SRINIVASA
ENGINEERING CO LEGE
(Appr Approv oved ed by AIC AICT , New Delhi Delhi and affili affiliate ated d to Anna Anna Univers Universit it , Chennai)
An ISO 9001:2008 Certified Institution PERAMBALUR 621212
DEPARTM NT OF AERONAUTI AL NGINEERING AE2355 AERO ENGINE LABORATORY M NUAL
TABLE OF CONTENTS
AE2355 AERO ENGINE LABORATORY MANUAL Expt
LIST OF EXPERIMENTS Introduction – piston engine
1
Dismantling Dismantli ng of a piston engine
2
Engine (Piston Engine) - cleaning, visual inspection, NDT checks.
3
Piston Engine Components - dimensional checks.
4
Study of carburetor.
5
Piston – Engine reassembly.
6
Dismantling Dismantli ng of a jet engine
7
Jet Engine – identification identificatio n of components & defects.
8
Jet Engine – NDT checks and dimensional checks
9
Jet Engine – reassembly.
10
Engine starting procedures.
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TABLE OF CONTENTS
AE2355 AERO ENGINE LABORATORY MANUAL Expt
LIST OF EXPERIMENTS Introduction – piston engine
1
Dismantling Dismantli ng of a piston engine
2
Engine (Piston Engine) - cleaning, visual inspection, NDT checks.
3
Piston Engine Components - dimensional checks.
4
Study of carburetor.
5
Piston – Engine reassembly.
6
Dismantling Dismantli ng of a jet engine
7
Jet Engine – identification identificatio n of components & defects.
8
Jet Engine – NDT checks and dimensional checks
9
Jet Engine – reassembly.
10
Engine starting procedures.
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INTRODUCTION PISTON ENGINE
Piston engines are internal combustion engines that burn a mixture of fuel and air inside a combustion chamber. The chamber is provided with a piston that moves within the compression chamber. The energy for the movement of the piston is provided by the air-fuel mixture. Piston engines operate similar to the car and other automobile engines. In its basic operation, a valve in the engine permits air into the chamber (called the cylinder) which is compressed by the moving piston. When an appropriate compression is reached, fuel is allowed into the compressed air through another inlet as a fine spray. Finally, the compressed fuel-air mixture is ignited with a spark provided by a spark plug, which causes the mixture to explode violently. The explosive power is used to move the piston back, and remove the exhaust gases from the compression chamber. The return movement of the piston is conveyed to the wheel and fans of the aircraft which causes it to rotate at high speed. In a propeller powered aircraft, much of the thrust is created by the propellers, which creates the upward lift for the aircraft. The general aircraft piston engine used for thrust generation, consist of the following basic components. (1) Crank case, (2) Bearings, (3) Crankshaft, (4) Connecting rod assemblies (5) Piston (6) Cylinders (7) Valves. GAS TURBINE ENGINE:
The gas turbine is an internal combustion engine that uses air as the working fluid. The engine extracts chemical energy from fuel and converts it to mechanical energy using the gaseous energy of the working fluid (air) to drive the engine and propeller, which in turn propel the airplane. In the turbine engine, however, these same four steps occur at the same time but in different places. As a result of this fundamental difference, the turbine has engine sections. 1. The inlet section 2. The compressor section 3. The combustion section (the combustor) 4. The turbine (and exhaust) section. The turbine section of the gas turbine engine has the task of producing usable output shaft power to drive the propeller. In addition, it must also provide power to drive the compressor and all engine accessories. It does this by expanding the high temperature, pressure, and velocity gas and converting the gaseous energy to mechanical energy in the form of shaft power.
EX. NO:1
DISMANTLING OF A PISTON ENGINE
AIM: To disman dismantle tle a piston piston engin engin e and study its particular components. TOOLS REQUIRED: Special Special tools tools for for notchi notchin n crank shaft. Universa Universall socke sockett for for spark plug Selected spanner no: 6-1 Ring spanner no: 6-22 Adjustable spanner Pliers, cutter and screwdr iver Value depression tool Crow foot spanner THEORY: Cyli Cylind nder erss may may be alig aligne ned d in in li li ne, in in a V confi configura guration tion,, horizon horizontally tally opposi opposi e each other, or radially around the crankshaft. pposed-piston engines put two pistons working at opposite ends of the same cylind cylinder er and this this has been been ext exten ende ded d into into tri trian angu gula larr arra arrang ngem emen ents ts s ch as the Napier Deltic. Some designs have set the cyl cylind inder erss in motio motion n arou around nd the the shaf shaft, t, su h as the Rotary engine. Internal combustion en gines operate through a sequence of strokes that admit and remove gases to and from the cy linder. These operations are repeated cyclically and an engine is said to be 2-stroke, 4-stroke or 6 -stroke depending on the number of strokes it akes to complete a cycle.
