PART A
1. Name four common engine classifications by cylinder arrangement
a) Inline engines
b) ‘V’ type engines
c) Opposed...
c) Number of stroke per cycle

7. Write short notes on Master Articulated Rod

The master articulated rod assembly is used...
9. What are the methods adopted for structural inspection of aero engine parts?
Or State the methods followed in ‘Non Dest...
16. Describe a Power check
The time during which an engine is operated at full power is referred to as a power
check. The ...
new parts and also Rebuilt engine must be functionally tested to meet the
requirements of a new engine.
22. Enumerate the ...
1. It reduces the total weight of the crank shaft
2. It provides the passage for the lubricating oil
3. It serves as a cha...
3. Examine each rod end i.e., threaded and observes whether the rod is screwed
into the socket body for enough to be seen ...
COMPRESSION TESTING OF AIRCRAFT ENGINE CYLINDERS
The purpose of testing the cylinder compression is to determine the inter...
Procedure:
1. Warm up the engine and shut it down.
2. Remove the spark plug as soon as possible.
3. Rotate the engine with...
5. Adjust the pressure regulator gauge to 80 psi; at this the cylinder Prague should
also register 80 psi.
6. Now turn the...
Trouble shooting is the step by step procedure used to determine the cause of a
given fault and then select the best and q...
Explain in sequence about servicing procedure of spark plug with neat diagram.
PURPOSE
Scheduled servicing intervals are d...
1. Removal
a. Shielded terminal connectors are removed by loosening the elbow nut with the
proper size crowfoot or open en...
c. To measure minimum and maximum widths for the gap, a spark plug gap gage
will have two wires.(0.011’-0.015’)
d. Smaller...
Explain the safety practices followed in preparation of for overhaul an engine in an
overhaul shop.
THE SAFETY PRACTICES F...
AUXILIARY IGNITION DEVICE
When attempting to start an engine, often the engine will not rotate thecrankshaft
fast enough t...
When the starter switch is closed battery voltage is applied to the vibrator
coilthrough the vibrator contact points and t...
Pressure carburetors do have some advantages over float-type carburetors,
theyoperate during all types of flight maneuvers...
thepoppet valve. The fuel flows through one or more metering jets in the
fuelcontrol unit and then to the discharge nozzle...
strength at the discontinuity. Magnetic particles are applied to themagnetized part
and concentrate in the areas of flux l...
1. Pre-oiling: Before the engine is started for the first time, it should bepreoiled to remove air trapped in oil passages...
If the following defects occur in trouble shooting of a piston engine,what are the
possible causes and remedial actions?
D...
Explain the term “condition monitoring”
Aviation maintenance and operations groups are continually striving toimprove the
...
What is the purpose of compressor wash?
The purpose of compressor wash is to remove the baked-on salt, dirt, orother types...
The function of the exhaust nozzle is to control the velocity andtemperature of the
exhaust gases. When a convergent nozzl...
What action to be taken when an engine has been operated with no oilpressure for
more than two minutes?
When an engine has...
Over speed inspection for a typical high-bypass fan engine is primarilyconcerned
with rotating assemblies. Manufacturer sp...
the one end is an eye piece with one or more lenses attachedto the light carrying tube. At
the end of the tube are a mirro...
A gas turbine engine operates with various performanceparameters at steady state
condition. Once the initial relationships...
To ensure that a gas turbine engine is in satisfactory operating condition,engine
and aircraft manufacturers specify certa...
4. Continue motoring the engine until the fuel flow is 500-600 lb/h or fora
maximum of 60s. Observe the starter operating ...
1.Set the engine power at nominal N2 speed as indicated on theappropriate chart for
the total air temperature (TAT).
2.Fou...
according to manual. No cracks are permitted in the fan blades. Blade tips
areexamined for curl, and the lightening holes ...
The scope of line maintenance consists of removal and installation of externalcomponents and
engine accessories as well as...
The compressor packs several tons of air into the combustion chamber every
minuteand works somewhat like a series of fans....
mounted on aground service cart or from the airplanes low pressure air supply. The
supply mustproduce a pressure of about ...
1.Inspect all surfaces of the shaft for cracks
2.Check the bearing surfaces for galling, scoring or other damage.
3.Check ...
AE2028 AEMR
Upcoming SlideShare
Loading in …5
×

AE2028 AEMR

2,594 views

Published on

Important qus

  • Be the first to comment

AE2028 AEMR

  1. 1. PART A 1. Name four common engine classifications by cylinder arrangement a) Inline engines b) ‘V’ type engines c) Opposed or flat type engines d) Radial type engines 2. What is the purpose of dynamic damper? The purpose of the dynamic dampers is to relieve the whip and vibration caused by the rotation of the crank shaft. They are suspended from or installed in specified crank cheeks. 3. What should be done if there is no indication of oil pressure shortly after starting the engine? After starting the engine, check for oil pressure immediately. If oil pressure does not register within the prescribed time (10-30 sec) shut down the engine and identifies the problem. 4. What is the function of the dimensional inspection during overhaul? Dimensional inspection is employed to determine the degree of wear foreparts of the engine where moving surfaces are in contact with other surfaces. If the wear between the surfaces exceeds the table of limits the parts must be replaced or repaired. 5. What are the methods and purpose of the preliminary visual inspection? Visual inspection is accomplished by direct examination and with the use of magnifying glass. In both case a strong light should be used to reveal the defects. Visual inspection reveals cracks, corrosion, nicks, scratches, and galling, scoring and other disturbances. Parts that are damaged beyond repair should be discarded and marked. So that they will not be reused. 6. How are aircraft piston engines classified? Aircraft piston engines are classified by a) Cylinder arrangement b) Cooling method
  2. 2. c) Number of stroke per cycle 7. Write short notes on Master Articulated Rod The master articulated rod assembly is used primarily for radial engines, although some ‘v’ type engines employed this type of rod assembly. It is made of alloy steel forging, machined, polished to final dimensions and heat treated to resist vibration and stresses. The master rod is similar to other connecting rods except that it is constructed to provide for the attachment of the articulated rods on the large end. Master rod bearings are of plain type and consist of a split or a sleeve. The articulated rods are hinged to the master rod flanges by means of knuckle pins 8. Enumerate the basic steps of the overhaul process. 1. Receiving inspection 2. Disassembly 3. Visual inspection 4. Cleaning 5. Structural inspection 6. Dimensional inspection 7. Repair and replacement 8. Reassembly 9. Installation 10. Engine testing and run in 11. Preservation and storage
  3. 3. 9. What are the methods adopted for structural inspection of aero engine parts? Or State the methods followed in ‘Non Destructive testing’ Engine parts are structurally inspected by the following methods 1. Magnetic particle testing 2. Liquid penetrate inspection 3. Eddy current inspection 4. Ultrasonic inspection 5. Radiography inspection 10. Explain the term “Manifold Absolute Pressure” (MAP) Manifold absolute pressure is the absolute pressure of the fuel air mixture immediately before it enters the intake port of the cylinder. Absolute pressure is the pressure above a complete vacuum and is indicated in pounds per square inch absolute or inches of mercury in metric system. 11. What is meant by Trouble shooting? Trouble shooting is the step by step procedure used to determine the cause of a given fault and then select the best and quickest solution. When troubleshooting, the technician must evaluate the performance of the engine by comparing data on how the engine should operate and how it is currently operating. 12. Why is ‘Compression Testing’ is carried out in piston engine? The purpose of testing the cylinder compression is to determine the internal condition of the combustion chamber by ascertaining if any appreciable leakage is occurring. 13. What is valve overlap? The angular distance through which both the valves are open is called valve over lap or valve lap. 14. What effect does exhaust back pressure have on engine performance? Exhaust back pressure has a decided effect on engine performance because any pressure above atmospheric at the exhaust port of a cylinder will reduce volumetric efficiency. Exhaust back pressure begins with at the cylinder exhaust port. So both size and shape of the opening and passage will affect the pressure. 15. How is the term “overhauled engine” defined? Overhauled engine, according to the FAA, (Federation of Aviation Authority)is one that has been disassembled, cleaned, inspected, repaired as necessary, reassembled, and tested according to the manufacturer instruction and specification.
