected by the elevators, the rear portion of the horizontal tail assembly. Yaw is controlled by the rudder, the rear portion of the vertical tail assembly. Stability and Control An aircraft must have sufficient stability to maintain aFigure 2-9. Wingtip vortices. uniform flightpath and recover from the various upsetting forces. Also, to achieve the best performance, the aircraftThe air on the upper surface has a tendency to move in toward must have the proper response to the movement of thethe fuselage and off the trailing edge. This air current forms a controls. Control is the pilot action of moving the flightsimilar vortex at the inner portion of the trailing edge of the controls, providing the aerodynamic force that induces thewing. These vortices increase drag because of the turbulence aircraft to follow a desired flightpath. When an aircraft isproduced, and constitute induced drag. said to be controllable, it means that the aircraft responds easily and promptly to movement of the controls. DifferentJust as lift increases with an increase in AOA, induced drag control surfaces are used to control the aircraft about eachalso increases as the AOA becomes greater. This occurs of the three axes. Moving the control surfaces on an aircraftbecause, as the AOA is increased, the pressure difference changes the airflow over the aircraft’s surface. This, in turn,between the top and bottom of the wing becomes greater. creates changes in the balance of forces acting to keep theThis causes more violent vortices to be set up, resulting in aircraft flying straight and level.more turbulence and more induced drag. Three terms that appear in any discussion of stability andCenter of Gravity (CG) control are: stability, maneuverability, and controllability.Gravity is the pulling force that tends to draw all bodies Stability is the characteristic of an aircraft that tends towithin the earth’s gravitational field to the center of the cause it to fly (hands off) in a straight-and-level flightpath.earth. The CG may be considered the point at which all the Maneuverability is the characteristic of an aircraft to beweight of the aircraft is concentrated. If the aircraft were directed along a desired flightpath and to withstand the stressessupported at its exact CG, it would balance in any position. imposed. Controllability is the quality of the response ofCG is of major importance in an aircraft, for its position has an aircraft to the pilot’s commands while maneuvering thea great bearing upon stability. aircraft.The CG is determined by the general design of the aircraft. Static StabilityThe designers estimate how far the CP travels. They then fix An aircraft is in a state of equilibrium when the sum of all thethe CG in front of the CP for the corresponding flight speed forces acting on the aircraft and all the moments is equal toin order to provide an adequate restoring moment for flight zero. An aircraft in equilibrium experiences no accelerations,equilibrium. and the aircraft continues in a steady condition of flight. A gust of wind or a deflection of the controls disturbs theThe Axes of an Aircraft equilibrium, and the aircraft experiences acceleration due toWhenever an aircraft changes its attitude in flight, it must the unbalance of moment or force.turn about one or more of three axis. Figure 2-10 shows thethree axes, which are imaginary lines passing through thecenter of the aircraft. 2-9
  • 82. Elevator Aileron Lateral axis Rudder Aileron Longitudinal axis Vertical axis A Banking (roll) control affected by aileron movement y Normal altitude Longitudinal axis B Climb and dive (pitch) control affected by elevator C Directional (yaw) control affected by rudder movement movement Normal altitude Lateral axis Vertical axis Normal altitudeFigure 2-10. Motion of an aircraft about its axes.The three types of static stability are defined by the character to return to equilibrium. Negative static stability, or staticof movement following some disturbance from equilibrium. instability, exists when the disturbed object tends to continuePositive static stability exists when the disturbed object tends in the direction of disturbance. Neutral static stability exists2-10
  • 83. when the disturbed object has neither tendency, but remains to motion in pitch. The horizontal stabilizer is the primaryin equilibrium in the direction of disturbance. These three surface which controls longitudinal stability. The action oftypes of stability are illustrated in Figure 2-11. the stabilizer depends upon the speed and AOA of the aircraft.Dynamic Stability Directional StabilityWhile static stability deals with the tendency of a displaced Stability about the vertical axis is referred to as directionalbody to return to equilibrium, dynamic stability deals with stability. The aircraft should be designed so that when it isthe resulting motion with time. If an object is disturbed from in straight-and-level flight it remains on its course headingequilibrium, the time history of the resulting motion defines even though the pilot takes his or her hands and feet off thethe dynamic stability of the object. In general, an object controls. If an aircraft recovers automatically from a skid, itdemonstrates positive dynamic stability if the amplitude has been well designed for directional balance. The verticalof motion decreases with time. If the amplitude of motion stabilizer is the primary surface that controls directionalincreases with time, the object is said to possess dynamic stability. Directional stability can be designed into an aircraft,instability. where appropriate, by using a large dorsal fin, a long fuselage, and sweptback wings.Any aircraft must demonstrate the required degrees of staticand dynamic stability. If an aircraft were designed with static Lateral Stabilityinstability and a rapid rate of dynamic instability, the aircraft Motion about the aircraft’s longitudinal (fore and aft) axiswould be very difficult, if not impossible, to fly. Usually, is a lateral, or rolling, motion. The tendency to return to thepositive dynamic stability is required in an aircraft design to original attitude from such motion is called lateral stability.prevent objectionable continued oscillations of the aircraft. Dutch RollLongitudinal Stability A Dutch Roll is an aircraft motion consisting of an out-of-When an aircraft has a tendency to keep a constant AOA phase combination of yaw and roll. Dutch roll stability canwith reference to the relative wind (i.e., it does not tend to be artificially increased by the installation of a yaw damper.put its nose down and dive or lift its nose and stall); it is saidto have longitudinal stability. Longitudinal stability refers Positive static stability Neutral static stability Negative static stability Applied Applied Applied force force force CG CG CG CGFigure 2-11. Three types of stability. 2-11
  • 84. Primary Flight Controls Balance tabs are designed to move in the opposite direction of the primary flight control. Thus, aerodynamic forces actingThe primary controls are the ailerons, elevator, and the on the tab assist in moving the primary control surface.rudder, which provide the aerodynamic force to make theaircraft follow a desired flightpath. [Figure 2-10] The flight Spring tabs are similar in appearance to trim tabs, but serve ancontrol surfaces are hinged or movable airfoils designed to entirely different purpose. Spring tabs are used for the samechange the attitude of the aircraft by changing the airflow purpose as hydraulic actuators—to aid the pilot in movingover the aircraft’s surface during flight. These surfaces are the primary control surface.used for moving the aircraft about its three axes. Figure 2-13 indicates how each trim tab is hinged to its parentTypically, the ailerons and elevators are operated from the primary control surface, but is operated by an independentflight deck by means of a control stick, a wheel, and yoke control.assembly and on some of the newer design aircraft, a joy-stick. The rudder is normally operated by foot pedals on mostaircraft. Lateral control is the banking movement or roll of an Control hornaircraft that is controlled by the ailerons. Longitudinal controlis the climb and dive movement or pitch of an aircraft that Tab Fixed surfaceis controlled by the elevator. Directional control is the leftand right movement or yaw of an aircraft that is controlledby the rudder. Control surface Trim tabTrim Controls Horn free to pivot on hinge axisIncluded in the trim controls are the trim tabs, servo tabs,balance tabs, and spring tabs. Trim tabs are small airfoilsrecessed into the trailing edges of the primary controlsurfaces. [Figure 2-12] Trim tabs can be used to correct anytendency of the aircraft to move toward an undesirable flightattitude. Their purpose is to enable the pilot to trim out any Servo tabunbalanced condition which may exist during flight, withoutexerting any pressure on the primary controls. Control horn Trim tabs Balance tab Control horn Spring cartridge Spring tab Figure 2-13. Types of trim tabs.Figure 2-12. Trim tabs.Servo tabs, sometimes referred to as flight tabs, are usedprimarily on the large main control surfaces. They aid inmoving the main control surface and holding it in the desiredposition. Only the servo tab moves in response to movementby the pilot of the primary flight controls.2-12
