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M15 > EXHAUSTS > Flashcards

EXHAUSTS Flashcards

1
Q

What aircraft is a clamshell door type reverser and bucket type used?

A

Older jet engines with low bypass ratio.

Clamshell- Pneumatically operated with bleed air from HP compressor)

Bucket- hydraulically operated

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2
Q

What do clamshell doors do?

A

Block normal flow path and use exit ducts and cascade vanes to direct gas in forward direction.

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3
Q

What is only deflected on turbofan engines for thrust reverse?

A

Cold fan air. (Fan reverser)

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4
Q

Why are reversers which use the hot core engine gas with the thrust reverse inefficient?

A

Hot environment needs excessive maintenance.

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5
Q

Commonly what type are most fan air reversers?

A

Cascade type with translating sleeves.

Pneumatically or hydraulically

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6
Q

What is a pivoting door reverser?

A

Four large reverser doors.

Hydraulically operated.

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7
Q

What is the common exhaust nozzles main advantage?

A

Reduces very high gas velocity’s of not gas by mixing both of the gas flows

(Higher propulsion efficiency)

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8
Q

How can we guarantee laminar vortex free and axially orientated exhaust gas flow?

A

The gases must expand completely in the exhaust nozzle.

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9
Q

How is exhaust airflow created?

A

Pressure ratio between the turbine discharge and ambient pressure.

(Higher engine speed higher pressure ratio)

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10
Q

What pressure ratio will convergent exhaust nozzles reach maximum airflow?

A

2:1

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11
Q

Why would a nozzle become choked?

A

Higher pressure ratios. In the smallest area of the nozzle the exhaust gas velocity equals the speed of sound.

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12
Q

Why would the exhaust jet burst into all directions?

A

If the pressure ratio is increased, airflow discharges at the exhaust with static pressure which is greater than ambient.

(Inefficient)

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13
Q

What ratio are convergent divergent nozzles build for?

A

More than 2:1

Higher gas velocity = Higher thrust

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14
Q

What aircraft are convergent divergent nozzles necessary for?

A

Aircraft which fly faster than the speed of sound .

Must be variable design as sensitive to RPM changes

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15
Q

Will high velocity gases increase or decrease propulsion efficiency?

A

Decrease

Cause turbulence with ambient air and loud exhaust noise

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16
Q

What exhaust do modern turbofan engines have?

A

Convergent, large enough to not choke.

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17
Q

What is the common unit used to express noise?

A

Effective perceived noise deciBel (EPNdB)

Sound pressure, pitch, duration

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18
Q

What are the two methods to adopted to reduce engine noise?

A
  • selection of design

- methods to dampen interior and exterior noise sources

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19
Q

How can the sound of turbofan engines be further reduced?

A

Increasing the bypass

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20
Q

How can we reduce internal noise?

A

Reducing airflow disruption by optimising number of blades and canes in compressors and distance between components

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21
Q

What is the method adopted to reduce the noise of transmissions?

A

Airflow linings use noise absorbent materials.

Porous surfaces, supported by honeycomb structure transferring sound into heat energy

22
Q

How can jet noise reduction be achieved?

A

Increasing the contact area of the exhaust gas with the atmosphere

23
Q

How is high frequency noise absorbed into the atmosphere?

A

Quickly

24
Q

What is a hush Kit?

A

Additional mixing of ambient air with exhaust gas before it enters the nozzle.

25
Q

What is the deflection of gas stream during thrust reverse?

A

45 - 60 degrees

180 degrees most efficient but bad for engine

26
Q

What airflow do modern turbofan engines use for thrust reverse?

A

Fan airflow as it produces most of the thrust.

27
Q

Why can the engine compressor stall during thrust reverse?

A

Airflow through the engine is disturbed.

28
Q

What speeds are thrust reversers most efficient?

A

High speeds.

29
Q

What can happen at low speeds with the thrust reverser?

A

Engine can ingest it’s own reverse flow.

Causing compressor stall and high temp exhaust gases

30
Q

How can some thrust reversers increase efficiency of brakes?

A

Reversed airflow can cause an air cushion below the wing decreasing load on main landing gear.

31
Q

How are the disadvantages of thrust reverse minimised?

A

Reverse airflow is matched to engine position.

32
Q

What is a problem with thrust reverse on a 4 engine aircraft?

A

Inner engine can ingest outer engines reverse airflow.

33
Q

How is the direction of reverse flow controlled to be as safe as possible?

A

Cascade vanes.

34
Q

Can an aircraft be deployed with a faulty thrust reverser?

A

Yes, must be deactivated properly.

35
Q

What are the 3 main subsystems of the thrust reverser?

A

Control system
Actuation system
Airflow deflection system

36
Q

What is the control system in the thrust reverser for?

A

Activate the thrust reverser.

Increase engine power for reverse thrust.

37
Q

What is the reverser actuation system for on thrust reversers?

A

Either pneumatic or hydraulic systems.

Moves airflow deflection mechanism by signals from control system.

38
Q

What is the airflow deflection system for on thrust reversers?

A

Directs airflow in optimum position for safe reverse thrust.

39
Q

What is the reverser control system always protected by to make sure they do not deploy in flight?

A

Air to ground logic.

40
Q

What is an advantage of using an alternate signal from the radio altimeter to allow deployment of thrust reversers?

A

On short runways can be deployed shortly before touchdown when altitude is less than 10 feet.

41
Q

What is the main task of an exhaust on jet engines?

A

Accelerate the airflow coming from the turbine to efficiently make thrust.

42
Q

What is the main task of an exhaust in a turbo prop engine?

A

Safely guide exhausts overboard.

43
Q

What does the exhaust cone do?

A

Guides discharged airflow and prevents excess turbulence.

Also prevents reverse flow of the exhaust gases to the hub of the rear turbine.

44
Q

Where are long ducted exhausts only found?

A

On older aircraft where engines are directly under the wing

45
Q

What two exhaust flows do modern turbofan engines have?

A

Hot exhaust from primary

Colder air via secondary

46
Q

What does a thrust reverser interlock system do?

A

Ensures engine power can only be increased once the reverser has been fully deployed.

47
Q

On what thrust reversers are pneumatic reservoir actuation systems only used?

A

Cascade type thrust reversers with translating sleeves.

Air motors operating drive shafts, gear boxes and ball screw actuators

48
Q

What do pneumatic reverser system use to lock the stowed reverser?

A

Brakes on air motors.

49
Q

What locks the reverser door in the stowed position in hydraulic systems?

A

Hook of the latch mechanism.

50
Q

What do reverse unlock messages indicate?

A

Reverser is not safe in stowed position (amber lights)

51
Q

What does a green light indicate for thrust reversers?

A

Reverser is fully deployed and interlock system is released (full power can be applied)

M15 (18 decks)

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