Bristol Mercury XII
| Mercury | |
|---|---|
 |
|
| Preserved Bristol Mercury VII on display at the Royal Air Force Museum London | |
| Type | Piston aero engine |
| Manufacturer | Bristol Aeroplane Company |
| Designed by | Roy Fedden |
| First run | 1925 |
| Major applications |
Bristol Blenheim Gloster Gladiator Fokker D.XXI |
| Number built | 20,700 |
| Developed from | Bristol Jupiter |
| Developed into | Bristol Pegasus |
The Bristol Mercury is a nine-cylinder, air-cooled, single-row, piston radial engine. Designed by Roy Fedden of the Bristol Aeroplane Company it was used to power both civil and military aircraft of the 1930s and 1940s. Developed from the earlier Jupiter engine, later variants could produce 800 horsepower (600 kW) from its capacity of 1,500 cubic inches (25 L) by use of a geared supercharger.
Almost 21,000 engines were produced, with a number also being built in Europe under licence. At least three Bristol Mercuries remain airworthy in 2010, with other preserved examples on public display in aviation museums.
The Mercury was developed by the Bristol Aeroplane Company in 1925 as their Bristol 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 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.
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