15.3 Inlet

Question 1

What are IGVs

Answer 1

Inlet Guide Vanes

Question 2

What is the purpose of IGVs?

Answer 2

To straighten airflow and direct it into the compressor first stage.

Question 3

What is the inlet duct a part of?

Answer 3

The airframe, not the engine.

Question 4

What happens to velocity, pressure and temperature at a divergent duct?

Answer 4

V decrease.
P increases.
T increases.

Question 5

What happens to velocity, pressure and temperature at a convergent duct?

Answer 5

V increases.
P decreases.
T decreases.

Question 6

How does supersonic air behave a convergent and divergent ducts?

Answer 6

Oppositely to subsonic air.

Question 7

On what engines can screens be found?

Answer 7

Turboprop and turboshaft.

Question 8

What is the purpose of screens?

Answer 8

They cover the inlet to prevent FOD.

Question 9

On what aircraft are divided entrance ducts found?

Answer 9

High speed military aircraft.

Question 10

What are the 2 types of divided ducts?

Answer 10

Wing root inlet or scoop inlet.

Question 11

What is the purpose of the turning vanes in the side scoop inlet?

Answer 11

They assist to straighten air preventing turbulence.

Question 12

What is the design drawback of divided entrance ducts?

Answer 12

Trying to design them to a reasonable length with as few bends as possible.

Question 13

Why is it difficult to obtain sufficient air scoop?

Answer 13

High drag.

Question 14

What is the problem with sudden flight manoeuvres for divided entrance ducts?

Answer 14

They cause imbalance in RAM air pressure between the 2 ducts, causing a slight power loss.

Question 15

What is the purpose of a variable geometry duct?

Answer 15

To provide the correct amount of air into the engine inlet.

Question 16

What is the purpose of the inlet duct of a variable geometry duct?

Answer 16

To act as a diffuser= divergent duct.

Question 17

What does the inlet duct of a variable geometry duct do to airs velocity and pressure?

Answer 17

V decreases.
P increases.

Question 18

What does the inlet duct of a variable geometry duct do to airs velocity and pressure?

Answer 18

V decreases.
P increases.

Question 19

How is the inlet of a variable geometry duct designed on a supersonic aircraft?

Answer 19

A sharp lip.

Question 20

What is the purpose of the variable geometry duct varying the inlet area?

Answer 20

To manipulate the normal shockwave to occur at intake.

Question 21

In relation to a variable geometry duct, what are the 3 methods to diffuse inlet air to slow air to subsonic speed?

Answer 21

Vary the inlet area.
Use variable airflow bypass arrangement.
A shockwave in the airstream.

Question 22

On what engines is a compressor inlet screen used?

Answer 22

Turboshaft and turboprop.

Question 23

What are the problems with the compressor inlet screen?

Answer 23

Causes loss in duct pressure.
Susceptible to icing.

Question 24

When is the retractable compressor inlet screen retracted?

Answer 24

After take off or in icing conditions.

Question 25

What is the problem with the retractable compressor inlet stage?

Answer 25

Prone to mechanical failure.

Question 26

When is the bell mouth compressor inlet used?

Answer 26

During testing only.

Question 27

What is the purpose of the bell mouth compressor inlet?

Answer 27

To obtain very high aerodynamic efficiency as duct loss is considered zero.

Question 28

What is the purpose of deflector doors in a turboprop and turboshaft compressor inlet?

Answer 28

To deflect ice and dirt away from the intake.

Question 29

What is the purpose to the conical spinner?

Answer 29

Doesn’t allow ice to build up.

Question 30

On what engines the conical spinner used?

Answer 30

Turboprop and turbofan.

Question 31

What is the purpose of the fan in turbofan engine inlet section?

Answer 31

Reduce engine damage due to FOD.

Question 32

What is used for inlet lip anti icing in a turbofan engine inlet section?

Answer 32

Warm bleed air draw from LP compressor of engine.

Question 33

What is used for turboprop inlet area anti icing?

Answer 33

Warm oil from the engine oil reservoir.

Question 34

What is used if only the engine cowls require anti icing?

Answer 34

Electrical heat strips.

Question 35

What is the thermal system subdivided into ?

Answer 35

Bleed air and electrical heating.

Question 36

On what engines is bleed air from the HP compressor used for anti icing?

Answer 36

On engines with high mass airflow.

Question 37

What does bleed air provide surface heating of?

Answer 37

IGVs, spinner, inlet lip.

Question 38

What is the purpose of anti ice valves?

Answer 38

Protect against over pressurisation and limit bleed air to prevent engine power loss.

Question 39

How can anti ice valves be operated?

Answer 39

Mechanically or automatically.

Question 40

When does the anti ice valve open?

Answer 40

When manually selected or when the ice is detected on the sensor.

Question 41

Anti icing valves are electrically selected, pressure operated and have cockpit indications for what?

Answer 41

Valve not in selected position. High pressure. Low pressure. High temperature. Low temperature.

Question 42

How is the regulator valve controlled?

Answer 42

Solenoid controlled.

Question 43

What function is available in case of valve or system failure?

Answer 43

Manual override.

Question 44

Anti icing with electronic engine control is controlled by what?

Answer 44

FADEC.

Question 45

What is the electro thermal anti icing system?

Answer 45

Electrical heat strips.

Question 46

When are electrical heat strips designed to operate?

Answer 46

When engine is running without air passing over it.

Question 47

What effect does increased aircraft speed have on thrust?

Answer 47

Decreases it.

Question 48

What is RAM recovery/ total pressure recovery?

Answer 48

Added pressure at engine inlet increases pressure and airflow to the engine.

Question 49

Why must a turbofan engine duct have a sufficiently straight section?

Answer 49

To ensure smooth airflow due to high airflow.