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The RAF 4 was 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]

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

• Armstrong Whitworth F.K.8
• Bristol F.2 Fighter
• Royal Aircraft Factory B.E.12
• Royal Aircraft Factory R.E.7
• Royal Aircraft Factory R.E.8
• Siddeley-Deasy R.T.1
• Vickers F.B.14

RAF 5

• Royal Aircraft Factory F.E.2
• Royal Aircraft Factory F.E.4

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)

See also

Related development

• RAF 1

Comparable engines

• Rolls-Royce Falcon

Related lists

• List of aircraft engines

References

Notes

Bibliography

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