JET PROPULSION Part 6 Thrust Augmentation and Reversers

Reheat or Afterburning 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 types of augmentation systems, Water Injection and Reheat or Afterburning

Water Injection Water Injection Systems cools the turbine, Operation of either Water or Water Methanol systems cools the turbine, and allows water to be injected into the fuel spray nozzles which cools the air flow in the combustor allowing more fuel to be added.

Water Injection Water Injection allows water to be injected Rolls-Royce Spey Turbo Fan Series Water flow Increased Primary Fuel flow Primary Fuel flow Combustion Chamber Water Injection allows water to be injected via additional nozzles built into the fuel spray nozzles. Operation of the water injection system automatically resets the fuel control unit to allow more fuel to flow.

Water Injection Water Injection allows water to be injected Rolls-Royce Spey Turbo Fan Series Water flow Increased Primary Fuel flow Primary Fuel flow Combustion Chamber Water Injection allows water to be injected via 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.

Water Injection Water cools the turbine, More Power. More Power. Rolls-Royce Spey Turbo Fan Series Water flow Increased Primary Fuel flow Primary Fuel flow Combustion Chamber Water cools the turbine, increases pressure and velocity More Power. Cooler turbine means more fuel can be added More Power.

Water Methanol Injection Dart Engine Turbo Prop Series Water Methanol Tank and Pump Water Methanol Control Unit The Control Unit has two functions: Switching water-methanol flow through the unit when the throttle moves to the take-off position. Regulating rate flow based upon engine power, and atmospheric pressure.

Water Methanol Injection Dart Engine Turbo Prop Series Water Methanol Tank and Pump Torque Pressure (ENGINE POWER) Water Methanol Control Unit Water cools the turbine, increases pressure & velocity More Power. Cooler turbine means more methanol can be added Even More Power. More power means coarser propeller pitch More Thrust.

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The Re-Heat/Afterburn System Provides extra thrust without increasing the engine's frontal area

The Re-Heat/Afterburn System Engine Rear End Reheat System (Afterburner) Heat Shields Variable Nozzle Closed Jet Pipe Spray Tubes Vapour Gutters 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 fuel in the jet pipe.

The Re-Heat/Afterburn System Variable Nozzle Opens Variable Nozzle Closed Jet Pipe Gas stream without reheat 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 pressure and to ensure reheat has no effect on the engine.

The Re-Heat/Afterburn System Visible ‘shock waves’ appear in the exhaust plume Concord was the only passenger aircraft to have Reheat/Afterburners. In military aircraft afterburner use is used for Take-off, In-flight acceleration and Combat only due to the extremely high fuel consumption rate.

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Thrust Reversal altering Jet reaction to a forward direction, 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.

Reverser Effects Thrust reversers reduce the landing roll out. Shorter Landing Roll-out Thrust reversers reduce 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 Diverting some or all of a rearward directed jet in an almost forward direction, will provide a reverse thrust. The gas stream should be directed in 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.

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Thrust Reversers Translating Cowl Type BLOCKER DOORS BLOCKER DOORS Reverse Thrust CASCADES Normal Forward Thrust Used on – The Tri-Star and C17 (illustrated) The C17 deployment is extremely unusual in 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.

Thrust Reversers Pivoting Door Type The RAF Sentinel R17 (illustrated) Reverse Thrust Normal Forward Thrust 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. SENTINEL LANDING – THRUST REVERSERS DEPLOYED

VC10 LANDING – THRUST REVERSERS DEPLOYED Clam Shell Door Type CLAM SHELL DOOR CLAM SHELL DOOR Reverse Thrust Normal Forward 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.

Thrust Reversers Target Door Type The Tornado (illustrated) Reverse Thrust Normal Forward 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 Reversers Other Methods REVERSE PITCH PROPELLER Reversing the pitch of the propeller blades, sends the thrust in a totally forward direction. Used on Hercules DROGUE PARACHUTE Parachutes can be deployed which increase the drag and increase the deceleration of the aircraft. Used on Vulcan

Thrust Reversers Translating Cowl Type Pivoting Door Type The Tri-Star and C17 Pivoting Door Type The Sentinel R17 Clam Shell Door Type The VC 10 Target Door Type The Tornado

Questions ?

Check of Understanding How does water injection increase power in a jet engine? It makes the combustion burn slower It heats the air flow into the engine allowing more fuel to be added It allows less fuel to be used It cools the air flow in the combustor allowing more fuel to be added

Check of Understanding Which of the following is a type of jet engine augmentation system? Rocket Boosting Water Injection Supercharging Turbocharging

Check of Understanding In a typical reheat system, oxygen is required in the jet pipe for combustion. Where does the reheat oxygen come from? Oxygen is pumped in with the extra fuel Slipstream air is scooped into the jet pipe Unburnt oxygen from the combustion chambers From on board oxygen bottles

Check of Understanding Which sentence is true? Afterburning…. is restricted for take-off and combat. adds more fuel to the reheat section. c. results in an extremely high fuel consumption. d. produces visible shock waves in the exhaust. A and C only A, C and D only A, B and D only A, B, C and D

Check of Understanding After-burning in a jet engine involves burning additional fuel in the: Combustion Chamber Compressor Jet pipe Turbine

Check of Understanding What is the function of the Spray tubes in the afterburner? To inject water to control the temperature To add more air to the combustion process To control the afterburner internal pressure To add more fuel to the combustion process

Check of Understanding When is reheat used in a combat aircraft? At take-off For in-flight acceleration During combat manoeuvrings All of the above

Check of Understanding In a modern reheat system, how is the flame ignited? By the heat from the combustor By catalytic igniters By igniter plugs in the jet pipe By heat and compression

Check of Understanding Thrust reversers generally fall into four types, what are these types? Transmission cowl, pilot doors, crab shell doors and bucket doors Translating cowl, balanced doors, clamshell doors and target doors Translating cowl, pivot doors, clamshell doors and target doors Transmission cowl, pilot doors, clamshell doors and target doors

Check of Understanding What is thrust reversing? Turning the engine to point in the opposite direction Redirecting the engine exhaust in a forward direction Making the engine shaft rotate in the opposite direction Driving the aircraft wheels backwards

Check of Understanding Which type of thrust reverser is shown in the illustration? Translating cowl Clamshell door Pivot door Target door

Check of Understanding Reverse thrust is simply a method of altering what? Primary air-flow The engine cooling Jet reaction The engine RPM

Check of Understanding Which type of thrust reverser is shown in the illustration? Translating cowl Clamshell door Pivot door Target door

Check of Understanding Which of the following aircraft use the clamshell door system? Tornado Sentinel R17 VC 10 Tristar

Check of Understanding Which type of thrust reverser is shown in the illustration? Translating cowl Clamshell door Pivot door Target door

Check of Understanding Which of the following aircraft use the target door system? Tornado Vulcan Hercules Tristar

Check of Understanding Which type of thrust reverser is shown in the illustration? Translating cowl Clamshell door Pivot door Target door

Check of Understanding Which of the following aircraft use the translating cowl system? C17 Globemaster Vulcan R17 Sentinel Hercules

Check of Understanding Which type of thrust reverser is shown in the illustration? Translating cowl Clamshell door Pivot door Target door

Check of Understanding Which of the following aircraft use the pivot door system? Tornado Sentinel R17 VC 10 Tristar

Check of Understanding Which of the following statements applies to the process of afterburning, as used in some jet engines? It provides extra thrust without: Increasing the exhaust velocity Removing any more oxygen from the exhaust gases Increasing the engine's frontal area The use of additional fuel

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JET PROPULSION End of Presentation