JET PROPULSION Part 6 Thrust Augmentation and Reversers.

JET PROPULSION

Part 6

Thrust Augmentationand Reversers

Thrust Augmentation

Is a method of extracting more power from Internal Combustion Engines.

It’s a form of ‘Power Boosting’

We shall examine two main typesof augmentation systems,

Water Injectionand

Reheat or Afterburning

Water Injection Systems

Operation of either Water or Water Methanol systems

cools the turbine, and allows water to be injected

into the fuel spray nozzleswhich cools the air flow in the combustor

allowing more fuel to be added.

Water Injection

Water InjectionRolls-Royce Spey Turbo Fan Series

Primary Fuel flow

Water flow

Water Injection allows water to be injectedvia additional nozzles built into the fuel spray nozzles.

Operation of the water injection systemautomatically resets the fuel control unit

to allow more fuel to flow.

IncreasedPrimary

Fuel flowCombustion Chamber


Primary Fuel flow

Water flow

Water Injection allows water to be injectedvia additional nozzles built into the fuel spray nozzles.

The water injection system automatically resets the fuel control unit to allow more fuel to flow.

Water cools the turbine, increases pressure and velocity.More Power.

Cooler turbine means more fuel can be added.More Power.

IncreasedPrimary

Fuel flowCombustion Chamber


Primary Fuel flow

Water flow

Combustion Chamber

IncreasedPrimary

Fuel flow

Water cools the turbine, increases pressure and velocity

More Power.

Cooler turbine means more fuel can be added More Power.

Water Methanol Control Unit

Water Methanol InjectionDart Engine Turbo Prop Series

Water Methanol Tank and Pump

The Control Unit has two functions:

1. Switching water-methanol flow through the unit when the throttle moves to the take-off position.

2. Regulating rate flow based upon engine power, and atmospheric pressure.

Water Methanol Control Unit

Water Methanol InjectionDart Engine Turbo Prop Series

Water Methanol Tank and Pump

Torque Pressure (ENGINE POWER)

More power means coarser propeller pitch More Thrust.

Cooler turbine means more methanol can be added Even More Power.

Water cools the turbine, increases pressure & velocityMore Power.

Questions ?

The Re-Heat/Afterburn System

Provides extra thrust

without increasing

the engine's frontal area

Engine Rear End Reheat System (Afterburner)


The system consists of a larger diameter jet pipe, with internal heat shields.

Inside are vapour gutters and fuel spray tubes.

The variable nozzle is closed (reheat off) or opened (reheat on)

Reheat/Afterburn consists of burning additional fuelin the jet pipe.

Spray Tubes Vapour Gutters Heat Shields

Jet PipeVariable NozzleClosed


Jet Pipe

The vapour gutters spray fuel into the gas stream.

The Spray Tubes add more fuel to the process, which is fired by catalytic igniters,

using oxygen from the combustion chambers.

The variable nozzles open to maintain pressureand to ensure reheat has no effect on the engine.

Gas stream without reheat

Variable NozzleOpens

Variable NozzleClosed


Visible ‘shock waves’ appear in the exhaust plume

Concord was the only passenger aircraftto have Reheat/Afterburners.

In military aircraft afterburner use is used for Take-off,

In-flight accelerationand Combat only

due to the extremely high fuel consumption rate.

Questions ?

Thrust Reversal

Thrust Reversal is simply a method of altering Jet reaction

from a rearward direction (which provides normal forward thrust)

to a forward direction,

providing reverse thrust(using the power as a decelerating force)

and is operated by the pilot on landing.

Thrust reversersreduce the landing roll out.

In civilian aircraft this is primarily to save wear and tear on the brakes, to clear busy runways and to achieve quick turn-rounds, i.e. keeping passenger delays to a minimum.

In military aircraft the above can apply, and also to give shorter landings for tactical reasons,i.e. the aircraft can land and unload supplies quickly,thus minimizing any risk in hostile environments.

Reverser Effects

Shorter Landing Roll-out

Diverting some or all of a rearward directed jetin an almost forward direction,will provide a reverse thrust.

The gas stream should be directedin a completely forward direction; but this is not possible for aerodynamic reasons.

Yet an angle of 90o to 45o forward is common,giving reverse thrust up to 50% of forward thrust.

Reverser Effects

Questions ?

Thrust ReversersTranslating Cowl Type

BLOCKER DOORS

BLOCKER DOORS

TRANSLATING COWL

TRANSLATING COWL

Reverse Thrust

CASCADESUsed on –

The Tri-Star and C17 (illustrated)

The C17 deployment is extremely unusualin that it can deploy the thrust reversers in flight

for a tactical descent from high altitude,thereby minimising the threat of

anti-aircraft fire etc in a hostile area.

