Bristol Pegasus

From Wikipedia, the free encyclopedia

Bristol Pegasus piston engine

For the vectored thrust engine, see Rolls-Royce Pegasus

Bristol Pegasus is also a motor-racing club in Bristol, England.

The Bristol Pegasus was a British 9-cylinder one-row air-cooled radial engine used in the 1930s and 1940s aircraft.

1 History
2 Specifications (Pegasus XVIII)
3 References
4 See also

[edit] History

The Pegasus was designed by Sir Roy Fedden as the follow-on to the Bristol Aeroplane Company's very successful Bristol Jupiter, following lessons learned in the Mercury effort. Confusingly, Bristol chose to reuse the name many years later for the engine used in the Hawker-Siddeley Harrier; that engine later became known as the Rolls-Royce Pegasus.

The Pegasus was the same size, displacement and general steel/aluminium construction as the Jupiter, but other improvements allowed the maximum engine speed to be increased from 1,950 to 2,600 rpm for take-off power. This improved performance considerably from the Jupiter's 580 hp (430 kW), to the first Pegasus II with 635 hp (474 kW), to 690 hp (515 kW) in the first production model Pegasus III, and eventually to the late-model Pegasus XXII with 1,010 hp (750 kW) thanks to the two-speed supercharger (introduced on the Pegasus XVIII) and 100-octane fuel. This gave rise to the claim "one pound per horsepower" reflecting the excellent power-to-weight ratio.

The most famous use of the Pegasus was on the Fairey Swordfish, Vickers Wellington, and Short Sunderland. It was also used on the Bristol Bombay, Vickers Wellesley, Westland Wallace, and Saro London. Like the Jupiter before it, the Pegasus was also licensed, but this time only by the PZL company in Poland. It was used it on PZL.23 Karaś and PZL.37 Łoś bombers.

Over 17,000 Pegasus engines were built.

Bristol Pegasus engine with some components labeled. Click image for a larger version.

[edit] Specifications (Pegasus XVIII)

General characteristics

Type: 9-cylinder supercharged air-cooled radial engine
Bore: 5.75 in (146 mm)
Stroke: 7.5 in (191 mm)
Displacement: 1,753 in³ (28.7 L)
Diameter: 55.3 in (1,405 mm)
Dry weight: 1,180 lb (535 kg)

Components

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

Performance

Power output:
- 1,000 hp (745 kW) at 2,600 rpm at 3,000 ft (915 m) with 87-octane fuel
- 885 hp (660 kW) at 2,600 rpm at 15,500 ft (4,730 m) with 87-octane fuel
- 1,065 hp (795 kW) at 2,600 rpm at 1,250 ft (380 m) with 100-octane fuel
- 965 hp (720 kW) at 2,600 rpm at 13,000 ft (3,965 m) with 100-octane fuel
Specific power: 0.60 hp/in³ (27.7 kW/L) at 1,250 ft (380 m) with 100-octane fuel
Compression ratio: 7:1
Power-to-weight ratio: 0.90 hp/lb (1.49 kW/kg)