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Module 15 Richard > 15.12 Air Systems > Flashcards

15.12 Air Systems Flashcards

1
Q

What 3 subsystems can the engine air system be divided into?

A

1) the compressor control system
2) the clearance control system
3) the cooling system

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2
Q

What is the purpose of the compressor air control system?

A

It prevents the compressor from stalling or surging and increases the efficiency

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3
Q

What is the purpose of the clearance control system?

A

It increases the engine efficiency by reducing the space between the rotating turbine blades and the casing (tip clearance)

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4
Q

What type of system is the engine cooling system usually?

A

Passive

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5
Q

What controls the compressor air control system?

A

The F.A.D.E.C or the hydro-mechanical fuel control unit

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6
Q

What are the three subsystems of the compressor air control system?

A

1) the variable bleed valve system
2) the variable stator vane system
3) the HP compressor bleed valve system

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7
Q

What are VBV’s?

A

Variable bleed valves

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8
Q

What are the VBV’s responsible for?

A

Varying the airflow to the high pressure compressor by bleeding air from the LP compressor to the bypass duct which prevents surging and stalling of the LP compresssor

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9
Q

What are VSV’s and what are they for?

A

Variable stator vanes
They are used in the HP compressor during engine start and during acceleration so that the airflow through the HP compressor is not too large (optimising efficiency)

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10
Q

Some engines may use bleed valves at the HP compressor stage. If so, where would these be found?

A

At the mid or aft stages if the HP compressor.

Known as start bleed valves (as usually only used on startup)

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11
Q

What is the purpose of a tip clearance control system?

A

It matches the expansion of the stator cases and the expansion of the engine rotors.

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12
Q

Where are clearance control systems usually found?

A

The HP and LP turbines

Some engines also include the HP compressor

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13
Q

What is an air passive control system?

A

An air system that cannot be switched off

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14
Q

What is an air active clearance control system?

A

An air system that has cooling air control valves. These systems optimise efficiency of the engine

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15
Q

How are the active clearance control systems controlled?

A

By the FADEC system or Hydro-mechanical fuel control unit

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16
Q

What air does compressor clearance control systems use?

A

Warm air heating the rotors instead of cool air cooling the case

17
Q

Why can’t you use cold air in the compressor clearance system?

A

The air available isn’t cold enough for case cooling

18
Q

What two parts is the engine cooling system divided into?

A
  • external cooling system

- internal cooling system

19
Q

How are the components in the fan case cooled?

A

By using RAM air

20
Q

What is the purpose of engine cooling?

A

It cools the engine and components making it more efficient and also prevents a build up of flammable gases

21
Q

Where does the air come from for the internal cooling system?

A

The LP or HP compressor

22
Q

What other purposes, other than cooling, does the internal air system have?

A
  • air for sealing in bearing compartments

- pressure balancing

23
Q

What is pressure balancing?

A

Using the internal air system of the engine to reduce axial thrust loading on the rotor bearings

24
Q

Where does the air that is used for sealing in an engine escape?

A

Through the hollow N1 shaft

25
Q

Which way does the pressure act on the…

  • compressors?
  • turbines?
A 
Compressors = forward on the rotors 
Turbines = in the aft direction on the rotors
26
Q

What type of intake is used for the air cooling of the fan case?

A

NACA air intake

27
Q

When is there positive ventilation of the core compartment of an engine?

A

When the engine is operating; by using fan air

28
Q

What is a bowed rotor?

A

The condition that can occur when an engine shuts down and cools at different rates

29
Q

How does an engine cool after it has been shut down?

A

By convection (warm air rises)

30
Q

If an engine has just been shut down, when can it be started again?

A

Depends on engine manufacturer - usually minimum waiting time between shut down and subsequent engine start

Module 15 Richard (18 decks)

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