Bentley Rotary Aero Engine

Bentley Rotary Aero Engine

The Bentley AR1 Rotary Aero Engine later to become the BR1. On loan from Bentley Motors, Picture by Tom Dine


From Dr Tom Dine – Aeroengine Researcher W O Bentley Memorial Foundation

When the name WO Bentley is mentioned most people visualise large green cars thundering down the Mulsanne straight on their way to another Le Mans victory.  However WO was not all British Racing Green and laurel wreaths, he cut his engine design teeth on aeroplane and Tank engines.

It was during the early part of the Great War that WO found himself as a newly commissioned RNVR Lieutenant working in Chiswick at Gwynnes Ltd attempting to improve the quality and reliability of the Clerget engines they were producing.  He was also tasked with introducing the innovation that had ensured he had won several car racing records at Brooklands pre-war, the Aluminium piston.

His work was successful and he squeezed an extra 20BHP out of the Clerget engine but identified several design defects.  He was asked to carry out research and design a modified engine eliminating the problems which were causing the RNAS pilots and ground crew so many problems. 

The research culminated in a nine cylinder engine, the Clerget 9J, which went into limited production and was fitted to a small number of Sopwith aircraft, the  Fleet Air Arm Museum Yeovilton, has an example in its Sopwith Baby), but WO knew he could do better.  Gwynnes were fully occupied with the output of the Clerget engines and could not focus on the research sufficiently so WO was sent to Coventry, to Humbers to be precise.

It was at Coventry that he designed the Bentley Rotary 1 (BR1) which came just in time and, mated to the Sopwith Camel airframe, allowed British pilots to regain air supremacy.  The Bentley-Camel, as the aeroplane was known to those who flew it, was the mount of the RNAS pilots, the RFC generally flying Camels with Clerget or Le Rhone engines as there were not enough Bentley engines to go round.

Having proved his design credentials WO went on to design the big brother of the BR1 the Bentley Rotary 2 (BR2).  This engine entered the war late fitted to the Sopwith Snipe but made a useful contribution, the most notable episode being the winning of the Victoria Cross by Major William Barker who took on a large formation of enemy aeroplanes in his Snipe dispatching 3 or 4. 

The Sopwith Snipe was eventually declared obsolete by the RAF in 1928.

All the while WO was carrying out his design work on the BR2 at Coventry he also kept abreast of the performance of his engines by visiting the squadrons, discussing the problems and carrying out modifications.

It would appear that he also moonlighted at Daimlers working on the engines fitted to the initial Tanks increasing the available horsepower, how this was achieved and what effects the work had is still the subject of research.

The WO Bentley Memorial Foundation is aiming to commemorate the 100th anniversary of the First World War and the impact of the work of WO by carrying out a project of research into how the engines developed and what effect they had on the people who used them and had to work on them.  The results will be disseminated through lectures to schools, colleges and clubs and displays in museums.  An important part of the project is an attempt to re-create the drawings of an AR1, the one which is currently in the WOBMF museum, and to produce a working replica engine.

The Foundation would like to hear of any members who would like to become involved in the research, drawings or practical engineering please contact us. -

 The W.O.Bentley Memorial Foundation, W O Bentley Memorial Building, Ironstone Lane, WROXTON, Banbury, Oxfordshire, OX15 6ED, England.  

Tel: +44(0)1295 738886, Fax: +44(0)1295 738811,     

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