  4. 4. 16. Describe a Power check The time during which an engine is operated at full power is referred to as a power check. The purpose of this check is to ensure satisfactory performance. 17. List the advantages of the opposed- type engine design. 1. The engine has a low weight power ratio. 2. Because of its flat shape it is very well adapted to streamlining and to horizontal installation in the nacelle. 3. It is reasonably free from vibration. 18. Name the four principle type of crankshaft. 1. Single- throw crank shaft 2. Double- throw crank shaft 3. Four- throw crank shaft 4. Six- throw crank shaft 19. What is the engine preheating procedure? Preheating an engine consists of forcing heated air into the engine area to heat the engine, lubricants, and accessories. Preheating is required for most aircraft reciprocating engines when outside temperatures are +10ºF and below as stipulated in the manufacturer´s instruction. 20. Explain the term ‘Backfiring’ Backing firing occurs during starting of a cold engine because of poor combustion. The F/A mixture is still burning at the time the intake valve opens, and the flame burns back through the intake valve. This sometimes causes a fire in the induction system. 21. Differentiate between overhauled engine and rebuilt engine. OVERHAULED ENGINE is one that has been disassembled, cleaned, inspected, repaired as necessary, reassembled, and tested as per manufacturer instructions and specifications. REBUILT ENGINE is one that has been disassembled, cleaned, inspected, repaired as necessary, reassembled, and tested as per manufacturer instructions and specifications. In addition the parts that are reused must meet the limits and tolerances specified for
  5. 5. new parts and also Rebuilt engine must be functionally tested to meet the requirements of a new engine. 22. Enumerate the precision measuring tools used in overhaul shop of a piston engine. 1. Depth gauges 2. Dial gauges 3. Height gauges 4. Micrometers 5. Small-hole gauges 6. Surface plate 7. Telescope gauges 8. V blocks 23. Define Fretting. The surface erosion caused by very slight movement between two surfaces which are tightly pressed together 24. Define ‘E’ gap In a magneto, the number of degrees of rotating between the neutral position and the position where the contact points open is called the E-gap angle, usually called E gap or Efficiency gap 25. What is meant by choke bored cylinder? In some cylinder, the cylinder is bored with a slight taper. The end of the bore nearest the head is made smaller than the skirt end to allow for the expansion caused by the greater operating temperature near the head. Such a cylinder is called chocked bore cylinder 26. Describe the two types of ‘antifriction’ bearings. Roller bearings called ‘antifriction’ bearings. They are straight roller bearings, tapered roller bearings. Because the rollers eliminate friction to a large extent. Straight roller bearings are used for radial loads. Tapered roller bearings are used for radial and thrust loads. 27. Why are crankpins usually hollow? Crankpins usually hollow for three reasons
  6. 6. 1. It reduces the total weight of the crank shaft 2. It provides the passage for the lubricating oil 3. It serves as a chamber for collecting carbon deposits, sludge, and other foreign substances. 28. What are the advantages of a dual-magneto ignition? 1. If one magneto or any part of one magneto system fails to operate, the other magneto system will furnish ignition. 2. When two spark, igniting the F/A mixture in each cylinder at different places, provide quicker and complete combustion than a single spark. 29. What is the spark plug rotation? Excessive electrode erosion is caused by magneto constant polarity firing and capacitance after firing. Constant polarity occurs with even numbered cylinder magnetos. To equalize this wear, during overhaul spark plugs are removed and all odd number cylinder plugs are fitted in even number cylinder and all even number cylinder plugs are fitted in odd number cylinder. This is called spark plug rotation. 30. Why exhaust valve stem or head is made hollow? Exhaust valves operate at high temperatures, to dissipate the heat rapidly the hallow stem or head is filled partly with metallic sodium which melts at 200°F and dissipate the heat through valve guide and valve head to atmosphere. PART B Explain the inspection and maintenance of engine control carried out in piston engines .Engine controls such as throttle, mixture control, propeller, and cowl flap controls need to be checked during 100hrs inspection. CHECKS 1. Inspect push- pull controls for wear and smooth operation. 2. Operate the system slowly and watch for any strain on the rods and tubing (may cause bending or twisting)
  7. 7. 3. Examine each rod end i.e., threaded and observes whether the rod is screwed into the socket body for enough to be seen through the inspection hole. 4. Eliminate any play by making certain that all the connections are tight. 5. Examine the guides to see if the rods bind too much on the guides, but do not mistake any binding for spring back. Replace guides that cause binding. 6. Adjust the length of screw end rods by screwing them into or out of the control end. Re-tighten the locknuts. 7. If any rod is removed, label it to show its location on reassembly. 8. Replace any ball bearing rod ends that cause lost motion. (i) What is the purpose of testing the cylinder compression? (ii) Name the two basic types of compression testers (iii) How are both compression testers utilized in checking the compression of aircraft cylinders? Explain the procedures with neat sketches. COMPRESSION TESTING
  8. 8. COMPRESSION TESTING OF AIRCRAFT ENGINE CYLINDERS The purpose of testing the cylinder compression is to determine the internal condition of the combustion chamber by ascertaining any appreciable leakage is occurring. TYPES OF COMPRESSION TESTERS 1. Direct compression tester 2. Differential- pressure tester DIRECT COMPRESSION TESTER Record all readings and compare to specifications. It indicates the actual pressure in the cylinder. 1. DRY COMPRESSION CHECK 2. WET COMPRESSION CHECK
  9. 9. Procedure: 1. Warm up the engine and shut it down. 2. Remove the spark plug as soon as possible. 3. Rotate the engine with a starter to expel any excess oil or loose carbons. 4. Install tester in one of the cylinder. 5. Using engine starter, rotate the engine three revolutions and note threading. (External power source e.g. battery can be used to run engine starter. 6. Compare the readings with each other. Any cylinder having approximately 15 psi lower than the other should be suspected defective. WET COMPRESSION CHECK 1. A wet compression check should be done on defective cylinder to find out the problematic area. 2. Squeeze oil or throw oil into the cylinder having low pressure reading 3. With the compression tester gauge re check the pressure. 4. If the compression gauge reading goes up while oiling the cylinder indicating problem in piston rings or wall of the cylinder. 5. If the readings remain same then valve or cylinder head gasket having the problem. DIFFERENTIAL- PRESSURE TESTER To check the compression of a/c engine by measuring the leakage through the cylinder that is caused by worn or damaged components. PRINCIPLE The regulator air pressure is applied to one side of the orifice with the air valve closed and no leakage on the other side of the orifice, and then both the pr. gauge will read the same. When the air valve is opened the leakage through the cylinder increases. The cylinder pr. gauge will record a proportionally low reading. PROCEDURE 1. Warm up the engine and shut it down. 2. Remove the spark plug as soon as possible. 3. With the air valve closed apply an external source of clean air approx.100-120 psi 4. Install an adapter in the spark plug bushing and connect the compression tester to one of the cylinder.
