AIR SYSTEMS

Question 1

What subsystems fan engine air systems be divided into?

Answer 1

• Compressor control
• clearance control
• engine cooling

Question 2

What is the purpose of the compressor control sub-system?

Answer 2

Prevents the compressors from stall or surge in all operating conditions

Question 3

What does the clearance control system optimise?

Answer 3

Tip clearance between the rotor blades and stator casing to increase engine efficiency

Question 4

What 3 subsystems are contained within the compressor control system?

Answer 4

• variable bleed valve
• variable stator vane
• HP compressor bleed valve
  (Controlled by FADEC or hydro-mechanical fuel control unit)

Question 5

How is the airflow into the high pressure compressor controlled?

Answer 5

VBV’S

Question 6

What do VBV’S do?

Answer 6

Bleed some air off the LP compressor into the fan air discharge duct.
(Protects the LP compressor against stall and surge)

Question 7

What do all modern HP compressors have to control the airflow into the compressor?

Answer 7

Several stages of Variable stator vanes

Question 8

What are bleed valves at the HP compressor for?

Answer 8

Improve engine start and acceleration capabilities

Mid and aft stage of the HP compressor

Question 9

What is the main purpose of the clearance control system?

Answer 9

Match the expansion of the stator case with expansion of the engine rotor
(Found in LP, HP turbines and HP compressor)

Question 10

What are passive clearance control systems?

Answer 10

Use cooling airflow that cannot be switch off

Cannot optimise tip clearances for pal operating conditions

Question 11

What is active clearance control?

Answer 11

Cooling air control valves. Control the amount of air used to cool.

(Controlled by FADEC or hydro-mechanical fuel control units)

Question 12

What air do compressor clearance control systems use to heat the rotor?

Answer 12

Warm air. (Increasing expansion and reducing tip clearance)

Question 13

What can the engine cooling system be divided into?

Answer 13

External cooling system

Internal air system

Question 14

Where does the external cooling system supply air to?

Answer 14

Cavities between engine cowlings and engine cases.

Using ram air or fan air

Question 15

What does the internal air system do?

Answer 15

Covers all airflow below the engine rotors and at bearing compartments.

(Using air from LP and HP compressor)

Internal cooling.

Question 16

Where is some air from the internal air system used for sealing?

Answer 16

Some bearing compartments. (LP compressor bleed air)

Prevents oil escaping.

Question 17

What is pressure balancing a method of?

Answer 17

Release axial loads on the thrust bearings in the engine.

Mostly internal airflow used

Question 18

Where does the air for sealing bearing compartments exit?

Answer 18

Hollow N1 rotor shaft.

Question 19

What does pressure balancing do?

Answer 19

Minimises the axial loads on the rotor bearing.

Question 20

What does external cooling do?

Answer 20

Cools engine cases and all components in the fan and core compartment.

Prevents flammable vapours collecting in the engine.

Question 21

What do NACA air intakes in the lower part of the fan cowls do?

Answer 21

Pick up ram air when the aircraft moves and ventilates the fan compartment.

Question 22

How is the core compartment usually ventilated and cooled?

Answer 22

Fan air.

Question 23

What is bowed rotor?

Answer 23

An engine can bend after engine shutdown due to expansion between the upper and lower engine zones.

Question 24

What can a bowed rotor lead to?

Answer 24

A hung start or rotor wear.

Recommended there be a minimum waiting time between engine shutdown and engine start

Question 25

How is an engine only cooled after shutdown ?

Answer 25

Convection.

Lower part gets colder than upper part. Warmer air leaves out the upper zones.