01aviation140aircraft Engine Types

8/13/2019 01aviation140aircraft Engine Types

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AIRCRAFT ENGINE TYPES

THE HEAT ENGINE


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THE HEAT ENGINE

Modern heavier-than-air aircraft utilize thrust to remainin flight.

This thrust is provided by a heat engine.

All heat engines convert chemical energy (fuel) intoheat energy.

This heat energy is converted into mechanical energywhich is harnessed to provide thrust.

In all heat engines the working fluid (fuel/air mixture) iscompressed to a high pressure relative to theatmosphere.


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ENGINE TYPES

Reciprocating - utilizes reciprocating pistons.

Turboprop - turbine-driven compressor.

Turbojet - turbine-driven compressor.

Ramjet - ram compression due to high flightspeed.

Pulse-jet - compression due to combustion. Rocket - compression due to combustion.


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GENERAL AVIATION REQUIREMENTS

Efficiency- the engine must be able to operate

efficiently under a wide range of atmosphericconditions.

Economy- the engine must be economic toproduce, run, and maintain.

Reliability- the engine must be able to endure

long periods of operation at high power settingswithout failure.


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OPERATION SPECIFIC ENGINES

The engine selected for an aircraft depends on the type of flyingit will do.

Propeller driven aircraft are more fuel efficient at low speeds,while jet powered aircraft are more efficient at high speeds.

This high speed efficiency is more economical on long trips.

Turboprop aircraft combine the reliability of a turbine engine withthe low speed (short trip) efficiency of a propeller driven aircraft.These turbine driven engines are able to operate at higher

altitudes, giving them an operational advantage. (these benefitscome at a cost)


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RECIPROCATING ENGINE TYPES

Reciprocating engines are normally

classified by cylinder arrangement. In-line

V-type

Radial

Horizontally opposed

Diesel


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RECIPROCATING ENGINE TYPES

They are further categorized by the number of cylinders and themethod of cooling.

Engines are either air cooled or liquid cooled. In either caseexcess heat is transferred to the surrounding air.

An air cooled engine transfers heat from the cylinders directly to

the air flow routed around the cylinders. A liquid cooled engine transfers heat from the cylinders to a

liquid coolant which in turn transfers the heat to the airflow

through the radiator. Most aircraft engines are air cooled. (this method is lighter and

cheaper but not as effective)


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In-line

Advantages:

streamlined (less drag)

visibility (if inverted)

Disadvantages: long crankshaft (limits power output)

ground clearance ineffective cooling of rear cylinders


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Horizontally Opposed

Advantages:

streamlined (less drag)

visibility

less vibration Disadvantages:

limited power (crankshaft length) uneven cooling


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V-type

Advantages:

visibility

Disadvantages:

limited power (crankshaft length)

uneven cooling


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Radial

Advantages:

power (rows of cylinders can be added while maintaining ashort crankshaft)

cooling

Disadvantages: drag hydraulicing (oil tends to pool in the low cylinder during

extended shutdown periods) This problem can cause majorengine damage if the engine is started. The problem can bedetected by hand pulling the engine and then draining the oilby removing the spark plug.


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Hydraulic Lock (hydraulicing)


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Multi-row Radial
http://upload.wikimedia.org/wikipedia/commons/4/45/Sternmotor_geschnitten_2.jpg


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Radial Engine


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Diesel

Advantages: fuel consumption

fuel cost

less maintenance (longer duration between overhauls)

fuel availability

Disadvantages: weight

cost

(both of these aspects have been improved upon as moreresearch driven by high fuel costs has been devoted todeveloping diesel engines for light aircraft)


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Reciprocating Engine Components

Basic components and mechanical principles are

shared by all reciprocating engines. Different types of cylinder arrangement, cooling type,

and fuel require different component arrangements.

Engine components are made of materials chosen for

their combination of strength, durability, weight, and

heat resistance (ability to maintain structural integrityover repeated heating and cooling cycles).


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Crankcase

The crankcase is the main structure of the engine which containsthe bearings for the crankshaft.

The crankcase is designed to house the crankshaft, camshafts,and lubricating oil.

Externally the crankcase must accommodate the cylinders and

peripheral or accessory components. Aircraft crankcases are usually made of cast or forged aluminum

alloy because of its lightweight and strength. (Forged steel is

used in some high output engines). The crankcase must be able to endure multidirectional forces,

vibration and extreme operating temperatures.


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Crankcase
http://upload.wikimedia.org/wikipedia/commons/a/ac/Cshaft.gif


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Crankshaft

The crankshaft transforms the reciprocating

(linear up and down) motion of the pistons intorotary force for the propeller.

The crankshaft is exposed to most of the forcesdeveloped by the engine.

The length of the crankshaft then becomes one

of the main limiting factors when designing anengine.
http://upload.wikimedia.org/wikipedia/commons/a/ac/Cshaft.gif


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Crankshaft


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Crankshaft Components

Main journal: rotates within the main bearing.

Rod journal: rotates within the connecting rodbearing.

Counterweight: used to balance the crankshaftand reduce vibration.


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Connecting Rod

The connecting rod connects the piston to the

crankshaft. It transmits forces between the piston and

crankshaft.


