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M15 Lewis > 15.6 > Flashcards

15.6 Flashcards

1
Q

How do tangential struts minimise stress caused by thermal expansion

A

if they expand they cause the hub to restate slightly so it shares it with the hub

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2
Q

How are radial struts designed and what does this design help to minimise

A

Designed to be as short as possible to minimised expansion of struts ans keeps the stress on the hub low

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3
Q

What’s the turbine frame ans how many turbine rotors does it support

A

It’s the aft major structural component of the engine
1 or 2

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4
Q

How are high pressure blades cooled

A

Internally by air from HP compressor

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5
Q

How are turbine discs attached to the drive shaft

A

Directly splined pr bolted

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6
Q

What’s a disadvantage of shrouded blades and how’s this offset

A

Adds weight and offset by making the blades thinner

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7
Q

What do shrouded blades help to prevent

A

Vibrations

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8
Q

What are the two types of turbine blades used in modern gas turbine engines

A

Open end - used in turbines with high rotational speeds
Shrouded- found in HP turbine

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9
Q

What type of mount designs are used for HP turbine blade attachment and why

A

Fir tree root

Has many contact surfaces so forces are smoothly transmitted to disc

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10
Q

What are the purpose of blade retainers

A

Hold blades in position so they don’t move as a result of gas loads

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11
Q

What’s the function of turbine discs

A

Holds rotor blades and transfers the torque from blades to the compressor shaft

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12
Q

How many guide vanes made up a vane segment in LP turbines

A

6-7

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13
Q

How many pieces are LP turbine cases made from

A

One piece

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14
Q

What’s the LP turbine case bolted to

A

Rear flange of HP turbine

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15
Q

What do the interstage seals in the nozzle guide vanes prevent

A

Gas flow through the gap between the rotor ans stator

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16
Q

How many nozzle guide vanes make up a vane segment

A

Two nozzle guide vanes

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17
Q

What holds nozzle guide vanes in place

A

Nozzle guide vanes supports

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18
Q

What’s the abradable ceramic surface on the wall segment provide

A

Optimum thermal resistance

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19
Q

How many pieces are the HP turbine cases made up of

A

One

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20
Q

When do engines with a hydro mechanical control unit operate

A

Only in climb and cruise

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21
Q

What’s the benefit of the tip clearance system

A

Saves a lot of feul

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22
Q

What’s used to actuate clearance control valves

A

Fuel pressure from hydro mechanical system

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23
Q

Why type of falafels are clearance control valves on new ac?
Old ac?

A

New - modulating
Old - shut off

24
Q

What shape are the HPT tubes? LPT tubes?

A

HPT- rectangle
LPT- circle

25
Q

What’s the difference between passive ans active clearance control methods

A

Passive- Continuous airflows (not regulated)

Active- controls the quantity of air

26
Q

What causes a longer expansion of rotor blades ( heat or centrifugal forces )

A

Centrifugal forces

27
Q

Why turbine casing expand faster than the rotor

A

It’s thinner than the rotor ans it’s in contact with higher temps

28
Q

How does a large tip clearance affect turbine

A

Reduces efficiency as large amount of gas is allowed to pass through the gap

29
Q

What’s meant by tip clearance

A

Gap between blade and casing

30
Q

What do active clearance control systems do

A

Keep tip clearance as small as possible during operating conditions

31
Q

What methods used to cool first stage nozzle guide vanes? First stage rotor blades?

A

Both of them use all 3 cooling methods
Impingement
Film cooling
Convection

32
Q

What methods are used to cool second stage guide vanes?
Second stage rotor blades?

A

Guide vanes= convection and impingement
Rotor= convection

33
Q

What’s the most effective cooling method and why

A

Film cooling as it reaches max cooling effect with the min amount of cooling air

34
Q

What purpose do the insert holes/small holes in the impingement cooling serve as

A

Jet nozzles

35
Q

How’s convection cooling done

A

Aids passed through hollow blades and nozzle vanes

36
Q

What’s the easiest way to cool turbines

A

Convection cooling

37
Q

Where’s the air used from to cool high pressure turbine nozzle guide vanes and rotor blades

A

HP compressor

38
Q

What two reasons are turbines cooled on modern engines

A

Increase service life
Better efficiency

39
Q

What’s the only way to reduce creep

A

Cooling turbine materials

40
Q

What two factors can cause creep of turbine blades

A

High engine speeds
High temps

41
Q

What’s creep ans what causes it

A

When the material won’t return to irs original shape and size due to high centrifugal loads over a long period of time

42
Q

During take off what must turbine blades be able to withstand

A

Several tonnes of centrifugal loads

43
Q

What should materials used for turbine blades be able to do

A

Withstand night temps and high centrifugal loads

44
Q

What two factors can reduce the service life of a turbine

A

Material fatugue from repeated cycles and corrosion

45
Q

What’s an impulse reaction engine also referred to as

A

Reaction turbine

46
Q

What’s an impulse turbine

A

A turbine which only rotates by impact of gas flow on rotor blades

47
Q

What must gas’s first pass through before a turbine

A

Nozzle guide vanes

48
Q

What does the turbine conver gas energy into

A

Torque

49
Q

What’s an advantage of a axial flow turbine

A

Allows very high airflow to create higher thrust

50
Q

What type of turbine is commonly used on GTE

A

Axial flow

51
Q

What type of turbine are radial flow turbine

A

Single stage turbines

52
Q

What’s an advantage and disadvantage of radial flow turbines

A

Small efficiency and airflow -‘s

Simple design +’s

53
Q

What’s the first main component of a turbine

A

Nozzle guide vanes

54
Q

What’s the purpose of turbines

A

Provides necessary power to drive compressor and accessory gear box

55
Q

What are the two types of turbines on GTE

A

Radial and axial

M15 Lewis (18 decks)

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