  • 85. Auxiliary Lift DevicesIncluded in the auxiliary lift devices group of flight controlsurfaces are the wing flaps, spoilers, speed brakes, slats,leading edge flaps, and slots.The auxiliary groups may be divided into two subgroups: Basic sectionthose whose primary purpose is lift augmenting and thosewhose primary purpose is lift decreasing. In the first group arethe flaps, both trailing edge and leading edge (slats), and slots.The lift decreasing devices are speed brakes and spoilers.The trailing edge airfoils (flaps) increase the wing area, Plain flapthereby increasing lift on takeoff, and decrease the speedduring landing. These airfoils are retractable and fair intothe wing contour. Others are simply a portion of the lowerskin which extends into the airstream, thereby slowing theaircraft. Leading edge flaps are airfoils extended from andretracted into the leading edge of the wing. Some installationscreate a slot (an opening between the extended airfoil and the Split flapleading edge). The flap (termed slat by some manufacturers)and slot create additional lift at the lower speeds of takeoffand landing. [Figure 2-14]Other installations have permanent slots built in the leadingedge of the wing. At cruising speeds, the trailing edge Slotted flapand leading edge flaps (slats) are retracted into the wingproper. Slats are movable control surfaces attached to theleading edges of the wings. When the slat is closed, it formsthe leading edge of the wing. When in the open position(extended forward), a slot is created between the slat and thewing leading edge. At low airspeeds, this increases lift andimproves handling characteristics, allowing the aircraft to Fowler flapbe controlled at airspeeds below the normal landing speed.[Figure 2-15]Lift decreasing devices are the speed brakes (spoilers). Insome installations, there are two types of spoilers. The groundspoiler is extended only after the aircraft is on the ground, Slotted Fowler flapthereby assisting in the braking action. The flight spoilerassists in lateral control by being extended whenever theaileron on that wing is rotated up. When actuated as speed Figure 2-14. Types of wing flaps.brakes, the spoiler panels on both wings raise up. In-flightspoilers may also be located along the sides, underneath thefuselage, or back at the tail. [Figure 2-16] In some aircraftdesigns, the wing panel on the up aileron side rises more thanthe wing panel on the down aileron side. This provides speed Fixed slotbrake operation and lateral control simultaneously. Slat Automatic slot Figure 2-15. Wing slots. 2-13
  • 86. Figure 2-19. The Beechcraft 2000 Starship has canard wings.Figure 2-16. Speed brake. Wing Fences Wing fences are flat metal vertical plates fixed to the upperWinglets surface of the wing. They obstruct spanwise airflow alongWinglets are the near-vertical extension of the wingtip the wing, and prevent the entire wing from stalling at once.that reduces the aerodynamic drag associated with vortices They are often attached on swept-wing aircraft to preventthat develop at the wingtips as the airplane moves through the spanwise movement of air at high angles of attack. Theirthe air. By reducing the induced drag at the tips of the purpose is to provide better slow speed handling and stallwings, fuel consumption goes down and range is extended. characteristics. [Figure 2-20] Figure 2-17 Shows an example of a Boeing 737 with winglets.Figure 2-17. Winglets on a Bombardier Learjet 60.Canard WingsA canard wing aircraft is an airframe configuration of a fixed- Figure 2-20. Aircraft stall fence.wing aircraft in which a small wing or horizontal airfoil isahead of the main lifting surfaces, rather than behind them as Control Systems for Large Aircraftin a conventional aircraft. The canard may be fixed, movable, Mechanical Controlor designed with elevators. Good examples of aircraft with This is the basic type of system that was used to controlcanard wings are the Rutan VariEze and Beechcraft 2000 early aircraft and is currently used in smaller aircraft whereStarship. [Figures 2-18 and 2-19] aerodynamic forces are not excessive. The controls are mechanical and manually operated. The mechanical system of controlling an aircraft can include cables, push-pull tubes, and torque tubes. The cable system is the most widely used because deflections of the structure to which it is attached do not affect its operation. Some aircraft incorporate control systems that are a combination of all three. These systems incorporate cable assemblies,Figure 2-18. Canard wings on a Rutan VariEze.2-14
  • 87. cable guides, linkage, adjustable stops, and control surface Many of the new military high-performance aircraft are notsnubber or mechanical locking devices. These surface locking aerodynamically stable. This characteristic is designed intodevices, usually referred to as a gust lock, limits the external the aircraft for increased maneuverability and responsivewind forces from damaging the aircraft while it is parked or performance. Without the computers reacting to thetied down. instability, the pilot would lose control of the aircraft.Hydromechanical Control The Airbus A-320 was the first commercial airliner to useAs the size, complexity, and speed of aircraft increased, FBW controls. Boeing used them in their 777 and neweractuation of controls in flight became more difficult. It soon design commercial aircraft. The Dassault Falcon 7X was thebecame apparent that the pilot needed assistance to overcome first business jet to use a FBW control system.the aerodynamic forces to control aircraft movement. Springtabs, which were operated by the conventional control High-Speed Aerodynamicssystem, were moved so that the airflow over them actually High-speed aerodynamics, often called compressiblemoved the primary control surface. This was sufficient aerodynamics, is a special branch of study of aeronautics.for the aircraft operating in the lowest of the high speed It is utilized by aircraft designers when designing aircraftranges (250–300 mph). For higher speeds, a power-assisted capable of speeds approaching Mach 1 and above. Because(hydraulic) control system was designed. it is beyond the scope and intent of this handbook, only a brief overview of the subject is provided.Conventional cable or push-pull tube systems link the flightdeck controls with the hydraulic system. With the system In the study of high-speed aeronautics, the compressibilityactivated, the pilot’s movement of a control causes the effects on air must be addressed. This flight regime ismechanical link to open servo valves, thereby directing characterized by the Mach number, a special parameterhydraulic fluid to actuators, which convert hydraulic pressure named in honor of Ernst Mach, the late 19th century physicistinto control surface movements. who studied gas dynamics. Mach number is the ratio of the speed of the aircraft to the local speed of sound andBecause of the efficiency of the hydromechanical flight determines the magnitude of many of the compressibilitycontrol system, the aerodynamic forces on the control effects.surfaces cannot be felt by the pilot, and there is a risk ofoverstressing the structure of the aircraft. To overcome As an aircraft moves through the air, the air molecules nearthis problem, aircraft designers incorporated artificial feel the aircraft are disturbed and move around the aircraft. Thesystems into the design that provided increased resistance air molecules are pushed aside much like a boat creates a bowto the controls at higher speeds. Additionally, some aircraft wave as it moves through the water. If the aircraft passes at awith hydraulically powered control systems are fitted with low speed, typically less than 250 mph, the density of the aira device called a stick shaker, which provides an artificial remains constant. But at higher speeds, some of the energy ofstall warning to the pilot. the aircraft goes into compressing the air and locally changing the density of the air. The bigger and heavier the aircraft, theFly-By-Wire Control more air it displaces and the greater effect compression hasThe fly-by-wire (FBW) control system employs electrical on the aircraft.signals that transmit the pilot’s actions from the flight deckthrough a computer to the various flight control actuators. This effect becomes more important as speed increases. NearThe FBW system evolved as a way to reduce the system and beyond the speed of sound, about 760 mph (at sea level),weight of the hydromechanical system, reduce maintenance sharp disturbances generate a shockwave that affects both thecosts, and improve reliability. Electronic FBW control lift and drag of an aircraft and flow conditions downstream ofsystems can respond to changing aerodynamic conditions the shockwave. The shockwave forms a cone of pressurizedby adjusting flight control movements so that the aircraft air molecules which move outward and rearward in allresponse is consistent for all flight conditions. Additionally, directions and extend to the ground. The sharp release of thethe computers can be programmed to prevent undesirable pressure, after the buildup by the shockwave, is heard as theand dangerous characteristics, such as stalling and spinning. sonic boom. [Figure 2-21] 2-15
  • 88. Additional technical information pertaining to high-speed aerodynamics can be found at bookstores, libraries, and numerous sources on the Internet. As the design of aircraft evolves and the speeds of aircraft continue to increase into the hypersonic range, new materials and propulsion systems will need to be developed. This is the challenge for engineers, physicists, and designers of aircraft in the future. Rotary-Wing Aircraft Assembly and Rigging The flight control units located in the flight deck of all helicopters are very nearly the same. All helicopters have either one or two of each of the following: collective pitchFigure 2-21. Breaking the sound barrier. control, throttle grip, cyclic pitch control, and directional control pedals. [Figure 2-22] Basically, these units do theListed below are a range of conditions that are encountered same things, regardless of the type of helicopter on whichby aircraft as their designed speed increases. they are installed; however, the operation of the control • Subsonic conditions occur for Mach numbers less system varies greatly by helicopter model. than one (100–350 mph). For the lowest subsonic conditions, compressibility can be ignored. Rigging the helicopter coordinates the movements of the • As the speed of the object approaches the speed flight controls and establishes the relationship between the of sound, the flight Mach number is nearly equal main rotor and its controls, and between the tail rotor and its to one, M = 1 (350–760 mph), and the flow is said controls. Rigging is not a difficult job, but it requires great to be transonic. At some locations on the object, precision and attention to detail. Strict adherence to rigging the local speed of air exceeds the speed of sound. procedures described