The Bristol Pegasus is a British nine-cylinder, single-row, air-cooled radial aero 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 Mercury and Jupiter engines, later variants could produce 1,000 horsepower (750 kW) from its capacity of 1,750 cubic inches (28 L) by use of a geared supercharger.
Further developments of the Pegasus created the fuel-injected Bristol Draco and the diesel cycle Bristol Phoenix, both types being produced in limited numbers. In contrast, by the end of production over 30,000 Pegasus engines had been built. Aircraft applications ranged from single-engine biplanes to the four-engined Short Sandringham and Sunderland flying boats. Several altitude and distance records were set by aircraft using the Pegasus.
The Bristol Siddeley company reused the name many years later for the turbofan engine used in the Hawker Siddeley Harrier and which became known as the Rolls-Royce Pegasus when Rolls-Royce took over that company. Two Bristol Pegasus engines remain airworthy in 2010, powering Fairey Swordfish aircraft operated by the Royal Navy Historic Flight, other examples are preserved and on public display in aviation museumss.
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.
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