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M15 Lewis > 15.4 > Flashcards

15.4 Flashcards

1
Q

What do bleed manifolds do

A

Collect bleed air from pick up points and distribute to consumers

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2
Q

What part of the engine supplies air to the pneumatic system

A

HP compressor

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3
Q

Why are variable stator vanes all connected to the same actuation lever?
What’s located at the end of variable stator vanes?

A

To ensure they are actuated simultaneously
Trunnion

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4
Q

Why do inner vane segments have an inner platform

A

To minimise vibrations caused by airflow

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5
Q

What does CDP stand for and what is a CDP seal

A

Compressor discharge pressure

Prevents pressure discharge airflow from escaping into bearing area below combustion chamber

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6
Q

What do knife edge seals in the HP compressor rotor assembly prevent

A

Reverse airflow through the gap between rotor and stator

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7
Q

How are components and rotor hubs connected in high pressure compressors in older systems

A

Using tie rods

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8
Q

What’s used to prevent spinner cone from being fitted incorrectly

A

Off set mounting holes

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9
Q

How can fan blade number one be identified

A

Index mark on fan disk or by offset hole

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10
Q

Where’s the moment weight usually marked on a fan blade

A

On the root

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11
Q

What units of measurement can moment weight be given in

A

Grams inches
Cmg
Ozinches

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12
Q

Whats moment weight

A

Product of blade mass and distance of c of g from rotational axis

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13
Q

What 3 parameters do centrifugal forces depend on

A

Blade mass
Rotor speed distance between c of g of fan blade to rotational axis

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14
Q

What’s the purpose of the fan frame struts

A

Connect internal and external section of the fan and carry loads from engine bearings and mount

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15
Q

What does the outer surface of the compressor fan frame do

A

Gives support for engine equipment

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16
Q

Where’s the compressor fan frame located

A

Between HP and LP compressors

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17
Q

Why do fan frames have bleed valves on there internal structure

A

Prevent LPC surge

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18
Q

What do outlet guide vanes act as at the fan stage of the engine

A

Stator vanes

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19
Q

What’s the purpose of abraidable shrouds

A

They abrade if come into contact with blades to ensure that the blades don’t get damaged

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20
Q

What’s the purpose of an acoustic panel

A

Reduces fan noise

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21
Q

What’s the purpose of a flange on the outer surface of the case

A

Stiffens the case and resists deformation

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22
Q

What’s the difference between a split stator case and a closed stator

A

Split stator cases are installed in two separate parts

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23
Q

What’s located between dovetail slots on rotor drums

A

Labyrinth seals

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24
Q

What’s another name for the low pressure compressor module

A

Booster module

25
Q

What’s the main advantage of wide chord fan blades over a conventional fan blade

A

More efficient and can withstand more fod damage due to flexibility

26
Q

What’s the purpose of a shroud

A

Keeps fan deflection within safe limits when heavy loads act on them

27
Q

What two stresses or loads do rotor blades commonly take

A

Centrifugal and air loads

28
Q

Why are loose fits of fam blade attachments required

A

So they don’t exceed the the max allowable stress limits when sudden torque loads or forces occur

29
Q

What type of fitting is used on most engines to attach fan blades

A

Dovetail

30
Q

What’s a fan rotor disc made from

A

Titanium alloy

31
Q

What else may the mounting bolts for the spinner cone be used for

A

To add balance weights

32
Q

What’s the purpose of the spinner cone

A

Allows a smooth aerodynamic fairing at engine inlet

33
Q

What’s an advantage and disadvantage for variable stator vanes

A

Optimum angle of attack on rotor blades can be reached for each engine speed

Complicated control system

34
Q

When do compressor bleed valves open and why?
What’s a disadvantage of compressor bleed valves?

A

Open at low engine speeds so excessive airflow can escape overboard

Cause large loss of efficiency

35
Q

What’s an advantage of multiplespool engine designs

A

Excellent acceleration capabilities

36
Q

What methods can be used to avoid stall and what ones most effective

A

Compressor bleed valves
Use of multiple spool engines
Variable stator vanes ( most popular )

37
Q

Why does fast deceleration cause compressor stall/surge?

A

As the LP compressor decreases in speed slower than the HP compressor meaning it’s supplying unwanted air to the HP compressor which wld cause a stall

38
Q

What are the two OPERATIONAL reason that compressor stall or surge might happen

A

Due to low engine speeds below design speed

At incorrect deceleration or acceleration

39
Q

What can cause a compressor stall or surge

A

Dents or ice on engine inlet
Damaged rotor blades
Dirty compressor or stator vanes
Damaged combuster components
Damaged turbine components

40
Q

What 3 things happen as a result of compressor surges

A

Thrust will decrease
Emgime speeds fluctuate
Exhaust gas temps increase

41
Q

Why does a compressor surge in the fwd stages in,t affect a portion of the blade

A

Because of there larger diameter

42
Q

What’s the name given to a sever compressor stall

A

Surge

43
Q

What do the low pressure zones causes as a result of compressor surge d9 to the direction of airflow

A

Stops and reverses direction

44
Q

Why’s the axial flow compressor cross sectional area gradually decreased ( tapered )

A

Keeps constant velocity through compressor

45
Q

What axis does airflow In a axial flow compressor travel along

A

Horizontal

46
Q

What are characteristics of a double face compressor

A

Higher airflow
Weight saving
Gives engine smaller frontal area

47
Q

Why are only two stages used in centrifugal flow compressors

A

most efficient

48
Q

What pressure ratio do most centrifugal compressors give ratios of

A

5:1

49
Q

What are the 3 main components of a centrifugal flow compressor

A

Impeller
Diffuser
Compressor manifold

50
Q

What do compressor cases provide and what purpose do they serve

A

Give support to the compressor rotor bearings

Improves and straightens airflow into compressor

51
Q

What are the two types of compressors

A

Axial type
Centrifugal type

52
Q

What’s the name given to a stator vane in front of the compressor stage?
What about in in the fan duct?

A

Front= inlet guide vanes
Fan= outlet guide vanes

53
Q

What’s the two main compressor components? What’s there purpose

A

Stator=guides and sloes airflow

Rotor = increases energy of airflow

54
Q

What comes first in the compressor, stator or rotors

A

Rotor

55
Q

What are the two ways airs compressed into engines and what ones used in GTE

A

Decreasing the volume of air in cyclinder by a piston

Bernoulli’s principle ( used in GTE )

56
Q

What happens to a of a when inlet air velocity decreases

A

Increases

57
Q

What’s the resultant inlet velocity a result of

A

Air inlet velocity and air speed

58
Q

Why are axial and centrifugal compressors sensitive to airflow changes

A

Because they only have one optimum operating condition for a given ratio, rotational speed and airflow

59
Q

What’s the pressure ration of axial flow compressors

A

1.3:1

M15 Lewis (18 decks)

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