15.7

Question 1

What colour do thrust reverser switches go when it’s not locked into position?
When it’s fully deployed?

Answer 1

Not locked Amber
Deployed Green

Question 2

What do cascade segments in thrust reverser do

Answer 2

Reverse the airflow away from any ac structure

Question 3

What type of thrust reverser systems use pneumatic reverser systems

Answer 3

Cascade type with translating sleeves

Question 4

What does the thrust reverser interlock do

Answer 4

Makes sure that engine power can only be increased after reversers are fully deployed

Question 5

When can thrust reversers be deployed

Answer 5

When alt is below 10 feet

Question 6

What do the following thrust reverser systems do
Control system
Actuation system
Airflow deflection system

Answer 6

Control= activates thrust reversers and can increase the engine power for reverse thrust
Actuation= pneumatic or hydraulic components that move the air deflection systems
Airflow deflection= deflects air into the optimum direction

Question 7

What advantage do thrust reverser cowlings on large with ac have

Answer 7

All engines have the same cowling so less spares are required

Question 8

What ac fly with faulty thrust reverser

Answer 8

Yes

Question 9

What’s important for installation of thrust reverser cowling on multiple engine ac

Answer 9

They have specific cowlings that have cascade vanes in certain positions to prevent airflow getting sucked back into the other engines so they must be rearranged

Question 10

Why is the angle that thrust reverser streams more important on 4 engine ac

Answer 10

Because it may be ingested by other engine

Question 11

How’s the disadvantages if thrust reverser engines minimised

Answer 11

By matching the reverse airflow to the engine position

Question 12

What are disadvantages of thrust reversers

Answer 12

Can cause compressor stall
Only efficient at high speeds
At slow speeds it can re ingest its reverse airflow
Can suck of FOD
Can cause an air cushion below the wing which would decrease the load on the wheels meaning the brake efficiency decreases

Question 13

What type of thrust reversers are fan reversers and how are they operated

Answer 13

Cascade type
Pneumatic and hydraulic

Question 14

What’s used on modern ac turbofan engines to give thrust reverse

Answer 14

Secondary air (cold fan air)

Question 15

Are bucket thrust reversers installed on ac with a low or high bypass ratio and how are they operated

Answer 15

Low bypass
Hydraulically

Question 16

Are clamshell thrust reversers installed on ac with high or low bypass ratio and how are they operated

Answer 16

Low
Pneumatic

Question 17

What angle is the thrust reversers usually operated at ( angle of reverse stream )

Answer 17

45-60 degrees

Question 18

What degree angle would be the most efficient for ac and why isn’t it used

Answer 18

180
Causes major issues for engine operation through gas recirculatiion and FOD damage

Question 19

How can ambient air be used to make thrust reversers quieter

Answer 19

Can be mixed with the ambient air before it leaves the exhaust

Question 20

How can external noise be reduced (jet noise)

Answer 20

By increasing the contact area of the exhaust gas stream with the atmosphere

Question 21

What do honeycomb sound reductions convert the sound energy into

Answer 21

Heat energy

Question 22

What two things can be done to reduce internal noise

Answer 22

Acoustic linings
Optimising number of blades and vanes and the distance between these components

Question 23

What unit is commonly used to express ac noise

Answer 23

EPNDB ( effective perceived noise decibels)

Question 24

Why should High exhaust gas velocities be avoided

Answer 24

They would decrease propulsion efficiency

Question 25

What happens when airflow exceeds max pressure ratios

Answer 25

Static pressure increases ans will cause exhaust jet gasses to burst rapidly in a,, directions making it very inefficient

Question 26

When are convergent-divergent nozzles used (what pressure ratio)

Answer 26

2:1

Question 27

What’s the choked condition

Answer 27

It’s the smallest part of the exhaust nozzle and the exhaust gas velocity is equal to the speed of sound

Question 28

What’s the max pressure ratio of a convergent exhaust

Answer 28

2:1

Question 29

How can exhaust pressure ratios be increased

Answer 29

By speeding up the ac

Question 30

What two things make up an exhaust pressure ratio

Answer 30

The ratio of the turbine discharge to the ambient air

Question 31

To achieve optimum thrust where must the exhaust gasses expand (in or aft the exhaust nozzle)

Answer 31

In the exhaust nozzle

Question 32

What does the special exhaust gas mixer provide

Answer 32

Mixes the hot and cold air to get higher propulsion efficiency

Question 33

What’s an advantage and disadvantage if common exhaust nozzles

Answer 33

Reduces high exhaust gas velocities by mixing the two gas flows which would then give it a better propulsion (+)

Increased weight

Question 34

What air goes through the primary nozzle and what air goes through the secondary nozzle ( hot and cold)

Answer 34

Hot
Cold

Question 35

What does the exhaust cone help to reduce and guide

Answer 35

Guides discharge flow
Prevents excessive turbulence and reverse flow

Question 36

What’s the tube attached to the exhaust system called

Answer 36

Exhaust duct or tail pipe

Question 37

What does the apu exhaust system use to reduce noises from the exhaust

Answer 37

Mufflers

Question 38

What other purposes does jet engine exhaust systems have

Answer 38

Accelerates airflow owing to the turbine to efficiently make thrust

Question 39

What’s the function of an exhaust system

Answer 39

Guides exhaust gasses from rear turbine to atmosphere