|Preserved Bentley BR1 at the Midland Air Museum|
|Major applications||Sopwith Camel|
|Developed from||Clerget 9B|
The Bentley BR.1 was a British rotary aircraft engine of the First World War. Designed by the motor car engine designer W. O. Bentley, the BR.1 was built in large numbers, being one of the main powerplants of the Sopwith Camel.
Design and development
The 130 horsepower (97 kW) Clerget 9B was an important engine for the British Royal Naval Air Service and Royal Flying Corps, being license-produced in Britain and powering a number of important British aircraft, including the Sopwith Camel. However, at £907 a copy it was expensive, and prone to overheating, so the Admiralty asked Lieutenant W. O. Bentley, an established pre-war engine designer, to produce a modified version to solve these problems.
Bentley came up with his idea of an engine - fitted with aluminium cylinders with cast iron liners, and aluminium pistons. Dual ignition was introduced to improve reliability (much as the 160 CV Gnome 9N had already been), and the stroke increased to 6.7 inches (17 cm) which allowed power to be increased to 150 horsepower (110 kW). The cost of the engine was also reduced, falling to £605 per engine.
The resulting engine, initially known as the A.R.1 for "Admiralty Rotary", but later called the BR.1 ("Bentley Rotary") was manufactured in quantity, although initially against Admiralty orders. It was standardised for the Camel in RNAS squadrons, but unfortunately there were never enough to entirely replace the older and more expensive Clerget engine in British service, and most RFC Camel squadrons continued to use Clerget engines; in fact licensed production of the Clerget continued.
Data from Jane's Fighting Aircraft of World War I 
- Type: 9-cylinder air-cooled rotary engine
- Bore: 4.72 inches (120 mm)
- Stroke: 6.69 inches (170 mm)
- Displacement: 1,055.9 cu in (17.303 L)
- Dry weight: 397 pounds (180 kg)
- Cooling system: Air-cooled
- Power output: 150 bhp (110 kW) at 1,250 rpm
- Fuel consumption: 11 gallon/hr (50 L/hr)
- Oil consumption: 12 pints/hr (6.8 L/hr)
- Power-to-weight ratio: 0.38 bhp/lb
- Barstow, Donald (1978). W.O. Bentley - Engineer. Sparkville, Somerset, UK: Haynes publications. ISBN 0-85429-215-2.
- Gunston, Bill (1999). The Development of Piston Engines (Second ed.). Sparkville, Somerset, UK: Patrick Stephens. ISBN 1-85260-599-5.
- Gunston, Bill (1986). World Encyclopedia of Aero Engines. London: Guild Publishing.
- Jane's Fighting Aircraft of World War I. London: Random House. 2001. p. 274. ISBN 1-85170-347-0.