Simple aircraft piston engine
PROCEDURE: 1. Remove spark plug and rocker curves. 2. Remove starter and accessories. 3. Turn the engine over such that cylinders are upper most. 4. Remove controls completely with universal joints. 5. Remove air scoop, plug leads, distribution covers. 6. Remove induction system with carburetor. 7. Unscrew push rod ball socket from rockers. 8. Take out push rod and push rod covers. 9. Remove cylinder baffle plate. 10. Remove cylinder. 11. Remove piston rings. 12. Extract gudgeon pin, air clip. 13. Withdraw gudgeon pin and piston. Remove magnetos. 14. Remove gearbox with timing gear cover. 15. Turn the engine cover on its stand. Remove starter. 16. Remove adaptor, thrust bearing cover and top cover. 17. Detach big and bearing caps. Withdraw connecting rod. 18. Remove main, intermediate bearing caps. 19. Lift crankshaft. Unscrew idle gear hub bolt. 20. Draw off gear wheel. Remove magneto drivers. 21. Unscrew camshaft gagging the gear. 22. Remove camshaft rear bearing bush. 23. Withdraw camshaft. Remove tappet and guides. 24. The parts are kept for visual inspection. RESULT:
Thus the stripping of piston engine is carried according to instructions in the manufacturer’s maintenance manual. VIVA QUESTIONS:
Explain overhaul What are the safety precautions while handling the engine? Explain the purpose of push rod What is the role of cam shaft
UNIVERSITY QUESTIONS: 1. Write the procedure for dismantling of aircraft piston engine.
2. Carry out the operation of stripping of piston engine.
EX. NO:2
ENGINE (PISTON ENGINE) - CLEANING, VISUAL INSPECTION, NDT CHECKS
AIM:
To study about the different types of cleaning procedures, various inspection methods, and NDT (Non Destructive Test) methods. APPARATUS REQUIRED:
Aircraft component
Kerosene
Lubricating oil
French chalk
Methylated spirit
Heating source
CLEANING
It is necessary to clean the engine externally before disassembly and to clean the parts after disassembly. Great care must be taken during the cleaning processes because the engine parts can be seriously damaged by improper cleaning or applications of the wrong types of the cleaners to certain engine parts. In every case, study the engine manufacturer’s recommendations regarding cleaning procedures and comply with the directions provided by the manufacturer of the cleaning agent or process.
In general two types of cleaning are required when an engine is overhauled. a. Degreasing, for removal of oil, soft types of dirt and soft carbon (sludge) b. De carbonizing, for removal of hard carbon deposits.
DEGREASING AFTER DISASSEMBLY
After the engine has been disassembled all oil and sludge should be removed from the parts before further cleaning is attempted, because the additional cleaning processes are much more
effective after the surface oil has been removed. Two principal methods for removing the lubricating oil and loose sludge are: 1. Washing in a petroleum solvent 2. Vapor degreasing Washing in a petroleum solvent
Cleaning with petroleum solvent can be done in a special cleaning booth where the parts are supported on a grill and sprayed with a solvent gun using air pressure of 50 to 100 psi (345690kPa). During the cleaning processes, particular care should be taken that all crevices, corners, and oil passages are cleaned. Vapor degreasing
A vapor degreaser consists of an enclosed booth in which a degreasing solution such as trichloroethylene is heated until it vaporizes. The engine parts are suspended above the hot solution, and the hot vapor dissolves the oil and soft residue. Several terms are used to describe defects detected in engine parts during inspection.
1. Abrasion – A roughened area where material has been eroded by foreign material being rubbed between moving parts or surfaces. 2. Burning – Surface damage due to excessive heat. It is usually caused by improper fit, defective lubrication or over temperature. 3. Burr – A sharp or rough edge of metal, usually the result of machine working, drilling, or cutting. 4. Chipping - The breaking away of small pieces of metal from a part as a result of careless handling or excessive stress. 5. Corrosion – electrolytic and chemical decomposition of a metal, often caused by joining of dissimilar metals in a situation where moisture exists. Surface corrosion is caused by moisture in combination with chemical elements in the air. 6. Crack - A separation of metal or other material, usually caused by various types of stress, including fatigue stress resulting from repeated loads. 7. Dent- A small, rounded depression in a surface usually caused by the part being struck with a rounded object.
8. Galling- A severe condition of chafing or fretting in which a transfer of metal from one part to another. It is usually caused by the slight movement of mated parts having limited relative motion and under high loads. 9. Nick- A sharp sided depression with a “V” shaped bottom, caused by careless handling of tools and parts. 10. Pitting- Small, deep cavities with sharp edges, may be caused in hardened- steel surfaces by high impacts or in any smooth part by oxidation. 11. Scoring- A series of deep scratches caused by foreign particles between moving parts, or careless assembly or disassembly techniques 12. Scratches- Shallow, thin lines or marks, varying in degree of depth and with, caused by presence of foreign particles during operation or contact with other parts during handling. 13. Indentation- Dent or depression in a surface caused by severe blows. 14. Peening- Depression in the surface of metal caused by striking of the surface by blunt objects or materials. 15. Fretting- The surface erosion caused by very slight movement between two surfaces which are tightly pressed together.
PROCEDURE:
I. For parts that can be removed from aircraft a) For these components, hot fluid chalk method is used cleaning must be done o
b) A mixture of three parts of kerosene and one part of lubricating oil is heated at 90 – 95 C. c) The removal components such as piston’s connection rods, cylinders, combustion chamber are dipped in the hot fluid d) Take the component out and dried out apply French chalk on it. e) Extra French chalk is to be removed by tapping. f) Then cool the component, the contraction of the piston on cooling will force the oil out of any crank and stain the French chalk with a yellowish color. II. For components that cannot be removed from aircraft. a) For a components that cannot be removed from aircraft such as landing gear mounting, cold fluid chalk method is used cleaning is done. b) French chalk is mixed with Methylated spirit and applied on the components that are to be checked c) Excess chalk is removed by tapping. d) Methylated spirit will evaporate off leaving the cracks stain with French chalk RESULT:
Thus the NDT checks have been performed on aircraft component. VIVA QUESTIONS:
What are the NDT techniques used in inspection?
