Bentley BR1

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.

Preserved Bentley BR1
Type Rotary engine
Manufacturer Humber Limited
Major applications Sopwith Camel
Developed from Clerget 9B

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,[1] to produce a modified version to solve these problems.[2]

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, and the stroke increased to 6.7 inches (17 cm) which allowed power to be increased to 150 horsepower (110 kW).[3] The cost of the engine was also reduced, falling to £605 per engine.[2]

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 inferior 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.[3]

The BR.1 was developed as the BR.2, a heavier, more powerful engine, which powered, among other types or aircraft, the Camel's eventual replacement, the Sopwith Snipe.



Data from Jane's Fighting Aircraft of World War I [4]

General characteristics


  • 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

See also

Related development

Comparable engines

Related lists


  1. Barstow, Donald (1978). W.O. Bentley - Engineer. Sparkville, Somerset, UK: Haynes publications. ISBN 0-85429-215-2.
  2. Gunston, Bill (1999). The Development of Piston Engines (Second ed.). Sparkville, Somerset, UK: Patrick Stephens. ISBN 1-85260-599-5.
  3. Gunston, Bill (1986). World Encyclopedia of Aero Engines. London: Guild Publishing.
  4. Jane's Fighting Aircraft of World War I. London: Random House. 2001. p. 274. ISBN 1-85170-347-0.
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