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Alvis Leonides


The Alvis Leonides was a British air-cooled nine-cylinder radial aero engines first developed by Alvis in 1936. Development of the nine-cylinder engine was led by Capt. George Thomas Smith-Clarke. The prototype engine, called 9ARS and which weighed 693 lb and developed 450 hp, was run in December 1936. In 1938 Airspeed (1934) Ltd lent their test pilot, George Errington, and their much rebuilt Bristol Bulldog (K3183), to carry out test flights. Development was continued at a reduced pace during the Second World War and following testing in an Airspeed Oxford and an Airspeed Consul (VX587) Alvis was ready to market the engine in 1947 as the Series 500 (502, 503 and sub-types) for aeroplanes and Series 520 for helicopters. (Most helicopter engines were direct drive - no reduction gearbox - with a centrifugal clutch and fan cooling). The first production use was the Percival Prince which flew in July 1948 and the Westland Sikorsky S-51 and Westland Dragonfly helicopters. From 1959 the stroke was increased to 4.8 inch for the Series 530 (mainly the Mk. 531 for Twin Pioneers) rated at 640 hp. It was Britain’s last high-power production piston aero-engine when manufacture ceased in 1966.

- Production -
Bristol Sycamore – 1x Mk. 173, 550 hp (410 kW)
Percival P.66 President/Prince - 2 x 503/7A, Mk 128 01/2, 540/560 hp (RAF: Pembroke, RN; Sea Prince)
Percival Provost – 1x 126, 550-hp (410 kW)
Scottish Aviation Pioneer – 1 x 503/7A, Mk 128 01/2, 540/560 hp
Scottish Aviation Twin PioneerCC1 – 2 x 514/8, 550 hp
Scottish Aviation Twin PioneerCC2 – 2 x 531/8,Mk138, 640 hp
Westland Dragonfly – 1x 521/1, 520shp (388 kW)
Westland Widgeon – 1x 521/1, 520shp (388 kW)

- Conversions
Harker Leo-cat – 1x 560 hp (418 kW)
Server-Aero Leo-cat – 1x 560 hp (418 kW)

- Prototypes
Agusta AZ8-L 4x 503/2
de Havilland Canada DHC-2 Beaver Mk.2 – 1x 502/4, 520 hp
Fairey Gyrodyne – one 525 hp to drive rotor and propeller
Fairey Jet Gyrodyne – one 525 hp to drive air compressor and propellers
Handley Page H.P.R.2 (WE505 only) – 1 x 502/4 550 hp
SR-N1 Hovercraft - the first hovercraft

Type: 9-cylinder supercharged air-cooled radial piston engine.
Bore: 4.8 inch (122 mm)
Stroke: 4.41 inch (112 mm)
Displacement: 718.6 in3 (11.8 L)
Diameter: 41 inch (1.04 m)
Dry weight: 815 lb (370 kg)
Valvetrain: Two pushrod-actuated poppet valves per cylinder with sodium-cooled exhaust valve.
Supercharger: Single speed, single stage, boost pressure automatically linked to the throttle.
Fuel system: Hobson single-point fuel injection unit.
Fuel type: Petrol, 115 Octane
Oil system: Dry sump
Cooling system: Air-cooled.
Power output: 550 hp (410 kW)



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