The Jupiter was designed during
World War I by
Roy Fedden of
Brazil Straker and later
Cosmos Engineering. The first Jupiter was completed by Brazil Straker in 1918 and featured three carburettors, each one feeding three of the engine's nine cylinders via a spiral deflector housed inside the induction chamber. During the rapid downscaling of military spending after the war, Cosmos Engineering 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. It was 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 was a fairly standard design but featured four valves per cylinder, which was uncommon at the time. The
cylinders were machined from steel forgings, and the cast
cylinder heads were later replaced with aluminium alloy following studies by the
Royal Aircraft Establishment. In 1927, a change was made to a forged head design due to the rejection rate of the castings. The Jupiter VII introduced a mechanically-driven supercharger. The Jupiter VIII was the first to be fitted with reduction gears. In 1925, Fedden started designing a replacement for the Jupiter using a shorter stroke to increase the
revolutions per minute (rpm), and included a
supercharger to increase power, resulting in the
Bristol Mercury of 1927. Applying the same techniques to the original Jupiter-sized engine in 1927 resulted in the
Bristol Pegasus. Neither engine would fully replace the Jupiter for a few years. In 1926 a Jupiter-engined
Bristol Bloodhound with the
registration G-EBGG completed an endurance flight of , during which the Jupiter ran for a total of 225 hours and 54 minutes without failure or replacement.
Licensed production The Jupiter saw widespread use in licensed versions, with fourteen countries eventually producing the engine. In France,
Gnome-Rhone produced a version known as the Gnome-Rhône 9 Jupiter that was used in several local civilian designs, as well as achieving some export success.
Siemens-Halske took out a licence in Germany and produced several versions of increasing power, eventually resulting in the
Bramo 323 Fafnir, which saw use in German wartime aircraft. In Japan, the Jupiter was licence-built from 1924 by
Nakajima, forming the basis of its own subsequent radial aero-engine design, the
Nakajima Ha-1 Kotobuki. It was produced in Poland as the PZL Bristol Jupiter, in Italy as the
Alfa Romeo 126-RC35, and in
Czechoslovakia by
Walter Engines. The most produced version was in the
Soviet Union, where its
Shvetsov M-22 version powered the initial Type 4 version of the
Polikarpov I-16 (55 units produced). Type 4 Polikarpovs can be identified by their lack of exhaust stubs, rounded NACA cowling and lack of cowling shutters, features which were introduced on the
Shvetsov M-25 powered Type 5 and later variants (total production 4,500+ units). Production started in 1918 and ceased in 1930. ==Variants==