Alvis Leonides

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Alvis Leonides at MOSI.jpg
Alvis Leonides radial engine preserved at the Museum of Science and Industry, Manchester
Type Radial engine
National origin United Kingdom
Manufacturer Alvis
First run 1936
Major applications Percival Pembroke
Scottish Aviation Twin Pioneer
Developed into Alvis Leonides Major

The Alvis Leonides was a British air-cooled nine-cylinder radial aero engine first developed by Alvis Car and Engineering Company in 1936.[1]

Design and development[edit]

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.



Leonides 173 as fitted to the Bristol Sycamore


  • Harker Leo-cat — 1x 560 hp (418 kW)
  • Server-Aero Leo-cat — 1x 560 hp (418 kW)



  • A Leonides 126 powered Hunting Percival Provost (G-KAPW) with CAA permission to fly as XF603, owned by the Shuttleworth Trust and based at Old Warden, Bedfordshire is airworthy as of 2017, and is displayed to the public at home airshows during the airshow season.[2]
  • The 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.[3]
  • Two privately owned Scottish Aviation Twin Pioneers are flying in Australia

Engines on display[edit]

Preserved Alvis Leonides engines are on public display at the following museums:

Specifications (Leonides)[edit]

Alvis Leonides radial engine preserved at the Midland Air Museum

General characteristics

  • 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)

See also[edit]

Related development
Comparable engines
Related lists


  • Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9
  • Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.

External links[edit]