Normal Forward Thrust

Thrust ReversersPivoting Door Type


Reverse Thrust

PIVOTING DOOR

PIVOTING DOOR

SENTINEL LANDING – THRUST REVERSERS DEPLOYED

Used on –

The RAF Sentinel R17 (illustrated)

It comprises of two doors on this system, but multi door systems are replacing

the translating cowl designs on high by-pass fan engines.

Thrust ReversersClam Shell Door Type


CLAM SHELL DOOR

CLAM SHELLDOOR

Reverse Thrust

VC10 LANDING – THRUST REVERSERS DEPLOYED

Used on –

The VC 10 (illustrated)

All four engines have the reverser fitted,but on RAF aircraft, the two inboard

reversers have been inhibited because the jet blast from all four

created too much buffeting on the fin and elevator.

TARGET DOOR

TARGET DOOR

Thrust ReversersTarget Door Type


Reverse Thrust

Used on –

The Tornado (illustrated)

This system does redirect the jet thrust slightly forward, witness the exhaust staining

on the aircraft fuselage and tail.

Thrust ReversersOther Methods

Reversing the pitch of the propeller blades, sends the thrust in a totally forward direction.

Used on Hercules

REVERSE PITCH PROPELLER

Parachutes can be deployed whichincrease the drag and increase thedeceleration of the aircraft.

Used on Vulcan

DROGUE PARACHUTE

Thrust Reversers

Translating Cowl TypeThe Tri-Star and C17

Pivoting Door TypeThe Sentinel R17

Clam Shell Door TypeThe VC 10

Target Door TypeThe Tornado

Questions ?

How does water injection increase power in a jet engine?

It cools the air flow in the combustorallowing more fuel to be added

It makes the combustion burn slower

It allows less fuel to be used

It heats the air flow into the engineallowing more fuel to be added

Check of Understanding


Which of the following is a type of jet engine augmentation system?

Turbocharging

Rocket Boosting

Supercharging

Water Injection

In a typical reheat system, oxygen is required in the jet pipe for combustion.

Where does the reheat oxygen come from?

From on board oxygen bottles

Oxygen is pumped in with the extra fuel

Unburnt oxygen from the combustion chambers

Slipstream air is scooped into the jet pipe


Which sentence is true? Afterburning….

a. is restricted for take-off and combat.

b. adds more fuel to the reheat section.

c. results in an extremely high fuel consumption.

d. produces visible shock waves in the exhaust.

A, B, C and D

A and C only

A, B and D only

A, C and D only


After-burning in a jet engine involves burning additional fuel in the:

Turbine

Combustion Chamber

Jet pipe

Compressor


What is the function of the Spray tubes in the afterburner?

To add more fuel to the combustion process

To inject water to control the temperature

To control the afterburner internal pressure

To add more air to the combustion process


When is reheat used in a combat aircraft?

All of the above

At take-off

During combat manoeuvrings

For in-flight acceleration


In a modern reheat system, how is the flame ignited?

By heat and compression

By the heat from the combustor

By igniter plugs in the jet pipe

By catalytic igniters


Thrust reversers generally fall into four types,what are these types?

Transmission cowl, pilot doors, clamshell doors and target doors

Transmission cowl, pilot doors, crab shell doors and bucket doors

Translating cowl, pivot doors, clamshell doors and target doors

Translating cowl, balanced doors, clamshell doors and target doors


Check of UnderstandingWhat is thrust reversing?

Driving the aircraft wheels backwards

Turning the engine to point in the opposite direction

Making the engine shaftrotate in the opposite direction

Redirecting the engine exhaust in a forward direction

Check of UnderstandingWhich type of thrust reverseris shown in the illustration?

Target door

Pivot door

Clamshell door

Translating cowl

Reverse thrust is simply a method of altering what?

The engine RPM

Primary air-flow

Jet reaction

The engine cooling



Target door

Translating cowl

Pivot door

Clamshell door

Which of the following aircraft use the clamshell door system?

Tristar

Tornado

VC 10

Sentinel R17



Target door

Translating cowl

Pivot door

Clamshell door

Which of the following aircraft use the target door system?

Tristar

Tornado

Hercules

Vulcan



Target door

Pivot door

Clamshell door

Translating cowl

Which of the following aircraft use the translating cowl system?

Hercules

C17 Globemaster

R17 Sentinel

Vulcan



Target door

Pivot door

Clamshell door

Translating cowl

Which of the following aircraft use the pivot door system?

Tristar

Tornado

VC 10

Sentinel R17


Which of the following statements applies to the process of afterburning,

as used in some jet engines? It provides extra thrust without:

The use of additional fuel

Increasing the exhaust velocity

Increasing the engine's frontal area

Removing any more oxygen from the exhaust gases


Questions ?

JET PROPULSION

End of Presentation

JET PROPULSION Part 6 Thrust Augmentation and Reversers.

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