AVIA122_Ch03

8/7/2019 AVIA122_Ch03

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Reciprocating Engine

Design and Construction

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Reciprocating Engine Design

and Construction� Basic Parts

� Crankcase

� Cylinders� Pistons

� Connecting rods

� Valves

� Valve-operating mechanism� Crankshaft

� Head

� Spark plugs

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and Construction� Crankcase

� Foundation of the engine, containing the

bearings in which the crankshaft revolves.

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and Construction� Crankcase

� Tight enclosure for lubricating oil.

� Support for attachment of the cylinders and the

powerplant to the aircraft.

� Must be rigid, strong and light.

� Cast of forged aluminum alloy.

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and Construction� Opposed Engine Crankcase

Bearings

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and Construction� Crankshafts

� Transforms the reciprocating motion of the

piston and connecting rod into rotary motion

for the propeller.

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and Construction� Crankshaft

� Backbone of engine.

� Forged from very strong alloy (Chromium-

nickel-molybdenum steel).

� Single or multi-piece.

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and Construction� Crankshaft

� Four-throw used on four-cylinder engines.

� Six-throw used on six-cylinder engines.

� Three Main Parts ± Journal

± Crankpin

± Crankcheek

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and Construction� Crankshaft Balance

� Dynamic dampers are used to reduce vibration

during engine operation.

� Pendulum which

is fastened to the

crankshaft.

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and Construction� Connecting Rods

� Link which transmits forces between the piston

and the crankshaft.

Master and Articulated

Plain

Fork and Blade

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and Construction� Master and Articulated Rod Assembly

� Commonly used in radial engines.

� One piston in each row is connected to the

master rod. Others are connected to themaster rod by articulated rods.

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and Construction� Fork And Blade Assembly

� Used primarily in V-type engines.

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and Construction� Plain Type Connecting Rod

� Used in in-line and opposed engines.

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and Construction� Pistons

� Acts as a moving wall within the combustion

chamber.

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and Construction� As the piston moves down it draws in fuel/air

mixture.

� As it moves up it compresses the charge.

� Ignition occurs, and expanding gases force thepiston down.

� This force is transmitted to crankshaft throughconnecting rod.

� On the return upward stroke, the piston forcesthe exhaust gas out.

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and Construction� Piston Construction

� Machined from aluminum alloy forgings.

� Grooves machined for piston rings.

� Cooling fins inside for

greater heat transfer.

� Piston pin (wrist pin)

joins the piston to the

connecting rod.

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and Construction� Piston Types

� Trunk Type

� Slipper Type

± Not used in aircraft

Slipper

Trunk

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and Construction� Piston Rings

� Compression Rings

� Oil Control Rings

� Oil Scraper Rings

Rings

Pin boss

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and Construction� Compression Rings

� Prevent the escape of gas past the piston

during engine operation.

� Number used depends on engine design.

� Cross section of the ring is either rectangular or wedge shaped

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and Construction

� Oil Control Rings

� Placed in grooves immediately below the

compression rings.

� One or more rings per piston.

� Regulate the thickness of the oil film on thecylinder wall.

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and Construction

� Oil Scraper Ring

� Installed in the groove at the bottom of the

piston skirt.

� Installed with the scraping edge away from the

piston head or in the reverse position.

� Returns surplus oil to the

crankcase.

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and Construction

� Cylinders

� The portion of the engine in which the power is

developed.

� Provides a combustion chamber where the

burning and expansion of gases take place.

� Houses the piston andthe connecting rod.

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and Construction

� Cylinders

� Either produced singly or cast in a block.

� Air-cooled engine uses

the overhead valve type.

� Two major parts: Head,

Barrel.

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and Construction

� Cylinder Heads

� Provides a place for combustion of the fuel/air

mixture.

� Gives the cylinder more heat conductivity for

cooling.

� Contains the intake valve, exhaust valve and

sparkplugs.

� Contains fins for cooling.

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and Construction

� Cylinder Barrels

� Made of a steel alloy forging with the inner

surface hardened to resist wear. (Nitrided)

� Worn Cylinder walls can be ground out and re-

nitrided or chrome plated.

� Chrome plated cylinders can be recognized by

orange paint mark on cylinder.

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and Construction

� Cylinder Numbering (Opposed Engine)

� Propeller

(Front)

� Accessory

(Rear)

� Left, right

(Pilot¶s view)

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and Construction

� Cylinder Numbering (Opposed Engine)

� Numbering is by no means standard.

� Continental starts from rear.

� Lycoming starts from front.

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and Construction

� Cylinder Numbering (Radial Engine)

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and Construction

� Cylinder Numbering (Radial Engine)

� Numbered clockwise as viewed from the

accessory end.

� Single-row, cylinder No. 1 is the top cylinder.

� Double-row, all odd-numbered cylinders are inthe rear, and all even numbered cylinders are

in the front.

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and Construction

� Firing Order

� The Sequence in which the power event occurs

in the different cylinders.

� Designed to provide for balance and to

eliminate vibration.

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and Construction

� Firing Order Single-Row-Radial

� First all odd numbered cylinders fire in

numerical succession.

� Then the even-numbered cylinders fire in

numerical succession.

