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Chapter 2  Principles Of  Flight
 

Chapter 2 Principles Of Flight

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  • Relative windDirection of airflow with respect to the bladeOpposite the flight path of the blade
  • Pitch angleAcute angle between blade chord and plane of rotationVaried by collective and cyclicNot to be confused with angle of attack
  • Acute angle between chord line and relative wind.Not always the same as pitch angle
  • LiftForce produced at right angle to the relative windOpposes gravityBased on Bernoulli’s principleIncreased velocity, decreases pressureDragResists airfoils movement through the airParallel to relative windPerpendicular to liftSlows rotor when angle of attack is increasedVaries with the square of velocity
  • Imaginary point where the result of aerodynamic forces are considered to be concentratedCan move as forces changeMoves great distances on unsymmetrical airfoilsMoves very little on symmetrical airfoils
  • Helicopter use both symmetrical and unsymmetrical airfoils
  • Streamlined airflow separates and reverse flow occursResults in loss of lift
  • Rotor DroopBlades droop due to gravity when at rest – Static rotor droopNot to be confused with dynamic rotor droopOvercome by centrifugal forceLift react perpendicular to centrifugal forceNew position is referred to as coningDepends on lift and weight of helicopterTip path plane. – Circular path that tip pass throughOut of track – Causes vibrations
  • Feathering axis required to change angle of attack of each blade as they pass along the disc.Note: pause and discuss collective and cyclic before next slide
  • Movement occurs 90 deg. from the force applied in the direction of rotationTo do this a swashplate is used
  • For every action there is an opposite and equal reactionFuselage moves in opposite direction of M/RSeveral designs to eliminateCoaxialIntermeshingTandemRamjet at the rotor tipsSingle Main with tail rotorTail rotor uses a great deal of engine powerDifferent methods used to reduce tail rotor power requirementsVertical fin that is offset keeps the fuselage straight in fwd flight
  • Velocity of airfoil section increases farther out from mastTwist is incorporated to increase to angle of attack for slower moving airfoil sectionsThis increase overall lift of the rotor system
  • Lift on retreating half less than advancing halfEarly inventors could not achieve fwd flightJuan De Cierva incorporated flapping hinge
  • Flapping hingeAllows advancing blade to move upThis reduces it’s liftRetreating blade moves downIncreases lift on retreating sideSeesawTwo bladed systemBlades are connected so if one moves up the other moves down
  • Coriolis EffectRotors with flapping hinge are subjected to it more than seesaw systemsChange in velocity to compensate for the change in distance in the centre of mass of the blades from the axis of rotation.As the blade flaps up it acceleratesAs the blade flaps down(retreating) it slows downLike a figure skaterCauses geometric imbalance.
  • Lead-Lag hingeAllows blade to huntCorrects the geometric imbalanceRequires dampers
  • Underslung RotorUsed with seesaw systemMounted below the top of the mastKeeps the distance from the C of G of the blades to the axis of rotation, smallLong masts, mounted with flexibility to absorb any geometric imbalance
  • Rigid headUses feathering axis onlyUnable to correct for dissymmetry of liftFibreglass blades allow for flappingHighly manoeuvrableBO 105 can perform a barrel roll and a loop
  • Simplified construction.Not dependant on the centrifugal force for rigidity.More subject to wind gustsBending forces are applied to the blade rootSemirigid rotors require underslinging of the rotor.Some are gimbaled for movement about the chordwise axisOthers use swashplate correction factors to compensate for coriolis effect.
  • The rotor disc may tilt without tilting the mast because of the flapping hinge.Flapping hinges relieve bending forces at the root of the blade, allowing coning of the rotor.The flapping hinge reduces gust sensitivity due to the individual blade flap.Flapping hinge bearing areas are subject to heavy centrifugal loads.The flapping hinge introduces geometric imbalance.This geometric imbalance requires an additional drag hinge.The drag hinge relieves bending stresses during acceleration of the rotor.Drag hinge bearings are subject to high centrifugal loads.The lead-lag hinge allows the main rotor blades to self align. Therefore, there is no need to statically align a fully articulated main rotor head assembly
  • Cyclic controls are sometimes used to offset translating tendency (tail rotor drift)
  • within half of rotor diameter to the groundDownward flowing air can’t escapeAir density increasesForms a ground cushionAt hover speeds. Lost above 3 to 5 mph
  • Correlation box changes engine power with collective movement

Chapter 2  Principles Of  Flight Chapter 2 Principles Of Flight Presentation Transcript

  • Principles of Flight
  • M/R & T/R Blade Terminology
    • Root
    • Span
    • Tip
    • Chord
    • Trailing edge
    • Leading edge
  • Fig. 2-1 Nomenclature of the blade
    Fig. 2-2 Nomenclature of the cross section of an airfoil.
