Bristol Mercury

The Mercury was a 9 cylinder one-row radial aircraft engine that was developed by the Bristol Aeroplane Company in 1925, as their Bristol Jupiter was reaching the end of its lifespan. At first there was little interest in an engine that was the same power as the Jupiter, but eventually the Air Ministry funded three prototypes and it became clear the design was another winner for Roy Fedden.

With the widespread introduction of superchargers to the aero industry, 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 stoke reduced by one inch. 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 then 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.

Specifications

For the Mercury VIII:

Bore / Stroke / Displacement: 5.75" x 6.5", 1519 cu in (24.9 litre)

Compression ratio: 7:1

HP: 840 hp at 2750 RPM (max continuous), 730 hp at 2650 RPM (take-off)

Weight: 980 lbs

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The Bristol Mercury was a newspaper from Bristol, published in the 1800s.