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Piston

The piston moves up and down within the

cylinder. It draws the fuel/air mixture into the cylinder and

drives the crankshaft on the downward stroke. It compresses the fuel/air mixture on the upward

stroke.


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Piston Rings

Piston rings fit into grooves on

the side of the piston and formthe seal between the piston and

cylinder wall.

The rings are designed with agap which is forced closed when

the piston is inserted into the

cylinder to form a spring loaded

seal.
http://upload.wikimedia.org/wikipedia/commons/9/93/Piston_rings.jpg


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Functions

Compression gas sealing: Piston rings

maintain gas compression between the pistonand cylinder wall. They prevent combustion gas

from escaping. A leak would cause a decreasein power.


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Functions

Lubricating oil film control: The cylinder walls

must be coated with a thin film of lubricating oil,to reduce friction, and prevent damage to the

cylinder and piston. The oil ring controls this thinfilm of oil.


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Functions

Piston support: piston rings help keep the

piston tracking properly within the cylinder. If thepiston were to incline within the cylinder and

touch the cylinder walls it would cause theengine to fail.


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Cylinders

The cylinder is the portion of the engine where the

power is developed. The cylinder forms the combustion chamber where the

fuel/air mixture is ignited and burned.

Factors affecting cylinder design: strong enough to withstand internal pressures.

lightweight construction.

heat-conducting properties for efficient cooling. easy and inexpensive to manufacture and maintain.
http://upload.wikimedia.org/wikipedia/commons/4/41/Newjug1.jpg


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http://upload.wikimedia.org/wikipedia/commons/4/41/Newjug1.jpg


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Cylinders

The cylinder heads of an air-cooled engine

house the intake and exhaust valves. The cylinder barrels house the piston and

connecting rod assembly. The cylinder head of an air-cooled engine is

usually made of aluminum alloy due to its heat

conductivity properties and light weight.


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Firing Order

The cylinders of a reciprocating engine are

always assigned numbers. The numbering theme varies depending on the

type of engine and the engine manufacturer.

The firing order is the sequence the firing of thecylinders occurs in.

The firing order of an engine is designated insuch a way as to reduce vibration.


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Valves

The fuel/air mixture or charge enters the

combustion chamber through the intake valvewhile the burned gases are expelled through the

exhaust valve. The valves are housed within the cylinder head.

Valves are subjected to extreme operating

conditions within the combustion chamber.


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http://upload.wikimedia.org/wikipedia/commons/d/d8/Pushrod2.PNG


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http://upload.wikimedia.org/wikipedia/commons/d/d8/Pushrod2.PNG


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Camshaft

Valve lift: the distance the valve is lifted off its

seat. Valve duration: the length of time the valve is

held open.

The camshaft is responsible for actuating thetappet, pushrod, and rocker arm assembly.

The shape of the cam lobes determine the valveduration and lift.
http://commons.wikimedia.org/wiki/Image:Cam-disc-3_frontview_animated.gifhttp://upload.wikimedia.org/wikipedia/commons/4/44/Nockenwelle_2005.jpghttp://upload.wikimedia.org/wikipedia/commons/2/26/Cam-disc-3_frontview_animated.gifhttp://upload.wikimedia.org/wikipedia/commons/5/58/Cam-disc-3_3D_animated.gif


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http://upload.wikimedia.org/wikipedia/commons/4/44/Nockenwelle_2005.jpghttp://upload.wikimedia.org/wikipedia/commons/2/26/Cam-disc-3_frontview_animated.gifhttp://upload.wikimedia.org/wikipedia/commons/5/58/Cam-disc-3_3D_animated.gif


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Camshaft

The camshaft is driven by a gear which is

directly connected to a gear attached to thecrankshaft.

The camshaft always rotates at half the speed of

the crankshaft.

This timing allows each piston to complete its

four-stroke cycle. (the valves will remain closedfor two of the four piston strokes)


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Bearings

Bearing: any surface which supports, or is

supported by another surface. Bearings are used within engines to reduce

friction between rotating components.

There are three distinct types of bearings:

Plain

Ball Roller


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Plain: designed to handle radial

loads. Used for the crankshaft, camshaft, connecting rods. Lubricated

through oil channels, or made of

self lubricating materials(bushings).

Roller: Can be designed to

withstand both radial and thrust

loads. Used for crankshafts is high

performance engines.

Ball: Used for superchargers

impeller shaft bearings, and some

rocker arm applications.


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REDUCTION GEARING

Propellers are efficient through a limited range of

rpm. Depending on engine output and propeller

design reduction gearing may be necessary.

Three common forms are:

Spur and pinion

Spur planetary Bevel planetary


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http://upload.wikimedia.org/wikipedia/commons/d/d5/Epicyclic_gear_ratios.png


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http://upload.wikimedia.org/wikipedia/commons/d/d5/Epicyclic_gear_ratios.pnghttp://upload.wikimedia.org/wikipedia/en/9/92/Epicyclic_carrier_locked.png


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Pictures\Gear Reduction.mpg
http://pictures/Gear%20Reduction.mpghttp://pictures/Gear%20Reduction.mpg

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