  • Wing Design
    Camber - the characteristic curve of the airfoil’s upper
    and lower surfaces.
    Chord line - an imaginary straight line
    drawn through the airfoil
    from the leading edge to
    the trailing edge.
    Angle of Attack - the angle between the chord line of the
    airfoil and the direction of the relative wind.
  • Wing Design
    Upwash-the deflection of the oncoming airstream
    upward and over the wing
    Trailing Edge - the portion of the
    airfoil where the
    airflow over the
    upper surface
    rejoins the lower
    surface airflow.
    Leading Edge - the part of the airfoil
    which meets the airflow first
    Downwash - the downward deflection of the
    airstream as it passes over the
    wing and past the trailing edge.
    As an airfoil moves through the air, it alters the air pressure around its surface. A typical subsonic airfoil has
    a rounded nose, or leading edge, a maximum thickness about one-third of the way back, and a smooth taper
    into a relatively sharp point at the rear or trailing edge.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Definitions of Aerodynamic Principles
    • Relative Wind
    • Pitch Angle
    • Angle of Attack
    • Lift
    • Drag
    • Center of Pressure
    • Blade Stall
  • FLIGHT PATH
    RELATIVE WIND
    FLIGHT PATH
    FLIGHT PATH
    RELATIVE WIND
    RELATIVE WIND
    FLIGHT PATH
    RELATIVE WIND
    Fig. 2-5 The relationship of the rotor blade and the relative wind.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Fig 2-6: The relationship of the pitch angle to the plane of rotation.
    Pitch Angle
  • Angle of Attack
    Fig 2-7: The angle of attack in relation to the relative wind.
  • Fig 2-8: Lift versus drag
  • Fig 5-57: Typical alignment point on a rotor blade.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Centre of Pressure
  • Asymmetrical = High speed airfoil, High lift airfoil
    Symmetrical = General purpose airfoil
    Fig. 2-9 Symmetrical and unsymmetrical airfoils.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Fig. 2-10 The stall angle of the airfoil.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Effects
    On
    Lift
    Fig. 2-11 Lift, thrust, weight, and drag components in relationship to the helicopter.
  • Fig 2-12: Rotor droop occurs when the rotor is at rest.
    Fig 2-13: A rotating rotor system.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Fig 2-14: A loaded rotating system.
    Fig 2-15: Coning is affected by the weight of the helicopter.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Fig 2-16: The rotor disc or tip path plane.
    Fig 2-17: In track and out of track condition.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Coning
  • Fig. 2-18 Aerodynamic force vectors applied during modes of flight.
  • Hovering
  • Thrust
    Thrust gives helicopter directional movement.
    Obtained by the movement of the tip path plane of the rotor or rotor disc.
  • FEATHERING AXIS
    Fig. 2-19 The feathering axis or pitch axis of the rotor.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Gyroscopic Precession
  • Gyroscopic Forces
    Fig 2-21: Basic principles of the swashplate.
  • Fig 2-22: The results of gyroscopic precession as applied to the main rotor system.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Torque
    Newton’s Third Law
  • Torque
    Newton’s Third Law
    ROTATION OF THE ROTOR
    COUNTER ROTATION
    OF THE FUSELAGE
    TAIL ROTOR
    Fig. 2-23 Anti-torque is applied by the tail rotor.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Blade Twist
    Fig 2-24: The rotor speed increases from the root of the blade outward.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • A
    B
    C
    Mast
    C
    A
    B
    A-A
    ROOT
    B-B
    CENTRE
    C-C
    TIP
    Fig. 2-25 More twist at the root of the blade increases the lift.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Blade Twist
  • Dissymmetry of Lift
    Flapping hinge
    Seesaw system
    Coriolis effect
    Drag or lead-lag hinge
    Underslung rotor
  • Dissymmetry of Lift
  • Fig 2-26: Forward speed increases the difference in speed between the advancing and retreating blades.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Fig. 2-27 The flapping hinge is used to control dissymmetry of lift.
