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, 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
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
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
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
Prop
Shaft
RR Dart
Reduction
Gearbox
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!)
JET ENGINE TYPES
Turbo Prop
Tyne
Reduction
Gearbox
9 Stage HP
Compressor
Prop Shaft
(via Reduction
Gearbox)
6 Stage LP
Compressor
1 Stage HP
Turbine
3 Stage LP
Turbine
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
Thrust
Strut
Turbine drives compressor and propeller
14 Stage HP
Compressor
Air
Intake
Output
Shaft
C130 Hercules, P3 Orion, Lockheed Electra, E2C Hawkeye.
4 Stage
Turbine
JET ENGINE TYPES
Turboshaft
Lycoming T55-GA-714 - with Free Power Turbine
Combining Transmission
Boeing CH47 Chinook
Front Rotor
Transmission
Rear Rotor
Transmission
JET ENGINE TYPES
Any Questions?