  10. 10. 5. Adjust the pressure regulator gauge to 80 psi; at this the cylinder Prague should also register 80 psi. 6. Now turn the crankshaft by hand in the direction of rotation until the piston is coming up on its compression stroke. 7. Open air valve and pressurize the cylinder to approx. 20 psi 8. Continue rotating the engine against the pressure until the piston reaches the TDC. 9. Open the air valve completely. Check the regulated pr and adjust, if necessary to 80 psi. 10. Observe the pressure indication on cylinder pr gauge 11. Compare the cylinder pr. Gauge with regulator pr. Gauge 12. The difference between the cylinder pr. and pr. of regulator pressure gauge is the amount of leakage through the cylinder 13. If the leakage is more than 25% go for the wet test. PROBLEMATIC AREA (when leakage occurs) 1. Air is leaking through crank case breather (leakage around the piston rings or hole in the piston) 2. Air leaking from the valve because of the carbon piece (can be hear air exiting from the exhaust stacks) Define trouble shooting and explain the six step trouble shooting procedure. TROUBLE SHOOTING
  11. 11. Trouble shooting is the step by step procedure used to determine the cause of a given fault and then select the best and quickest solution. SIX STEP TROUBLE SHOOTING PROCEDURE 1. SYSTEM RECOGNITION: The first step in trouble shooting – involves having knowledge of engine condition that is not normal and knowing to what extent the fault is affecting the engines performance. 2. SYMTEM ELABORATION: It is the next logical step, once a fault or malfunction has been detected. Test equipment helps the technician to evaluate the performance of the engine and its components. The technicians should use these aids to assess the effects of the symptoms and to provide additional information to further define the symptoms. 3. LIST OF PROBABLE FAULTY FUNCTIONS When the technician has located all the symptoms of malfunction or fault it is the third step to list the possible causes. To aid this process, manufacturer manual list the ‘probable cause’ for the symptom and corrective action. 4. LOCALIZING THE FAULT Localizing the fault means, to determine which functional system of the engine is creating problem. This trouble may be traced by trouble shooting charts. 5. ISOLATING THE FAULT TO A COMPONENT Once the malfunction is isolated to one system, additional testing is done to isolate the fault to a specific component. The technicians use test equipments to measure the correct output for various components. 6. FAILURE ANALYSIS Once the fault or malfunction traced to a specific component, attempt to be made to determine the cause of failure. Without analyzing the reason, substituting a new component into the system will damage the new component. If the component is the probable cause for all the abnormal symptoms noticed earlier steps, then it can be assumed that the component is at fault. SPARK PLUG
  12. 12. Explain in sequence about servicing procedure of spark plug with neat diagram. PURPOSE Scheduled servicing intervals are determined by the individual aircraft operator. These intervals will vary according to the operating conditions, engine models, and spark plug types. The principal determining factor in the removal and servicing of spark plug is the width of the spark –gap that is, the distance between the electrodes where the spark is produced. SERVICING PROCEDURE
  13. 13. 1. Removal a. Shielded terminal connectors are removed by loosening the elbow nut with the proper size crowfoot or open end wrench. (Care must be taken to avoid damage to the elbow and sleeve or the barrel insulator. B.Remove the spark plug from the cylinder by using the proper size of deep-socket wrench.(recommended 6point wrench) C.Removed spark plug should be placed in a tray with numbered holes so that the engine cylinder from which the spark plug has been removed can be identified. D.Spark plug should not be dropped on hard surface because cracks may occur in ceramic insulation which is not apparent on visual inspection. Any plug which has been dropped should be rejected or returned 2. PRELIMINARY INSPECTION a. Immediately after removal, the spark plug should be given a careful visual examination. All unserviceable plugs should be discarded.(spark plugs with cracked insulators, badly eroded electrodes, damaged shells or threads should be rejected) 3. DEGREASING a. All oil and grease should be removed from both interior and exterior of the plug according to the approved degreasing method.(Either vapor degreasing) 4. DRYING a. After degreasing spark plugs should be dried inside and outside either by compressed air or a drying oven. 5. CLEANING a. Spark plug should be cleaned for lead and carbon deposits form on the ceramic core, the electrodes, and inside of the spark plug shell by abrasive blasting machine designed for cleaning spark plug. B.Immediately after cleaning by the wet-blast method the plugs must be oven dried to prevent rusting and to ensure satisfactory electrical test. 6. REGAPPING a. The tools and methods used to set spark plug gaps will vary with shape, type, and arrangement of electrodes. b. The gap in any spark plug is measured by round wire gages
  14. 14. c. To measure minimum and maximum widths for the gap, a spark plug gap gage will have two wires.(0.011’-0.015’) d. Smaller dimension gage must pass through and larger dimension gage must be too large to pass through the gap. e. If the gap is too large it is closed by means of a special gap setting tool 7. INSPECTION AND TESTING a. Visual inspection is done with a magnifying glass. Good lighting must be provided. b. The following item are examined: threads, electrodes, shell hexagons, ceramic insulation, and the connector seat. c. Spark plugs are tested by applying high voltage, equivalent to normal ignition voltage. While plug is under pressure. d. Spark plug which fails to function properly during the pressure test should be baked in an oven for about 4hrs at 225ºF. 8. GASKET SERVICING a. When spark plugs are installed either new or recondition gasket should be used. b. Used gaskets should be annealed by heating to a cherry red and immediately quenched in light motor oil. C. After quenching oil to be removed with a solvent. d. Then immerse it in a solution of 50%water and 50% nitric acid to remove oxides. e. After the acid bath gasket should be rinsed in running water and air dried. 9. PLUG ROTATION a. Excessive electrode erosion is caused by magneto constant polarity firing and capacitance after firing. b. To equalize this wear, keep the plugs in engine sets, placing them in the tray identified by cylinder locations. After the plugs have been serviced, rotate them as instructed. 10. INSTALLATIONS a. Before installing, proper type of the plug to be selected. b. Long and short reach should not be interchanged. c. Before installing plug and cylinder threads are to be cleaned d. Anti seize compound to be applied on the threads e. Install the plug along with gasket and tighten with hand f. At last tighten them with wrench.
  15. 15. Explain the safety practices followed in preparation of for overhaul an engine in an overhaul shop. THE SAFETY PRACTICES FOLLOWED IN PREPARATION FOROVERHAUL OF AN ENGINE IN AN OVERHAUL SHOP. 1.Arrangement of the shop should be such that crowding does not exist. 2.Materials and parts must be stored in proper racks and containers. 3.Walk ways should be painted on the floor and kept free of obstructions atall times other than equipment movement. 4.Suitable engine overhaul stands must be provided. 5.Adequate work station and bench space should be provided. 6.All machinery must be in good condition and provide with safety guards. 7.Electric equipment and power outlets must be correctly identified forvoltage and power handling capability. 8.Electric outlets must be designed so that it is not possible to plug inequipment other than designed for the voltage and the type of currentsupplied at the outlet. 9.Adequate lighting must be provided for all areas. 10.Cleaning areas must be adequately ventilated to remove all dangerousfumes from solvents, degreasing agents, and volatile liquids. 11.Proper engine hoisting equipment must be available for engine lifting. 12.Operators should wear safety shoes to prevent injuries to their feetincase heavy equipment or parts are dropped. 13.Operators of lathes, machine tools, drills, and grinders must wear safetygoggles. 14.Operators of cleaning equipment must wear protective clothing, rubbergloves, and face shields. 15.The floor of the shop should have a surface which does not becomeslippery. 16.Grease, oil and similar materials should be removed from the floorimmediately after they are spilled. 17.Proper type of fire extinguishers should be available to the shoppersonnel. 18.Personnel should take care to stay clear of an engine which is beinghoisted except as necessary to prevent it from swaying or turning. 19.All areas must be kept free of sand, dust, grease, dirty rags, and othertypes of contaminants. 20.Greasy or oily rags must be stored in closely covered metal cans. 21.Flammable liquids must be stored in an approved fire proof area. 22.The area where engines are run should be paved and kept free of debriswhich could be picked up by air currents caused by a propeller or jet intake. Name the auxiliary ignition devices and with the help of neat diagramdescribe the operation of an induction vibrator
  16. 16. AUXILIARY IGNITION DEVICE When attempting to start an engine, often the engine will not rotate thecrankshaft fast enough to produce the required coming in speed of themagneto. In these instances a source of external high-tension current isrequired for ignition purposes. These various devices are called IGNITIONBOOSTERS OR AUXILIARY IGNITION DEVICES 1.Impulse coupling 2.Booster coil 3.Induction vibrator INDUCTION VIBRATOR The function of the induction of the induction vibrator is to supply low voltage(pulsating direct current) for the magneto primary coil, which induces asufficiently high voltage in the secondary coil for starting. OPERATION
  17. 17. When the starter switch is closed battery voltage is applied to the vibrator coilthrough the vibrator contact points and through the retardContact points in the left magneto. As the coil is energized, the breaker pointsopen and interrupt the current flow, thus de energizing the coil, VC. Throughspring action the contact points close and again energizes the coil, causing thepoints to open. Thus the contact points of the vibrator continue to make andbreak contact many times per second, sending an interrupted current throughboth the main and retard contact points of the magneto.The vibrator sends an interrupted battery current through the primary windingof the magneto coil. The magneto coil then acts as a battery ignition coil andproduces high tension impulses, which are distributed through the distributorrotor, distributor block, and cables to the spark plug.These high tension impulses are produced during the entire time that both setsof magneto contact points are open. When the contact points are closed, spark cannot be generated. Although the vibrator continues to send interruptedcurrent impulses through the magneto contact points, the interrupted currentwill flow through the contact points to ground. With the help of a simplified diagram, explain the fundamental operation of a pressure injection carburetor. PRESSURE INJECTION CARBURETOR The basic principles of the pressure injection carburetor can be explained thatmass air flow is utilized to regulate the pressure of fuel to a metering systemwhich in turn governs the fuel flow. The carburetor increases the fuel flow inproportion to mass air flow and maintains a correct F/A ratio in accordancewith the throttle and mixture settings of the carburetor
  18. 18. Pressure carburetors do have some advantages over float-type carburetors, theyoperate during all types of flight maneuvers (including aerobatics), andcarburetor icing is less of a problem. The main parts of a pressure injection carburetor system: 1. The throttle unit,2. The regulator unit, 3. The fuel control unit. When the carburetor is operating, the air flows the air flows through thethrottle unit. At the entrance to the air passage are impact tubes which developa pressure proportional to the velocity of the incoming air. This pressure isapplied to chamber A in the regulator unit. As the air flows through theventuri, a reduced pressure is developed in accordance with the velocity of theair flow. The reduced pressure is applied to chamber B in the regulator unit.The high pressure in chamber A and the low pressure in chamber B will createa differential pressure across the diaphragm between the two chambers. Theforce of this pressure differential is called the Air Metering force,and as thisforce increases it opens the poppet valve and allows fuel under pressure fromthe fuel pump to flow into chamber D. This unmetered fuel exerts force on thediaphragm between chamber D and chamber C and thus tends to close
  19. 19. thepoppet valve. The fuel flows through one or more metering jets in the fuelcontrol unit and then to the discharge nozzle. Chamber C of the regulator unitis connected to the output of the fuel control unit to provide metered fuelpressure to act against the diaphragm between chamber C and D. Thus,unmetered fuel pressure acts against the D side of the diaphragm, and meteredfuel pressure acts against the chamber C side. The fuel pressure differentialproduces a force called the fuel meteringforce. When the throttle opening is increased, the air flow through the carburetor isincreased and the pressure in the venturi is increased. So the pressure inchamber B is lowered, the impact pressure to chamber is increased, and the diaphragm between chambers A & B moves to the right because of thedifferential pressure. (Air metering force) This movement opens the poppetvalve and allows more fuel to flow into chamber D. This increases pressure inchamber D and tends to move the diaphragm and poppet valve to the leftagainst the air metering force, however this movement is modified by thepressure of metered fuel in chamber C. The pressure differential betweenchamber C & D (fuel metering force) is balanced against the air metering forceat all times when the engine is operating at a given setting. C The chamber pressure is established approximately 5psi by the spring-loaded, diaphragm-operated main discharge nozzle valve. This valve preventsleakage from the nozzle when the engine is not running. Explain the various methods adopted for Non-Destructive Testing (NDT)techniques. The various methods adopted for Non- Destructive testing are 1.Magnetic particle testing 2.Liquid penetrant inspection 3.Eddy current inspection 4.Ultrasonic inspection 5.Radiography Magnetic particle testing Magnetic particle testing is a nondestructive method for locating surface andsubsurface discontinuities (cracks or defects) in ferromagnetic materials suchas steel. The parts are magnetized by passing a strong electric current throughor around them. An electric current is always accompanied by a magnetic field.The magnetic lines of flux travel through the part when it is magnetized. A crack or discontinuity will create a flux leakage. A flux leakage occurs whenthe lines of flux leave the surface of the material, resulting in a concentrationof magnetic
  20. 20. strength at the discontinuity. Magnetic particles are applied to themagnetized part and concentrate in the areas of flux leakage, giving a sign of discontinuity.After the parts have been inspected, they must be demagnetized. If this is notdone the parts will pick up and hold small steel particles, which can causeserious damage in the engine during operation. Liquid penetrant inspection Engine parts made of aluminum alloys, magnesium alloys, bronze, or any othermetal which cannot be magnetized are inspected by means of a fluorescentpenetrant, a dyepenetrant, ultrasonic equipment, or eddy current equipment.The parts are thoroughly cleaned and stripped of paint. The penetrant isapplied to the part and allowed to enter any surface discontinuities. The excesspenetrant is cleaned off, and then the part is given a coat of developer. Thedeveloper draws out any penetrant that may have entered surfacediscontinuities, making them visible either under white light in the case of visible penetrant or black light in the case of fluorescent penetrant. Eddy current inspection Eddy current inspection is to discover defects inside metal parts. The eddycurrent tester applies high frequency electromagnetic waves to the metal, andthese waves generate eddy currents inside the metal. If the metal is uniform inits structure, the eddy current will flow in a uniform pattern and this will beshown by the indicator. If a discontinuity exists, the effect of the eddy currentswill be changed and the indicator will produce a reading greater than normalfor the particular test. Ultrasonic inspection Ultrasonic inspection utilizes high frequency sound waves to reveal flaws inmetal parts. The element transmitting the waves is placed on the part, and a reflected wave is received and registered on a oscilloscope. If there is a flaw inthe part, the reflected wave will show a “blip “on the oscilloscope trace. Theposition of the blip indicates the depth of the flaw. Radiography X ray or radiographic inspection is to detect certain types of metal defects. Thexray is effective in detecting discontinuities inside casting, forging and welds.A power full x-ray can penetrate metal or several inches and produce an imagewhich will reveal defects within the metal. Write short notes onorPiston engine testing procedure after overhaul
  21. 21. 1. Pre-oiling: Before the engine is started for the first time, it should bepreoiled to remove air trapped in oil passages and lines and to ensurethat all bearing surfaces are lubricated. One method: One spark plug is removed from each cylinder. Thecrankcase or external oil tank to be filled with oil for run in, and theengine is cranked with the starter until an oil pressure indication is readon the oil pressure gage. Another method: oil is forced by means of a pressure oiler at aprescribed pressure, through the oil galleries until it comes out an oiloutlet or the opposite end of an oil gallery. Power check: Manufacturer’s overhaul manual provides instructionand run in schedule for a newly overhauled engine. The purpose of run inis to permit newly installed parts to burnish or wear in, piston rings toseat against cylinder wall, and valves to become seated. And also makesit possible to observe the engines operation under controlled conditionsand to ensure proper operation from idle to 100 percent power. The timeduring which an engine is operated at full power is referred to as powercheck. The run in should be accomplished with the engine installed in atest cell equipped as specified in the manufacturer’s overhaul manual. Oil consumption run: Anoil consumption run is made at the end of thetest. Record the oil temperature. Stop the engine. Place a previouslyweighed container under the oil tank or oil sump and remove the drainplug. Allow the oil to drain for 15 mints. Replace the drain plug. Weighthe oil and the container. Record the weight of the oil (total weight lessthe weight of the container). Replace the oil in the tank or sump. Start theengine, warm up the engine to the specified rpm± 20rpm and operate atthis speed for 1 hour. At the end of one hour of operation with the sameoil temperature drain the oil as before. The difference in oil weights atthe start and end of the run will give the amount of oil used in 1hour.
