|Preserved RB.108 at the Royal Air Force Museum Cosford|
|Major applications||Short SC.1|
|Developed into||Rolls-Royce RB145|
Design and development
The RB108 was the first direct-lift turbojet produced by Rolls-Royce. It originated from a VTOL concept in which Alan A. Griffith proposed using a small number of specialised lift engines in a VTOL aircraft, separate from the engines which provided forward propulsion. Its power output (thrust) was not high enough for use as a practical engine in a production aircraft and was used only for research into VTOL. It was constructed from conventional materials. The next engine, the RB162, would have a compressor built mainly from glass-fibre composite and have a higher T/W ratio. The RB108 bearings and oil system were designed to operate with an engine attitude envelope which covered engine and aircraft tilting while transitioning between hovering and forward flight. When a fifth engine was installed in the SC.1 to provide forward thrust it had to be mounted at about 45 degrees to remain within the envelope. The exhaust was directed horizontally with a curved jetpipe.
The RB.108 was used in the Short SC.1, which used four for lift with an additional one mounted at an angle at the rear for propulsion, and the Mirage Balzac, which used eight vertically mounted RB.108s for lift. The Vereinigte Flugtechnische Werke (VFW) SG 1262 used five RB.108s, three mounted in tandem on the centreline, with one RB.108 either side.
The RB.108 was also the intended powerplant for several other VTOL aircraft designs, including one by Dornier.
Data from Aircraft engines of the World 1964/65 
- Type: Single-spool turbojet
- Length: 48.3 in (1,230 mm)
- Diameter: 20.8 in (530 mm)
- Dry weight: 267 lb (121 kg)
- Compressor: 8-stage axial flow
- Combustors: Annular
- Turbine: 2-stage axial flow
- Fuel type: JP-1 (D.Eng.R.D.2494)
- Oil system: Non-return, total loss with metering pumps at 20 psi (140 kPa)
- Maximum thrust:
- No bleed air: 2,500 lbf (11 kN) at 17500 rpm
- 11% Bleed air: 2,210 lbf (9.8 kN) at 17500 rpm (4.3 lb/s (2.0 kg/s) bleed)
- Overall pressure ratio: 5.33:1
- Air mass flow: 38.8 lb/s (17.6 kg/s)
- Turbine inlet temperature: 1,346 °F (730 °C; 1,003 K) (Turbine Inlet Temperature (TIT))
- Specific fuel consumption: 1.06 lb/lbf/h (108 kg/kN/h)
- Oil Consumption: 0.4 lb/lbf/h (41 kg/kN/h)
- Thrust-to-weight ratio: 9.3 lbf/lb (0.091 kN/kg)
- Rolls-Royce From The wings 1925-1971 Military Aviation, R.W.Harker, Oxford Illustrated Press Ltd., ISBN 0 902280 38 4, p.121
- Wilkinson, Paul H. (1964). Aircraft engines of the World 1964/65 (21st ed.). London: Sir Isaac Pitman & Sons Ltd. p. 138.
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