15.12 Air Systems

Question 1

Where is the hottest section of an engine?

Answer 1

Around the turbines

Question 2

What is the cooling purpose of secondary air ?

Answer 2

Cools the combustion chamber liners

Question 3

What does the construction of the combustion chamber liners force the formation of ?

Answer 3

A fast moving film of air moving over both inner and outer surfaces of the liner

Question 4

Other than oil, what else do some engines use to cool bearings ?

Answer 4

Air

Question 5

Where is secondary cooling air tapped from and where is this air provided to ?

Answer 5

Tapped from Early stages of the compressor and is used to cool turbine disks, vanes, combustion chamber lining and exhaust bearings

Question 6

How is circulated cooling air removed from the engine?

Answer 6

Air is vented into the exhaust stream

Question 7

How is the exterior of the engines and the nacelles cooled ?

Answer 7

By passing fan air around them

Question 8

What are the three primary zones that are isolated by fireproof bulkheads ?

Answer 8

• fan case compartment
  -the intermediate compressor case compartment
  The core engine compartment

Question 9

Where is fireproof zone 1 ?

Answer 9

Around the fan case that contains the accessory case and the EEC

Question 10

Where is fireproof zone 2 ?

Answer 10

Cooled by fan air from the upper part of the fan duct, and is exhausted at the lower end back into the fan air stream

Question 11

Where is fireproof zone 3?

Answer 11

The area around the high pressure compressor to the turbine cases. This zone also contains fuel lines, oil lines and other accessories

Question 12

Where is fireproof zone 3?

Answer 12

The area around the high pressure compressor to the turbine cases. This zone also contains fuel lines, oil lines and other accessories

Question 13

What are the disadvantages of ice formation on the engines?

Answer 13

-Reduces efficiency,
- possibility for chunks of Ice to break off and break or damage the compressor blades

Question 14

What abnormal condition can cause ice to form when it’s not supposed to ?

Answer 14

Ice can form on the inlet when there is fast air speeds at temperatures up to 5°C

Question 15

How are anti ice systems controlled ?

Answer 15

Automatically via a switch or flight crew can manually select functions if it is required

Question 16

Where can an indication that anti ice valves are open be seen ?

Answer 16

On the engine parameters page

Question 17

What are the five internal cooling systems ?

Answer 17

-compressor cooling
-combustion chamber cooling
-turbine disc cooling
-turbine nozzle guide vanes and blade cooling
-accessory section

Question 18

What is the temperature range at the rear stages of the compressor ?

Answer 18

350-400 °C

Question 19

Where is compressor drawn cooling air supplied to ?

Answer 19

Compressor’s rotors

Question 20

What is special about the lining of the combustion chamber and what is their purpose ?

Answer 20

It is perforated to cool combustion gasses. Air is supplied via primary and secondary airflow

Question 21

What percentage of primary and secondary air is used to cool the combustion chamber ?

Answer 21

20-30% primary airflow is sent into the perforated liner
70-80% secondary airflow is sent around the combustor’s periphery

Question 22

What are the two ways the perforated lining provides cooling?

Answer 22

-Cool air removes heat from the combustion liner
- cooling creates a film which acts as a thermal barrier between hot gasses and the combustion liner

Question 23

How much more effectiveness does cooling give on turbine blades and vanes ?

Answer 23

They can operate up to 300-400°C higher than the materials operating range

Question 24

What is the major limiting range of gas turbine engines?

Answer 24

Temperature

Question 25

What is the most common method of cooling the turbine ?

Answer 25

By utilising bleed air

Question 26

How does the turbine disc heat up ?

Answer 26

By conduction of the heat on the blades

Question 27

What is the hottest part of the turbine disc ?

Answer 27

The disc rim

Question 28

How is the turbine disc cooled ?

Answer 28

By directing cooled air over each side of the disk

Question 29

Why are turbine nozzle guide vanes cooled ?

Answer 29

To increase life expectancy due to high temperatures

Question 30

Where does the air come from to flow out of the NGV and turbine blade cavaliers ?

Answer 30

Compressor discharge air

Question 31

Where is air drawn from to cool accessories and computers?

Answer 31

From intakes in the fan cowlings or a stage from the compressors

Question 32

What is used to cool oil for oil cooled generators or lubrication oil cooling ?

Answer 32

Air cooled oil cooler when fan air is used as the cooling medium

Question 33

What is used for sealing of the engine bearing chambers?

Answer 33

The low pressure compressor bleed air

Question 34

What does pressurised air acts as?

Answer 34

Acts on the air seals and oil seals and has an additional sealing effect that prevents oil from escaping out of the bearing chamber

Question 35

Where does air go from the bearing compartments?

Answer 35

Vents overboard through the hollow N1 rotor shaft

Question 36

What do engine bleed air external surfaces include?

Answer 36

Cabin pressurisation heating and cooling, De-icing and anti-icing, pneumatic starting of engines, auxiliary drive units (ADU)

Question 37

What are bleed ports?

Answer 37

Small openings in the compressor case adjacent to the stage from which the air is bled from

Question 38

Where does the external cooling system cool

Answer 38

External area between the cowlings and the engine casings

Question 39

What are the two areas below the engine cowlings?

Answer 39

The fan compartment and the core apartment