What techniques is used for inspecting internal defect
Explain some defects occur in piston engine components?
How to monitor the health of engine condition?
UNIVERSITY QUESTIONS:
1. Carry out the NDT inspection on aircraft piston engine. 2. Write the procedure for NDT inspection of various components
EX. NO:3
PISTON ENGINE COMPONENTS - DIMENSIONAL CHECKS. 3.(a) VIEWING PROCEDURE OF CONNECTING ROD
AIM:
To perform maintenance and inspection on connecting rod. TOOLS REQUIRED:
Surface plate
Micrometer
Dial gauge
Vernier caliper
Telescopic gauge
Tapered sleeve
Arbors
Plug gauge
THEORY:
Connecting rod is the link which transmits forces between the piston and crankshaft of an engine. It transmits the reciprocating motion of the piston to the rotating movement of the crank shaft. The principle type of connecting assemblies are the
Plain type
Fork and handle type
Articulated type
PROCEDURE:
1. Check the connecting rod conditions, the big end caps for cracks and other surface defects by hot oil and chalk method. 2. Check the rod for notches and abrasion. 3. Measure small end diameter and compare with external diameter of gudgeon pin. 4. Check the nip in the big end bearings. 5. Measure and check the diameter with internal dimensions of cylinder bore gauge. 6. To carry out the nip check, assemble connecting rod shell and cap as per assembly sequence and tighten the bolts. 7. Tighten to 840 pounds inch and check diameter of big end bearing. 8. Check connecting rod for alignment. 9. Check connecting rod bolts for elongation and nuts for threads. 10. Check for hardness.
RECTIFICATION:
1. During the NIP check, if 0.004” doesn’t go inside machine the big end cap. If 0.006” goes inside replace the bearing cap. 2. Fitting and searing can be removed by stoning and polishing if not too deep. RESULT:
Thus the connecting rod is viewed and its dimensions are measured as per instructions in the manufacturers’ maintenance manual. VIVA QUESTIONS:
Which type of material used to manufacture the connecting rod?
Different types of connecting rod?
What refer the big and small ends of connecting rod?
What is connecting rod?
UNIVERSITY QUESTIONS:
1. Perform the inspection of piston connecting rod.
3.(b) VIEWING PROCEDURE OF CRANK SHAFT
AIM:
To view the crankshaft and check out its dimensions. TOOLS REQUIRED:
Surface table
V-blocks
Dial indicator
Vernier caliper
Micrometer
Magnifying glass
THEORY:
The crankshaft transforms the reciprocating motion of the piston to rotating motion for turning the propeller. It is a shaft composed of one or more cranks located at definite places between the ends. Since the crank shaft is the backbone of the engine it is subjected to all forces developed within the engine and hence should be strongly constructed.
FOUR THROW CRANKSHAFT
PROCEDURE:
1. Check for cracks by contact current method. 2. Check for corrosion, pitting etc.. 3. Check for ovality and taperness using micrometer. 4. Check external dimensions of crank pin and journals. 5. Carry out rip check before measuring internal dimensions. 6. Check for central journal errors due to ovality. 7. Check the crank web for parallelism. 8. Check crank pin for parallelism. Error allowed is 0.0016” per unit length. 9. Check if propeller shaft has a tapered end in the hub. 10. Check propeller shaft for threads and keyways for burrs and beveling. 11. Check oil seal retainer and sealing for burrs and correct seating. 12. Carry out static and dynamic hardness tests.
RECTIFICATION:
1. Score, taper and ovality can be removed by grinding. 2. Slight score and pitting can be removed by grinding or dressing with carbonundum or polishing with emery paper.
RESULT:
Thus the crankshaft is viewed and its dimensions are checked with the manufacturers’ maintenance manual. VIVA QUESTIONS:
What is the purpose of crankshaft?
What is a journal?
What is the purpose of counter weight?
UNIVERSITY QUESTIONS:
1. Carry out the inspection on piston engine crankshaft.
3.(c) VIEWING PROCEDURE OF CYLINDER ASSEMBLY AIM: To perform the task of maintenance and inspection of cylinder assembly. TOOLS REQUIRED: DIP basket Stud removing tool Spark plug insert tool Hand vice drill bit Drift and bore gauge THEORY: The cylinder of an IC engine converts chemical heat energy of the fuel to mechanical energy and transmits it through the connecting rods to the rotating crank shaft. The cylinder assembly used for present day engines usually includes cylinder barrel, cylinder head, valve grid, valve seats, rocker arms, cooking fins
CYLINDER BARREL PROCEDURE: CLEANING: Clean the cylinder head with petroleum solvent. Dip it in petroleum agent using cleaning basket. VISUAL INSPECTION: 1. Inspect the cylinder head visually using a magnifying glass. 2. Inspect the cylinder for 3. Loose damaged studs.(replace new ones) 4. Loose spark plug (insert new oversize ones.) 5. Loose cracked valve guide. 6. Damaged mounting ports, rocker box cover
7. Cracked or damaged fins DIMENSIONAL CHECKS: 1. Check internal dimensions of intake and exhaust valves. 2. Check diameter and roundness of guide bore with gauge. 3. Check wear and tear in rocker arm bush. 4. Dimension checks are done in processes. CYLINDER BARREL: TOOLS REQUIRED: Cleaning basket Feeler gauge Dial gauge Bore gauge PROCEDURE: CLEANING: Clean the barrel using petroleum solvent dipping it on the cleaning basket. VISUAL INSPECTIONS: 1. In cooling fins, check for nicks and notches. 2. In barrel, check for cracks (result in rejection) 3. In skirt, check for cracks, bends, and breaks. 4. In mounting flange, check for nicks, cracks and warping. 5. Inside the barrel inspect for corrosion and scoring. DIMENSIONAL CHECKS: 1. Maximum clearance between piston skirt and cylinder is 0.021” 2. Maximum taper of cylinder wall in 0.018”. 3. Maximum ovality is 0.018”. RESULT: Thus the inspection of the cylinder assembly is carried out as per instructions given in manufacturer’s maintenance manual. VIVA QUESTIONS:
What is cylinder head temperature? Why fins are used?