in the manufacturer’s maintenance Compressibility effects are most important in manuals and service instructions is a must. Adjustments, transonic flows and lead to the early belief in a sound clearances, and tolerances must be exact. barrier. Flight faster than sound was thought to be impossible. In fact, the sound barrier was only an Rigging of the various flight control systems can be broken increase in the drag near sonic conditions because down into the following three major steps: of compressibility effects. Because of the high drag 1. Placing the control system in a specific position— associated with compressibility effects, aircraft are holding it in position with pins, clamps, or jigs, then not operated in cruise conditions near Mach 1. adjusting the various linkages to fit the immobilized • Supersonic conditions occur for numbers greater control component. than Mach 1, but less then Mach 3 (760–2,280 2. Placing the control surfaces in a specific reference mph). Compressibility effects of gas are important position—using a rigging jig, a precision bubble in the design of supersonic aircraft because of the protractor, or a spirit level to check the angular shockwaves that are generated by the surface of the difference between the control surface and some fixed object. For high supersonic speeds, between Mach 3 surface on the aircraft. [Figure 2-23] and Mach 5 (2,280–3,600 mph), aerodynamic heating 3. Setting the maximum range of travel of the various becomes a very important factor in aircraft design. components—this adjustment limits the physical • For speeds greater than Mach 5, the flow is said to movement of the control system. be hypersonic. At these speeds, some of the energy of the object now goes into exciting the chemical After completion of the static rigging, a functional check of bonds which hold together the nitrogen and oxygen the flight control system must be accomplished. The nature molecules of the air. At hypersonic speeds, the of the functional check varies with the type of helicopter and chemistry of the air must be considered when system concerned, but usually includes determining that: determining forces on the object. When the Space 1. The direction of movement of the main and tail rotor Shuttle re-enters the atmosphere at high hypersonic blades is correct in relation to movement of the pilot’s speeds, close to Mach 25, the heated air becomes an controls. ionized plasma of gas, and the spacecraft must be insulated from the extremely high temperatures.2-16
  • 89. Cyclic control stick Controls attitude and direction of flight Throttle Controls rpm Collective pitch stick Controls altitude Pedals Maintain headingFigure 2-22. Controls of a helicopter and the principal function of each. 2. The operation of interconnected control systems (engine throttle and collective pitch) is properly Main rotor rigging protractor coordinated. 3. The range of movement and neutral position of the pilot’s controls are correct. CAUTION 4. The maximum and minimum pitch angles of the main Make sure blade dampers are positioned against rotor blades are within specified limits. This includes auto-rotation inboard stops checking the fore-and-aft and lateral cyclic pitch and collective pitch blade angles. 25° 20° 5. The tracking of the main rotor blades is correct. 15° 10° 6. In the case of multirotor aircraft, the rigging and 5° 0° movement of the rotor blades are synchronized. 5° 10° 7. When tabs are provided on main rotor blades, they are 15° correctly set. 8. The neutral, maximum, and minimum pitch angles and coning angles of the tail rotor blades are correct. 9. When dual controls are provided, they functionFigure 2-23. A typical rigging protractor. correctly and in synchronization. Upon completion of rigging, a thorough check should be made of all attaching, securing, and pivot points. All bolts, nuts, and rod ends should be properly secured and safetied as specified in the manufacturers’ maintenance and service instructions. 2-17
  • 90. Configurations of Rotary-Wing AircraftAutogyroAn autogyro is an aircraft with a free-spinning horizontalrotor that turns due to passage of air upward through therotor. This air motion is created from forward motion of theaircraft resulting from either a tractor or pusher configuredengine/propeller design. [Figure 2-24] Figure 2-26. Dual rotor helicopter. Types of Rotor Systems Fully Articulated Rotor A fully articulated rotor is found on aircraft with more than two blades and allows movement of each individual blade in three directions. In this design, each blade can rotate aboutFigure 2-24. An autogyro. the pitch axis to change lift; each blade can move back and forth in plane, lead and lag; and flap up and down through aSingle Rotor Helicopter hinge independent of the other blades. [Figure 2-27]An aircraft with a single horizontal main rotor that providesboth lift and direction of travel is a single rotor helicopter.A secondary rotor mounted vertically on the tail counteracts Pitch change axisthe rotational force (torque) of the main rotor to correct yawof the fuselage. [Figure 2-25] Flipping hinge Drag hingeFigure 2-25. Single rotor helicopter. Figure 2-27. Articulated rotor head.Dual Rotor HelicopterAn aircraft with two horizontal rotors that provide both thelift and directional control is a dual rotor helicopter. Therotors are counterrotating to balance the aerodynamic torqueand eliminate the need for a separate antitorque system.[Figure 2-26]2-18
  • 91. Semirigid Rotor In sideward flight, the tip-path plane is tilted sideward in theThe semirigid rotor design is found on aircraft with two rotor direction that flight is desired, thus tilting the total lift-thrustblades. The blades are connected in a manner such that as vector sideward. In this case, the vertical or lift componentone blade flaps up, the opposite blade flaps down. is still straight up, weight straight down, but the horizontal or thrust component now acts sideward with drag acting toRigid Rotor the opposite side.The rigid rotor system is a rare design but potentially offersthe best properties of both the fully articulated and semirigid For rearward flight, the tip-path plane is tilted rearward androtors. In this design, the blade roots are rigidly attached to the tilts the lift-thrust vector rearward. The thrust is then rearwardrotor hub. The blades do not have hinges to allow lead-lag or and the drag component is forward, opposite that for forwardflapping. Instead, the blades accommodate these motions by flight. The lift component in rearward flight is straight up;using elastomeric bearings. Elastomeric bearings are molded, weight, straight down.rubber-like materials that are bonded to the appropriate parts.Instead of rotating like conventional bearings, they twist and Torque Compensationflex to allow proper movement of the blades. Newton’s third law of motion states “To every action there is an equal and opposite reaction.” As the main rotor of aForces Acting on the Helicopter helicopter turns in one direction, the fuselage tends to rotateOne of the differences between a helicopter and a fixed-wing in the opposite direction. This tendency for the fuselage toaircraft is the main source of lift. The fixed-wing aircraft rotate is called torque. Since torque effect on the fuselage isderives its lift from a fixed airfoil surface while the helicopter a direct result of engine power supplied to the main rotor,derives lift from a rotating airfoil called the rotor. any change in engine power brings about a corresponding change in torque effect. The greater the engine power, theDuring hovering flight in a no-wind condition, the tip-path greater the torque effect. Since there is no engine powerplane is horizontal, that is, parallel to the ground. Lift and being supplied to the main rotor during autorotation, therethrust act straight up; weight and drag act straight down. The is no torque reaction during autorotation.sum of the lift and thrust forces must equal the sum of theweight and drag forces in order for the helicopter to hover. The force that compensates for torque and provides for directional control can be produced by various means. TheDuring vertical flight in a no-wind condition, the lift and defining factor is dictated by the design of the helicopter,thrust forces both act vertically upward. Weight and drag both some of which do not have a torque issue. Single mainact vertically downward. When lift and thrust equal weight rotor designs typically have an auxiliary rotor located onand drag, the helicopter hovers; if lift and thrust are less than the end of the tail boom. This auxiliary rotor, generallyweight and drag, the helicopter descends vertically; if lift referred to as a tail rotor, produces thrust in the directionand thrust are greater than weight and drag, the helicopter opposite the torque reaction developed by the main rotor.rises vertically. [Figure 2-25] Foot pedals in the flight deck permit the pilot to increase or decrease tail rotor thrust, as needed, to neutralizeFor forward flight, the tip-path plane is tilted forward, thus torque effect.tilting the total lift-thrust force forward from the vertical. Thisresultant lift-thrust force can be resolved into two components: Other methods of compensating for torque and providinglift acting vertically upward and thrust acting horizontally in directional control include the Fenestron® tail rotor system,the direction of flight. In addition to lift and thrust, there is an SUD Aviation design that employs a ducted fan enclosedweight, the downward acting force, and drag, the rearward by a shroud. Another design, called NOTAR®, a McDonaldacting or retarding force of inertia and wind resistance. Douglas design with no tail rotor, employs air directed through a series of slots in the tail boom, with the balanceIn straight-and-level, unaccelerated forward flight, lift equals exiting through a 90° duct located at the rear of the tail boom.weight and thrust equals drag. (Straight-and-level flight is [Figure 2-28]flight with a constant heading and at a constant altitude.)If lift exceeds weight, the helicopter climbs; if lift is lessthan weight, the helicopter descends. If thrust exceeds drag,the helicopter increases speed; if thrust is less than drag, itdecreases speed. 2-19
