Alvis Leonides
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. Variants. "Notes:" LE designations from Air Ministry system ( where known); 500 series designations from Alvis company designation system; Mark numbers for civil variants. Engines on display. Preserved Alvis Leonides engines are on public display at the following museums: