Important qus

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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.