Aircraft Engines

Question 1

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

Answer 1

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)

Question 2

What are the 4 strokes of the engine?

Answer 2

Intake
Compression
Power
Exhaust

Question 3

What are the 5 events for the piston engine?

Answer 3

Intake
Compression 
Ignition
Power
Exhaust

Question 4

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

Answer 4

At bottom dead centre (BDC)

Question 5

Describe the induction phase.

Answer 5

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

Question 6

Describe the compression stroke

Answer 6

Both valves are closed, piston rises and compressed mixture.

Question 7

When does the power stroke begin?

Answer 7

Before the piston reaches the top.

Question 8

What happen in the ignition phase?

Answer 8

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

Question 9

What happens in the exhaust stroke?

Answer 9

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

Question 10

What is the carburettor?

Answer 10

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

Question 11

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

Answer 11

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

Question 12

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

Answer 12

To each cylinder of the engine

Question 13

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

Answer 13

Air temperature drop

Question 14

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

Answer 14

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

Question 15

What is a problem with the Venturi type of carburettors?

Answer 15

They are prone to icing.

Question 16

How much may Air temperature drop by in the carburettor?

Answer 16

As much as 20 degrees

Question 17

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

Answer 17

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

Question 18

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

Answer 18

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

Question 19

What conditions are likely to cause ice for a carburettor?

Answer 19

Flying through cloud

High humidity

Question 20

What is Pitch?

Answer 20

The distance the propeller travels per turn.

Question 21

What does a propeller provide?

Answer 21

Thrust (lift forwards)

Question 22

What is blade pitch?

Answer 22

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

Question 23

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

Answer 23

Coarse pitch

Question 24

When pitch angle is small it is said to be a

Answer 24

Fine pitch

Question 25

What is a coarse pitch used for?

Answer 25

Cruising

Question 26

What is fine pitch used for?

Answer 26

Take-off/climbing

Question 27

What is standard pitch?

Answer 27

Compromise between coarse and fine

Question 28

What is a variable pitch propeller?

Answer 28

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

Question 29

What is reverse pitch?

Answer 29

A reverse pitch angle that generates reverse thrust.

Question 30

What propeller system creates reverse pitch?

Answer 30

Certain constant speed propellers

Question 31

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

Answer 31

True.

Question 32

What are the advantages of a piston engine? | 5things

Answer 32

- more efficient at low speeds - Faster initial acceleration than jet - Cheaper - Propwash over wings - immediate reaction to pilot input

Question 33

What are the disadvantages to a propeller engine?

Answer 33

- limited to supersonic blade tip speed | - not as fast as jets

Question 34

Jet engines accelerates a small volume of air by a large amount. True or False?

Answer 34

True.

Question 35

Force =

Answer 35

Mass x acceleration F=MxA

Question 36

What are the basic parts of a jet engine?

Answer 36

``` 1 Air intake 2 Compression stage 3 Combustion Chamber 4 Turbine Stage 5 Exhaust ```

Question 37

Describe briefly how a turbojet works

Answer 37

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

Question 38

List some types of jet engines | 7 in total

Answer 38

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

Question 39

What are the two types of compressors?

Answer 39

Centrifugal | Axial

Question 40

Describe a centrifugal flow compressor.

Answer 40

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.

Question 41

Describe an Axial flow compressor

Answer 41

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

Question 42

Advantages of centrifugal flow compressor are: | 4 things

Answer 42

Large frontal area Simplicity Ruggedness Easy to make

Question 43

What are the advantages of the axial flow compressors?

Answer 43

Longer and thinner | Needs more stages to increase pressure

Question 44

Why was the turbo fan bypass engine built?

Answer 44

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

Question 45

What are the advantages of a high bypass ratio? | 3 things

Answer 45

- more efficient - after burner (reignite gasses, more thrust) - further for less at high alt

Question 46

What are the disadvantages of high bypass ratio?

Answer 46

- High cost | - longer to acceleration that piston engine

Question 47

What is a turboprop engine?

Answer 47

A jet engine attached to propellers.

Question 48

How does a turboprop work?

Answer 48

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

Question 49

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

Answer 49

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

Question 50

What basic parts does a turboprop consist of?

Answer 50

Compressor Combustion chamber Turbine

Question 51

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

Answer 51

True

Question 52

What are the advantages of a turboprop engine? | 4 things.

Answer 52

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

Question 53

What are the disadvantages of a turboprop?

Answer 53

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.