Bristol Pegasus

:"For the vectored thrust engine, see Rolls-Royce Pegasus"

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

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. 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.

The Pegasus was the same size, displacement and general steel/aluminum 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 famous 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 it on 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 Alfa Romeo 126-RC34 and civil version as the 126-RC10.Cite web|url=http://www.aroca-qld.com/library_articles/alfa_romeo_aero_engines.php|title=Alfa Aero Engines|accessdate=2007-08-25|work=aroca-qld.com]

Over 17,000 Pegasus engines were built.

pecifications (Pegasus XVIII)

pistonspecs

ref=cite book|last=Tsygulev|title=Aviacionnye motory voennykh vozdushnykh sil inostrannykh gosudarstv ( _ru. Авиационные моторы военных воздушных сил иностранных государств)|publisher=Gosudarstvennoe voennoe izdatelstvo Narkomata Oborony Soyuza SSR|location=Moscow|year=1939|url=http://base13.glasnet.ru/text/aviamotory/t.htm]
type=Nine-cylinder single-row supercharged air-cooled radial engine
bore=5.75 in (146 mm)
stroke=7.5 in (190.5 mm)
displacement=1,752.8 in³ (28.72 L)
length=54.72 in (1,390 mm)
diameter=55.31 in (1,405 mm)
width=
height=
weight=1,111 lb (504 kg)
valvetrain=Four pushrod-actuated valves per cylinder — two intake and two sodium-filled exhaust
supercharger=Two-speed centrifugal type supercharger
turbocharger=
fuelsystem=Claudel-Hobson carburetor
fueltype=87 octane rating gasoline
oilsystem=Dry sump with one combination pressure/scavenge pump
coolingsystem=Air-cooled
power=
* 952 hp (710 kW) at 2,475 rpm for takeoff
* 986 hp (736 kW) at 2,600 rpm at 3,000 ft (915 m), first supercharger gear
* 873 hp (651 kW) at 2,600 rpm at 15,500 ft (4,730 m), second supercharger gear
specpower=0.56 hp/in³ (25.64 kW/l)
specfuelcon=0.52 lb/(hp•h) (319 g/(kW•h))
oilcon=0.28 oz/(hp•h) (11 g/(kW•h))
power/weight=0.89 hp/lb (1.46 kW/kg)
compression=6.4:1
reduction_gear=Farman epicyclic gearing, 0.5:1
components_other=Propeller: Rotol three-blade with variable pitch

Applications

;LTU
*ANBO IV;NED
*Fokker C.X;POL
*LWS-6 Żubr
*PZL.23 Karaś
*PZL.37 Łoś;GBR:
*Blackburn Baffin
*Boulton Paul Overstrand
*Bristol Bombay
*Handley Page Hampden
*Handley Page Harrow
*Saro London
*Short Empire
*Short Mayo Composite
*Short Sunderland
*Supermarine Stranraer
*Supermarine Walrus
*Vickers Vespa
*Vickers Victoria
*Vickers Vildebeest
*Vickers Vincent
*Vickers Valentia
*Vickers Wellington
*Vickers Wellesley
*Westland Wallace;ITA:
*Savoia-Marchetti SM.95

ee also

* Bristol Jupiter
* Bristol Mercury
* Bristol Phoenix

References

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