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M15 Lewis > 15.12 > Flashcards

15.12 Flashcards

1
Q

What can a bowed rotor lead to and what recommended as a result of this

A

Rotor wear or a hung start

A Min waiting time between engine shut down and engine start is recommended

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2
Q

What causes a bowed rotor

A

After engine shut down and engine start bend can occur due to different expansion between upper ans lower engine

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3
Q

When’s there only positive ventilation of Core components

A

During engine operation

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4
Q

What picks up the ram air that’s used for ventilating fan compartment on the lower part of the engine fan cowl

A

Naca air inlet

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5
Q

What does the external cooling system prevent from collecting in the engine compartments

A

Prevents flammable vapours

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6
Q

What happens as a result of opposite axial forces

A

Compressor gas loads push the rotors in fwd direction and turbine loads push rotors in the aft directions

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7
Q

What does pressure balancing do

A

Minimises axial loads on rotor bearings

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8
Q

What can also be used to cool the rotor drum of the HP compressor

A

Airflow from the LP compressor

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9
Q

What’s used to cool the first stage nozzles ans rotor drum of LP turbine

A

Bleed turbine stages of HP compressor

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10
Q

What areas of the engine are especially important to be cooled with internal air

A

Turbines

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11
Q

What’s LP compressor bleed air used for

A

Sealing engine bearing compartments to prevent oil escaping out of the bearin pg compartments

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12
Q

What’s the best method for releasing axial loads on thrust bearings in the engine

A

Pressure Balancing

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13
Q

What are some of the common tasks of the internal air system

A

Internal cooling
Internal sealing
Pressure balancing

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14
Q

What else can internal air be used for in the bearing compartments

A

Sealing

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15
Q

What does the internal air cooling system supply cool air to and where’s the air come from

A

Below engine rotor ans bearing compartments
Pick up points at LP and HP compressors

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16
Q

What does the external cooling system supply cold air to

A

In cavities between engine cowlings and casings

17
Q

Where’s the air used for external cooling system sourced from

A

Ram air from fan compartment

18
Q

What type of aid is used for clearance control systems

A

Warm air to heat rotor to cause them to expand so tip clearance increases

19
Q

What controls the active tip clearance control valves

A

Hydro mechanical fuel control unit or the FADEC system

20
Q

What type of clearance control system optimises the tip clearance for all operating conditions

A

ACTIVE CLEARANCE CONTROLS

21
Q

Where are clearance control systems usually found

A

HP AND LP turbines on some engines even HP compressors

22
Q

What’s the purpose of the tip clearance control system

A

Matches the expansion of the stator case with the expansion of engine rotor

23
Q

Where can bleed valuables In the compressor be found

A

Mid of aft

24
Q

What do some engines use at the HP compressor to improve engine start and acceleration capabilities

A

Bleed valves

25
Q

What 2 methods are do HP compressors used to prevent Stall and surge

A

Compressor bleed valves

Several stage variable stator vanes to control airflow into the compressor

26
Q

What’s in place in the compressor to help prevent against stall ans surge

A

Variable bleed valve to control airflow into compressor

27
Q

What’s the 3 subsystems of the compressor system

A

Variable bleed system
Variable stator vane system
HP compressor bleed valve system

28
Q

What does the clearance control system do

A

Optimises tip clearance between rotor blades and stator causing an increase in efficiency

29
Q

What do the compressor control system do

A

Protectors compressor from stall

30
Q

What controls all the engines air systems

A

Hydro mechanical fuel control or FADEC system

31
Q

What are the 3 subsections the air system can be divided into

A

Compressor control
Clearance control system
Engine cooling system

M15 Lewis (18 decks)

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