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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 system on a jet engine?

A

Accelerate airflow from the turbine to generate thrust

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2
Q

What is the main task of the exhaust on a turboprop and APU?

A

Exhaust gases overboard

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3
Q

What is an additional feature of an APU exhaust?

A

Mufflers, for noise reduction

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4
Q

What are the components of the exhaust section?

A
  • Exhaust cone
  • Tailpipe
  • Exhaust nozzle
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5
Q

The exhaust cone is what, to decrease velocity and increase the static pressure?

A

Diverging

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6
Q

What does the exhaust cone assembly consist of?

A
  • Outer shell
  • Inner cone
  • Hollow struts (sole support for the inner cone)
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7
Q

What are the purposes of the radial struts in the exhaust?

A
  • Support the inner cone by connecting it to the outer shell
  • Straighten out airflow from the low pressure turbine
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8
Q

How is the tail pipe usually constructed?

A

Semi-flexible

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9
Q

What does the bellow arrangement allow for?

A

Movement in installation, maintenance and thermal expansion

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10
Q

What are the two methods for protecting the fuselage structure?

A
  • Insulation blankets
  • Shrouds
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11
Q

What are the two types of exhaust nozzle design?

A
  • Converging (Subsonic)
  • Converging-diverging (Supersonic)
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12
Q

What effect does a converging nozzle have on exhaust gases?

A

Increase in velocity, causing an increase in thrust (15-20%)

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13
Q

What are the two types of exhaust nozzle?

A
  • Fixed
  • Variable
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14
Q

When is a variable area nozzle used?

A

When there is an augmenter or afterburner.

Supersonic aircraft, making it divergent allows for supersonic airflow. As after mach 1 divergent ducts increase velocity and decrease static pressure, convergent have the opposite effect

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15
Q

What effect does changing the area/diameter of the exhaust nozzle have?

A
  • Engine performance
  • Exhaust Gas Temperature (EGT)
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16
Q

What section of a convergent-divergent exhaust handles air at subsonic speed?

A

Convergent

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17
Q

GTE’s require what for operations in airports or high population areas?

A

Noise suppression

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18
Q

What are the 3 sources of GTE noise?

A
  • Air intake
  • Engine housing vibration
  • Engine exhaust (by far the most)
19
Q

Noise levels vary with what?

A

Engine thrust

20
Q

Why is a turbofan engine quieter than a turbojet?

A
  • Slower moving cooler air
  • Greater mass flow of air
21
Q

What are the two types of noise suppressor?

A
  • Corrugated perimeter
  • Multitube
22
Q

What does the noise absorbing lining convert acoustic energy into?

A

Heat

23
Q

What does the noise absorbing lining consist of?

A

Porous skin supported by honeycomb backing

24
Q

What do thrust reversers do once operated?

A

Reduce braking distance

25
Q

How does a thrust reverser provide braking force?

A

Deflecting exhaust gas stream in the opposite direction

26
Q

What airflow is reversed in a high-bypass turbofan engine?

A

Fan air

27
Q

When would a bucket type reverser be used?

A

Low-bypass engines

28
Q

What do turbofans with a low-bypass ratio usually have?

A

A common exhaust nozzle

29
Q

Where are clamshell reversers located on a low-bypass engine?

A

In front of the exhaust nozzle

30
Q

Where are the bucket-type reversers located?

A

After the exhaust nozzle

31
Q

In clamshell reversers, what do exit ducts have?

A

Cascade vanes

32
Q

How are clamshell reversers operated?

A

Pneumatically

33
Q

What are fan reversers?

A

Cascade type reversers with translating sleeves

34
Q

How may fan reversers be operated?

A
  • Hydraulically
  • Pneumatically
35
Q

What moves rearwards when the thrust reversers are activated in the cockpit?

A

Translating sleeve

36
Q

What closes off the fan discharge duct?

A

Blocker doors

37
Q

How are pivoting door type reversers activated?

A

Hydraulically

38
Q

What are some effects of reversers?

A
  • Engine compressor can surge and stall
  • At very low aircraft speeds the engine can ingest its own reversed airflow
  • FOD ingestion
38
Q

Where are pivot doors reversers when they are not activated?

A

Flush with the cowling

39
Q

How are the disadvantages of reversers minimised?

A

Reversed airflow is matched to the engine position

40
Q

On four engine aircraft, why is the angle of reverse stream more important?

A

Airflow from inner engines can be ingested by outer engines

41
Q

How is thrust vectoring accomplished?

A

Relocating/moving the exhaust nozzle

42
Q

The inward-pointing airflow is directed at such an angle that it cannot blow into what?

A

Main wheel well

43
Q

If the engines are far enough apart that the reverse flow does not effect the adjacent engines, what is an advantage of this configuration?

A

All engines can have the same cowlings, meaning fewer parts

CAA Module 15 (18 decks)

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