The Alvis Leonides was a British air-cooled nine-cylinder radial aero engine first developed by Alvis Car and Engineering Company in 1936.
Design and development
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 WS-51 Dragonfly helicopters. From 1959 the stroke was increased to 4.8 inches 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.
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 hpScottish Aviation Twin PioneerCC1 — 2 x 514/8, 550 hpScottish Aviation Twin PioneerCC2 — 2 x 531/8,Mk138, 640 hpWestland Dragonfly — 1x 521/1, 520shp (388 kW)Westland Widgeon — 1x 521/1, 520shp (388 kW)Harker Leo-cat — 1x 560 hp (418 kW)Server-Aero Leo-cat — 1x 560 hp (418 kW)Agusta AZ.8L 4x 503/2de Havilland Canada DHC-2 Beaver Mk.2 — 1x 502/4, 520 hpFairey Gyrodyne — one 525 hp to drive rotor and propellerFairey Jet Gyrodyne — one 525 hp to drive air compressor and propellersHandley Page H.P.R.2 (WE505 only) — 1 x 502/4 550 hpSR.N1 Hovercraft — the first hovercraftThe world’s only surviving Gloster Gauntlet, formerly powered by a Bristol Mercury VI engine, is now powered by a Leonides 503.A privately owned, Leonides-powered Percival Pembroke remains airworthy in March 2010."Two privately owned Scottish Aviation Twin Pioneers are flying in AustraliaPreserved Alvis Leonides engines are on public display at the following museums:
Fleet Air Arm MuseumGatwick Aviation MuseumMidland Air MuseumMuseum of Science and Industry (Manchester)Royal Air Force Museum CosfordShuttleworth CollectionThe Helicopter Museum (Weston)Cranwell Aviation Heritage CentreSolent SkyType: 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 OctaneOil system: Dry sumpCooling system: Air-cooled.Power output: 550 hp (410 kW)