Michael Palmer, whose superb Triumph Twin we featured recently, has also sent  these photographs of a tremendous Bentley BR2 made earlier.

Origins of the engine were in the French 130 horsepower Clerget 9B, an important engine for the British Royal Naval Air Service and Royal Flying Corps produced under licence in Britain and powering a number of important British aircraft including the Sopwith Camel. However, it was expensive at £907 and prone to overheating.

Lieutenant W. O. Bentley was asked to solve its problems. Bentley came up with a modified engine - fitted with aluminium cylinders, cast iron liners, and aluminium pistons. Dual ignition was added to improve reliability, and the stroke increased which allowed power to be increased to 150 horsepower. The cost of the engine reduced to £605.

The resulting engine was initially known as the A.R.1 for ‘Admiralty Rotary’, and later the BR.1 ‘Bentley Rotary’. The BR.1 developed into the BR.2, a heavier, more powerful engine.

Lew Blackmooor won the Duke of Edinburgh Challenge Trophy with his model of this engine and then produced a detailed book. No castings are required. Drawings are available at https://www.sarikhobbies.com/product/bentley-rotary-pe33/