Rolls-Royce_RB.108 Knowpia

RB.108
	Preserved RB.108 at the Royal Air Force Museum Cosford
Type	Turbojet
Manufacturer	Rolls-Royce Limited
First run	1955
Major applications	Short SC.1
Developed into	Rolls-Royce RB145 lift/cruise engine

The Rolls-Royce RB.108 was a British jet engine designed in the mid-1950s by Rolls-Royce specifically for use as a VTOL lift engine. It was also used to provide horizontal thrust in the Short SC.1.

Design and development edit

The RB.108 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^[1] and was used only for research into VTOL. It was constructed from conventional materials. (The next lift engine, the RB.162, would have a compressor built mainly from glass-fibre composite and have a higher T/W ratio.) The RB.108 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.

Operational history edit

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 Dassault Balzac V, 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.

A similar lift jet was designed by Bristol Siddeley, the BS.59, with a thrust of 8,000 lb the engine was intended for the projected Focke-Wulf Fw 260.^[2]

Applications edit

Specifications (RB.108) edit

Data from Aircraft engines of the World 1964/65.^[3]

General characteristics

Type: Single-spool turbojet
Length: 48.3 in (123 cm)
Diameter: 20.8 in (53 cm)
Dry weight: 267 lb (121 kg)

Components

Compressor: 8-stage axial flow
Combustors: Annular
Turbine: 2-stage axial flow
Fuel type: JP-1
Oil system: Non-return, total loss with metering pumps at 20 psi (140 kPa)

Performance

Maximum thrust:

No bleed air: 2,500 lbf (11 kN) at 17,500 rpm

11% Bleed air: 2,210 lbf (9.8 kN) at 17,500 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

References edit

Notes edit

^ Rolls-Royce From The wings 1925-1971 Military Aviation, R.W.Harker, Oxford Illustrated Press Ltd., ISBN 0 902280 38 4, p.121
^ "bristol siddeley | 1962 | 1015 | Flight Archive". www.flightglobal.com. Archived from the original on 4 November 2012.
^ Wilkinson, Paul H. (1964). Aircraft engines of the World 1964/65 (21st ed.). London: Sir Isaac Pitman & Sons Ltd. p. 138.