RAF 4

RAF 4
	Preserved RAF 4a engine at the Science Museum (London)
Type	Piston inline aero engine
Manufacturer	Royal Aircraft Factory
Designer	A.J. Rowledge
First run	December 1914
Major applications	Royal Aircraft Factory R.E.8
Number built	>3,600
Developed from	RAF 1

The RAF 4 is a British air-cooled, V12 engine developed for aircraft use during World War I. Based on the eight–cylinder RAF 1 it was designed by the Royal Aircraft Factory but produced by the two British companies of Daimler and Siddeley-Deasy. The RAF 5 was a pusher version of the same engine.^[1]

Turbocharger

A turbocharged experimental version of the RAF 4, the RAF 4d, was developed using a Rateau exhaust-driven turbocharger. The engine was test-flown in a R.E.8, but the turbocharging experiments were abandoned after the turbine failed on 4 May 1918.^[2]

Variants

RAF 4: 1914 - Prototype engine, 140 horsepower (104 kW).
RAF 4a: 1917 - Main production variant, 150 horsepower (112 kW). 3,608 built.
RAF 4d: 1916 - 180 horsepower (134 kW), experimental supercharger installation. 16 built.
RAF 4e: 1917 - 240 horsepower (180 kW), strengthened cylinders and enlarged valves.
RAF 5: 1915 - 150 horsepower (112 kW), pusher version with fan-cooling.
RAF 5b: 170 horsepower (127 kW), increased bore version of RAF 5.

Applications

RAF 4

RAF 5

Engines on display

A preserved RAF 4a engine is on public display at the Science Museum (London).

Specifications (RAF 4a)

Data from Lumsden^[3]

General characteristics

Type: 12-cylinder, upright, 60-degree Vee engine
Bore: 3.94 in (100 mm)
Stroke: 5.51 in (140 mm)
Displacement: 806.15 cu in (13.2 L)
Dry weight: 680 lb (308 kg)

Components

Valvetrain: EOI (side-valve inlet, exhaust overhead)
Fuel system: Twin Claudel-Hobson Mk.1A carburettors
Cooling system: Air-cooled
Reduction gear: 0.5:1, Left-hand tractor

Performance

Power output: 163 hp (122 kW) at 1,800 rpm (takeoff power)
Specific power: 0.2 hp/cu in (9.2 kW/L)
Compression ratio: 4.3:1
Power-to-weight ratio: 0.24 hp/lb (0.4 kW/kg)

References

Notes

^ Gunston, 1989, p. 156.
^ Hare 1990, p. 265
^ Lumsden 2003, p. 224.

Bibliography

Gunston, Bill. World Encyclopaedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9
Hare, Paul R. The Royal Aircraft Factory. London: Putnam, 1990. ISBN 0-85177-843-7
Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.