  22. 22. If the following defects occur in trouble shooting of a piston engine,what are the possible causes and remedial actions? Defects 1. High cylinder Head temperat ure 2. Engine will not Start Cause 1.Octane rating of fuel too low 2. Improper manual leaning Procedure 3. Bent or loose cylinder baffles 4. Dirt between cooling fins 1. 2. 3. 4. 5. 6. Remedy 1. Drain fuel and fills with correct Grade 2. Use leaning procedure set for thin the operators Manual 3. Inspect for condition and correct it 4. Remove dirt No fuel in the tank 1. Fill fuel in the tank Fuel valves turned off 2. Turn on fuel valve Fuel line plugged 3. Starting at carburetor, check Defective or stuck fuel line back to tank. Clear mixture control obstruction Pressure discharge nozzle 4. Check for operation valve diaphragm ruptured of mixture control Primer system in operative 5. Replace it 6. Repair primer system Name the events during which special inspections are carried out ingas turbine engine. Events which may cause the engine to require special inspections areforeign object ingestion, bird ingestion, ice ingestion, over limitoperation (temperature and rpm), excessive “G” loads and any otherevent that could cause internal and external engine damage. What is twin spool axial compressor? A dual compressor jet engine utilizes two separate compressors, eachwith its own driving turbine. This type of engine is called a “twin spool”or “split compressor” engine Write the two main methods of measuring and correcting anyunbalance of gas turbine engine. The two main methods of measuring and correcting unbalance are single plane (static) balancing and two plane (dynamic) balancing.
  23. 23. Explain the term “condition monitoring” Aviation maintenance and operations groups are continually striving toimprove the service reliability of their gas turbine engines and, at thesame time, reduce the operating costs. One tool which can aid both of these efforts is engine performance monitoring. Define ‘online maintenance’ Maintenance work that is required to maintain an engine and its systemsin an air worthy condition while it is installed in an aircraft is called online maintenance. List the different types of fuel spray nozzles. 1.Simplex nozzle 2.Variable port nozzle 3.Duplex nozzle 4.Spill type nozzle 5.Air spray nozzle Describe gas-turbine starter. Gas turbine starter is used for some jet engines and it is completely self contained. It has its own fuel and ignition system, starting system,(electric or hydraulic) a self contained oil system. This type of starter iseconomical to operate and provides high power output for acomparatively low weight. State the methods of balancing of Gas-turbine components The two main methods of measuring and correcting unbalance are singleplane (static) balancing andtwo plane (dynamic) balancing. Compare a gas-turbine igniter plug with a spark plug. 1. Design and configuration of igniter plug and spark plug are different. 2. Since igniter plug is designed to operate at a lower surroundingpressure than is a spark plug, the spark gaps in an igniter are greater. 3. Spark discharge of an igniter causes much more rapid erosion of theelectrodes than the spark provided by the spark plug. At what engine speed does the starter system disengage in a jetengine? The starter is coupled to the engine through a reduction gear and ratchetmechanism or clutch, which automatically disengages after the enginehas reached a selfsustaining speed.
  24. 24. What is the purpose of compressor wash? The purpose of compressor wash is to remove the baked-on salt, dirt, orother types of contamination deposits. Because during engine operationsthe deposits accumulate on engine compressor and turbine blades anddeteriorating the engine performance. Describe the purpose of trend analysis. Trend analysis involves the recording and analysis of gas-turbine engineperformance and certain mechanical parameters over a period of time.The primary aim of trend analysis is to provide a means of detectingsignificant changes in the performance parameters resulting fromchanges in the mechanical condition of the engine. What is “hung start” or “false” start? If the engine fails to accelerate properly or does not reach the idle rpmposition, the starting attempt is called a false start or a hung start. Enumerate the operational checks to ensure that a gas turbine engineis in satisfactory operating condition. To ensure that a gas turbine engine is in satisfactory operating condition,engine and aircraft manufacturers specify certain operational checks to beroutinely performed. They are 1.Dry motoring check 2.Wet motoring check 3.Idle check 4.Power assurance check . What is the purpose of bell mouth air inlet being used in test stand? The operation of an engine on a test stand is usually accomplishedwith a bell mouth air inlet. The purpose of this type of inlet is toeliminate any loss of air pressure at the compressor inlet. .What is scheduled maintenance? Scheduled maintenance includes the periodic recurring inspections thatmust be carried out in accordance with the engine section of the aircraftmaintenance schedule. Usually calculated in aircraft flying hours. What is the function of the exhaust nozzle?
