M15.7

Question 1

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

Answer 1

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

Question 2

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

Answer 2

To safely guide the exhaust gases overboard

Question 3

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

Answer 3

Because most of the energy has gone into powering the turbines

Question 4

What is the job of the APU exhaust system?

Answer 4

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

Question 5

What does a muffler do in the exhaust system?

Answer 5

It reduces the noise

Question 6

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

Answer 6

It prevents excessive turbulence and prevents reverse flow

Question 7

What is the exhaust called for the hot gas flow?

Answer 7

Primary nozzle

Question 8

What is the exhaust called for the cold gas flow?

Answer 8

Secondary nozzle

Question 9

What is a combined exhaust nozzle?

Answer 9

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

Question 10

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

Answer 10

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

Question 11

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

Answer 11

The gases must expand completely in the exhaust nozzle

Question 12

How is the exhaust airflow caused?

Answer 12

By the pressure ratio between the turbine discharge and ambient pressure

Question 13

When would the pressure ratio of the exhaust change?

Answer 13

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

Question 14

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

Answer 14

2:1

Question 15

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

Answer 15

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

Question 16

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

Answer 16

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

Question 17

What type of aircraft use convergent-divergent nozzles?

Answer 17

Aircraft that fly faster than the speed of sound

Question 18

Why do most modern turbofan engines have large exhausts?

Answer 18

To prevent choking

Question 19

Why must high exhaust gas velocities be avoided?

Answer 19

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

Question 20

What is the unit commonly used to express noise?

Answer 20

Effective perceived noise decibel (EPNdB)

Question 21

What type of engine is the quietest?

Answer 21

High bypass ratio jets

Question 22

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

Answer 22

• selection of a design engine

- selection of dampening methods

Question 23

What are aircraft linings made from to reduce noise?

Answer 23

Porous surfaces supported by honeycomb structure

Question 24

Why is honeycomb used to reduce noise?

Answer 24

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

Question 25

What is a hush kit?

Answer 25

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

Question 26

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

Answer 26

It would cause major damage to the engine

Question 27

What is the normal angle of thrust reversers?

Answer 27

45-60 degrees

Question 28

Why can’t thrust reversers be used in flight?

Answer 28

Because it will cause very dangerous aerodynamics

Question 29

Where are clam shell door type thrust reversers used?

Answer 29

On older jet engines with low bypass ratios

Question 30

How are clamshell door thrust reversers operated?

Answer 30

By pneumatic bleed air from the high pressure compressor

Question 31

Where are bucket door type thrust reversers used?

Answer 31

On older jets with a low bypass ratio

Question 32

How are bucket door type reversers operated?

Answer 32

Hydraulically

Question 33

What are reverse thrusters that deflect cold air called?

Answer 33

Fan reversers

Question 34

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

Answer 34

Because it would need a lot of maintenance on them

Question 35

How are thrust reverser sleeves operated?

Answer 35

Pneumatically by drive motors or hydraulically by actuators

Question 36

How many doors does the pivoting door thrust reversers have?

Answer 36

4

Question 37

How are pivoting door thrust reversers operated?

Answer 37

Hydraulically

Question 38

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

Answer 38

Because the airflow through the engine will be disturbed

Question 39

Why is operating the thrust reversers at low speeds bad?

Answer 39

Because it can ingest its own reversed airflow

Question 40

What does ingestion from its own thrust reversers cause?

Answer 40

Severe compressor stall and high exhaust gas temperatures

Question 41

How would reverse thrusters flow affect FOD?

Answer 41

It kicks up dirt and dust from the runway

Question 42

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

Answer 42

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

Question 43

What is special about the inward airflow from thrust reversers?

Answer 43

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

Question 44

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

Answer 44

Don’t blow reversed air into the other engines

Question 45

What must happen to a faulty thrust reverser?

Answer 45

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

Question 46

What are the three main subsystems to a thrust reverser?

Answer 46

- control system - actuation system - airflow deflection system

Question 47

What is the control system for thrust reversers?

Answer 47

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

Question 48

What is the reverse actuation system?

Answer 48

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

Question 49

What is the airflow deflection system?

Answer 49

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

Question 50

What is the main component of the control system?

Answer 50

The reverse lever in the cockpit

Question 51

What is the reverse control system always protected by?

Answer 51

The air ground logic so it cant work in flight

Question 52

What is the reverse interlock system used for?

Answer 52

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

Question 53

Why must the hydraulic reverser systems be synchronised?

Answer 53

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

Question 54

Where are pneumatic reverser actuation systems only used on?

Answer 54

Translating sleeves

Question 55

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

Answer 55

An amber reverse unlock message

Question 56

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

Answer 56

When it is fully deployed and the throttle interlock is released