  • 92. Figure 2-28. Aerospatiale Fenestron tail rotor system (left) and the McDonnell Douglas NOTAR® System (right).Gyroscopic ForcesThe spinning main rotor of a helicopter acts like a gyroscope. Examine a two-bladed rotor system to see how gyroscopicAs such, it has the properties of gyroscopic action, one of precession affects the movement of the tip-path plane.which is precession. Gyroscopic precession is the resultant Moving the cyclic pitch control increases the angle of attackaction or deflection of a spinning object when a force is (AOA) of one rotor blade with the result that a greater liftingapplied to this object. This action occurs approximately 90° force is applied at that point in the plane of rotation. Thisin the direction of rotation from the point where the force same control movement simultaneously decreases the AOAis applied. [Figure 2-29] Through the use of this principle, of the other blade the same amount, thus decreasing the liftingthe tip-path plane of the main rotor may be tilted from the force applied at that point in the plane of rotation. The bladehorizontal. with the increased AOA tends to flap up; the blade with the Axis New axis Old axis 90 Upward force applied here Reaction occurs here Gyro tips down here Gyro tips up hereFigure 2-29. Gyroscopic precession principle.2-20
  • 93. decreased AOA tends to flap down. Because the rotor disk in the plane of rotation. The blade with the increased AOAacts like a gyro, the blades reach maximum deflection at a tends to rise; the blade with the decreased AOA tends topoint approximately 90° later in the plane of rotation. As lower. However, gyroscopic precession prevents the bladesshown in Figure 2-30, the retreating blade AOA is increased from rising or lowering to maximum deflection until a pointand the advancing blade AOA is decreased resulting in approximately 90° later in the plane of rotation.a tipping forward of the tip-path plane, since maximumdeflection takes place 90° later when the blades are at the rear In a three-bladed rotor, the movement of the cyclic pitchand front, respectively. In a rotor system using three or more control changes the AOA of each blade an appropriateblades, the movement of the cyclic pitch control changes the amount so that the end result is the same, a tipping forwardAOA of each blade an appropriate amount so that the end of the tip-path plane when the maximum change in AOAresult is the same. is made as each blade passes the same points at which the maximum increase and decrease are made for the two-The movement of the cyclic pitch control in a two-bladed bladed rotor as shown in Figure 2-30. As each blade passesrotor system increases the AOA of one rotor blade with the 90° position on the left, the maximum increase in AOAthe result that a greater lifting force is applied at this point occurs. As each blade passes the 90° position to the right,in the plane of rotation. This same control movement the maximum decrease in AOA occurs. Maximum deflectionsimultaneously decreases the AOA of the other blade a like takes place 90° later, maximum upward deflection at the rearamount, thus decreasing the lifting force applied at this point and maximum downward deflection at the front; the tip-path plane tips forward. Low pitch applied High flap result Blade rotation Low flap result Blade rotation High pitch appliedFigure 2-30. Gyroscopic precession. 2-21
  • 94. Helicopter Flight Conditions the engine turns the main rotor system in a counterclockwise direction, the helicopter fuselage tends to turn clockwise. TheHovering Flight amount of torque is directly related to the amount of engineDuring hovering flight, a helicopter maintains a constant power being used to turn the main rotor system. Remember,position over a selected point, usually a few feet above the as power changes, torque changes.ground. For a helicopter to hover, the lift and thrust producedby the rotor system act straight up and must equal the weight To counteract this torque-induced turning tendency, anand drag, which act straight down. [Figure 2-31] While antitorque rotor or tail rotor is incorporated into mosthovering, the amount of main rotor thrust can be changed helicopter designs. A pilot can vary the amount of thrustto maintain the desired hovering altitude. This is done by produced by the tail rotor in relation to the amount of torquechanging the angle of incidence (by moving the collective) produced by the engine. As the engine supplies more powerof the rotor blades and hence the AOA of the main rotor to the main rotor, the tail rotor must produce more thrust toblades. Changing the AOA changes the drag on the rotor overcome the increased torque effect. This is done throughblades, and the power delivered by the engine must change the use of antitorque pedals.as well to keep the rotor speed constant. Translating Tendency or Drift During hovering flight, a single main rotor helicopter tends to drift or move in the direction of tail rotor thrust. This drifting Thrust tendency is called translating tendency. [Figure 2-32] Lift otation Tor de r qu Bla e Drift Weight Drag e qu Tor tion Blade rotaFigure 2-31. To maintain a hover at a constant altitude, enough lift Tail rotor downwash Tail rotor thrustand thrust must be generated to equal the weight of the helicopterand the drag produced by the rotor blades. Figure 2-32. A tail rotor is designed to produce thrust in a directionThe weight that must be supported is the total weight of the opposite torque. The thrust produced by the tail rotor is sufficienthelicopter and its occupants. If the amount of lift is greater to move the helicopter laterally.than the actual weight, the helicopter accelerates upwardsuntil the lift force equals the weight gain altitude; if thrust isless than weight, the helicopter accelerates downward. When To counteract this drift, one or more of the following featuresoperating near the ground, the effect of the closeness to the may be used. All examples are for a counterclockwise rotatingground changes this response. main rotor system. • The main transmission is mounted at a slight angle toThe drag of a hovering helicopter is mainly induced drag the left (when viewed from behind) so that the rotorincurred while the blades are producing lift. There is, mast has a built-in tilt to oppose the tail rotor thrust.however, some profile drag on the blades as they rotate • Flight controls can be rigged so that the rotor disk isthrough the air. Throughout the rest of this discussion, the tilted to the right slightly when the cyclic is centered.term drag includes both induced and profile drag. Whichever method is used, the tip-path plane is tilted slightly to the left in the hover.An important consequence of producing thrust is torque. Asdiscussed earlier, Newton’s Third Law states that for every • If the transmission is mounted so the rotor shaft isaction there is an equal and opposite reaction. Therefore, as vertical with respect to the fuselage, the helicopter2-22
  • 95. “hangs” left skid low in the hover. The opposite is Coriolis Effect (Law of Conservation of Angular true for rotor systems turning clockwise when viewed Momentum) from above. The Coriolis effect is also referred to as the law of • In forward flight, the tail rotor continues to push to conservation of angular momentum. It states that the value the right, and the helicopter makes a small angle with of angular momentum of a rotating body does not change the wind when the rotors are level and the slip ball is unless an external force is applied. In other words, a rotating in the middle. This is called inherent sideslip. body continues to rotate with the same rotational velocity until some external force is applied to change the speed ofGround Effect rotation. Angular momentum is moment of inertia (massWhen hovering near the ground, a phenomenon known times distance from the center of rotation squared) multipliedas ground effect takes place. This effect usually occurs at by speed of rotation. Changes in angular velocity, known asheights between the surface and approximately one rotor angular acceleration and deceleration, take place as the massdiameter above the surface. The friction of the ground of a rotating body is moved closer to or further away fromcauses the downwash from the rotor to move outwards from the axis of rotation. The speed of the rotating mass increasesthe helicopter. This changes the relative direction of the or decreases in proportion to the square of the radius. Andownwash from a purely vertical motion to a combination excellent example of this principle is a spinning ice skater.of vertical and horizontal motion. As the induced airflow The skater begins rotation on one foot, with the other legthrough the rotor disk is reduced by the surface friction, the and both arms extended. The rotation of the skater’s body islift vector increases. This allows a lower rotor blade angle for relatively slow. When a skater draws both arms and one legthe same amount of lift, which reduces induced drag. Ground inward, the moment of inertia (mass times radius squared)effect also restricts the generation of blade tip vortices due to becomes much smaller and the body is rotating almost fasterthe downward and outward airflow making a larger portion than the eye can follow. Because the angular momentumof the blade produce lift. When the helicopter gains altitude must remain constant (no external force applied), the angularvertically, with no forward airspeed, induced airflow is no velocity must increase. The rotor blade rotating about thelonger restricted, and the blade tip vortices increase with rotor hub possesses angular momentum. As the rotor beginsthe decrease in outward airflow. As a result, drag increases to cone due to G-loading maneuvers, the diameter or thewhich means a higher pitch angle, and more power is needed disk shrinks. Due to conservation of angular momentum,to move the air down through the rotor. the blades continue to travel the same speed even though the blade tips have a shorter distance to travel due to reduced diskGround effect is at its maximum in a no-wind condition over diameter. The action results in an increase in rotor rpm. Mosta firm, smooth surface. Tall grass, rough terrain, and water pilots arrest this increase with an increase in collective pitch.surfaces alter the airflow pattern, causing an increase in rotor Conversely, as G-loading subsides and the rotor disk flattenstip vortices. [Figure 2-33] out from the loss of G-load induced coning, the blade tips Out of Ground Effect (OGE) In Ground Effect (IGE) No Large blade tip vortex wind hover Blade tip vortex Downwash pattern equidistant 360°Figure 2-33. Air circulation patterns change when hovering out of ground effect (OGE) and when hovering in ground effect (IGE). 2-23
