M15.7 (exhausts)

Question 1

On a turboprop engine how much thrust is provided by the exhaust system?

Answer 1

Only a small amount

Question 2

What is the purpose of the muffler?

Answer 2

To reduce noise coming from the exhaust

Question 3

What is the exhaust tube called?

Answer 3

Exhaust duct or tail pipe

Question 4

Where would you usually find a long exhaust duct?

Answer 4

Old a/c where engines are installed directly under the wing

Question 5

What’s the advantage of the common exhaust nozzle?

Answer 5

Gives a higher propulsion efficiency

Question 6

What is the disadvantage of the common exhaust nozzle?

Answer 6

Increase weight of the engine

Question 7

What are the 2 exhaust streams? And where do they come from?

Answer 7

Hot gas from primary nozzle
Cold fan air from secondary nozzle

Question 8

What does the exhaust gas mixer do?

Answer 8

Improves mixing of hot and cold gasses to get a higher proposition

Question 9

What’s the purpose of the exhaust cone?

Answer 9

Guides the discharge flow and prevents turbulence as well as gas re-ingestion

Question 10

What must happen to gas flow in the exhaust nozzle?

Answer 10

Must expand fully to give a laminar vortex free and axially oriented gas flow

Question 11

What is exhaust airflow caused by?

Answer 11

Pressure ratio between turbine discharge and ambient pressure

Question 12

Increasing engine speed does what to the pressure ratio?

Answer 12

Increases it

Question 13

What happens if you increase the pressure ratio too much?

Answer 13

It will get to a point where it’s impossible to get more air through the smallest area of the nozzle

Question 14

What is the maximum pressure ratio?

Answer 14

2:1

Question 15

What is chocked condition?

Answer 15

The smallest in the area of the nozzle the exhaust gas velocity equals the speed of sound

Question 16

When would a convergent duct be used?

Answer 16

When there’s a pressure ratio of more then 2:1

Question 17

Why must convergent dusts be variable?

Answer 17

Because their sensitive to changes in rpm

Question 18

What type of engines will you find high exhaust gasses?

Answer 18

Turbojet engines and old turbofan engines

Question 19

Why must high exhaust gasses be avoided?

Answer 19

Because they decrease the proposition efficacy

Question 20

Engine noise is expressed in what units?

Answer 20

EPNdb

Question 21

EPNdb?

Answer 21

Effective Perceived Noise deciBel

Question 22

How is a reduction of internal noise achieved?

Answer 22

By reducing the airflow disruption by optimising the number of blades and vanes in the compressor

Question 23

What is used in airflow linings to reduce noise and how is it achieved?

Answer 23

Honey comb acoustic liners that convert noise energy into heat energy

Question 24

What are the 2 types of noise absorbent liner?

Answer 24

Single layer liner
Double layer liner

Question 25

How can external noises be reduced?

Answer 25

If mixing with the atmosphere is performed in a short region done by increasing the contact area of the exhaust gas stream