What is cold spark plug?
UNIVERSITY QUESTIONS: 1. Carry out the inspection on piston engine cylinder assembly.
3.(d) VIEWING PROCEDURE OF PISTON ASSEMBLY
AIM:
To carry out inspection on the piston assembly.
TOOLS REQUIRED:
Cleaning basket
Feeler gauge
Scale 12”
Telescopic gauge
Micrometer
Vernier caliper
THEORY:
The piston is a plunger that moves back and forth or up and down within the engine cylinder barrel. It transmits the force of the burning and expanding gases in the cylinder through the connecting rod to the engine crank shaft. As the piston moves down the cylinder, during intake stroke, it draws in the air fuel mixture. As it moves up it compresses the charge. Ignition takes place and the expanding gases cause the piston to move towards the crank shaft. The piston forces the burnt gases out of the combustion chamber during the next stroke.
PISTON AND PISTON RINGS PROCEDURE:
1. Check for completeness of the piston assembly and clean it by dipping in petroleum solvent using cleaning basket. 2. Examine the piston surface thoroughly for excessive pitting, cavaties or surface distortion. 3. Check the piston rings, grooves, piston pinholes and holes base for any damage. 4. Check side clearance between piston rings and piston (0.004”-0.0025”). 5. Check end clearance on wedge type piston rings. 6. Check inside diameter of piston pinhole (0.03”-0.004”). 7. Check clearance between piston skit and cylinder and piston dia top and bottom(0.021”). 8. Check outside diameter of piston pin against inside diameter of hole in piston(0.0002”0.001”). 9. Measure fit between piston and plug and check outside diameter of plugs(0.0002”0.001”). 10. Examine two interior surface of piston pin hole for corrosion and fitting.
RESULT:
The maintenance and inspection of the piston assembly has been performed according to manufacturer’s maintenance manual.
VIVA QUESTION:
What is manufacturer’s maintenance manual?
Explain the piston types?
Why piston rings are used?
What is meant by clearance?
What types of rings are used?
UNIVERSITY QUESTIONS:
1. Carry out the inspection on piston assembly.
EXP.NO.4
STUDY OF CARBURETOR
Aim
To study about the requirements, construction, principles, and operation of the piston engine Carburetor. INTRODUCTION
A carburetor has only one purpose, and that is to deliver a finely atomized fuel at the correct air-fuel ratio to the engine under all operating conditions. The carburetor mounts to the engine’s air induction system. The intake system is also called intake manifold. The carburetor often has an adaptor to match the opening and bolt patterns of the engine and carburetor base. A downdraft carburetor mounts above the engine and an up-draft carburetor mounts below the engine. Side-draft carburetors have a horizontal connection to the engine. Air entering the carburetor comes from a duct that extends into the airplane’s airstream, either at the front of the engine, or at its side. In some cases, the intake duct extends to the aircraft’s wings. Before the air enters the carburetor, it may pass through an air filter in some applications, and through a valve arrangement that allows hot air radiating from the engine exhaust pipe to mix into the air moving to the carburetor. This valve arrangement provides carburetor heat that prevents ice formation in the air duct and carburetor There are two types of proportioning carburetors and there are two types of fuel injection systems in use on aircraft. The simplest of the carburetors is the float-type. The other proportioning carburetor is the pressure carburetor. Fuel injection systems differ in how the fuel is distributed. One system continuously sprays fuel into the air induction system, the other sprays the fuel into the engine cylinder just when needed. In addition to providing the correct fuel-air ratio, a carburetor: •
Is the point where the aircraft’s fuel system is connected.
•
Measures how much air is entering the engine.
•
Measures the correct amount of fuel for good combustion for the measured air.
•
Delivers and mixes the fuel into the air moving in the air induction system
CARBURETOR WORKING Venturi
The method most commonly used is with a venturi through which the airflow entering the engine’s induction system. We know that the air velocity through the venturi must increase to
pass that same volume of air. The increase in velocity causes a pressure reduction that is in proportion to the air velocity. A low pressure in the venturi (a partial vacuum) indicates that high velocity air airflow is present. Because of this, the venturi’s variable vacuum represents the volume of air passing through it. This method of determining the volume of air entering the engine is much more reliable than most of the earlier methods
Main Metering System
The main metering system begins at the main metering jet, which establishes a specific reduction in fuel pressure, as described earlier in the jet section of this article. The reduction in pressure will be constant, no matter how much fuel flows through the jet. The fuel flows to the main discharge nozzle, which is usually located in the center of the carburetor’s main airflow venturi. Often, the main discharge jet is located within a small secondary or boost venturi suspended in the center of the main airflow venturi. The reduced air pressure in the venturi determines the amount of fuel drawn out of the discharge nozzle. The reduction in pressure is dependent upon the volume of air flowing through the venturi. The fuel will start flowing when sufficient differential pressure lifts the fuel from the fuel bowl level up to the level of the nozzle discharge openings. The amount of differential pressure controls the rate of fuel flow. The main metering circuit will provide a constant fuel–air ratio at any engine speed and condition above the engine’s idle speed. Experimentation found that admitting a small amount of air into the fuel passage to the discharge nozzle reduced the fuel droplet size, resulting in better fuel vaporization.
