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M15 > 15.7 > Flashcards

15.7 Flashcards

1
Q

In simple terms, what does the exhaust do?

A

Guides gases from rear of turbine into atmosphere

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2
Q

The exhaust nozzle does what?

A

Accelerates exhaust gases which leave the engine

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3
Q

What does the exhaust cone do?

A

Guides the discharge flow and prevents excessive turbulence of gases
Additionally stops reverse flow

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4
Q

Advantage of common exhaust nozzle?

A

Reduces high gas velocities of hot gas

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5
Q

Disadvantage of common exhaust nozzles is what?

A

Increases the weight of the engine

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6
Q

What do mixers do?

A

Mix hot and cold gas flow to get higher propulsion properties

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7
Q

Disadvantage of mixers?

A

Add weight

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8
Q

Why must exhaust gases expand completely in exhaust nozzles?

A

To achieve optimum thrust from a given mass

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9
Q

The exhaust airflow is caused by the pressure ratio between what?

A

Turbine discharge and ambient temperature

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10
Q

Increasing pressure ratio eventually leads to what?

A

To a point where it is impossible to get more air through the smallest area of the nozzle

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11
Q

Convergent exhaust nozzles reach max airflow at pressure ratios of what?

A

Approx 2:1

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12
Q

The choked condition means what?

A

Means that in the smallest area of the nozzle, exhaust gas velocity equals speed of sound

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13
Q

Convergent divergent nozzles are used for pressure ratios of more than what?

A

2:1

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14
Q

C-D nozzles are only necessary for a/c that fly at what speed?

A

Faster than speed of sound

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15
Q

Convergent duct is used for what speed?

A

Sub sonic

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16
Q

Convergent divergent nozzles are used for what speeds?

A

Supersonic

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17
Q

What is the unit used to express noise?

A

Effective perceived noise decibel (EPNdB)

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18
Q

Noise is minimised how?

A

Reducing airflow disruption which causes turbulence

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19
Q

How is reduction of noise achieved?

A

Optimising numbers of blades and vanes in compressor
Noise absorbent materials

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20
Q

Noise absorbent materials convert sound energy to what?

A

Heat energy

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21
Q

When air leaves the engine, how does the exit nozzle size correlate to sound?

A

The larger the exit nozzle the lower the sound

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22
Q

Noise of exhaust jet decreases with what?

A

Decreasing outlet velocity
Achieved by high bypass ratio

23
Q

What do thrust reversers do?

A

Produce the braking force by deflecting the exhaust gas stream to the opposite direction

24
Q

What is the ideal deflection degree?
Why don’t we use this and what is the actual degree?

A

180 to completely reserve thrust
We only use 45-60 as anything more would cause major issues for engine

25
Q

What type of reverser is installed on older jet engine?

A

Clamshell door type

26
Q

How is a clamshell door type reverser operated?

A

Pneumatically operated by HP compressor

27
Q

How is a bucket door type reverser operated?

A

Hydraulically operated

28
Q

On modern turbofan engine with high bypass ratio, what type of air is deflected to give reverse thrust?
What is this called?

A

Only cold air
Called fan reverser

29
Q

How are pivoting type doors actuated?

A

Hydraulically

30
Q

What are some effects of thrust reverser operation?

A

-Engine compressor can stall as airflow in engine is disturbed by deployed reverser
-Most efficient at high speeds, at touchdown, reverser gas stream is deflected by ambient airflow
-at very low speeds, the engine can ingest its own reversed airflow

31
Q

How are disadvantages minimised for thrust reverser operation?

A

The reversed airflow is matched to engine position

32
Q

What is significant about thrust reversers on four engine aircraft?

A

The angle of reverse stream is more important as as reversed airflow of inner engines can be ingested by the outer engines

33
Q

If distance between engines is large enough what effect does reverse airflow have on neighbouring engines?

A

No effect

34
Q

Can faulty thrust reversers be released to service?

A

Yes
As they are just additional braking

35
Q

What is used to activate thrust reversers and increase engine power for reverse thrust?

A

Control system

36
Q

What is the reverser actuation system?

A

Made up of pneumatic and hydraulic components
Moves airflow deflection mechanism by signals from the reverser control system

37
Q

What does the airflow deflection system do?

A

Directs airflow in the optimum direction for safe reverse thrust

38
Q

How does the thrust reverser lever work?

A

When pulled a reverser control switch below control pedestal is activated
-used to start reverser operation and control direction of thrust reverser movement

39
Q

Where is the thrust reverser lever located?

A

In cockpit

40
Q

Thrust reverser lever is always protected by what?

A

Air ground logic

41
Q

What does the air ground logic do?

A

Ensures thrust reversers aren’t deployed during flight

42
Q

What is the thrust reverser interlock?

A

Sub system of reverser control system
Ensures engine power can only be increased after reverser is fully deployed

43
Q

Where is the thrust reverser actuation system located?

A

Located on reversers with large blocker doors

44
Q

All thrust reversers must have what to ensure reversers are kept safe in stowed position?

A

Locking system

45
Q

When a reverser door is stowed, the hook of the latch mechanism does what?

A

Secures the blocker door in the stowed position

46
Q

Where is airflow deflection system found?

A

Found in reverser cowling

47
Q

What is the airflow deflection system made up of?

A

A fixed part
A movable part
Translating sleeve

48
Q

Blocker doors move with movement of what?

A

Translating sleeve

49
Q

The cascade vane segments are bolted together to what?

A

A fixed part of reverser cowling

50
Q

Different angles of cascade segments?

A

Some deflect 45 degrees upwards
Some 45 degrees downwards
Some 90 degrees straight out of fan air duct
Some segments blocked

51
Q

The case case segments do what to direction of airflow?

A

Direct it away from aircraft structure and to the ground

52
Q

Reverse unlock messages indicate what?
What colour light?

A

Reverser is not safe in stowed position
Amber light

53
Q

A green reverse light indicates what?

A

Reverser is fully deployed and throttle interlock is released so that engine power can be increase for reverse thrust

M15 (18 decks)

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