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.
In April 1918 a turbocharged experimental version of the RAF 4d was developed using a Rateau turbocharger, the engine being flown in the R.E.8 B738.
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.
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
Royal Aircraft Factory F.E.2
Royal Aircraft Factory F.E.4
A preserved RAF 4a engine is on public display at the Science Museum (London).
Data from Lumsden
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)
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
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)