This is an example of an air bleed as the jet in the airstream controls the amount of bleed air admitted into the fuel passage
FLOAT TYPE CARBURETOR Idle Circuit
When closed, the engine throttle has a very slight clearance that allows just enough air for the engine to operate at idle speed. With the throttle set at idle, the engine continues drawing whatever air is in the induction system into the engine cylinders, thereby reducing the pressure in the intake manifold. The volume of air flowing through the carburetor is very low, and there is not enough differential pressure to lift the fuel up to the outlet openings at the discharge nozzle. An alternate fuel circuit meters fuel when the throttle is at idle. The idle system consists of a small drilled hole that connects the main air circuit past the throttle to the idle circuit jet,
allowing the manifold pressure differential to draw fuel from the main metering fuel supply into the main air circuit. The idle jet often has a tapered needle valve within it to adjust the fuel flow. Some idle systems use an air bleed to control fuel flow. A small transfer orifice is located just before air passes the closed throttle plate, near when it is nearest to the carburetor’s wall. This feature is the "secondary idle orifice" The transfer orifice connects to the idle circuit fuel supply. The orifice gradually transfers additional fuel into the main air circuit from the idle circuit fuel supply as the throttle transitions from closed to open. Both the idle passage and the transfer orifice are inactive when the air entering the pressure differential is below that needed to draw fuel into the idle circuit. Accelerator Pump Circuit
When the throttle is briskly opened, the idle passage no longer functions, as it relies on the high velocity air moving between the throttle plate and the idle passage outlet. Once the throttle opens, air quickly fills the intake manifold. With low engine speed, there is little air flowing through the carburetor. The transfer slot cannot provide enough fuel, nor can the main fuel discharge nozzle properly meter fuel, as there is a small delay as the fuel overcomes its inertia. The engine will falter slightly until there is sufficient vacuum in either the main or the idle circuit to start fuel flowing again. A small pump incorporated into the carburetor overcomes this lack of fuel flow. It can be a vacuum operated diaphragm, a plunger or a simple well where extra fuel is available for that purpose. Early carburetors used acceleration well. The well is a small amount of fuel located at the base of the discharge nozzle that is available as needed. This fuel was limited to just the volume of the well, as it could only refill at a low rate. The plunger pump replaced the acceleration well. Either manifold vacuum or a mechanical linkage to the throttle operated the plunger. When mechanically operated, as the throttle is opened the pump plunger pushes a volume of fuel out of the pump, spraying it through passages leading to the main air circuit. "Pumping" the throttle would make subsequent volumes spray into the intake manifold, possibly flooding the engine with too much fuel, resulting in a fire. The linkage arrangement, the volume of the pump and the size of the spray nozzle outlet determine the characteristics of this accelerator pump. Power Enrichment Circuit
An engine operating at full throttle may not have enough rpm to create the necessary airflow, especially when operating under a heavy load. With a limited airflow and throttle wide open, the fuel mixture may not have enough fuel carried with it into the engine cylinder, causing a leaner than normal combustion which may then run hotter than normal. The engine may also run too hot when operating at full speed. Extra fuel overcomes these problems. The fuel added to the normal mixture cools the cylinder walls as it evaporates just prior to combustion. This cooling lowers the fuel-air mixture temperature. The cooler mixture lowers the temperature and pressure in the combustion chamber, reducing the risk of detonation. The extra fuel comes from the fuel in the fuel bowl. An enrichment valve and enrichment jet connect the fuel supply with
the fuel delivery nozzle. The enrichment valve is either a mechanical linkage connected to the throttle, or a diaphragm lifted by the high venturi suction created by full-throttle operation, connecting the fuel bowl to the enrichment jet. Some carburetor manufacturers refer to the enrichment circuit as an "economizer circuit", in that there is reduced fuel consumption when the valve is closed, thereby improving fuel economy at medium and low power levels. The engine now has the correct fuel-air mixture necessary for all operating conditions found at engine idle, take-off, and cruise power settings. Mixture Control Circuit
Once at cruising altitude and speed, it is beneficial to reduce the amount of fuel consumed in order to increase range or for economic operation, and that is the job of the mixture control circuit. A manual control located near the pilot’s throttle control operates a device that changes the overall fuel–air ratio to a slightly leaner cruise mixture. Leaning the mixture at cruise power increases range and conserves fuel. The lower power level and the available engine cooling allow operating with this leaner mixture, without causing harm to the engine. For that reason the lean setting should never be used when full power is needed, or may be immediately needed, such as when a landing turns into a missed approach, or when full power is needed to arrest a high sink rate. The mixture control can provide a number of pre-determined mixture settings, and stops the engine at the conclusion of the flight or engine run. Mixture settings start at "Idle-cutoff", a position that closes the fuel passages, stopping fuel flow through the carburetor. The mixture changes from lean to rich as the mixture control moves to its full rich position. RESULT:
Thus studied about requirements, construction, principle and operation of the reciprocating engine carburetor.
VIVA QUESTIONS:
What the types of carburetor?
What is venturi?
What is the ratio of rich fuel/air mixture?
