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M15 > M15.7 > Flashcards

M15.7 Flashcards

1
Q

What is the main job of the exhaust on a jet engine?

A

To accelerate the airflow coming from the turbine to efficiency make thrust

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2
Q

What is the main job of the exhaust on a turbo-prop?

A

To safely guide the exhaust gases overboard

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3
Q

Why does the exhaust system only make a small amount of thrust?

A

Because most of the energy has gone into powering the turbines

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4
Q

What is the job of the APU exhaust system?

A

It guides all gases overboard because all the energy has gone into the turbine

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5
Q

What does a muffler do in the exhaust system?

A

It reduces the noise

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6
Q

Why do some exhaust systems have a tube called the exhaust duct or tall pip?

A

It prevents excessive turbulence and prevents reverse flow

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7
Q

What is the exhaust called for the hot gas flow?

A

Primary nozzle

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8
Q

What is the exhaust called for the cold gas flow?

A

Secondary nozzle

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9
Q

What is a combined exhaust nozzle?

A

A larger exhaust that mixes the hot and cold exhaust gases which gives a higher propulsion efficiency

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10
Q

Why would a special mixer be used on the exhaust system?

A

To get a higher propulsion efficiency compared to the combined exhaust nozzle

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11
Q

To achieve optimum thrust from a given mass what must happen in the exhaust?

A

The gases must expand completely in the exhaust nozzle

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12
Q

How is the exhaust airflow caused?

A

By the pressure ratio between the turbine discharge and ambient pressure

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13
Q

When would the pressure ratio of the exhaust change?

A

When the engine speed changes (increase in speed gives an increase in ratio)

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14
Q

What is the highest pressure ratio a convergent exhaust can go up to?

A

2:1

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15
Q

What happens if the pressure ratio of the exhaust is too high?

A

The static pressure is greater than the ambient pressure which causes a burst in all direction which is very inefficient

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16
Q

What are used for pressure ratio exhausts higher than 2:1?

A

A convergent-divergent nozzle (also called C-D nozzles)

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17
Q

What type of aircraft use convergent-divergent nozzles?

A

Aircraft that fly faster than the speed of sound

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18
Q

Why do most modern turbofan engines have large exhausts?

A

To prevent choking

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19
Q

Why must high exhaust gas velocities be avoided?

A

Because they decrease propulsion efficiency, cause great turbulence, and therefore make a loud exhaust noise

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20
Q

What is the unit commonly used to express noise?

A

Effective perceived noise decibel (EPNdB)

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21
Q

What type of engine is the quietest?

A

High bypass ratio jets

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22
Q

What are the two methods used to reduce noise level of an engine?

A
  • selection of a design engine

- selection of dampening methods

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23
Q

What are aircraft linings made from to reduce noise?

A

Porous surfaces supported by honeycomb structure

24
Q

Why is honeycomb used to reduce noise?

A

It allows sound to waves to be reflected in the chambers which converts sound energy into heat energy

25
Q

What is a hush kit?

A

It mixes ambient air to the exhaust gas before it enters the nozzle to reduce noise

26
Q

Why cant thrust reversers be used at the ideal angle of 180 degrees?

A

It would cause major damage to the engine

27
Q

What is the normal angle of thrust reversers?

A

45-60 degrees

28
Q

Why can’t thrust reversers be used in flight?

A

Because it will cause very dangerous aerodynamics

29
Q

Where are clam shell door type thrust reversers used?

A

On older jet engines with low bypass ratios

30
Q

How are clamshell door thrust reversers operated?

A

By pneumatic bleed air from the high pressure compressor

31
Q

Where are bucket door type thrust reversers used?

A

On older jets with a low bypass ratio

32
Q

How are bucket door type reversers operated?

A

Hydraulically

33
Q

What are reverse thrusters that deflect cold air called?

A

Fan reversers

34
Q

Why are reverse thruster not used on the hot core of the engine?

A

Because it would need a lot of maintenance on them

35
Q

How are thrust reverser sleeves operated?

A

Pneumatically by drive motors or hydraulically by actuators

36
Q

How many doors does the pivoting door thrust reversers have?

A

4

37
Q

How are pivoting door thrust reversers operated?

A

Hydraulically

38
Q

Why would the engine compressor sometimes stall when thrust reversers are deployed?

A

Because the airflow through the engine will be disturbed

39
Q

Why is operating the thrust reversers at low speeds bad?

A

Because it can ingest its own reversed airflow

40
Q

What does ingestion from its own thrust reversers cause?

A

Severe compressor stall and high exhaust gas temperatures

41
Q

How would reverse thrusters flow affect FOD?

A

It kicks up dirt and dust from the runway

42
Q

On some aircraft reversed airflow causes air cushions, why is this bad?

A

It decreases the load on the main landing gear which decreases brake efficiency

43
Q

What is special about the inward airflow from thrust reversers?

A

They don’t direct the airflow into the wheel wells or into the group to whirl up dirt

44
Q

What is important to remember about a four engine aircraft thrust reverser system?

A

Don’t blow reversed air into the other engines

45
Q

What must happen to a faulty thrust reverser?

A

It must be reactive properly so it doesn’t deploy in flight

46
Q

What are the three main subsystems to a thrust reverser?

A
  • control system
  • actuation system
  • airflow deflection system
47
Q

What is the control system for thrust reversers?

A

To activate the thrust reversers and to increase the engine power for reverse thrust

48
Q

What is the reverse actuation system?

A

It moves the airflow deflection mechanism by signals from the reverser control system

49
Q

What is the airflow deflection system?

A

It directs the airflow in the optimum direction for safe reverse thrust

50
Q

What is the main component of the control system?

A

The reverse lever in the cockpit

51
Q

What is the reverse control system always protected by?

A

The air ground logic so it cant work in flight

52
Q

What is the reverse interlock system used for?

A

It makes sure that the engine power can only be increased when the reverser are fully deployed

53
Q

Why must the hydraulic reverser systems be synchronised?

A

So they all deploy at the same time to prevent uneven reverse thrust

54
Q

Where are pneumatic reverser actuation systems only used on?

A

Translating sleeves

55
Q

What is the indication in the cockpit that the thrust reversers aren’t in the stowed position?

A

An amber reverse unlock message

56
Q

When would a green reverse light come up in the cockpit?

A

When it is fully deployed and the throttle interlock is released

M15 (15 decks)

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