1-3-5-7-9-2-4-6-8

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and Construction

� Firing Order Double-Row-Radial

� Arranged with the firing impulse occurring in a

cylinder in one row and then in a cylinder in theother row.

� Two cylinders in the same row never fire in

succession.

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and Construction

� Firing Order Opposed Engine

� Lycoming and Continental number their

cylinders differently which gives us two sets of firing orders.

� But the firing impulses are the same.

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and Construction

� Firing Order Opposed Engine

1-4-2-3

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and Construction

Valves

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and Construction

� Valves

� Fuel/air mixture enters the cylinders through

the intake valve.

� Burned gases are expelled through the exhaust

valve.

� Mushroom or tulip type depending on shape.

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and Construction

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and Construction

� Valve Construction

� Intake valves, because of lower operating

temperatures, can be made of chrome-nickelsteel.

� Exhaust valves are made of exotic metals such

as inconel, silicon-chromium or cobalt-chromium alloys.

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and Construction


Head

Face

Neck

Tip

Stem

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and Construction� Valve Construction

� Valve head has ground face which forms a sealagainst the ground valve seat in the cylinder head.

� Valve face ground to an angle of either 30° or 45°.

� Valve face made more durable by theapplication of stellite (an alloy of cobalt andchromium).

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and Construction


� Valve stem acts as a pilot for the valve head

and rides in the valve guide.

� Surface-hardened to resist wear.

� Some stems are hollow and partially filled withmetallic sodium.

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and Construction


� The neck is the part that forms the junction

between the head and the stem.

� The tip is hardened to with stand the

hammering of the valve rocker arm.

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and Construction


� Machined groove near tip receives the split-

ring keys which form a lock ring to hold thevalve spring retaining washer.

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and Construction

� Valve-Operating Mechanism

� Each valve must open at the proper time, stay

open for the required length of time, and closeat the proper time.

� Timing of the valves is controlled by the valve-

operating mechanism.

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and Construction� Valve-Operating Mechanism

� Intake valves open just before the pistonreaches top dead center, and exhaust valves

remain open after top dead center.

� At this particular instant both valves are openat the same time (end of the exhaust stroke and

beginning of the intake stroke).

� This valve overlap results in better volumetricefficiency and lower operating temperatures.

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and Construction

� Valve-Operating Mechanism (Opposed engine)

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and Construction

� Valve-Operating Mechanism

(Radial engine)

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and Construction

� Camshaft

� Valve-operating mechanism is operated by a

camshaft.

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and Construction

� Camshaft

� The camshaft is

driven by a gear that mates with

another gear

attached to the

crankshaft.

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and Construction

� Tappet Assembly

� Converts rotational movement of the cam lobe

into reciprocating motion.

� Transmits this motion to the push rod, rocker

arm, and then to the valve tip.

� Opening the valve at the proper time.

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and Construction

� Tappet Assembly

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and Construction

� Hydraulic Valve Tappets

� Designed to automatically keep the valve

clearance at zero.

� Ball check valve traps oil in the pressure

chamber and.

� Acts as a cushion as the camshaft rotates.

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and Construction

� Hydraulic Valve Tappets

PUSH ROD SOCKET

HIGH PRESSURE

OIL SOURCE

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and Construction

� Push Rod

� Transmits the force from the valve tappet to the

rocker arm.

� Tubular form used because of its strength

� Permits lubricating oil to pass through thehollow rod to the ball ends.

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and Construction

� Rocker Arms

� Transmits the lifting force from the cam to the

valve.

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and Construction

� Valve Springs

� Function is to

close the valveand to hold the

valve securely

on the valve

seat.

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and Construction

� Valve Springs

� Two or more springs used to eliminate spring

vibration or surging during different enginespeeds.

� Held in place by split locks installed in the

recess of the valve spring upper retainer

washer.

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and Construction

� Bearings

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and Construction� Bearings

� Any surface which supports, or is supportedby, another surface.

� Composed of material that is strong enough towithstand the pressure imposed on it.

� Permit the other surface to move with aminimum of friction and wear.

� Lubricated bearings.

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and Construction

� Bearings

� Three types of lubricated bearings used:

± Plain Bearings

± Ball Bearings

± Roller Bearings

� Bearings are required to take radial loads,

thrust loads, and a combination of the two.

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and Construction

� Plain Bearings

� Used for crankshaft, cam ring, camshaft,

connecting rods, and accessory drive shaft.

� Subjected to radial

loads.

� Made of nonferrousmetals.

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and Construction

� Ball Bearings

� Used in supercharger impeller shaft bearings

and rocker arm bearings.

� Special deep groove ball bearings are used in

some aircraft engines to transmit propeller

thrust to the engines nose section.

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and Construction

� Roller Bearings

� Straight roller bearings used where the bearing

is subjected to radial loads only.

� Tapered roller bearings used where bearing is

subjected to both radial and thrust loads.

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and Construction� Propeller Reduction Gearing

� Turns the propeller at a slower speed than theengine.

� Increases propeller efficiency.

� Three types:

± Spur Planetary ± Bevel Planetary

± Spur and Pinion

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and Construction

Spur Planetary

Spur and Pinion

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and Construction

� Propeller Shafts

Taper

Spline

Flange

Documents

AVIA122_Ch03