UNIVERSITY QUESTIONS:
1. Describe briefly about the carburetor used in aircraft.
EX. NO: 5
REASSEMBLY OF PISTON ENGINE
AIM:
To reassemble the piston engine after inspection checks. TOOLS REQUIRED:
Special universal socket for spark plug
Set spanners 6’-19’
Ring spanners 6’-22’
Adjustable spanner
Pliers and cutters
Screwdriver different sizes
Hammer
Value depression tool
Crow foot spanner
PROCEDURE:
1. Insert the tappet and the guides in the crank case. 2. Fix the camshaft after positioning bearing bush. 3. Fix the magneto drive gear. 4. Fix the idle gear and screw the hub bolt. 5. Fix the crankshaft and position the bearing caps. 6. Fix the connecting rod and the bearing caps. 7. Position the top crankcase and then tighten all bolts and nuts. 8. Fix the gearbox with timing gear cover. 9. Fix the magnetos. 10. Fix the position in the connecting rod.
SINGLE CYLINDER PISTON ENGINE
11. Assemble the piston rings on the piston groove and insert the cylinder over piston and tighten all cylinder large nuts. 12. Fix the cylinder baffle plates. 13. Position the push rod covers and push rods.
14. Fix the rocker shafts. 15. Fix the induction system and carburetor. 16. Fix the air scoop, plug heads with distribution cover. 17. Fix the carburetor controls with universal rods. 18. Fix the starter and other accessories. 19. Fix the spark plug in cylinder head bush and tighten to connect torques and connect the plug leads. 20. Fix the rocker covers. RESULT:
Thus the piston engine in reassembled as per maintenance manual instruction VIVA QUESTION:
What is ignition timing?
What is timing advance?
Define engine firing order?
What is backfiring?
UNIVERSITY QUESTION:
1. Write the procedure for reassembly of piston engine.
EX.NO:6
DISMANTLING OF A JET ENGINE
AIM:
To dismantle the turbojet engine in a proper sequence. TOOLS REQUIRED:
¾ *1/4 BS or 12-13 set spanner
10-11 set of ring spanner
8-9 set of ring spanner
C-spanner
Common screw driver
Ball peen spanner
Pliers and side cutter
JET ENGINE
THEORY:
Air breathing jet engines are gas turbines optimized to produce thrust from the exhaust gases, or from ducted fans connected to the gas turbines. Jet engines that produce thrust from the direct impulse of exhaust gases are often called turbojets, whereas those that generate thrust with the addition of a ducted fan are often called turbofans or (rarely) fan-jets. Gas turbines are also used in many liquid propellant rockets, the gas turbines are used to power a turbo pump to permit the use of lightweight, low pressure tanks, which saves considerable dry mass.
PROCEDURE:
1. Loosen the fine nuts using appropriate spanner and r3emove the inlet case from the accessory case. 2. Loosen the 10 nuts using no 10-11 set of ring spanner and detach air casing from compressor case. 3. Remove 15 bolts using no 8-9 set spanner. Detach compressor casing from diffuser. 4. Loosen retaining nut with C-spanner and remove centrifugal impeller. 5. Remove front roller bearing and the sleeve. 6. Remove 2 ignition connection and fuel turners from the combustion chamber outer case. 7. Now take out the turbine along with the shaft from the rear side. 8. Take out the combustion chamber. 9. Loosen the bolts and nuts from the exhaust pipe flange and detach the exhaust pipe from the combustion chamber. 10. Loosen the clamps of the propelling nozzle and disconnect the nozzle from the exhaust pipe. 11. Keep all the removed parts separately in the cleaned tray in sequence so that there is no possibility of mixing with each other. 12. Wherever blanking is required, blank it and place identification slips. RESULT:
Thus the turbojet engine in dismantled and the components are studied.
VIVA QUESTION:
What is operating principle of jet engine?
What is the temp of air entering the combustion chamber?
How much should be turbine blade tip clearance?
What is compressor recovery wash?
UNIVERSITY QUESTION:
1. Carry out the operation of dismantle the turbojet engine
EX.NO:7
JET ENGINES – IDENTIFICATION OF COMPONENTS & DEFECTS
AIM:
To study about the jet engine components and its defects. APPARATUS REQUIRED:
Jet engine. . INTRODUCTION: The major components of a jet engine are similar across the major different types of engines, although not all engine types have all components. The major parts include:
Gas Turbine Major Components Cold Section: Air intake (Inlet) — The standard reference frame for a jet engine is the aircraft itself. For subsonic aircraft, the air intake to a jet engine presents no special difficulties, and consists essentially of an opening which is designed to minimize drag, as with any other aircraft component. However, the air reaching the compressor of a normal jet engine must be travelling below the speed of sound, even for supersonic aircraft, to sustain the flow mechanics of the compressor and turbine blades. At supersonic flight speeds, shockwaves form in the intake system and reduce the recovered pressure at inlet to the compressor. So some supersonic intakes use devices, such as a cone or ramp, to increase pressure recovery, by making more efficient use of the shock wave system. Compressor or Fan — The compressor is made up of stages. Each stage consists of vanes which rotate, and stators which remain stationary. As air is drawn deeper through the compressor, its heat and pressure increases. Energy is derived from the turbine passed along the shaft.
Bypass ducts much of the thrust of essentially all modern jet engines comes from air from the front compressor that bypasses the combustion chamber and gas turbine section that leads directly to the nozzle or afterburner (where fitted). The two common types of compressors are 1. Axial flow compressor. 2. Centrifugal flow compressor. COMPRESSOR DEFECTS
1. Impeller damage due to bird hit, fatigue. 2. Hub damage 3. Tangential vanes (Diffuser) defects.
Diffuser section: - This section is a divergent duct that utilizes Bernoulli's principle to decrease the velocity of the compressed air to allow for easier ignition. And, at the same time, continuing to increase the air pressure before it enters the combustion chamber.
