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Mod 15: Engines > John's Notes > Flashcards

John's Notes Flashcards

1
Q

Gas turbine engine is what kind of cycle?

A

Gas Turbine Engine is the brayton cycle

meaning combustion occurs at constant pressure

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2
Q

What type of cycle is a piston engine?

A

Constant volume cycle

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3
Q

A turbojet engine has no _____

A

fan

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4
Q

Do fan blades change pitch like propeller blades?

A

No, fan blades are fixed pitch blades (always even number and typically 40)

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5
Q

What is ram ratio?

A

Ram ratio = compressor inlet pressure / ambient pressure

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6
Q

What is Ram temperature rise?

A

Ram temperature rise = compressor inlet temperature / ambient temperature

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7
Q

What is the simplest, most effective and most common type of inlet?

A

pitot type

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8
Q

What is a bifurcated intake?

A

2 inlets for the one engine

used on military aircraft

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9
Q

All subsonic ducts are ______ ducts

A

divergent

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10
Q

Dump and spill valves are used in which type of intake?

A

Moveable wedge intake

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11
Q

Bellmouth intake is gently ______ (divergent/convergent)

what is it used for?

A

convergent

helicopters and engine test cells

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12
Q

Compressor primary and secondary functions are

A

Primary = increase pressure

Secondary = cool engine hot parts, pressurise bearings, engine anti ice

Also supply customer service bleed air

CUstomer is airframe (pneumatics etc)

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13
Q

Compressor pressure ratio =

A

Outlet pressure / inlet pressure

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14
Q
A
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15
Q

What is the vaneless space in a compressor?

A

It is the space that exists between the impeller vane tips and the diffuser

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16
Q

What are the methods of securing compressor blades and why is a little bit of play given?

A

Fir tree and dove tail

To relieve stress and strains

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17
Q

Compressor stators and rotors are ________
while the overall compressor casing is _______

(convergent or divergent)

A

divergent

convergent

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18
Q

What is the compressor rise of an axial compressor vs centrifugal compressor?

A

1 or 2:1 per rotor/stator compressor but able to fit more on engine

Centrifugal is 10 or 15:1 but can only fit max 2 on engine

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19
Q

What is high aspect ratio means in relation to compressor blades?

A

Long and thin blades

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20
Q

What is a wide chord type compressor blade?

A

short and stubby

(type of aspect ratio)

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21
Q

There is always an ______ number of blades on a compressor for balancing reasons

A

even

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22
Q

Blade scatter is what?

A

Blades moving against each other

'’The blades , on moving, lean their shrouds onto the adjacent blades shroud’’

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23
Q

Compressor surge is what?

A

Surge is a reversal of airflow at the high pressure end

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24
Q

Another word for a mild stall is

A

transient stall

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25
Q

Another word for a severe stall is

A

Hung stall

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26
Q

The most efficient angle of attack of a compressor blade is _____ degrees

The AOA is based on what 2 vectors?

A

4

Engine RPM

Air Inlet velocity

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27
Q

Stoichometric ratio is what?

A

Stoichometric ratio is the ideal ratio to burn fuel in air and is 15:1, note it is by weight

15:1 represents

15 pounds of PRIMARY AIR and 1 pound of fuel

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28
Q

Name the 4 types of combustors?

A
  1. Multiple Combustion chambers
  2. Can-annular or tubo-annular combustion chambers
  3. Annular combustion chambers (most common)
  4. Annular reverse flow (turboprops)
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29
Q

There is only ever _____ (#) of igniters in a combustion section

There is fuel nozzles in every chamber however (2 sets of 10)

A

2

30
Q

Primary air is what?

A

Primary air is that portion of air which mixes with the fuel for combustion purposes.

31
Q

Tertiary air is what?

A

Tertiary air is air which acts as a cooling agent.

It takes no part in combustion

32
Q

Secondary air is what?

A

Secondary air is that part of the air, which is metered into the combustion chamber to complete combustion

33
Q

Swirl vanes do what and are located where?

A

Swirl vanes are located in the compressor section and act to slow down the air

34
Q

Compressor blades are made of what material?

A

alluminium alloy, titanium or steel (cold section)

35
Q

Turbine blades are made of what material?

Turbine casing is made of what material?

A

Turbine blades are made of nickel or nimonic based super alloy

Turbine casing is made of incanel

36
Q

In general, describe Turbine nozzle guide vanes

A

Turbine nozzle guide vanes are convergent ducts that accelerate gases onto turbine blades

Internally cooled with compressor bleed air

(generally whether NGV’s are either straight or convergent is determined by if they are reaction or impulse, respectively)

37
Q

Are turbine stators before or after the rotors?

A

Turbine stators are located in front of the rotors (turbine blades) and they are generally convergent increasing their velocity while reducing temp and press.

NOTE: Compressor stators are behind the compressor rotors(blades) and both are divergent to increase pressure

38
Q

What is convection cooling in terms of Turbine blades?

A

Convection cooling is where compressor bleed air comes from the very bottom of the blade (fir tree area) and exits out the tip of the blade or at the trailing edge into the airflow.