  25. 25. The function of the exhaust nozzle is to control the velocity andtemperature of the exhaust gases. When a convergent nozzle is used, thevelocity of the gas is increased and the thrust is in line with the engine. Enumerate the techniques required for Non routine inspections. The techniques required for Non routine inspections are a.Visual inspection b.Inspection with lights c.Use of magnifying glass d.Applications of fluorescent or dyepenetrants e.Use of bores cope or video scope f.Use of radiography. Define “trouble shooting. Trouble shooting is the step by step procedure used to determine the causeof a given fault and then select the best and quickest solution. Whentrouble shooting, the technician must evaluate the performance of theengine by comparing data on how the engine should operate and how it iscurrently operating. What are the three major sections of a gas turbine engine? A gas turbine engine has three major sections, an air compressor, acombustion section, and a turbine section. What is the purpose of turbine? The purpose of the turbine is to extract kinetic energy from the highvelocity gases leaving the combustion section of the engine. The energyis converted to shaft horse power for the purpose of driving thecompressor. What is the function of the diffuser in gas turbine engine? The function of the diffuser is to reduce the velocity of the air. As thevelocity of the air decreases, its static pressure increases. As the staticpressure increases, the ram pressure decreases. The diffuser is the pointof highest pressure within the engine Enumerate the instruments used for Non- routine inspection of gas-turbine engine. a. Borescope or video scope b. Fiberscope c. Electronic imaging
  26. 26. What action to be taken when an engine has been operated with no oilpressure for more than two minutes? When an engine has been operated with no oil pressure for more than twominutes the engine must be removed for overhaul. What is “hot start”? During the starting of a gas turbine engine, the EGT (exhaust gastemperature) exceeds the prescribed safe limit, the engine is said to have had a hot start. Explain the procedure of carrying out “A” check inspectionperformed on gas Turbine engine after 100 hrs operation. A typical airline may designate standard service operations andinspections by such names as “No. 1 service, No. 2 service, “A” check,“B” check “No. 1 service:It is performed by station personnel each time theairplane lands or after several landings. The service will includecorrection of critical log items as well as regular service (fuel andresupply), and a walk around inspection. “No. 2 service:Review of the flight log and cabin log, check of engineoil quantity, visual inspection of the engine with cowls open. “A” check: It is performed after approximately 100hrs of operation.Inspection and service related to the engine are as follows. 1.Fill oil tanks and enter the quarts added for each engine in theinspection records. 2.Service the constant- speed drive as required. 3.Check engine inlet, cowling, and pylon for damage, irregularities, andleakage. 4.Inspect the engine exhaust section for damage using a stronginspection light and note the condition of rear turbine. 5.Check the thrust- reverser ejector and reverser buckets for security anddamage. 6.Check the reverser system, with ejectors extended, for cracks,buckling, and damage. PERIODIC INSPECTIONS Periodic inspections are required after a given number of operation hours,flight cycles, or a combination of both. These inspections are classified asroutine, minor, or major. Scheduling of inspections is established by theoperator of the aircraft. Explain over speed inspection for a typical high- bypass fan engine
  27. 27. Over speed inspection for a typical high-bypass fan engine is primarilyconcerned with rotating assemblies. Manufacturer specifies the followinginspections if the fan has been operated at speed from 116 to 120 percent rpm. 1.Check the fan rotor for freedom of rotation. 2.Check the first-stage fan shroud for excessive rub. 3.Inspect the low pressure compressor with a borescope. 4.Inspect the inlet and exhaust nozzles for particles. 5.Inspect all four stages of the LPT with a borescope for blade and vanedamage. Inspect the fourth stage blades through the exhaust nozzle. 6.If the fan speed has exceeded120percent, the fan rotor, fan mid shaft, andLPT rotor must be removed, disassembled, and inspected in accordancewith instructions. 7.If the core- engine rotor (high pressure compressor, high pressureturbine) has been operated at speeds from 107 to 108.5 percent, thefollowing inspections are to be carried out. a.Inspect the exhaust nozzle for particles. b.Inspect the core compressor with a borescope for blade and vanedamage. c.Inspect the HPT with a borescope for blade damage. 8.If the core engine rotor has been operated above 108.5 percent, theengine must be removed, disassembled, and inspected according toinstruction. State and explain in detail about the instruments used during Nonroutine inspections. During the operation of the gas turbine engine, various events may occurwhich cause the engine to require immediate special inspection to determinewhether the engine has been damaged and what corrective actions must betaken. Among some of the events which require special inspections areforeign object injection, bird ingestion, ice ingestion, over limit operation(temperature and rpm), excessive “G” loads, and any other event that couldcause internal and external engine damage.Instruments used for Non routine inspections a.Borescope b.Fiberscope c.Electronic imaging BORESCOPE The borescope was used for examining the insides of cylinder bores onreciprocating engine and is now extensively used on turbine engines. Theborescope is a rigid instrument that may be compared with a smallperiscope. At
  28. 28. the one end is an eye piece with one or more lenses attachedto the light carrying tube. At the end of the tube are a mirror, a lens, andstrong light. The tube is inserted through engine borescope ports located in the enginecase at points necessary to allow for examination of all critical areas insidethe engine. The ports are normally closed.When the borescope inspections are to be performed, the technician shouldidentify the plugs which are removed to be sure that they are reinstalled inthe same ports. FIBERSCOPE A variation of the rigid borescope is the fiberscope. The flexible fiberscopehas a controllable bending section near the tip so that the observer can directthe scope after it has been inserted into an engine inspection port. Thebending action allows the fiberscope to scan the area inside the engine onceinside the port. Many times it is necessary to inspect around the cornersinside the engine when no inspection entry port is available to allow a directline of sight. ELECTRONIC IMAGING A new imaging technique, Electronic imaging, is able to produce sharp,true-color, magnified images that can be seen on a video monitor. One suchsystem is the video- probe 2000.A video imaging system includes an inspection probe, a video processor, anda video monitor for displaying the image. The system uses a tiny charged-coupled device (CCD) sensor in the tip of the probe. The CCD sensor actslike a miniature TV camera to transmit the image electronically to a videomonitor.First light is transmitted to the inspection area, either by light emitting diodesor by fiber –optic light guides. A fixed focus lens in the tip of the probegathers reflected light from the area and directs it to the surface of the CCDsensor. The signal then travels down the length of the probe throughamplifiers. The video processor receives the signal, digitizes it, assembles it,and outputs it directly to a video monitor, video tape recorder. Discuss about condition monitoring of the engine on ground and at altitude. Aviation maintenance and operations groups are continually striving toimprove the reliability of the gas turbine engines and, at the same timereduce operating cost by monitoring engine performance through trendanalysis. Trend analysis involves the recording and analysis of gasturbine engine performance and certain mechanical parameters over aperiod of time. The primary aim of trend analysis is to provide a means of detecting significant changes in the performance parameters resulting fromchanges in mechanical condition of the engine
  29. 29. A gas turbine engine operates with various performanceparameters at steady state condition. Once the initial relationships have beenestablished for the various parameters, a specific change will not varysignificantly from this calibration unless some external force affects it.Thus, abnormal performance of an engine will be indicated by parameterrelationships deviating from the norm. Data collection methods will vary depending on whether thedata are collected manually or by an onboard computer. Data should becollected at regular intervals. Variable loads extracted from the engine, suchas generator, hydraulic, air conditioning, and bleed air, will have an effecton trend accuracy. To minimize these effects, each time a set of reading istaken, with regard to altitude and power. To reduce fluctuations in the data,ensure that the engine parameters are stabilized before taking the datareadings. Condition monitoring devices are designed to give anindication of any engine deterioration at the earliest possible stage. Thisfacilitates quick diagnosis which can be followed by either furthermonitoring or immediate action on the problem. Condition monitoringdevices and equipment can be categorized into the areas of flight recordersand ground indicators. How is the balancing of gas turbine engine carried out? Explain. Because of the high rotational speed, any unbalance in the main rotatingassembly of a gas turbine engine is capable of producing vibrations andstresses which increase as the square of the rotational speed. Therefore veryaccurate balancing of the rotating assembly is necessary.The two main methods of measuring and correcting unbalance are singleplane (static) balancing and two plane (dynamic) balancing. Single planebalancing is used when the unbalance is in one plane only, that is, theunbalance goes centrally through the component at 90° to the axis. The singleplane method is appropriate for component such as individual compressors andturbine discs. For compressor assemblies and turbine rotor assembliespossessin g appreciable actual length, unbalance may be present at manypositions along the axis. Therefore two plane balancing may be required. Explain in brief the routine operation checks performed to ensurethe gas turbine engine is in satisfactory operating condition.Or Explain the following operational checks in gas turbine engine.