Hot section: Combustor or Can or Flame holders or Combustion Chamber — this is a chamber where fuel is continuously burned in the compressed air.
The primary function of combustion chamber is to burn the air /fuel mixture. The common types of combustion chamber are 1. Can type combustion chamber 2. Annular type combustion chamber 3. Can- Annular type combustion chamber. DEFECTS
1. IOD- internal object damage (confirmation through Boroscope) 2. Thermal stress 3. Cracks 4. Carbon deposits.
COMBUSTOR Turbine — The turbine is a series of bladed discs that act like a windmill, gaining energy from the hot gases leaving the combustor. Some of this energy is used to drive the compressor, and in some turbine engines (i.e. turboprop, turboshaft or turbofan engines), energy is extracted by additional turbine discs and used to drive devices such as propellers, bypass fans or helicopter rotors. One type, a free turbine, is configured such that the turbine disc driving the compressor rotates independently of the discs that power the external components. Relatively cool air, bled from the compressor, may be used to cool the turbine blades and vanes, to prevent them from melting.
Turbine is of two types. They are 1. Impulse type turbine, 2. Reaction type turbine DEFECTS
1. Thermal stress 2. Fractured blade, disc 3. Missing blades
4. Rupture cracks 5. Creep 6. Fatigue fracture.
Afterburner or reheat (chiefly UK) — (mainly military) Produces extra thrust by burning extra fuel, usually inefficiently, to significantly raise Nozzle Entry Temperature at the exhaust. Owing to a larger volume flow (i.e. lower density) at exit from the afterburner, an increased nozzle flow area is required, to maintain satisfactory engine matching, when the afterburner is alight. Exhaust or Nozzle — Hot gases leaving the engine exhaust to atmospheric pressure via a nozzle, the objective being to produce a high velocity jet. In most cases, the nozzle is convergent and of fixed flow area. DEFECTS
1. Discoloration 2. Thermal cracks 3. Fuel wash
4. Nozzle tip cracks 5. Deformation due to EGT RESULT: Thus the jet engine components and defects are studied VIVA QUESTIONS:
What is EGT?
What is a creep?
Why it called gas turbine engine?
UNIVERSITY QUESTIONS:
1. Identify the different components of jet engine and defects occurs on those components.
EXP.NO. 8
JET ENGINE NDT AND DIMENSIONAL CHECKS
Aim
To study about the jet engine NDT checks and dimensional checks on jet engine components as per the engine maintenance manual. NON-DESTRUCTIVE TESTING
Nondestructive testing or Non-destructive testing (NDT) is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage. In aircraft maintenance it is important to inspect the mechanical damage and assess the extent of the repair work. But in schedule maintenance it is a difficult to finding the defects rapidly, as the maintenance of aircraft must be accomplished within scheduled time and same to be released in time for commercial operation. During Nondestructive testing (NDT) is the most economical way of performing inspection and this is the only way of discovering defects. In simply we can say, NDT can detect cracks or any other irregularities in the airframe structure and engine components which are obviously not visible to the naked eye. Structures & different assemblies of aircraft are made from various materials, such as aluminium alloy, steel, titanium and composite materials. To dismantle the aircraft in pieces and then examine each component would take a long time, so the NDT method and equipment selection must be fast and effective. In the present trend of NDT application on aircraft 70-80% of NDT is performed on the airframe, structure, landing gears and the rest carried out on engine & related components. In order to maintain the aircraft defects free and ensure a high degree of quality & reliability and as a part of inspection program, usually following NDT methods are applied;1) Liquid penetrant 2) Magnetic particle, 3) Eddy current 4) Ultrasonic 5) Radiography (x-ray/gama ray) 6) Visual/Optical 7) Sonic/Resonance 8) Infrared Thermography. Jet engine dimensional checks
Jet engine dimensional inspection consists of measuring specific components to ensure that they are within the limits and tolerances given in the table of limits in the manual. Some of the components are measured at each overhaul because only a small amount of wear or distortion is permissible. Other components are measured only when condition found during visual inspection, requires dimensional verification. During overhauling after the cleaning of the components they are visually and dimensionally inspected to establish their general condition and then further inspected for cracks.
Dimensional checks which are carried out on jet engine components
1. Compressor blade tip clearance with compressor shroud (to be checked and compared with table of limits) 2. Turbine blade tip clearance with turbine shroud (to be checked and compared with table of limits) 3. Length of the turbine blades are to be checked (elongation of blades take place due to high temperature) 4. Internal and external diameter of the bearings and compressor, turbine shafts are checked and compared with table of limits. 5. Jet nozzle diameter of the engine is checked and compared with the table of limits. 6. Some of the jet engines cordon shaft end play is checked and compared with table of limits. 7. Internal and external splines are checked for dimension and compared with table of limits. 8. Compressor blades and turbine blades cracks, dents, nicks
Result
Thus studied about the jet engine components NDT checks and dimensional checks which are carried out as per the maintenance manual. VIVA QUESTIONS:
What is the difference between reaction and impeller turbine?
What is twin spool engine?
