JET ENGINE PROPULSION Chapter 4 Types

JET ENGINE TYPES There are two ways of using the power from a jet engine. By taking as little power from the engine to turn the engine and using most of the power as thrust out of the exhaust. Or by taking most of the power from the engine to turn the engine and a drive shaft, which can be used to drive a piece of machinery. i.e. propeller, rotor or pump. The engine designer will look at the requirements and then decide on the best design for the job.

We need to look at the development of Gas Turbine Engines JET ENGINE TYPES Different types: - Turbo Jet Avon, Olympus 593 Bypass Engine Small Bypass Conway, Spey, BR700 Medium Bypass Pegasus, BR715, V2500 Large Bypass RB211, Trent Series Turbo Prop Propeller Dart, Tyne, BR715TP Turbo Shaft Helicopter Gem RN Ships Marine Spey Power Generation Industrial Spey and Trent To understand what is meant by ‘Turbo Jet’, ‘Bypass’, ‘Turbo Prop and ‘Turbo Shaft’ We need to look at the development of Gas Turbine Engines

JET ENGINE TYPES Rolls-Royce AVON Basic Shape and Layout Turbo Jet 17 Stage Compressor driven by: - a 3 Stage turbine With RPM (I.e. Thrust) changes, the airflow velocity does not change in proportion to engine RPM This can cause problems at low RPM. The rear of the compressor cannot cope with all of the air from the front of the compressor.

JET ENGINE TYPES Turbo Jet This can result in the rear end of compressor ‘choking’ i.e. NO or insufficient rearward movement of air So air blasts forwards Flame almost goes out - no power – no thrust This is called: - Compressor SURGE To alleviate this problem we need to get rid of some of the air at the rear of the compressor.

JET ENGINE TYPES Turbo Jet Rear end of compressor ‘unchoked’ Rearward movement of air restored Air dumped overboard Power restored BUT: - air dumped sideways out of the engine (aircraft) produces no thrust This is done through a Bleed Valve.

‘Excess’ air is dumped overboard through a valve Turbo Jet JET ENGINE TYPES ‘Bleed’ valve ‘Excess’ air is dumped overboard through a valve

JET ENGINE TYPES Turbo Jet Air dumped overboard Air dumped overboard reduces thrust and wastes fuel So a more efficient system was required Enter - Multiple shaft engines and the Bypass system

JET ENGINE TYPES Turbo Jet Allows front end of compressor to slow down – move less air AND Allows rear end of compressor to speed up – move more air driven by HPC HPT driven by LPC LPT Two shaft layout (Twin Spool System) Compressor surges lessened No wasted energy/thrust

JET ENGINE TYPES Bypass Layout Low Bypass Rolls-Royce Spey Adour BR 710 series Known as the core engine. Bypass allows air not required in the HPC to flow around the outside of it

JET ENGINE TYPES Pegasus Bypass Layout Medium Bypass Two shaft layout – Contra-rotation LP and HP AXIAL Flow Compressors In USAF Service – Harrier series Core flow to ‘Hot’ (rear) Nozzles Bypass flow to ‘Cold’ (front) Nozzles

JET ENGINE TYPES Bypass Layout High Bypass Engine RB211 Series (Trent) Three shaft layout – all rotate same direction LP(Fan) IP and HP AXIAL Flow Compressors Boeing 747 and later series, Airbus A330 and larger a/c

JET ENGINE TYPES The fan produces a large amount of thrust from the volume of air it moves backwards. The core engine has a two stage compressor which receives pressure air from the fan and so improves efficiency. The ratio of the air bypassing the core engine to the air in the core engine gives a dimension to the power split between the fan and the core. A normal bypass ratio is 5 or 4 to 1. i.e. 5 times more thrust from the fan.

JET ENGINE TYPES Rolls Royce Trent

JET ENGINE TYPES Turbo Prop RR Dart Dart RDa6 = 2 stage turbine Reduction Gearbox Prop Shaft Dart RDa6 = 2 stage turbine Dart RDa7 = 3 stage turbine Turbine drives 2 stage CENTRIFUGAL Compressor and Propeller Over 70 different Marks of Engine – basically different power levels – 15 different aircraft Was in service with RAF – Andover and Argosy Transport Aircraft. Fokker F27, Fairchild F27, Briguet Alize, (and P51 Mustang and Dakota!)

(via Reduction Gearbox) JET ENGINE TYPES Turbo Prop Tyne Reduction Gearbox 9 Stage HP Compressor 1 Stage HP Turbine 6 Stage LP Compressor 3 Stage LP Turbine Prop Shaft (via Reduction Gearbox) C160 Transall, Shorts Belfast, Bristol Britannia, Brequet Atlantic, Avro Lincoln, Canadair CL44, Vickers Vanguard, Aeritalia 222.

JET ENGINE TYPES Turbo Prop RR Allison T56-A-15 Reduction Gearbox Turbine drives compressor and propeller Thrust Strut 14 Stage HP Compressor 4 Stage Turbine Output Shaft Air Intake C130 Hercules, P3 Orion, Lockheed Electra, E2C Hawkeye.

JET ENGINE TYPES Turboshaft Lycoming T55-GA-714 - with Free Power Turbine Combining Transmission Rear Rotor Transmission Boeing CH47 Chinook Front Rotor Transmission

JET ENGINE TYPES Any Questions?