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CAA Module 15 > Module 15.7 Exhaust > Flashcards

Module 15.7 Exhaust Flashcards

1
Q

What is the main task of the exhaust?

A

Accelerate the airflow coming from the turbine to efficiently generate thrust.

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2
Q

What are the components of the exhaust?

A

Exhaust cone, tailpipe, and the exhaust nozzle.

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3
Q

What does the exhaust cone do?

A

Collects the exhaust gases (swirling flow) from the turbine section and gradually converts them into a solid flow of gases.

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4
Q

What happens to the pressure and velocity of the air at the first part of the exhaust nozzle and why?

A

Velocity decreases and pressure increases.

Because of the diverging passage between the outer duct and the inner cone.

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5
Q

What does the exhaust cone assembly consist of?

A

An outer shell (duct), inner cone, radial struts and tie rods.

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6
Q

What is the outer shell (duct) attached to?

A

The rear flange of the turbine case.

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7
Q

Are the struts solid or hollow?

A

Hollow

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8
Q

How are the struts secured in their position?

A

Welded to the inside surface of the duct and the inner cone.

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9
Q

What do the radial struts do?

A

Provide support and straighten the swirling exhaust gases.

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10
Q

Why does the exit tip of the cone have a small hole?

A

To allow cooling air to be circulated into the interior of the cone.

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11
Q

Is the tailpipe flexible or semi-flexible?

A

Semi-flexible

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12
Q

What do the insulation blankets consist of?

A

Layers of aluminium foil separated by a layer of fibreglass.

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13
Q

What do the insulation blankets do?

A

Protect the fuselage from heat radiation and reduce heat loss from the exhaust system.

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14
Q

What are the two types of exhaust nozzles?

A

Converging

Converging-diverging

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15
Q

What type of duct do supersonic subsonic gas velocities use?

A

Converging-diverging

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16
Q

What type of duct do subsonic subsonic gas velocities use?

A

Converging

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17
Q

What types of duct turbofan engines are there?

A

Ducted and unducted

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18
Q

What are ducted fan engines?

A

An engine that takes the fan airflow and directs it through closed ducts along the engine.

The core exhaust flow and the fan flow mix at the rear and flow from the engine through the nozzle.

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19
Q

What are unducted fan engines?

A

An engine with two nozzles. one for the fan airflow and one for the core airflow.

Both flows release into ambient air separately.

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20
Q

When is a variable exhaust nozzle used?

A

When an augmenter or afterburner is used.

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21
Q

Why do augmenters or afterburners need a variable exhaust nozzle?

A

Due to the increased mass of flow when the afterburner is activated.

22
Q

When does the variable exhaust nozzle open and close?

A

Opens when the afterburner is selected. Closes when it’s off.

23
Q

What happens to the pressure and velocity of the air at the second part of the exhaust nozzle and why?

A

Velocity increases and pressure decreases because of the convergent exhaust nozzle.

24
Q

What happens in a convergent-divergent exhaust nozzle?

A

Subsonic airflow in the convergent part decreases in pressure and increases in velocity until it reaches supersonic.

At the divergent part, the supersonic flow increases in velocity further and creates the thrust.

25
Q

What are the sources of noise on the engine?

A

The fan, compressor and exhaust discharge.

26
Q

What is exhaust noise caused by?

A

A high degree of turbulence of a high-velocity jet stream moving through a relatively quiet atmosphere.

27
Q

Are turbojet or turbofan engines louder during take off?

A

Turbojet

28
Q

Why are turbofan engines quieter than turbojet engines during take-off?

A

The exhaust gas velocities ejected at the engine tailpipe are slower.

29
Q

How is noise reduction for a turbojet done?

A

By changing the noise pattern or the frequency of the noise emitted by the jet nozzle.

30
Q

What typical noise suppressors are current in use?

A

Corrugated perimeter type

Multi-tube type

31
Q

How do noise suppressors work?

A

They break up the single main jet exhaust stream into several smaller jet streams.

32
Q

How does the nacelle also reduce noise?

A

The cowl has acoustic linings surrounding the engine.

33
Q

What do thrust reversers do?

A

Reduce the braking distance.

34
Q

How does the nacelle cowl acoustic linings reduce noise?

A

It converts acoustic energy into heat.

35
Q

How do thrust reversers produce braking force?

A

By deflecting the exhaust gas stream in the opposite direction. This deflection causes a thrust force opposite to the direction of movement.

36
Q

What airflow is reversed on turbofans engines with a high bypass ratio?

A

Only the fan airflow is reversed because this airflow creates most of the engine thrust.

37
Q

When can thrust reversers be used?

A

Only on the ground?

38
Q

Where are clamshell type reversers installed?

A

In front of the exhaust nozzle.

39
Q

Where are bucket type reversers installed?

A

At the rear of the exhaust nozzle.

40
Q

Which aircraft use clamshell and bucket type reversers?

A

Older jet engines with a low bypass ratio.

41
Q

How is the clamshell type reverser operated?

A

Pneumatically operated by bleed air from the HP compressor.

42
Q

How are bucket type thrust reversers operated?

A

Hydraulically

43
Q

How does a fan reverser work?

A

The translating sleeves move rearwards and uncover the cascade vanes.

Blocker doors close off the fan discharge duct so that all the fan air can only discharge through the cascade vanes.

44
Q

How are fan thrust reversers operated?

A

Pneumatically or hydraulically.

45
Q

How are pivoting door reversers actuated?

A

Hydraulically

46
Q

What engines use pivoting door engines?

A

Modern turbofan engines.

47
Q

When are thrust reversers most efficient?

A

At high speed shortly after touchdown.

48
Q

What can happen to the reversers gas stream as the aircraft slows down?

A

It can get to the front of the engine.

49
Q

If the reversed flow from the reverser gets ingested what can happen?

A

Severe compressor stalls and high exhaust gas temperatures.

50
Q

Why do military aircraft use thrust vectoring?

A

To change direction.

CAA Module 15 (18 decks)

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