15.7 Exhaust

Question 1

What is the function of the exhaust on jet engines?

Answer 1

To accelerate airflow efficiently to generate thrust.

Question 2

What is the function of the exhausts on turboprop engines?

Answer 2

To safely guide exhaust gasses overboard.

Question 3

What is the function of the exhaust on the APU?

Answer 3

To guide gasses overboard as gas energy will be absorbed by the turbines.

Question 4

What does the APU have to reduce the noise of exhaust gasses?

Answer 4

Mufflers

Question 5

What are the features of the exhaust?

Answer 5

Exhaust cone.
Tailpipe.
Exhaust nozzle.

Question 6

What does the exhaust cone create?

Answer 6

A diverging passage between the outer duct and inner cone.

Question 7

The exhaust cone is made of an inner shell, outer shell and 3 to 4 radial hollow struts. What does the radial hollow struts do?

Answer 7

Aid the struts in supporting inner cone from the outer duct.

Question 8

What is another purpose of radial struts?

Answer 8

They also straighten swirling exhaust gasses.

Question 9

Why is there a small hole located in the exit tip of the exhaust core?

Answer 9

Allows cooling air to be circulated.

Question 10

What allows for movement in the installation, maintenance and thermal expansion of the tailpipe?

Answer 10

Bellow arrangement.

Question 11

What are the 2 methods of insulation in the tailpipe?

Answer 11

Blankets and shrouds.

Question 12

What are the 2 exhaust nozzle designs and when are they used?

Answer 12

Converging = subsonic.
Converging - diverging = supersonic.

Question 13

What is the effect does a converging nozzle increasing velocity have ?

Answer 13

It increases thrust by 15-20%.

Question 14

What amount of thrust does a turboprop exhaust nozzle provide?

Answer 14

Small amounts between 10-15%

Question 15

When is a variable exhaust nozzle used?

Answer 15

When an augmented or afterburner is used at supersonic speeds.

Question 16

How does a convergent nozzle reduce turbulence?

Answer 16

The exhaust nozzle and plug form a divergent duct before air flows through the convergent component.

Question 17

Why is converging - diverging nozzle used at supersonic speeds?

Answer 17

Due to a resulting higher pressure across the engine exhaust nozzle.

Question 18

What are common noise suppressors?

Answer 18

Integral or engine exhaust nozzle.

Question 19

What are the 3 sources of noise in an engine?

Answer 19

Air intake.
Vibration of engine housing.
Engine exhaust (loudest).

Question 20

What size engine is quieter?

Answer 20

A larger engine with greater mass flow of air.

Question 21

What are the 2 types of noise suppressors?

Answer 21

Perimeter type.
Multi tube type.

Question 22

What is in the engine nacelle for noise suppression?

Answer 22

A noise absorbing lining material which converts acoustic energy to heat.

Question 23

What does the noise absorbing lining consist of?

Answer 23

Porous skin.

Question 24

What is the purpose of thrust reversers?

Answer 24

To bring the aircraft to a rest.

Question 25

What effect do thrust reversers have on icy or snow covered runways?

Answer 25

They reduce the braking distance.

Question 26

What air do modern turbofan engines reverse?

Answer 26

Only fan airflow.

Question 27

Where can thrust reversers be used?

Answer 27

Only on the ground.

Question 28

What engines have a common exhaust nozzle for hot and cold air?

Answer 28

Turbofan engines with a low bypass ratio.

Question 29

Where is clamshell door thrust reverser found?

Answer 29

In front of exhaust nozzles.

Question 30

Where is the bucket door type thrust reverser found?

Answer 30

At the exhaust nozzle.

Question 31

The clamshell door and bucket door thrust reversers are used on what engines?

Answer 31

Older jet engines with a low bypass ratio.

Question 32

How are clamshell door thrust reversers operated?

Answer 32

Pneumatically by bleed air from the compressor.

Question 33

What is only found on the clamshell door thrust reverser to deflect air forwards?

Answer 33

Cascade vanes.

Question 34

How is the bucket door thrust reverser operated?

Answer 34

Hydraulically.

Question 35

On what engines are fan thrust reversers used?

Answer 35

On engines with a high bypass ratio.

Question 36

What is the most common fan thrust reversers?

Answer 36

A cascade type with translating sleeves.

Question 37

How are fan thrust reversers operated?

Answer 37

Pneumatically by drive motors or hydraulically by actuators.

Question 38

What is another type of fan thrust reverser?

Answer 38

Pivoting door thrust reverser.

Question 39

How is a pivoting door thrust reverser activated?

Answer 39

Hydraulically.

Question 40

What negative effects can thrust reverser operation have ?

Answer 40

Engine compressor can stall.
At low speeds they can inject its own reversed air.
FOD

Question 41

How are the negatives of thrust reverser operation minimised?

Answer 41

The reverser airflow is matched to engine position.

Question 42

What must be considered when operating thrust reversers on 4 engine aircraft?

Answer 42

Reversed airflow from the inner engine can be injected by the outer engine, if the distance between the engines is too small.

Question 43

When is thrust vectoring used?

Answer 43

On military aircraft for manoeuvring.