The air makes a couple of passes through the blade to cool it

39
Q

What is film/impingement cooling in terms of Turbine blades?

A

Film/impingement cooling is where compressor bleed air comes from the blade bottom (fir tree area) and passes through blade cooling it before being released through the leading edge of the blade forming a heat shield around it.

The more advanced version is called '’Transpiration’‘

40
Q

What is the more advanced version of Film/impingement turbine blade cooling called?

A

'’Transpiration’‘

41
Q

What is turbine blade creep?

A

Turbine blade creep is the elongation of turbine blades

It is divided into primary, secondary and tertiary creep

42
Q

Single crystal construction is a turbine blade manufacturing method used to stave off _________

A

tertiary creep

43
Q

Turbine blades are made out of what material?

A

Nimonic alloy, nickel based alloy

44
Q

The future of turbine blade manufacture will be blades manufactured from reinforced _______

A

ceramics

45
Q

Blisk is a combination of what?

A

A Blade and a Disk

both made as one

46
Q

What are Reaction Turbine Blades?

A

Nozzle guide vanes are straight ducts that change the direction of the airflow onto the blades

The blades are convergent meaning they accelerate the airflow, reducing its pressure and temp

47
Q

Describe Impulse Turbine Blades

A

Nozzle guide vanes or stator vanes are convergent to accelerate airflow onto blades

Turbine blades are straight ducts so velocity of airflow remains the same

These are usually found in pnuematic air starters

48
Q

What are Impulse reaction turbine blades?

A

A combination of impulse and reaction turbine blades, varies with designer how much of each

49
Q

What type of turbine blades are used with pnuematic air starters?

A

Pnuematic air starters = Impulse Turbine blades

50
Q

Exhaust is a _____ duct

A

convergent

also called propelling nozzle

51
Q

What is the only way to get more gas out of a ‘‘choked’’ nozzle?

A

To increase the gases temperature and thus its mach number

52
Q

Afterburner of reheat is what?

A

Surplus oxgen

convergent-divergent duct always increasing velocity as starts supersonic

Area of nozzle opens up

53
Q

As a basic rule, any sound over _____ dB is considered intense

Human earss can evalualte noise up to _____ dB

Anything over this is _______

A

100

120

damaging

54
Q

What is a corrugated nozzle?

A

Cold air goes from fan duct across exhaust and mixes with hot air from core to get rid of thermal shock noise

55
Q

Describe Multi-lobe nozzle?

A

splits exhaust into mulitple smaller exhausts increasing frequency of sound above what human ears can hear

56
Q

The greatest reduction in noise level is achieved by the _____________

A

high by-pass ratio turbo-fan engine

57
Q

Honeycomb structure in an engine is used for what?

A

noise supression

58
Q

Name the hot thrust reversers

Name the cold thrust reversers

A

Hot = Bucket doors and clamshell doors

cold = translating sleeve and blocker doors

cascade vanes are incorporated into both

59
Q

What is a meant by pour point of an oil?

A

The lowest temperature at which oil will gravity flow

60
Q

Which has a lower freezing point:

Jet A1 or Jet A fuel

A

Jet A1

61
Q

Explain flash point

Does fuel need a high or low flash point?

A

Flash point is the lowest temperature at which a liquid can give off vapor to form an ignitable mixture in air near the surface of the liquid. The lower the flash point, the easier it is to ignite the material

Fuel needs a high flash point

62
Q

> _____ parts per million of free water (entrained water) is damaging and can cause engine flame out

A

30

63
Q

If the amount of water detected in a fuel water test kit, the kit should turn ______

but in reality it will turn _______ _______

A

blue

greenish torquoise

64
Q

Which type of water is dangerous in fuel?

Entrained (free) undissolved water or

dissolved water

A

Free water = entrained water or undissolved water and blobs of it in fuel are visible and problematic as if they freeze, they will block filters etc

Dissolved water is not a problem

65
Q

Kerosene is ‘Hydroscopic’, explain

A

It absorbs moisture into itself, the warmer it is the more moisture it will absorb

66
Q

What is meant by a ‘wet sump’ system?

A

Oil reservoir located at the lowest part of the engine as it uses gravity to return oil.

Oil reservoir is integrated into bottom of engine

67
Q

What is meant by ‘‘dry sump’’ system?

A

The oil reservoir is located away from the engine near compressor or fan case (cold sections)

Needs scavenge return filters

68
Q

Scavenge pumps are of atleast _____% capacity of the pressure system as ____ also comes back with oil in addition to oil expanding as hotter

A

150

air

69
Q

Name and briefly describe the 3 types of oil pump?

A
  1. Gear pump (drive and driven pumps)
  2. Gerotor pump (male and female gears, cocentric, male has 1 less tooth)
  3. Vane pump (more tolerant of debris, prone to high rates of vane tip wear)
70
Q

Filters are filtered _________ as greater surface area outside

A

Out-to-In

71
Q

A micron is ________ of a meter

A

one millionth

Mod 15: Engines (28 decks)

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