  30. 30. To ensure that a gas turbine engine is in satisfactory operating condition,engine and aircraft manufacturers specify certain operational checks to beroutinely performed by maintenance personnel. The particular types of checksand the procedures to be followed vary, depending on the type of engine andaircraft involved. DRY MOTORING CHECKS The dry motoring check is required during or after inspection or maintenanceto ensure that the engine rotates freely, that instrumentation function properly,starter operation meets speed requirements for successful starts. This check is also used to prime and leak checks the lubrication system when maintenancehas required replacement of system components. PROCEDURE 1. Ascertain that all conditions required prior to a normal start are met. 2.Position engine controls and switches as follows: 1. Ignition, OFF 2. Fuel shutoff lever, OFF 3. Throttle, Idle 4. Fuel Booster Pump, ON 3.Energize the starter and motor the engine as long as necessary tocheck instruments for positive indications of engine rotation and oilpressure. 4.De-energize the starter and make the following checks during coastdown: (a)Listen for unusual noises. Check for roughness. (b)Inspect the lubricating system lines, fittings and accessoriesfor leakage. (c)Check the oil level in the oil tank. WET MOTORING CHECK It is necessary to check the operation of fuel system components afterremoval and replacement or to perform a de preservation of the fuelsystem. PROCEDURE 1.Position engine controls and switches as follows: 1. Ignition, OFF 2. Fuel shutoff lever, OFF 3. Throttle, Idle 4. Fuel Booster Pump, ON 2. Energize the starter. 3. when core engine speed(N2) reaches 10 percent, move the fuel shutoff lever to ON and check for oil pressure indication.
  31. 31. 4. Continue motoring the engine until the fuel flow is 500-600 lb/h or fora maximum of 60s. Observe the starter operating limits. 5. Move the fuel shutoff lever to OFF and continue motoring the engine for at least 30 s to clear the fuel from the combustion chamber . check tosee that fuel flow drops to zero. 5.De-energize the starter and, during coast down, check for unusual noises. 6.Inspect the fuel system lines, fittings and accessories for leakage. 7.Check the concentric fuel shroud for leakage. No leakage is permitted. 8.Inspect the lubrication system for leakage. 9.Check the oil level in the oil tank. IDLE CHECK The idle check consists of checking for proper engine operation asevidenced by leak free connections, normal operating noise, and correctindications on engine related instruments. Engine drain lines must bedisconnected from drain cans to check for leakage. PROCEDURE 1.Start the engine according to approved procedure. 2.Stabilize the engine at the ground idle. 3.Check fan speed (N1), Core engine speed (N2), Oil pressure, andexhaust gas temperature (EGT) should be within the proper rangesaccording to the ground idle speed chart and engine specifications. 4.Visually inspect fuel, lubrication, and pneumatic lines, fittings and accessories for leakage. 5.De-energize flight idle solenoid. During operations above groundidle, do not exceed the open cowling limitations imposed by theairframe manufacturer. 6.Stabilize at flight idle and check the same parameters checked forground idle. See that they are within the limitations set forth on theflight idle speed charts. POWER ASSURANCE CHECK The power assurance check is performed to make sure that the enginewill achieve takeoff power on a hot day without exceeding rpm andtemperature limitations. During the tests the engine is not used to supplypower for any aircraft systems (Electric, Hydraulic or other). The engine istested at 50% and, 75%, and maximum power.During the power assurance check EGT must be observed constantly toavoid the possibility of over temperature. If the EGT approach maximumallowable, the throttle must be retarded sufficiently to hold the EGT withinlimits. PROCEDURE
  32. 32. 1.Set the engine power at nominal N2 speed as indicated on theappropriate chart for the total air temperature (TAT). 2.Four minutes after the throttle lever is set, record the average readingsof TAT, N1 speed,N2speed, EGT, EPR (Engine Pressure Ratio) andfuel flow (Wf ) 3.Using N1(where N1= Target N1 - observed N1) as a correction factor,adjust readings according to the parameter adjustments set forth in theoperations manual. 4.Before a hot engine is shut down it should be operated at ground idlespeed for about 3 minutes to permit temperature reduction andstabilization. As soon as the engine is shut down the EGT gauge should be observed to see that EGT start decrease. If the EGT doesnot decrease, an internal fire is indicated, and the engine should be drymotored at once to blow out the fire. After the engine is shut down, technician should listen for unusualnoises in the engine such as scraping, grinding, bumping and squealing. Explain the special inspection carried out after the gas turbine engineexperienced the snags of “Foreign object damage” and ‘Blade damage’ Foreign object damage to a gas-turbine engine may consist of anything from small nicksand scratches to complete disablement or destruction of the engine. The flight crew of anaircraft may or may not aware that FOD has occurred during a flight. If damage issubstantial, however, it will be indicated by vibration and by changes in the engine’soperating parameters. When FOD has occurred, the inspections required depend on thenature of the foreign objects. If an external inspection indicates substantial damage to thefan section or to the inlet guide vanes, the engine must be removed and overhauled. If thedamage to the forward section of the engine is slight, a boroscope inspection of theinterior of the engine is necessary. Damage to vanes, fan blades, compressor blades can berepaired if it does not exceed the limits specified by the manufacturer. If the engineoperates normally after repairs are made, it can be placed back in service. FAN BLADE SHINGLING Fan blade shingling is the overlapping of the midspan shrouds of the fan blades.Shingling will take place, when the blades of a rotating fan encounter resistance whichforces them sideways an appreciable distance. Shingling can be caused by engine stall, bird strike, FOD, or engine over speed, in whichcase the fan must be inspected at both the upper and lower surfaces of the midspanshrouds for chafing, scoring, and other damage adjacent to the interlock surfaces. Allblades that are overlapped or show indications of overlapping must be removed and inspected
  33. 33. according to manual. No cracks are permitted in the fan blades. Blade tips areexamined for curl, and the lightening holes are checked for cracks and deformation.Inspection of the abradable material for damage due to rubbing of fan blade tips andinspects the fan speed sensor head for damage due to blade contact. 8.What are the checks and inspections carried out on a connecting rod duringoverhaul? The inspection and repair of connecting rods include 1.Visual inspection 2.Checking of alignment 3.Re- bushing 4.Replacement of bearings VISUAL INSPECTION Visual inspection should be done with magnifying glass or bench microscope. Arod which is bent or twisted should be rejected. Inspect all surfaces of the rod for cracks,corrosion, pitting, galling or other damages. Evidence of any galling is sufficient reasonto reject the complete rod assembly. CHECKING ALIGNMENT Check bushings that have been replaced to determine if the bushing and rod boresare square and parallel to each other. The alignment can be checked several ways. Onemethod which requires a push fit arbor, a surface plate, and two parallel blocks of equalheight.To measure the squareness, or twist insert the arbors into the rod bores. Place theparallel blocks on a surface plate. Place the ends of the arbors on the parallel blocks.Check the clearance at the points where the arbors rest on the blocks, using a thickness gauge. This clearance, divided by the separation of blocks in inches will give the twist perinch of the length. To determine the bushing or bearing parallelism (convergence), insert the arbors inthe rod bores. Measure the distance between arbors on each side of the connecting rod atpoints that are equidistance from the rod centre line. For exact parallelism distancechecked on both the sides should be the same. Consult the manufacturer’s table of limitsfor the amount of misalignment permitted.Other inspections and operations must be performed to be referred from themanufacturer’s overhaul manual. 9.What are line maintenance and heavy maintenance? Explain in detail aboutmaintenance practices.