  • 96. now have a longer distance to travel at the same tip speed. ResultantThis action results in a reduction of rotor rpm. However, ifthis drop in the rotor rpm continues to the point at which it Liftattempts to decrease below normal operating rpm, the enginecontrol system adds more fuel/power to maintain the specifiedengine rpm. If the pilot does not reduce collective pitch asthe disk unloads, the combination of engine compensation Thrustfor the rpm slow down and the additional pitch as G-loadingincreases may result in exceeding the torque limitations orpower the engines can produce. Drag Helicopter movementVertical FlightHovering is actually an element of vertical flight. Increasingthe AOA of the rotor blades (pitch) while keeping their Weightrotation speed constant generates additional lift and thehelicopter ascends. Decreasing the pitch causes the helicopter Resultantto descend. In a no wind condition, when lift and thrust areless than weight and drag, the helicopter descends vertically.If lift and thrust are greater than weight and drag, the Figure 2-35. The power required to maintain a straight-and-levelhelicopter ascends vertically. [Figure 2-34] flight and a stabilized airspeed. In straight-and-level (constant heading and at a constant altitude), unaccelerated forward flight, lift equals weight and thrust equals drag. If lift exceeds weight, the helicopter Thrust accelerates vertically until the forces are in balance; if thrust Vertical ascent Lift is less than drag, the helicopter slows until the forces are in balance. As the helicopter moves forward, it begins to lose altitude because lift is lost as thrust is diverted forward. However, as the helicopter begins to accelerate, the rotor system becomes more efficient due to the increased airflow. The result is excess power over that which is required to hover. Continued acceleration causes an even larger increase in airflow through the rotor disk and more excess power. In Weight order to maintain unaccelerated flight, the pilot must not Drag make any changes in power or in cyclic movement. Any such changes would cause the helicopter to climb or descend. Once straight-and-level flight is obtained, the pilot should make note of the power (torque setting) required and not make major adjustments to the flight controls. [Figure 2-36]Figure 2-34. To ascend vertically, more lift and thrust must begenerated to overcome the forces of weight and drag. Translational Lift Improved rotor efficiency resulting from directional flight isForward Flight called translational lift. The efficiency of the hovering rotorIn steady forward flight with no change in airspeed or vertical system is greatly improved with each knot of incoming windspeed, the four forces of lift, thrust, drag, and weight must gained by horizontal movement of the aircraft or surfacebe in balance. Once the tip-path plane is tilted forward, the wind. As incoming wind produced by aircraft movement ortotal lift-thrust force is also tilted forward. This resultant surface wind enters the rotor system, turbulence and vorticeslift-thrust force can be resolved into two components—lift are left behind and the flow of air becomes more horizontal.acting vertically upward and thrust acting horizontally in the In addition, the tail rotor becomes more aerodynamicallydirection of flight. In addition to lift and thrust, there is weight efficient during the transition from hover to forward flight.(the downward acting force) and drag (the force opposing the Translational thrust occurs when the tail rotor becomes moremotion of an airfoil through the air). [Figure 2-35] aerodynamically efficient during the transition from hover2-24
  • 97. found on most helicopters which tends to bring the nose 800 of the helicopter to a more level attitude. Figure 2-37 and Maximum continuous power available Figure 2-38 show airflow patterns at different speeds and how airflow affects the efficiency of the tail rotor. GE Increasing power for rO decreasing airspeed ove 600 Effective Translational Lift (ETL) oh Power required (horsepower) dt While transitioning to forward flight at about 16–24 knots, ire C A B the helicopter experiences effective translational lift (ETL). qu re As mentioned earlier in the discussion on translational lift, er w 400 Po Increasing power for the rotor blades become more efficient as forward airspeed decreasing airspeed increases. Between 16–24 knots, the rotor system completely outruns the recirculation of old vortices and begins to work Maximum in relatively undisturbed air. The flow of air through the 200 continuous rotor system is more horizontal, therefore induced flow level (horizontal) and induced drag are reduced. The AOA is subsequently Minimum power flight increased, which makes the rotor system operate more for level flight(VY) airspeed (VH) efficiently. This increased efficiency continues with increased 0 0 40 60 80 100 120 airspeed until the best climb airspeed is reached, and total drag is at its lowest point. Indicated airspeed (KIAS) As speed increases, translational lift becomes more effective,Figure 2-36. Changing force vectors results in aircraft the nose rises or pitches up, and the aircraft rolls to the right.movement. The combined effects of dissymmetry of lift, gyroscopic precession, and transverse flow effect cause this tendency.to forward flight. As the tail rotor works in progressively It is important to understand these effects and anticipateless turbulent air, this improved efficiency produces more correcting for them. Once the helicopter is transitioningantitorque thrust, causing the nose of the aircraft to yaw left through ETL, the pilot needs to apply forward and left(with a main rotor turning counterclockwise) and forces the lateral cyclic input to maintain a constant rotor-disk attitude.pilot to apply right pedal (decreasing the AOA in the tail [Figure 2-39]rotor blades) in response. In addition, during this period, theairflow affects the horizontal components of the stabilizer b y aft se cti sed on of ro su to r e c ul e m ol 1–5 knots r y of ai locit rd ve Do wnwaFigure 2-37. The airflow pattern for 1–5 knots of forward airspeed. Note how the downwind vortex is beginning to dissipate and inducedflow down through the rear of the rotor system is more horizontal. 2-25
  • 98. Airflow pattern just prior to effective translational lift 10–15 knotsFigure 2-38. An airflow pattern at a speed of 10–15 knots. At this increased airspeed, the airflow continues to become more horizontal.The leading edge of the downwash pattern is being overrun and is well back under the nose of the helicopter. Direction of Flight More horizontal No recirculation flow of air of air Retreating Side Advancing Side a tion rot de a Bl 16–24 knots Blade tip Blade tip Relative wind Relative wind speed speed minus plus helicopter helicopter speed speed Reduced induced flow Tail rotor operates in (200 knots) (400 knots) increases angle of attack relatively clean air io n at rot BladeFigure 2-39. Effective translational lift is easily recognized in actualflight by a transient induced aerodynamic vibration and increased Forward flight at 100 knotsperformance of the helicopter. Figure 2-40. The blade tip speed of this helicopter is approximatelyDissymmetry of Lift 300 knots. If the helicopter is moving forward at 100 knots, theDissymmetry of lift is the differential (unequal) lift between relative windspeed on the advancing side is 400 knots. On theadvancing and retreating halves of the rotor disk caused by the retreating side, it is only 200 knots. This difference in speed causesdifferent wind flow velocity across each half. This difference a dissymmetry of lift.in lift would cause the helicopter to be uncontrollable in anysituation other than hovering in a calm wind. There must If this condition was allowed to exist, a helicopter with abe a means of compensating, correcting, or eliminating this counterclockwise main rotor blade rotation would roll to theunequal lift to attain symmetry of lift. left because of the difference in lift. In reality, the main rotor blades flap and feather automatically to equalize lift acrossWhen the helicopter moves through the air, the relative airflow the rotor disk. Articulated rotor systems, usually with three orthrough the main rotor disk is different on the advancing side more blades, incorporate a horizontal hinge (flapping hinge)than on the retreating side. The relative wind encountered to allow the individual rotor blades to move, or flap up andby the advancing blade is increased by the forward speed down as they rotate. A semirigid rotor system (two blades)of the helicopter; while the relative windspeed acting on utilizes a teetering hinge, which allows the blades to flap asthe retreating blade is reduced by the helicopter’s forward a unit. When one blade flaps up, the other blade flaps down.airspeed. Therefore, as a result of the relative windspeed, theadvancing blade side of the rotor disk produces more lift thanthe retreating blade side. [Figure 2-40]2-26
