Bristol Mercury

The Bristol Mercury was a 9-cylinder one-row piston radial engine used on British aircraft in the 1930s and 1940s.

History

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 stoke 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.

Variants

Mercury VIII - 730 hp (545 kW) at 2,650 rpm for takeoff, 840 hp (625 kW) at 2,750 rpm maximum continuous power
Mercury XV - 840 hp (625 kW) at 2,750 rpm at 14,000 ft (4,270 m) maximum power with 87-octane fuel; 995 hp (740 kW) at 2,750 rpm at 9,250 ft (2,820 m) maximum power with 100-octane fuel
Mercury XX - 870 hp (650 kW) at 2,650 rpm at 4,500 ft (1,370 m) maximum power

Specifications (Mercury XV)

General characteristics

Type: 9-cylinder supercharged air-cooled radial engine
Bore: 5.75 in (146 mm)
Stroke: 6.5 in (165 mm)
Displacement: 1,520 in³ (24.9 L)
Diameter: 51.5 in (1.307 m)
Dry weight: 1,065 lb (485 kg)

Components

Valvetrain: Four pushrod-actuated valves per cylinder, two inlet and two sodium-cooled exhaust valves
Supercharger: High-speed centrifugal, single-stage single-speed
Fuel system: Claudel-Hobson carburetor with automatic boost and mixture control
Fuel type: 87- or 100-octane gasoline
Oil system: Dry sump with one combination pressure/scavenge pump

Performance

Power output:
840 hp (625 kW) at 2,750 rpm at 14,000 ft (4,270 m) maximum power with 87-octane fuel
995 hp (740 kW) at 2,750 rpm at 9,250 ft (2,820 m) maximum power with 100-octane fuel
Specific power: 0.65 hp/in³ (29.7 kW/L) with 100-octane fuel
Compression ratio: 7:1
Specific fuel consumption: 1.0 lb/(hp·h) (0.61 kg/(kW·h))
Power-to-weight ratio: 0.93 hp/lb (1.53 kW/kg)

References

Bridgman, L, (ed.) (1998) Jane's fighting aircraft of World War II. Crescent. ISBN 0-517-67964-7

External links

Recorded sound of the Bristol Mercury VI engine used in PZL P.11c (mp3 format)