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Note: This is a sub-section of Bristol Engine Co
The name Mercury was first given to a 14-cylinder radial engine designed by Roy Fedden and Leonard Butler at Brazil, Straker and Co; it was notable for having the cylinders arranged helically instead of as two rows.
Later these designers re-used the name for another engine, better known than the first, which was made by the Bristol Engine Co. The Bristol Mercury was a 9-cylinder one-row piston radial engine used on British aircraft in the 1930s and 1940s.
The Mercury was developed by the Bristol Engine Co in 1925 because their Jupiter was reaching the end of its lifespan. Although the Mercury initially failed to attract much interest, the Air Ministry eventually funded three prototypes and it became another winner for the designer Roy Fedden.
With the widespread introduction of superchargers to the aviation industry in order to improve altitude performance, Fedden felt it was reasonable to use a small amount of boost at all times in order to improve performance of an otherwise smaller engine. Instead of designing an entirely new block, the existing Jupiter parts were re-used with the stroke reduced by one inch (25 mm). The now-smaller capacity engine was then boosted back to Jupiter power levels, while running at higher rpm and thus requiring a reduction gear for the propeller. The same techniques were applied to the original Jupiter-sized engine to produce the Pegasus.
The Mercury's smaller size was aimed at fighter use, and it powered the Gloster Gauntlet and its successor, the Gloster Gladiator. It was intended that the larger Pegasus would be for bombers, but as the power ratings of both engines rose the Mercury found itself being used in almost all roles. Perhaps its most famous use was in a twin-engine light bomber, the Bristol Blenheim. Outside the United Kingdom, Mercury was licence-built in Poland and used in their PZL P.11 fighters. It was also built by NOHAB in Sweden and used in the Swedish Gloster Gladiator fighters and in the Saab 17 dive-bomber. In Italy, it was built by Alfa-Romeo as the Mercurius.
Each cylinder head of the engine weighs 56 lb as a forging. It emerges as a finished head weighing 17lb having passed through 106 operations.
1938 The King visited the Austin factory where controls for variable pitch airscrews and other components were being assembled for Mercury VIII engines.
General characteristics (Mercury XV)