JET ENGINE PROPULSION Chapter 4 Types JET

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.

JET ENGINE TYPES Different types: Turbo Jet Avon, Olympus 593 Bypass Engine Small Bypass Conway, Spey, BR 700 Medium Bypass Pegasus, BR 715, V 2500 Large Bypass RB 211, Trent Series Turbo Propeller Dart, Tyne, BR 715 TP 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 17 Stage Compressor driven by: - Turbo Jet 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.

Turbo Jet JET ENGINE TYPES 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.

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

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

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

Turbo Jet JET ENGINE TYPES Allows front end of compressor to slow down – move less air AND Allows rear end of compressor to speed up – move more air HPC LPC driven by HPT driven by 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 Bypass allows air not required in the HPC to flow around the outside of it Known as the core engine.

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

JET ENGINE TYPES Bypass Layout High Bypass Engine RB 211 Series (Trent) Three shaft layout – all rotate same direction LP(Fan) IP and HP AXIAL Flow Compressors Boeing 747 and later series, Airbus A 330 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 Shaft RR Dart Reduction Gearbox Dart RDa 6 = 2 stage turbine Dart RDa 7 = 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 F 27, Fairchild F 27, Briguet Alize, (and P 51 Mustang and Dakota!)

Turbo Prop Tyne JET ENGINE TYPES Reduction Gearbox 9 Stage HP Compressor Prop Shaft (via Reduction Gearbox) 6 Stage LP Compressor 1 Stage HP Turbine 3 Stage LP Turbine C 160 Transall, Shorts Belfast, Bristol Britannia, Brequet Atlantic, Avro Lincoln, Canadair CL 44, Vickers Vanguard, Aeritalia 222.

JET ENGINE TYPES Turbo Prop RR Allison T 56 -A-15 Reduction Gearbox Thrust Strut Turbine drives compressor and propeller 14 Stage HP Compressor Air Intake Output Shaft C 130 Hercules, P 3 Orion, Lockheed Electra, E 2 C Hawkeye. 4 Stage Turbine

JET ENGINE TYPES Turboshaft Lycoming T 55 -GA-714 - with Free Power Turbine Combining Transmission Boeing CH 47 Chinook Front Rotor Transmission Rear Rotor Transmission

JET ENGINE TYPES Any Questions?