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Bristol Pegasus

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The Bristol Pegasus is a British nine-cylinder single-row air-cooled radial engine. Used mainly for military aircraft in the 1930s and 1940s, Bristol reused the name many years later for the turbofan engine used in the Hawker Siddeley Harrier; that engine later became known as the Rolls-Royce Pegasus.

Two Bristol Pegasus engines remain airworthy in 2009, powering Fairey Swordfish aircraft operated by the Royal Navy Historic Flight.

Design and development

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. The Mercury was a small engine that produced about as much power as the Jupiter, through a combination of supercharging that improved the "charge", and various changes to improve the operating RPM. Power of a piston engine can be calculated by multiplying the charge per cylinder by the number of cycles per second; the Mercury improved both and thereby produced more power for a given size. The primary advantage was a much improved power-to-weight ratio due to better volumetric efficiency.[1]

Bristol Pegasus fitted to a Fairey Swordfish

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.

Some notable users of the Pegasus were the Fairey Swordfish, Vickers Wellington, and Short Sunderland. It was also used on the Anbo 41, Bristol Bombay, Saro London, Short Empire, Vickers Wellesley and the Westland Wallace. Like the Jupiter before it, the Pegasus was also licensed by the PZL company in Poland. It was used on the PZL.23 Karaś and PZL.37 Łoś bombers.

In Italy, Alfa Romeo built both the Jupiter (126-RC35) and the Pegasus under licence, with the engine based on the Pegasus designated as the Alfa Romeo 126-RC34 with the civil version as the 126-RC10.[2] In Czechoslovakia it was built by Walter Engines and was known as the Pegas.[3]

Approximately 32,000 Pegasus engines were built.[1] The Pegasus set three height records: in 1932, 1936 and 1937. It was used for the first flight over Mount Everest, and in 1938 set the world's long-distance record.[4]


Note:[5] Template:Multicol



Engines on display

Bristol Pegasus engines can be viewed installed in aircraft at the Royal Air Force Museum and the Imperial War Museum Duxford. An unrestored Pegasus recovered from the sea bed is on display at the Bristol Aero Collection, Kemble Airport, Gloucestershire.


As of August 2009 two Bristol Pegasus engines remain airworthy in England. They power the two Fairey Swordfish aircraft operated by the Royal Navy Historic Flight.[6]

Specifications (Pegasus XVIII)

File:Bristol Pegasus labeled.jpg
Bristol Pegasus engine with some components labelled


See also

Related development

Related lists



  1. 1.0 1.1 Lumsden 2003, p.104.
  2. Alfa Aero Engines. Retrieved on 3 August 2009.
  3. Walter engines history - Retrieved: 3 August 2009
  4. Bridgman (Jane's) 1998, p.270.
  5. List from Lumsden (British aircraft only), the Pegasus may not be the main powerplant for these types
  6. Royal Navy Historic Flight - Aircraft Retrieved: 3 August 2009


  • Bridgman, L, (ed.) (1998) Jane's fighting aircraft of World War II. Crescent. ISBN 0-517-67964-7
  • Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9
  • Gunston, Bill. Development of Piston Aero Engines. Cambridge, England. Patrick Stephens Limited, 2006. ISBN 0-7509-4478-1
  • Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.

Further reading

  • Gunston, Bill. Development of Piston Aero Engines. Cambridge, England. Patrick Stephens Limited, 2006. ISBN 0-7509-4478-1

External links

Wikimedia Commons has media related to:

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This article is licensed under the GNU Free Documentation License.
It uses material from the Wikipedia article "Bristol Pegasus".