The Jupiter was designed during World War I by Roy Fedden of Cosmos Engineering.  During the rapid downscaling of military spending after the war, Cosmos became bankrupt in 1920 and was eventually purchased by the Bristol Aeroplane Company on the strengths of the Jupiter design and the encouragement of the Air Ministry. 

The engine matured into one of the most reliable on the market and the first air-cooled engine to pass the Air Ministry full-throttle test, the first to be equipped with automatic boost control, and the first to be fitted to airliners.  The Jupiter engine was fairly standard in design, but featured four valves per cylinder, which was uncommon at the time.  The cylinders were also machined from steel forgings with cast cylinder heads.  The Jupiter VIII and IXF engines were fitted to various versions of the Westland Wapiti aircraft from 1931 and the Bristol Jupiter IXF engine with forged cylinder heads delivered 550 hp with a compression ratio of 5.3:1.

The engine on display which originated from the Air Armaments School at Youngsfield, was recovered from the scrap yard of S.A. Metal in Salt River.  The Armstrong Siddeley Panther engine was also fitted to the Westland Wapiti.  Aircraft fitted with this engine had the prefix “P” before their serial numbers.