  • 99. As the rotor blade reaches the advancing side of the rotor During aerodynamic flapping of the rotor blades as theydisk, it reaches its maximum upward flapping velocity. compensate for dissymmetry of lift, the advancing blade[Figure 2-41A] When the blade flaps upward, the angle achieves maximum upward flapping displacement over thebetween the chord line and the resultant relative wind nose and maximum downward flapping displacement overdecreases. This decreases the AOA, which reduces the the tail. This causes the tip-path plane to tilt to the rear andamount of lift produced by the blade. At position C, the rotor is referred to as blowback. Figure 2-42 shows how the rotorblade is at its maximum downward flapping velocity. Due disk is originally oriented with the front down followingto downward flapping, the angle between the chord line and the initial cyclic input. As airspeed is gained and flappingthe resultant relative wind increases. This increases the AOA eliminates dissymmetry of lift, the front of the disk comesand thus the amount of lift produced by the blade.The combination of blade flapping and slow relative windacting on the retreating blade normally limits the maximumforward speed of a helicopter. At a high forward speed, theretreating blade stalls due to high AOA and slow relativewind speed. This situation is called “retreating bladestall” and is evidenced by a nose-up pitch, vibration, anda rolling tendency—usually to the left in helicopters withcounterclockwise blade rotation.Pilots can avoid retreating blade stall by not exceeding thenever-exceed speed. This speed is designated VNE and isindicated on a placard and marked on the airspeed indicator Figure 2-42. To compensate for blowback, move the cyclic forward.by a red line. Blowback is more pronounced with higher airspeeds. B Angle of attack over nose Chord line Resultant relative wind n atio B rot de a Bl C Angle of attack at 9 o’clock position A Angle of attack at 3 o’clock position Chord Chord line line C A Resultant relati ve wind wind Resultant relative Upflap velocity Downflap velocity D D Angle of attack over tail Chord line Relative wind Angle of attack Resultant relative windFigure 2-41. The combined upward flapping (reduced lift) of the advancing blade and downward flapping (increased lift) of the retreatingblade equalizes lift across the main rotor disk counteracting dissymmetry of lift. 2-27
  • 100. up, and the back of the disk goes down. This reorientation tilt. At higher forward speeds, the pilot must continue toof the rotor disk changes the direction in which total rotor move the cyclic forward. This further reduces pitch anglethrust acts; the helicopter’s forward speed slows, but can be on the advancing blade and further increases pitch angle oncorrected with cyclic input. The pilot uses cyclic feathering the retreating blade. As a result, there is even more tilt to theto compensate for dissymmetry of lift allowing him or her rotor than at lower speeds.to control the attitude of the rotor disk. This horizontal lift component (thrust) generates higherCyclic feathering compensates for dissymmetry of lift helicopter airspeed. The higher airspeed induces blade(changes the AOA) in the following way. At a hover, equal flapping to maintain symmetry of lift. The combination oflift is produced around the rotor system with equal pitch and flapping and cyclic feathering maintains symmetry of lift andAOA on all the blades and at all points in the rotor system desired attitude on the rotor system and helicopter.(disregarding compensation for translating tendency). Therotor disk is parallel to the horizon. To develop a thrust force, Autorotationthe rotor system must be tilted in the desired direction of Autorotation is the state of flight in which the main rotormovement. Cyclic feathering changes the angle of incidence system of a helicopter is being turned by the action of airdifferentially around the rotor system. Forward cyclic moving up through the rotor rather than engine power drivingmovements decrease the angle of incidence at one part on the rotor. In normal, powered flight, air is drawn into thethe rotor system while increasing the angle at another part. main rotor system from above and exhausted downward, butMaximum downward flapping of the blade over the nose and during autorotation, air moves up into the rotor system frommaximum upward flapping over the tail tilt both rotor disk and below as the helicopter descends. Autorotation is permittedthrust vector forward. To prevent blowback from occurring, mechanically by a freewheeling unit, which is a specialthe pilot must continually move the cyclic forward as the clutch mechanism that allows the main rotor to continuevelocity of the helicopter increases. Figure 2-42 illustrates turning even if the engine is not running. If the engine fails,the changes in pitch angle as the cyclic is moved forward at the freewheeling unit automatically disengages the engineincreased airspeeds. At a hover, the cyclic is centered and from the main rotor allowing the main rotor to rotate freely.the pitch angle on the advancing and retreating blades is the It is the means by which a helicopter can be landed safely insame. At low forward speeds, moving the cyclic forward the event of an engine failure; consequently, all helicoptersreduces pitch angle on the advancing blade and increases must demonstrate this capability in order to be certificated.pitch angle on the retreating blade. This causes a slight rotor [Figure 2-43] Normal Powered Flight Autorotation ht flig Direction of flight of on cti re DiFigure 2-43. During an autorotation, the upward flow of relative wind permits the main rotor blades to rotate at their normal speed. Ineffect, the blades are “gliding” in their rotational plane.2-28
  • 101. Rotorcraft Controls stationary swash plate by a uniball sleeve. It is connected to the mast by drive links and is allowed to rotate with the mainSwash Plate Assembly rotor mast. Both swash plates tilt and slide up and down asThe purpose of the swash plate is to transmit control inputs one unit. The rotating swash plate is connected to the pitchfrom the collective and cyclic controls to the main rotor horns by the pitch links.blades. It consists of two main parts: the stationary swashplate and the rotating swash plate. [Figure 2-44] There are three major controls in a helicopter that the pilot must use during flight. They are the collective pitch control, Pitch link cyclic pitch control, and antitorque pedals or tail rotor control. In addition to these major controls, the pilot must also use the Stationary swash plate throttle control, which is mounted directly to the collective pitch control in order to fly the helicopter. Collective Pitch Control The collective pitch control is located on the left side of the pilot’s seat and is operated with the left hand. The collective Rotating swash plate is used to make changes to the pitch angle of all the main Control rod rotor blades simultaneously, or collectively, as the name implies. As the collective pitch control is raised, there is a simultaneous and equal increase in pitch angle of all mainFigure 2-44. Stationary and rotating swash plate. rotor blades; as it is lowered, there is a simultaneous and equal decrease in pitch angle. This is done through a seriesThe stationary swash plate is mounted around the main rotor of mechanical linkages, and the amount of movement in themast and connected to the cyclic and collective controls collective lever determines the amount of blade pitch change.by a series of pushrods. It is restrained from rotating by an [Figure 2-45] An adjustable friction control helps preventantidrive link but is able to tilt in all directions and move inadvertent collective pitch movement.vertically. The rotating swash plate is mounted to theFigure 2-45. Raising the collective pitch control increases the pitch angle by the same amount on all blades. 2-29
  • 102. Throttle Control In piston helicopters, the collective pitch is the primaryThe function of the throttle is to regulate engine rpm. If the control for manifold pressure, and the throttle is the primarycorrelator or governor system does not maintain the desired control for rpm. However, the collective pitch control alsorpm when the collective is raised or lowered, or if those influences rpm, and the throttle also influences manifoldsystems are not installed, the throttle must be moved manually pressure; therefore, each is considered to be a secondarywith the twist grip to maintain rpm. The throttle control is control of the other’s function. Both the tachometer (rpmmuch like a motorcycle throttle, and works almost the same indicator) and the manifold pressure gauge must be analyzedway; twisting the throttle to the left increases rpm, twisting to determine which control to use. Figure 2-47 illustratesthe throttle to the right decreases rpm. [Figure 2-46] this relationship. If manifold and rpm is Solution pressure is Increasing the throttle increases LOW LOW manifold pressure and rpm Twist grip throttle Lowering the collective pitch HIGH LOW decreases manifold pressure and increases rpm Raising the collective pitch LOW HIGH increases manifold pressure and decreases rpm Reducing the throttle decreases HIGH HIGH manifold pressure and rpm Figure 2-47. Relationship between manifold pressure, rpm,Figure 2-46. A twist grip throttle is usually mounted on the end collective, and throttle.of the collective lever. The throttles on some turbine helicoptersare mounted on the overhead panel or on the floor in the cockpit. Cyclic Pitch Control The cyclic pitch control is mounted vertically from theGovernor/Correlator cockpit floor, between the pilot’s legs or, in some models,A governor is a sensing device that senses rotor and engine between the two pilot seats. [Figure 2-48] This primary flightrpm and makes the necessary adjustments in order to keep control allows the pilot to fly the helicopter in any horizontalrotor rpm constant. Once the rotor rpm is set in normal direction; fore, aft, and sideways. The total lift force is alwaysoperations, the governor keeps the rpm constant, and there perpendicular to the tip-path place of the main rotor. Theis no need to make any throttle adjustments. Governors are purpose of the cyclic pitch control is to tilt the tip-path planecommon on all turbine helicopters (as it is a function of the in the direction of the desired horizontal direction. The cyclicfuel control system of the turbine engine), and used on some control changes the direction of this force and controls thepiston-powered helicopters. attitude and airspeed of the helicopter.A correlator is a mechanical connection between the The rotor disk tilts in the same direction the cyclic pitchcollective lever and the engine throttle. When the collective control is moved. If the cyclic is moved forward, the rotorlever is raised, power is automatically increased and when disk tilts forward; if the cyclic is moved aft, the disk tiltslowered, power is decreased. This system maintains rpm aft, and so on. Because the rotor disk acts like a gyro, theclose to the desired value, but still requires adjustment of mechanical linkages for the cyclic control rods are riggedthe throttle for fine tuning. in such a way that they decrease the pitch angle of the rotor blade approximately 90° before it reaches the direction ofSome helicopters do not have correlators or governors and cyclic displacement, and increase the pitch angle of therequire coordination of all collective and throttle movements. rotor blade approximately 90° after it passes the directionWhen the collective is raised, the throttle must be increased; of displacement. An increase in pitch angle increases AOA;when the collective is lowered, the throttle must be decreased. a decrease in pitch angle decreases AOA. For example, ifAs with any aircraft control, large adjustments of either the cyclic is moved forward, the AOA decreases as the rotorcollective pitch or throttle should be avoided. All corrections blade passes the right side of the helicopter and increases onshould be made with smooth pressure. the left side. This results in maximum downward deflection2-30
