Aero Engine

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INTRODUCTION AIRCRAFT RECIPROCATING ENGINE COMPONENTS AND CONSTRUCTIONS The general aircraft engine used in any aircraft for thrust generation consist of the following basic components. CRANK CASE: The crank case of an engine is the housing that houses the various components surrounding the crankshaft. Therefore it is the basic foundation of the engine. The crank case performs the following functions: It contains bearings in which crankshaft revolves. It provides a tight enclosure for lubricating oil. It supports various internal and external mechanism of power plant It provides a support for attachment of cylinder. It prevents the misalignment of the shaft and its bearings. BEARINGS: Bearing is any surface that supports or is supported by another surface. The bearings in any aircraft engine are designed to minimize the friction and wear resistance. They must reduce the friction of moving parts and also take the thrust loads, radial loads or combination of both. CRANK SHAFT: 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 end. 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. CONNECTING ROD ASSEMBLIES: 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 PISTON: 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

compreses 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. CYLINDERS: The cylinder of an IC engine converts chemical heat energy of the fulel 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 VALVES: In general a valve is a device for regulating or determining the check on the flow of a liquid or a gas by a movable part which opens or closes into a passage.The main purpose of a valve in IC engine is to open and close parts which are into the combustion chamber of the engine namely intake and exhaust ports.The valves are associated with valve guides,valve seats and valve springs. PROPELLERS: They are essential aircraft parts that provide the necessary thrust for moving the aircraft.The propeller is connected to the engine by means of a shaft.The propeller consists of two or more blades and a central hub to which the blades are attached. Engines and their components are designed and built to provide many years of service.For an aircraft to remain in an airworthy condition the following conditions have to be fulfilled. Periodic inspection Repairs Overhauls and replacements TROUBLE SHOOTING: It is the step by step procedure used to determine cause of a given fault and then select a quick and best solution.

STRIPPING OF PISTON ENGINE AIM: To dismantle a piston engine and study its particular components. TOOLS REQUIRED: Special tools for notching crank shaft. Universal socket for spark plug Selected spanner no: 6-19 Ring spanner no: 6-22 Adjustable spanner Plier, cutter and screwdriver Value depression tool Crow foot spanner PROCEDURE: Remove spark plug and rocker curves. Remove starter and accessories. Turn the engine over such that cylinders are upper most. Remove controls completely with universal joints. Remove airscoop, plug leads, distribution covers. Remove induction system with carburetor. Unscrew push rod ball socket from rockers. Take out push rod and push rod covers. Remove cylinder baffle plate. Remove cylinder. Remove piston rings. Extract gudgeon pin, air clip. Withdraw gudgeon pin and piston. Remove magnetos. Remove gearbox with timing gear cover. Turn the engine cover on its stand. Remove starter. Remove adaptor, thrust bearing cover and top cover. Detach big and bearing caps. Withdraw connecting rod. Remove main, intermediate bearing caps. Lift crankshaft. Unscrew idle gear hub bolt. Draw off gear wheel. Remove magneto drivers. Unscrew camshaft gagging the gear. Remove camshaft rear bearing bush. Withdraw camshaft. Remove tappet and guides. The parts are kept for visual inspection. RESULT: Thus the stripping of piston engine is carried according to instructions in the manufacturers maintenance manual.

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 PROCEDURE: Check for cracks by contact current method. Check for corrosion, pitting etc.. Check for ovality and taperness using micrometer. Check external dimensions of crank pin and journals. Carry out rip check before measuring internal dimensions. Check for central journal errors due to ovality. Check the crank web for parallelism. Check crank pin for parallelism. Error allowed is 0.0016 per unit length. Check if propeller shaft has a tapered end in the hub. Check propeller shaft for threads and keyways for burrs and beveling. Check oil seal retainer and sealing for burrs and correct seating. Carry out static and dynamic hardness tests.

RECTIFICATION: Score,taper and ovality can be removed by grinding. Slight score and pitting can be removed by grinding or dressing with carborundum or polishing with emery paper.

RESULT: Thus the crankshaft is viewed and its dimensions are checked with the manufacturers maintenance manual.

VIEWING PROCEDURE OF CONNETING 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 PROCEDURE: Check the connecting rod conditions,the big end caps for cracks and other surface defects by hot oil and chalk method. Check the rod for notches and abtrasion. Measure small end dia and compare with external dia of gudgeon pin. Check the nip in the big end bearings. Measure and check the diameter with internal dimensions of cylinder bore gauge. To carry out the nip check,assemble connecting rod shell and cap as per assembly sequence and tighten the bolts. Tighten to 840 pounds inch and check diameter of big end bearing. Check connecting rod for alignment. Check connecting rod bolts for elongation and nuts for threads. Check for hardness. RECTIFICATION: During the NIP check, if 0.004 doesnt go inside machine the big end cap. If 0.006 goes inside replace the bearing cap. Fitting and searing can be removed by stoning and polishing if not too deep.


Thus the connecting rod is viewed and its dimensions are measured as per instructions in the manufacturers maintenance manual. VIEWING PROCEDURE OF PISTON ASSEMBLY AIM: To carry out inpection on the piston assembly. TOOLS REQUIRED: Cleaning basket Feeler gauge Scale 12 Telescopic gauge Micrometer Vernier caliper PROCEDURE: CLEANING: Check for completeness of the piston assembly and clean it by dipping in petroleum solvent using cleaning basket. Examine the piston surface thoroughly for excessive pitting, cavaties or surface distortion. Check the piston rings, grooves, piston pinholes and holes base for any damage. Check side clearance between piston rings and piston (0.004-0.0025). Check end clearance on wedge type piston rings. Check inside diameter of piston pinhole (0.03-0.004). Check clearance between piston skit and cylinder and piston dia top and bottom(0.021). Check outside diameter of piston pin against inside diameter of hole in piston(0.0002-0.001). Measure fit between piston and plug and check outside diameter of plugs(0.0002-0.001). 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 manufacturers maintenance manual.

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 PROCEDURE: CLEANING: Clean the cylinder head with petroleum solvent.Dip it in petroleum agent using cleaning basket. VISUAL INSPECTION: Inspect the cylinder head visually using a magnifying glass. Inspect the cylinder for Loose damaged studs.(replace new ones) Loose spark plug (insert new oversize ones.) Loose cracked valve guide. Damaged mounting ports, rocker box cover Cracked or damaged fins

DIMENSIONAL CHECKS: Check internal dimensions of intake and exhaust valves. Check diameter and roundness of guide bore with gauge. Check wear and tear in rocker arm bush. Dimension checks are done in processes.


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: In cooling fins, check for nicks and notches. In barrel, check for cracks (result in rejection) In skirt, check for cracks, bends, and breaks. In mounting flange, check for nicks, cracks and warping. Inside the barrel inspect