M15.07 Exhuast Flashcards by Meg Bazeley

What is the main function of the exhaust system?

Accelerate the airflow coming from the turbine to make thrust

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On a jet engine the exhaust system releases gas too?

The atmosphere

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How does the APU reduce the noise of the exhaust?

By using mufflers in the exhaust duct

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On jet engines the exhaust system has a tube, what it’s is called?

Exhaust duct or tail pipe

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What is the purpose of the exhaust nozzle at the aft end of exhaust duct??

Accelerates the exhaust gases which leave the engine

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What does the exhaust cone prevent?

. Prevent reverse flow
. Excessive turbulence
. Guides the discharge flow

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Modern turbofan engines have two exhaust steams, why?

. Hot gas flows via primary nozzle
. Cold fan air via secondary nozzle

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The most common exhaust nozzle on long range aircraft is??

. Combined exhaust nozzle

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How does the combined exhaust nozzle work??

. Mixes hot and cold gas flow to reduce velocity of exhaust gases

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What’s the advantage of combined exhaust nozzle??

. Gives higher propulsion efficiency

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What’s a disadvantage of the combined exhaust nozzles??

. Increases weight if the engine

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To achieve optimum thrust what must happen?

The exhaust gases must expand completely in an exhaust nozzle

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By having the gases completely expand in the exhaust nozzle, what does this ensure?

. Creates a laminar vortex free and axially oriented exhaust gas flow

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The exhaust airflow can happen due too?

The pressure ratio between the turbine discharge and ambient pressure

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What is the maximum airflow pressure ratio on a convergent exhaust nozzle?

2:1
(At high pressure ratios, do not get a higher airflow as it will get chocked)

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what nozzle is used for pressure ratios more than 2:1??

Convergent - divergent nozzles

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What type of aircraft are convergent - divergent nozzles used on?

Aircraft that fly faster than speed of sound

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What type of exhaust nozzle do modern turbofan engines have??

Convergent exhaust nozzles with wide exhaust nozzles that don’t choke

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What unit is used to express noise??

. Effective perceived noise deCiBel (EPNdB)

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How can internal noise be minimised in the exhaust nozzle?

By reducing airflow distribution which causes turbulence

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What provides very powerful noise suppression?

Acoustic linings which turns sound energy into heat energy by the sound waves being reflected

What is a disadvantage if acoustic linings?

Increases engine weight

What is the main external noise source?

exhaust jet

What are the two methods an external jet noise be reduced?

. Mixing it with the atmosphere in a short mixing region
. Additional mixing of ambient air to exhaust gas before going to nozzle

What is the main function of thrust reversers??

Produce extra braking force by deflecting the exhaust gas stream in opposite direction

What angle deflection would be ideal?

180 degrees

What is the actual angle deflection??

. 45-60 degrees deflection

On modern turbofan engines with a high bypass ratio, what air is used for thrust reversers?

. Only fan airflow because it creates the most amount of thrust

Can thrust reversers be used on the ground or during flight?

On the ground only

How is the clamshell door ( on old aircraft) operated?

Pneumatically by bleed air from HP compressor

How is the bucket door ( in older aircraft) reverser operated?

. Hydraulically operated

On turbo fan engines with a high bypass ratio, what air is used for thrust reversers??

Only the cold fan air is deflected give reverse thrust

What is the most common type of fan reversers??

Cascade type reversers with translating sleeves

What is another type of thrust reversers?

. Pivoting door - hydraulically activated

What are the main disadvantages of thrust reversers and their operation?

. Has problems operating at low speeds ( can ingest their own reverse thrust) . Can cause stall due to disturbed airflow . Whirls up a lot of dust and dirt from runway causing FOD

How can you minimise the disadvantages of reverse operation??

. Airflow need to be matched to engine position angle.

On four engine aircraft’s, reversers stream is important as it may get ingested by the outer engines, how to prevent?

. Each airflow directs the airflow to the safest possible direction

If there is a faulty reverse thruster, what can still happen?

. The aircraft can be released for service, but all of the have to be deactivated as only an extra breaking

What are the 3 main subsystems on a thrust reverser?

. The control system . The reverser actuation system . The airflow deflection system

What does the control system do?

Activates thrust reversers and increases power fit reverse thrust

What does the reverser actuation system do?

Either pnumatically or hydraulically component Moves the airflow deflection mechanism by signals from the reverser control system

What does the airflow deflection system do?

Directs airflow in the optimum direction for safe reverse thrust

What is the purpose of the thrust reverser interlock system??

. Ensures engine power can only be increased after the reverser is fully deployed

What type of hydraulic causation systems used on?

. On reversers with large blocker doors

What make’s hydraulics reverser systems more complicated?

Because they need to be synchronised

Pneumatic reverser actuation systems are only used in??

Cascade toe thrust reversers with translating sleeves (Usually have air motors from bleed air)

All thrust reversers actuation systems must have what to ensure safety??

. A locking system to ensure the reverser is kept safe in towed position and cannot move unintentionally

Cascade segments all look different, yet they all deflect airflow fwd but??

. Some deflect airflow 45 degrees upward . Some deflect airflow 45 degrees downwards . Some deflect airflow 90 degrees straight out of fan air duct . Some segments are totally blocked

What does the reverse unlock message mean??

Indicates the reverser is not in a safe stowed position or is in movement

What colour is the reverse unlock message in??

Amber

What does a green reverse light indicate??

. Reverser is fully deployed . Throttle interlock is realised so engine power can be increased for reverse thrust