  • 103. Cyclic pitch control Cyclic pitch control Figure 2-49. Antitorque pedals compensate for changes in torque and control heading in a hover. Helicopters that are designed with tandem rotors do not have an antitorque rotor. These helicopters are designed with both rotor systems rotating in opposite directions to counteract the torque, rather than using a tail rotor. Directional antitorque pedals are used for directional control of the aircraft while in flight, as well as while taxiing with the forward gear off theFigure 2-48. The cyclic pitch control may be mounted vertically ground. With the right pedal displaced forward, the forwardbetween the pilot’s knees or on a teetering bar from a single cyclic rotor disk tilts to the right, while the aft rotor disk tilts tolocated in the center of the helicopter. The cyclic can pivot in all the left. The opposite occurs when the left pedal is pusheddirections. forward; the forward rotor disk inclines to the left, and the aft rotor disk tilts to the right. Differing combinations of pedalof the rotor blade in front of the helicopter and maximum and cyclic application can allow the tandem rotor helicopterupward deflection behind it, causing the rotor disk to tilt to pivot about the aft or forward vertical axis, as well asforward. pivoting about the center of mass.Antitorque Pedals Stabilizer SystemsThe antitorque pedals are located on the cabin floor by Bell Stabilizer Bar Systemthe pilot’s feet. They control the pitch and, therefore, thethrust of the tail rotor blades. [Figure 2-49] Newton’s Arthur M. Young discovered that stability could be increasedThird Law applies to the helicopter fuselage and how it significantly with the addition of a stabilizer bar perpendicularrotates in the opposite direction of the main rotor blades to the two blades. The stabilizer bar has weighted ends, whichunless counteracted and controlled. To make flight possible cause it to stay relatively stable in the plane of rotation. Theand to compensate for this torque, most helicopter designs stabilizer bar is linked with the swash plate in a manner thatincorporate an antitorque rotor or tail rotor. The antitorque reduces the pitch rate. The two blades can flap as a unit and,pedals allow the pilot to control the pitch angle of the tail therefore, do not require lag-lead hinges (the whole rotorrotor blades which in forward flight puts the helicopter in slows down and accelerates per turn). Two-bladed systemslongitudinal trim and while at a hover, enables the pilot to require a single teetering hinge and two coning hinges toturn the helicopter 360°. The antitorque pedals are connected permit modest coning of the rotor disk as thrust is increased.to the pitch change mechanism on the tail rotor gearbox and The configuration is known under multiple names, includingallow the pitch angle on the tail rotor blades to be increased Hiller panels, Hiller system, Bell-Hiller system, and flybaror decreased. system. 2-31
  • 104. Offset Flapping Hinge Helicopter Vibration TypesThe offset flapping hinge is offset from the center of the rotorhub and can produce powerful moments useful for controlling Frequency Level Vibrationthe helicopter. The distance of the hinge from the hub (the Extreme low frequency Less than 1/rev PYLON ROCKoffset) multiplied by the force produced at the hinge produces Low frequency 1/rev or 2/rev type vibrationa moment at the hub. Obviously, the larger the offset, the Medium frequency Generally 4, 5, or 6/revgreater the moment for the same force produced by the blade. High frequency Tail rotor speed or faster Figure 2-50. Various helicopter vibration types.The flapping motion is the result of the constantly changingbalance between lift, centrifugal, and inertial forces. This Low Frequency Vibrationrising and falling of the blades is characteristic of most Low frequency vibrations (1/rev and 2/rev) are caused by thehelicopters and has often been compared to the beating of rotor itself. 1/rev vibrations are of two basic types: verticala bird’s wing. The flapping hinge, together with the natural or lateral. A 1/rev is caused simply by one blade developingflexibility found in most blades, permits the blade to droop more lift at a given point than the other blade develops atconsiderably when the helicopter is at rest and the rotor is the same point.not turning over. During flight, the necessary rigidity isprovided by the powerful centrifugal force that results from Medium Frequency Vibrationthe rotation of the blades. This force pulls outward from the Medium frequency vibration (4/rev and 6/rev) is anothertip, stiffening the blade, and is the only factor that keeps it vibration inherent in most rotors. An increase in the level offrom folding up. these vibrations is caused by a change in the capability of the fuselage to absorb vibration, or a loose airframe component,Stability Augmentation Systems (SAS) such as the skids, vibrating at that frequency.Some helicopters incorporate stability augmentation systems(SAS) to help stabilize the helicopter in flight and in a hover. High Frequency VibrationThe simplest of these systems is a force trim system, whichuses a magnetic clutch and springs to hold the cyclic control High frequency vibrations can be caused by anything in thein the position at which it was released. More advanced helicopter that rotates or vibrates at extremely high speeds.systems use electric actuators that make inputs to the The most common and obvious causes: loose elevator linkagehydraulic servos. These servos receive control commands at swashplate horn, loose elevator, or tail rotor balance andfrom a computer that senses helicopter attitude. Other inputs, track.such as heading, speed, altitude, and navigation informationmay be supplied to the computer to form a complete autopilot Rotor Blade Trackingsystem. The SAS may be overridden or disconnected by the Blade tracking is the process of determining the positionspilot at any time. of the tips of the rotor blade relative to each other while the rotor head is turning, and of determining the correctionsSAS reduces pilot workload by improving basic aircraft necessary to hold these positions within certain tolerances.control harmony and decreasing disturbances. These systems The blades should all track one another as closely as possible.are very useful when the pilot is required to perform other The purpose of blade tracking is to bring the tips of allduties, such as sling loading and search and rescue operations. blades into the same tip path throughout their entire cycle of rotation. Various methods of blade tracking are explained inHelicopter Vibration the following paragraphs.The following paragraphs describe the various types ofvibrations. Figure 2-50 shows the general levels into which Flag and Polefrequencies are divided. The flag and pole method, as shown in Figure 2-51, shows the relative positions of the rotor blades. The blade tips areExtreme Low Frequency Vibration marked with chalk or a grease pencil. Each blade tip shouldExtreme low frequency vibration is pretty well limited to be marked with a different color so that it is easy to determinepylon rock. Pylon rocking (two to three cycles per second) the relationship of the other tips of the rotor blades to eachis inherent with the rotor, mast, and transmission system. other. This method can be used on all types of helicoptersTo keep the vibration from reaching noticeable levels, that do not have jet propulsion at the blade tips. Refer totransmission mount dampening is incorporated to absorb the applicable maintenance manual for specific procedures.the rocking.2-32
  • 105. Curtain 80° to Curtain 0° Leading edge 7 Blade BLADE Pole Position of chalk mark (approximately 2 inches long) Pole Handle Line parallel to longitudinal axis of helicopter Curtain 1/2" max spread (typical) Approximate position of chalk marks PoleFigure 2-51. Flag and pole blade tracking.Electronic Blade TrackerThe most common electronic blade tracker consists ofa Balancer/Phazor, Strobex Tracker, and Vibrex Tester. Meter[Figures 2-52 through 2-54] The Strobex blade tracker A Channel Bpermits blade tracking from inside or outside the helicopter A B TRACKwhile on the ground or inside the helicopter in flight. The COMMONsystem uses a highly concentrated light beam flashing in MAGNETIC PICKUP FUNCTION Band-pass filter BALANCERsequence with the rotation of the main rotor blades so that a MODEL 177M-6A RPM TONEfixed target at the blade tips appears to be stopped. Each blade X10 X100 X1 PUSH FORis identified by an elongated retroreflective number taped or SCALE 2attached to the underside of the blade in a uniform location. RPM RANGE Phase meterWhen viewed at an angle from inside the helicopter, the taped DOUBLE TEST 10 11 12 1 2numbers will appear normal. Tracking can be accomplished PHAZOR 9 8 4 3with tracking tip cap reflectors and a strobe light. The tip 7 5 6caps are temporarily attached to the tip of each blade. Thehigh-intensity strobe light flashes in time with the rotatingblades. The strobe light operates from the aircraft electricalpower supply. By observing the reflected tip cap image, it is Figure 2-52. Balancer/Phazor.possible to view the track of the rotating blades. Tracking isaccomplished in a sequence of four separate steps: groundtracking, hover verification, forward flight tracking, and autorotation rpm adjustment. 2-33
