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M15 New > 15.7 > Flashcards

15.7 Flashcards

1
Q

What does exhaust do in a jet engine

A

Accelerate airflow from the turbine to efficiently generate thrust

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2
Q

How does APU reduce noise

A

Mufflers

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3
Q

What does the exhaust do in a turboprop engine

A

Guide gases overboard

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4
Q

Why does APU exhaust gases go overboard

A

All gas energy is absorbed by the turbine

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5
Q

Components of exhaust

A

Cone

Tailpipe

Exhaust nozzle

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6
Q

What does exhaust cone do

A

Collects exhaust gases from turbine section and gradually confers them into solid flow of gases

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7
Q

Exhaust cone assembly

A

Outer shell/ duct

Under cone

3/4 radial hollow struts/fins

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8
Q

What do radial struts do

A

Support inner cone

Straighten swirling exhaust gases that would of came out at a 45 degree angle

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9
Q

What’s the purpose for the hole at the tip of the cone

A

Allows cooling air to be circulated from the aft end of the cone

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10
Q

How is the tail pipe constructed

A

So it’s semi flexible in a bellows arrangement

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11
Q

What’s the need for a bellows arrangement

A

Allows movement in instillation , maintenance and thermal expansion

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12
Q

Two most common methods of protecting the fuselage structure

A

Blankets and shrouds

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13
Q

What’s the two types of exhaust nozzle designs

A

Converging for Subsonic gas velocities

Converging-diverging for supersonic gas velocities

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14
Q

What increases exhaust gases velocity

A

Converging nozzle

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15
Q

What % does thrust increase by increasing velocity

A

15-20%

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16
Q

How much thrust does a turboprop exhaust nozzle give you

A

10-15%

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17
Q

Why is the fixed type nozzle simplest

A

No moving parts

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18
Q

2 types of exhaust nozzle

A

Fixed or variable

19
Q

When is a variable nozzle used

A

Augmenter or after burner is used

20
Q

After the turbine what duct is there

A

Divergent to reduce turbulence in the airflow

21
Q

When exhaust gases exceed Mach 1 what nozzle is would you use

A

Convergent - divergent

22
Q

Advantage of convergent divergent nozzle

A

At high Mach numbers because of the resulting higher pressure ratio across the engine exhaust nozzle

23
Q

Where does engine noise come from

A

Fan

Compressor

Air discharge from core of engine

24
Q

Sources of noise

A

Air intake

Vibration

Engine exhaust

25
Q

What happens in terms of noise with more thrust

A

High gas stream velocity and higher noise levels

26
Q

What are the two types of noise suppressors

A

Perimeter type or the multi tube type

27
Q

What’s the purpose of acoustic linings

A

Noise absorbing which coverts acoustic energy into heat

(Forms a porous skin)

28
Q

Where is acoustic linings

A

In the nacelle between the engine and cowl

29
Q

How do thrust reverses produce braking force

A

Deflecting exhaust gas steam in the opposite direction which creates a thrust force in the opposite direction of movement

30
Q

Where can thrust reversers be used

A

Only on ground

31
Q

Where is the deflection mechanism when not in operation

A

Flush with the wall so it doesn’t disturb normal exhaust gas stream

32
Q

What aircraft is clamshell doors used on

A

Older jet engines with a low bypass ratio

33
Q

How is a clamshell door operated

A

Pneumatically operated by bleed air from the HP compressor

34
Q

What’s different about a bucket type door

A

Found on the same aircraft and clamshell but opened hydraulically

35
Q

What conditions would thrust reverser be used

A

Wet , icy or snowy runway

36
Q

What gives fan reverser its name

A

The fact that only cold fan air is deflected

37
Q

What type of thrust reverser is a fan reverser

A

Cascade type with translating sleeves

Operated either pneumatically (drive motors) or hydraulically (actuators)

38
Q

How does a pivoting door reverser work

A

Hydraulically activated

Closes off fan discharge airflow when deployed

39
Q

When are thrust reverses most efficient

A

During high speed and shortly after touchdown

40
Q

Disadvantages to thrust reversers ingesting reversers airflow

A

Compressor stall and high exhaust gas temperatures

Picks up FOD

41
Q

How do we minimise disadvantages caused my thrust reverser operation

A

Reversed airflow is matched to the engine position

42
Q

What’s an advantage to engines having the same cowlings

A

Fewer spare parts needed

43
Q

What must you do with a defective thrust reverser system

A

Deactivate before flying to ensure it doesn’t deploy unintentionally

44
Q

What’s thrust vectoring

A

Moving the direction of the exhaust nozzle to direct thrust to move in your desired path

M15 New (18 decks)

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