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Aircraft > Aircraft Engines > Flashcards

Aircraft Engines Flashcards

1
Q

What are the 3 difference between a car’s piston engine and an a/c’s piston engine?

A

1) most are Air cooled
(saves weight and safer)

2) Duel ignition (2 independent magnetos and spark plugs)
3) Fuel/Air mix. (Manual control of fuel/Air ratio for high/low alt operations)

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2
Q

What are the 4 strokes of the engine?

A

Intake
Compression
Power
Exhaust

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3
Q

What are the 5 events for the piston engine?

A 
Intake
Compression 
Ignition
Power
Exhaust
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4
Q

Where is the piston at the end of the intake stroke?

A

At bottom dead centre (BDC)

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5
Q

Describe the induction phase.

A

Piston movies downwards, intake valve opens. Descending piston creates vacuum and draws in air-fuel mix

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6
Q

Describe the compression stroke

A

Both valves are closed, piston rises and compressed mixture.

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7
Q

When does the power stroke begin?

A

Before the piston reaches the top.

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8
Q

What happen in the ignition phase?

A

The spark plug ignites the mixture which forces the piston down turning the crank shaft.

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9
Q

What happens in the exhaust stroke?

A

Exhaust valve opens and the burned gassed escape , clearing the cylinder.

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10
Q

What is the carburettor?

A

A device which provides a suitable mixture of fuel to air to the cylinder for ignition

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11
Q

As Air passes through the venturi section, what 3 things happen?

A

1) Air accelerates
2) Air pressure drops
3) Causes fuel to be drawn through main jet where it mixes with air in the Venturi

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12
Q

Where is the fuel/Air mix fed to from the carburettor?

A

To each cylinder of the engine

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13
Q

Where the air accelerates the pressure drops and accompanied by an instant __________________

A

Air temperature drop

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14
Q

What is released when petrol changes from a liquid to a vapour?

A

Latent heat of Evaporation . This energy goes into the metal of the carburettor, cooling the air further.
The refrigeration effect.

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15
Q

What is a problem with the Venturi type of carburettors?

A

They are prone to icing.

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16
Q

How much may Air temperature drop by in the carburettor?

A

As much as 20 degrees

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17
Q

What happens if the water vapour in the carburettor turns to ice?

A

It may form around the fuel inlet, and throttle valve/Venturi tube chocking the engines air supply. Worst case stopping the engine.

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18
Q

What are the 3 precautions a pilot should take when flying in conditions likely to cause ice?

A

1) Avoid areas where icing is likely
2) Turn on carburettor heating system
3) During descents apply engine power frequently (keeps engine warm)

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19
Q

What conditions are likely to cause ice for a carburettor?

A

Flying through cloud

High humidity

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20
Q

What is Pitch?

A

The distance the propeller travels per turn.

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21
Q

What does a propeller provide?

A

Thrust (lift forwards)

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22
Q

What is blade pitch?

A

The angle made by the chord of the propeller blade and it’s plane of rotation

23
Q

When the pitch angle is great it is said to be a what pitch?

A

Coarse pitch

24
Q

When pitch angle is small it is said to be a

A

Fine pitch

25
Q

What is a coarse pitch used for?

A

Cruising

26
Q

What is fine pitch used for?

A

Take-off/climbing

27
Q

What is standard pitch?

A

Compromise between coarse and fine

28
Q

What is a variable pitch propeller?

A

Allows the pitch of the propeller to be altered by the pilot.

29
Q

What is reverse pitch?

A

A reverse pitch angle that generates reverse thrust.

30
Q

What propeller system creates reverse pitch?

A

Certain constant speed propellers

31
Q

Extra blades allow the power of the engine to be absorbed more efficiently. True or False?

A

True.

32
Q

What are the advantages of a piston engine?

5things

A
  • more efficient at low speeds
  • Faster initial acceleration than jet
  • Cheaper
  • Propwash over wings
  • immediate reaction to pilot input
33
Q

What are the disadvantages to a propeller engine?

A
  • limited to supersonic blade tip speed

- not as fast as jets

34
Q

Jet engines accelerates a small volume of air by a large amount.

True or False?

A

True.

35
Q

Force =

A

Mass x acceleration

F=MxA

36
Q

What are the basic parts of a jet engine?

A 
1 Air intake 
2 Compression stage 
3 Combustion Chamber 
4 Turbine Stage
5 Exhaust
37
Q

Describe briefly how a turbojet works

A

Air taken in

Compressed 3-12 times original pressure

Fuel added to air and burned in combustion chamber (1,100-1,300 F)

Hot air passes through turbine, driving compressor

Pressure discharged will twice the amount as air pressure.

Produces high velocity stream of gas creating thrust

38
Q

List some types of jet engines

7 in total

A 
Turbo jet (1st type) 
Low bypass turbofan 
High bypass turbofan 
Turboprop
Ram jet 
Scram Jet
Turbo shaft ( helicopter)
39
Q

What are the two types of compressors?

A

Centrifugal

Axial

40
Q

Describe a centrifugal flow compressor.

A

Uses an impeller to accelerate air and a diffuser to increase pressure. air leaves compressor at 90 degrees to flight direction. Must be turned back to combustion chamber.

41
Q

Describe an Axial flow compressor

A

Employs alternate rows of rotating blades to accelerate air. And stationary vanes (Stator) to diffuse air until pressure rise is obtained.

42
Q

Advantages of centrifugal flow compressor are:

4 things

A

Large frontal area
Simplicity
Ruggedness
Easy to make

43
Q

What are the advantages of the axial flow compressors?

A

Longer and thinner

Needs more stages to increase pressure

44
Q

Why was the turbo fan bypass engine built?

A

To increase efficiency and reduce noise by surrounding jet with a stream of slower moving air, bypassing the central core of the engine

45
Q

What are the advantages of a high bypass ratio?

3 things

A
  • more efficient
  • after burner (reignite gasses, more thrust)
  • further for less at high alt
46
Q

What are the disadvantages of high bypass ratio?

A
  • High cost

- longer to acceleration that piston engine

47
Q

What is a turboprop engine?

A

A jet engine attached to propellers.

48
Q

How does a turboprop work?

A

Turbine at the back is turned by the hot gases, this turns a shaft that drives the propeller via a gear box.

49
Q

What is needed to prevent the speed of turboprop propeller blades reaching supersonic levels?

A

Reduction gearing ratio of between 5:1 to 20:1

50
Q

What basic parts does a turboprop consist of?

A

Compressor
Combustion chamber
Turbine

51
Q

Turboprop has the best propulsion efficiency below 500mph compared to turbojet. True or False?

A

True

52
Q

What are the advantages of a turboprop engine?

4 things.

A
  • higher efficiency than jet at low levels
  • operate into shorter runways
  • propeller can be feathered to minimise drag
  • mechanically reliable
53
Q

What are the disadvantages of a turboprop?

A

Propeller loses efficiency at high altitude

High vibration levels (pax discomfort)

Enroute weather can cause problems

Older ones are slow

Pax discomfort due cruising level.

Aircraft (13 decks)

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