  • 106. Strobe flash tube RPM dial RPM STROBEX MODEL 135M-11Figure 2-53. Strobex tracker. Interrupter plate Motor Figure 2-55. Tail rotor tracking. TES • The strobe-type tracking device may be used if TER available. Instructions for use are provided with the device. Attach a piece of soft rubber hose six inches long on the end of a ½ × ½ inch pine stick or other flexible device. Cover the rubber hose with Prussian blue or similar type of coloring thinned with oil. NOTE: Ground run-up shall be performed by authorized personnel only. Start engine in accordance with applicable maintenance manual. Run engine with pedals in neutral position. Reset marking device on underside of tail boomFigure 2-54. Vibrex tracker. assembly. Slowly move marking device into disk of tail rotorTail Rotor Tracking approximately one inch from tip. When near blade is marked,The marking and electronic methods of tail rotor tracking stop engine and allow rotor to stop. Repeat this procedureare explained in the following paragraphs. until tracking mark crosses over to the other blade, then extend pitch control link of unmarked blade one half turn.Marking Method Electronic MethodProcedures for tail rotor tracking using the marking method,as shown in Figure 2-55, are as follows: The electronic Vibrex balancing and tracking kit is housed in a carrying case and consists of a Model 177M-6A Balancer, • After replacement or installation of tail rotor hub, a Model 135M-11 Strobex, track and balance charts, an blades, or pitch change system, check tail rotor rigging accelerometer, cables, and attaching brackets. and track tail rotor blades. Tail rotor tip clearance shall be set before tracking and checked again after tracking.2-34
  • 107. The Vibrex balancing kit is used to measure and indicate the Reciprocating Enginelevel of vibration induced by the main rotor and tail rotor of The reciprocating engine consists of a series of pistonsa helicopter. The Vibrex analyzes the vibration induced by connected to a rotating crankshaft. As the pistons move upout-of-track or out-of-balance rotors, and then by plotting and down, the crankshaft rotates. The reciprocating enginevibration amplitude and clock angle on a chart the amount gets its name from the back-and-forth movement of itsand location of rotor track or weight change is determined. In internal parts. The four-stroke engine is the most commonaddition, the Vibrex is used in troubleshooting by measuring type, and refers to the four different cycles the enginethe vibration levels and frequencies or rpm of unknown undergoes to produce power. [Figure 2-56]disturbances. Intake valve Exhaust valveRotor Blade Preservation and StorageAccomplish the following requirements for rotor bladepreservation and storage: • Condemn, demilitarize, and dispose of locally any blade which has incurred nonrepairable damage. Spark plug • Tape all holes in the blade, such as tree damage, or Piston foreign object damage (FOD) to protect the interior of the blade from moisture and corrosion. • Thoroughly remove foreign matter from the entire exterior surface of blade with mild soap and water. • Protect blade outboard eroded surfaces with a light coating of corrosion preventive or primer coating. Crankshaft Connecting rod • Protect blade main bolt hole bushing, drag brace 1. Intake 2. Compression retention bolt hole bushing, and any exposed bare metal (i.e., grip and drag pads) with a light coating of corrosion preventive. • Secure blade to shock-mounted support and secure container lid. • Place copy of manufacturer’s blade records, containing information required by Title 14 of the Code of Federal Regulations (14 CFR) section 91.417(a)(2)(ii), and any other blade records in a waterproof bag and insert into container record tube. • Obliterate old markings from the container that pertained to the original shipment or to the original 3. Power 4. Exhaust item it contained. Stencil the blade National Stock Number (NSN), model, and serial number, as applicable, on the outside of the container. Figure 2-56. The arrows indicate the direction of motion of the crankshaft and piston during the four-stroke cycle.Helicopter Power SystemsPowerplant When the piston moves away from the cylinder head onThe two most common types of engines used in helicopters are the intake stroke, the intake valve opens and a mixture ofthe reciprocating engine and the turbine engine. Reciprocating fuel and air is drawn into the combustion chamber. As theengines, also called piston engines, are generally used cylinder moves back toward the cylinder head, the intakein smaller helicopters. Most training helicopters use valve closes, and the fuel/air mixture is compressed. Whenreciprocating engines because they are relatively simple and compression is nearly complete, the spark plugs fire and theinexpensive to operate. Turbine engines are more powerful compressed mixture is ignited to begin the power stroke.and are used in a wide variety of helicopters. They produce a The rapidly expanding gases from the controlled burning oftremendous amount of power for their size but are generally the fuel/air mixture drive the piston away from the cylindermore expensive to operate. head, thus providing power to rotate the crankshaft. The 2-35
  • 108. piston then moves back toward the cylinder head on the flight conditions. The main components of the transmissionexhaust stroke where the burned gases are expelled through system are the main rotor transmission, tail rotor drivethe opened exhaust valve. Even when the engine is operated system, clutch, and freewheeling unit. The freewheeling unit,at a fairly low speed, the four-stroke cycle takes place several or autorotative clutch, allows the main rotor transmission tohundred times each minute. In a four-cylinder engine, each drive the tail rotor drive shaft during autorotation. Helicoptercylinder operates on a different stroke. Continuous rotation transmissions are normally lubricated and cooled with theirof a crankshaft is maintained by the precise timing of the own oil supply. A sight gauge is provided to check thepower strokes in each cylinder. oil level. Some transmissions have chip detectors located in the sump. These detectors are wired to warning lightsTurbine Engine located on the pilot’s instrument panel that illuminate in theThe gas turbine engine mounted on most helicopters is event of an internal problem. The chip detectors on modernmade up of a compressor, combustion chamber, turbine, helicopters have a “burn off” capability and attempt to correctand accessory gearbox assembly. The compressor draws the situation without pilot action. If the problem cannot befiltered air into the plenum chamber and compresses it. The corrected on its own, the pilot must refer to the emergencycompressed air is directed to the combustion section through procedures for that particular helicopter. discharge tubes where atomized fuel is injected into it. Thefuel/air mixture is ignited and allowed to expand. This Main Rotor Transmissioncombustion gas is then forced through a series of turbine The primary purpose of the main rotor transmission iswheels causing them to turn. These turbine wheels provide to reduce engine output rpm to optimum rotor rpm. Thispower to both the engine compressor and the accessory reduction is different for the various helicopters. As angearbox. Power is provided to the main rotor and tail rotor example, suppose the engine rpm of a specific helicoptersystems through the freewheeling unit which is attached is 2,700. A rotor speed of 450 rpm would require a 6:1to the accessory gearbox power output gear shaft. The reduction. A 9:1 reduction would mean the rotor would turncombustion gas is finally expelled through an exhaust outlet. at 300 rpm. Most helicopters use a dual-needle tachometer[Figure 2-57] or a vertical scale instrument to show both engine and rotor rpm or a percentage of engine and rotor rpm. The rotor rpmTransmission System indicator normally is used only during clutch engagement toThe transmission system transfers power from the engine to monitor rotor acceleration, and in autorotation to maintainthe main rotor, tail rotor, and other accessories during normal rpm within prescribed limits. [Figure 2-58] Gearbox Compression Section Turbine Section Combustion Section Section Exhaust air outlet N2 Rotor Stator N1 Rotor Compressor rotor Igniter plug Air inlet Fuel nozzle Gear Inlet air Compressor discharge air Output Shaft Combustion liner Combustion gases Exhaust gasesFigure 2-57. Many helicopters use a turboshaft engine to drive the main transmission and rotor systems. The main difference betweena turboshaft and a turbojet engine is that most of the energy produced by the expanding gases is used to drive a turbine rather thanproducing thrust through the expulsion of exhaust gases.2-36
  • 109. Clutch In a conventional airplane, the engine and propeller are 20 E R permanently connected. However, in a helicopter there is 15 25 3 10 2 4 30 110 100 110 100 a different relationship between the engine and the rotor. Because of the greater weight of a rotor in relation to the 90 90 1 5 80 80 R RPM 70 70 5 35 R power of the engine, as compared to the weight of a propeller X X100 60 60 50 50 ROTOR 0 40 ENGINE % RPM and the power in an airplane, the rotor must be disconnected from the engine when the starter is engaged. A clutch allows % RPM the engine to be started and then gradually pick up the load 120 110 of the rotor. 105 50 60 70 On free turbine engines, no clutch is required, as the gas ROTOR 80 100 40 EE