UNIVERSITY QUESTIONS:
1. Carry out dimensional checks on jet engine components .
EX.NO:9
ASSEMBLY OF TURBO JET ENGINE
AIM:
To assemble a turbojet engine in a proper sequence. TOOLS REQUIRED:
¾ *1/4 BS or 12-13 set spanner 10-11 set of ring spanner 8-9 set of ring spanner C-spanner Common screwdriver Ball peen spanner plier and side cutter
PROCEDURE:
1. Remove all blanking and clean them thoroughly. 2. Attach air intake case front accessory by tightening all the 5 nuts using 12-13 set hammer 3. Attach air intake case rear to the compressor case by tightening all the nuts using 10-11 set ring spanner
4. Now assemble the compressor in the front and turbine at the rear of the shaft by inserting the shaft in front of the diffuser case. 5. Enclose the combustion chamber outer case over the flame tube and tighten all the 15 bolts. 6. Encage 2 ignitions and 5 fuel burners’ connection and tighten the nuts. 7. Encage the exhaust pipe to combustion chamber outer case flange and tighten all the bolts and nuts. 8. Attach the propelling nozzle to the rear side exhaust pipe and together with the clamp.
RESULT:
Thus the turbojet engine is assembled as per the maintenance manual instructions. VIVA QUESTION:
How does the turbine transmit power to the compressor? What are interconnectors? What are two stage turbines? What is the max r.p.m of a turbine engine?
UNIVERSITY QUESTION: 1. Carry out the action of assembles a turbojet engine.
EXP.NO. 10
ENGINE STARTING PROCEDURE
AIM
To start the given airplane engine according to the maintenance manual instructions. PRESTARTING INSPECTION:
The inspection is done to determine the general conditions of aircraft and engine. EXTERNAL CHECKS:
1. 2. 3. 4. 5. 6. 7. 8. 9.
Head the airplane against wind direction. Remove all protective covers and control locks. Position chocks in front and rear main wheel. Position carbon-di-oxide fire extinguisher midway between the port wing tip and cockpit. Position technicians at port and starboard wing tips togive clearance before starting. All panels and cowlings should be in place, flaps open. Check fuel for water content and oil for grade. Turn the propeller 5-8 times to remove hydraulic locks. Check for correct tyre pressure and shock strut extension.
INTERNAL CHECKS:
1. Slide the canopy open. 2. Enter the cockpit and take a convenient position. 3. Check instrument panel for completion and correction. 4. Apply parking brakes to up position. 5. Retract flaps to fully up position. 6. Take clearance and switch on the battery. 7. Open throttle approximately to 1/4th position. 8. Turn the booster pump “ON” 9. Move mixture control to fuel rich position until steady flow. 10. Return mixture control to idle cut off position. 11. Move throttle fully back and switch off booster pump. PROCEDURE FOR STARTING THE ENGINE PISTON ENGINE:
1. Turn the auxiliary fuel pump on if a/c is so equipped. 2. Place the mixture control to the piston recommended for the engine and carburetor combination being started. As a general rule, the mixture control should be in the ‘idle cut off’ position for pressure type carburetors and in the ‘full rich’ for float type carburetors.
3. Many light a/c are equipped with a mixture control pull rod which has no defended intermediate position when such controls are pushed in flush with the instrument panel the mixture is set in the ‘full rich’ position conversely when the control rod is fulled all the way out the carburetor is in the ‘idle cut off’ or ‘full bean’ position. Unmarked intermediate position b/w these two extremes can be selected by the operator to achieve any desired mixture setting. 4. Open the throttle to a position that will provide 1000 to 1200 rpm. 5. Leave the preheat or alternate air control in the ‘cold’ position to prevent damage and fire in case of backfire. This auxiliary heating devices should be used of ten the engine warms up. The improve fuel vaporization, prevent fouling of the spark plug oil formation and climate icing in the induction system. 6. Energize the starter after the propeller has made at least two compile revolutions and twin the ignition switch on one engine equipped with on induction vibrator turn switch to the ‘both’ position. When starting on engine; that uses on impulse coupling magnetic turn by ignition switch to the ‘left’ position. Place the ignition switch to the ‘start’ when the magnetic incorporation a retard breaker assembly. Do not crank the engine continuously with the starter for more than 1 minute. Allow a 3 to 5 minute period for cooling the starter between successive attempts. Otherwise the starter may be burned out due to overheating. 7. Move the primer switch to ‘on’ intermittently or prime with one or three stokes of priming pump, depending of on how the aircraft is equipped. When the engine begin to fire, hold the primer on, while gradually opening throttle to obtained smooth operation. 8. After the engine is operating smoothy on the primer, move the mixture control to the ‘full rich’ position. Release the primer as soon as drop in r.p.m indicates the engine in receiving additional from the carburetor. JET ENGINE:
1. Place the start selector switch to the desired engine and the start arming switch (if so equipped) to ‘start position’ 2. Turn the a/c boost pumps on 3. Place the fuel and ignition switch on 4. Position the low rpm switch in low or normal (high) 5. Make sure that the power lever is in the ‘start’ position: If the propellar is not at the ‘start’ position. Difficulty may be encountered in making a start. 6. Depress the start switch and if printing is necessary depress the primer button. 7. Make sure the fuel pump parallel light comes on at or above 2200 rpm and remains on upto 900 rpm. 8. Check the oil pressure and temperature maintain the power level at the ‘start’ position until the specified minimum oil temperature is reached. 9. Disconnect the ground power supply.
RESULT: Thus the starting procedure and pre-flight inspections are performed in aircraft engine and studied. VIVA QUESTION:
What is a need of booster pump? What equipment is driven from the engine? How is the maximum r.p.m. controlled? What is a starting by-pass?
UNIVERSITY QUESTION: 1. Write the aircraft engine starting procedure.