    Fig. 2-28 This seesaw action is used on semirigid rotors.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Coriolis Effect (Hook’s Joint Effect)
  • BLADE MOVEMENT
    LEAD LAG
    HINGE
    ROTOR HUB
    Fig. 2-29 Lead-lag action is required on systems using the flapping design.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
    BCIT Aerospace www.bcit.ca/transportation/aerospace
  • Underslung Feathering Axis
  • Underslung Feathering Axis
  • Rotor Heads
    Rigid rotor
    Semirigid
    Fully articulated
  • Rigid Head
  • BO 105
  • Fig. 2-31 The head shown in the top view has
    movement on two axes while the bottom head
    has movement on only one axis only.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Semirigid
  • Main Rotor Head Fully Articulated
  • Aerodynamic Characteristics
    • Translating tendency
    • Ground Effect
    • Transitional Lift
  • Translating Tendency
    This is a tendency for the whole helicopter to drift in the direction of the tail rotor thrust.
  • Sometimes the mast is offset to correct for this.
    Fig 2-32: Mast tilt is sometimes used to cancel translating tendency.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Ground Effect
  • Effective Translational Lift
  • Fig 2-33: The variation in downward airflow causing the transverse flow effect.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Blade Tip Stall
    • Insufficient airspeed
    • Too great an angle of attack
    • Heavy wing loading
  • Fig 2-34: Forward speed is a major factor in retreating blade stall.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Fig 2-35: Stall occurs first on the retreating half of the disc.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Autorotation
  • Fig. 2-36 The autorotative region changes in forward flight.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • AutorotativeForce
  • Fig 2-37: Autorotation is not safe at low altitude and low airspeed.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Fig 5-121: Autorotation chart used on Hughes 500.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Ground Resonance
    Is a self-exciting vibration which occurs on the ground.
    Aerodynamic phenomenon associated with fully articulated rotor systems.
    Blades move out of phase with each other.
  • Ground Resonance
  • Causes
    Soft Oleo
    Improper tire pressure
    Uneven ground
    Soft ground
    Improperly rigged flight controls
  • Stability
    • Static stability
    • Dynamic stability
  • Stability
    1. Tendency to return to it’s original position.
    2. Dynamic stability is related to all objects that possess static stability.
    3. Bell uses a stab bar and some manufacturers use an offset flapping hinge.
  • DISTURBING FORCE ORIGINAL
    FORCE APPLIED RELEASED POSITION
    POSITIVE STATIC STABILITY
    Fig. 2-38 All aircraft must be able to demonstrate stability.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • FORCE APPLIED CONE FALLS CONE FAILS TO
    RETURN TO ORIGINAL
    POSITION
    Fig. 2-39 Negative stability will result in problems of controllability.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • DISTURBANCE
    Fig. 2-40 The helicopter is usually considered statically stable
    and dynamically unstable.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • The Bell method
    Fig. 2-41 The stabilizer bar is the most common
    method used to obtain dynamic
    stability on semirigid rotors.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • OFFSET FLAPPING
    HINGE
    Fig. 2-42 Two methods used with fully articulated heads are shown here.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Primary Flight Control Terminology
    Collective
    Anti-torque pedals
    Cyclic control
  • EXAMPLE OF ALL THREE FLIGHT CONTROLS
    CYCLIC
    ANTI-TORQUE PEDALS
    COLLECTIVE
  • CYCLIC
    COLLECTIVE
    PEDALS
    Fig. 2-43 Controls used to maintain flight.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Collective Pitch
    • Location: Left hand side of pilot seat.
    • Moves blades up and down equally.
    • Also known as “power lever”.
  • Fig. 2-44 Raising of the collective requires more engine power.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Anti-Torque Pedals
    • Primary function is to counteract Newton’s 3rd law.
    • Secondary function is directional control.
    • Anti-torque pedals are sometimes known as tail rotor pedals.
  • TAIL MOVES
    NEGATIVE OR LOW POSTIVE PITCH
    Fig. 2-45 The movement
    of the anti-torque pedals
    is directly related to the
    amount of main rotor
    pitch.
    MEDIUM POSITIVE PITCH
    HIGH POSITVE PITCH
    TAIL MOVES
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Cyclic Controls
    Used to tilt main rotor disk in desired direction of flight
  • DIRECTION OF ROTATION
    DECREASED PITCH
    SWASH PLATE TILTED FORWARD
    INCREASED PITCH
    Fig. 2-20 Cyclic pitch change through the swashplate.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Fig. 2-48 The cyclic control is used to obtain directional control of the helicopter.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Fig 2-49: A typical movable horizontal stabilizer.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • Fig 2-50: A typical fixed position horizontal stabilizer.
    Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007
  • ATA System Format
    ATA Code Differences between Fixed & Rotary Winged Aircraft.
    Helicopters use ATA Chapter 67 for Flight Controls verses Chapter 27 for Airplanes.
    Helicopters also use Chapters 62 thru 66 specifically.
  • Gyroscopic Precession Blade Flapping