  34. 34. The scope of line maintenance consists of removal and installation of externalcomponents and engine accessories as well as hot section inspection. Much of the work considered to be line maintenance is removal and replacement of malfunctioning linereplaceable units (LRU). HEAVY MAINTENANCE Heavy maintenance consists of removal, installation and repair of components consideredbeyond the capabilities of the line maintenance facility. Heavy maintenance proceduresrequire considerable equipment and engine knowledge. Heavy maintenance normallyperformed at an overhaul facility. MAINTENANCE PRECAUTIONS 1.The ignition system is potentially lethal, therefore any work done on the highenergy ignition units, the igniter plugs or the harness must be disconnected and atleast 1 min allow to elapse before the high tension lead is disconnected. 2.Before carrying out work on electrical system, make sure that the system is safe, byswitching off the power or by tripping and tagging the appropriate circuit breakers. 3.When the oil system is replenished, care must be taken so that no oil is spilled. If any oil is accidentally spilled, clean it off immediately. 4.Before inspecting the air intake or the exhaust system, make sure that there is nopossibility of the starter system being operated or the ignition system beingenergized. 5.After any repair, adjustment, or component change, ensure that no loose items havebeen left inside the air intake and exhaust system. 6.Observe fire safety precautions at all times when procedures involve the use of fuelsor similar combustibles. Explain the working principle of operation of gas Turbineengine. The basic operation of the gas turbine or turbo jet engine is relatively simple. Air isbrought into the front of the turbine engine and compressed. Fuel is mixed with this airand burned and the heated exhausted gases rush out the back of the engine. The parts of the turbo jet engine work together to change fuel energy to energy of motion to cause thegreatest thrust. A turbine engine has major 3 sections such as: 1.Air compressor 2.Combustion section 3.Turbine section The engine may also be divided into cold section and hot section. The front part of theengine contains the air compressor which is the cold section. The Combustion and theturbine sections make up the hot section of the engine.
  35. 35. The compressor packs several tons of air into the combustion chamber every minuteand works somewhat like a series of fans. The fuel is forced into the combustion chamberthrough nozzles, a spark provides ignition, and the mixture burns, creating hot exhaustgases. These gases expand and are ejected from the rear of the engine. As the gasesleave, they spin a turbine which is located behind the combustion chamber. By means of an interconnecting shaft, the rotating turbine is connected to and turns the compressor,completing the cycle. After rushing by the turbine, the hot gases continue to expand and blast out throughthe exhaust nozzle with a high velocity, creating the force which propels a jet aircraft. Enumerate the various starters used for starting the gas turbine engines andexplain in detail the operation of any one of them Starters for gas turbine engines may be classified as Air turbine starters, Electricstarters, and Fuel Air (F/A) combustion starters. ELECTRIC STARTERS The comparatively small gas turbine engines (6000lbs of thrust) are equipped withheavy duty electric starters or starter generators. These are simply electric motors ormotor generator units which produce very high starting torque because of the largeamounts of electric power they consume. The electric starter is coupled to the engine through a reduction gear and a ratchetmechanism or clutch, which automatically disengages after the engine has reached a self sustaining speed. The electric supply, which may be of a high or low voltage, is passed through asystem of relays and resistances to allow the full voltage to be build up progressively asthe starter gain speed. The electric supply also provides the power for the operation of theignition system. The electric supply is automatically cancelled when the starter load isreduced, either the engine has started satisfactorily or the time cycle is completed. AIR TURBINE STARTERS This type of starters requires a high volume air supply, which is provided by aground starter unit, a compressed air bottle on the airplane, an auxiliary power unit on theaircraft, or compressed bleed air from other engines on the aircraft.The low pressure air turbine starter is designed to operate with a high volume, lowpressure air supply, usually obtained from an external turbo compressor unit
  36. 36. mounted on aground service cart or from the airplanes low pressure air supply. The supply mustproduce a pressure of about 35 psig and a flow of more than 100 lbs/min. The starter is light weight turbine air motor equipped with a rotating assembly, areduction gear system, a splined output shaft, a cut out switch mechanism, an over speedswitch scroll assembly and a gear housing. The low pressure air introduced into the scroll through a 3” duct. From the scroll,air passes through nozzles vanes to the outer rim of the turbine wheel. Since this is aninward flow turbine design the air expands radially inward toward the centre of the wheeland is then expelled through the exducer. The exhausted air passes through the screenand out to the atmosphere. The expansion of air from a pressure about 35 psig toatmospheric pressure imparts energy to the turbine wheel, causing it to reach a speed of about 55,000 rpm. This low torque high speed is converted to a high torque low speed bymeans of the 23.2: 1 reduction gearing. COMBUSTION STARTERS The two types of combustion starters are the gas turbine starters, and the cartridgetype starters. A gas turbine starter is completely self-contained. It has its own fuel and ignitionsystem, its own starting system (usually electric or hydraulic) and a self contained oilsystem. This type of starter provides a high power output for a low weight. The starter consists of a small, compact gas turbine engine, having a turbine drivencentrifugal compressor, a reverse flow combustion system and a mechanicallyindependent free power turbine. The free power turbine connected to the main engine viaa two stage reduction gear, an automatic clutch and output shaft.When the starting cycle is initiated the gas turbine starter is rotated by its ownstarter motor until it reaches a self sustaining speed at which point the starting and ignitionsystems automatically switch off. Then the acceleration continues up to a control speed of 60,000 rpm. When it is accelerating, the exhaust gas is being directed via nozzle guidevanes, on to the free power turbine to drive the main engine. Once the main enginereaches a self sustaining speed, a cut out switch operates and shut down the gas turbinestarter. As the starter runs down, the clutch automatically disengages from the outputshaft and the main engine accelerates up to idling rpm under its own power. Explain the various checks and alignment in crankshaft during overhaul
  37. 37. 1.Inspect all surfaces of the shaft for cracks 2.Check the bearing surfaces for galling, scoring or other damage. 3.Check oil transfer tubes for tightness. 4.Carry out visual inspection and Non destructive testing such as magnetic particletesting or radiography. 5.Check the crankshaft for straightness. PROCEDURE a.Place the crank shaft in ‘v’ blocks supported at the locations specified in theapplicable engine overhaul manual. b.Using a surface plate and a dial indicator to measure the run out. c.Crank shaft run out or bending is checked by mounting the shaft on ‘v’ blocksplaced on a level surface plate and rotating the shaft while reading the run out onthe dial gauge. d.Crank shaft run out should be checked at the centre main journals while the shaft issupported at the thrust and rear journals. e.It should also be checked at the propeller flange or at the front propeller bearingseat. f.If the total indicator reading exceeds the dimensions given in the manufacturer’stable and limits, the shaft must not be reused. g.A bent crankshaft should not be straightened. Any attempt to do so will result in rupture of the nitride surface of the bearing journals. h.Measure the outside diameter of the crankshaft main and rod bearing journals andcompare the reading with the table of limits.

×