Royal Aircraft Factory RAF 4 / RAF 5
Designed by A.J. Rowledge, the RAF 4 was a British air-cooled, V-12 engine developed for aircraft use during World War I. Based on the eight–cylinder RAF 1 it was designed at the Royal Aircraft Factory, first run in December 1914, but produced by the two British companies of Daimler and Siddeley-Deasy.
More than 3600 were built.
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.
1914 - Prototype engine, 140 horsepower (104 kW).
1917 - Main production variant, 160 horsepower (119 kW). 3,608 built.
1916 - 180 horsepower (134 kW), experimental supercharger installation. 16 built.
1917 - 240 horsepower (180 kW), strengthened cylinders and enlarged valves.
1915 - 150 horsepower (112 kW), pusher version with fan-cooling.
170 horsepower (127 kW), increased bore version of RAF 5.
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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)