Bristol Hercules

The Bristol Hercules is a 14-cylinder two-row radial aircraft engine designed by Sir Roy Fedden and produced by the Bristol Engine Company starting in 1939. It was the first of their single sleeve valve (Burt-McCollum, or Argyll, type) designs to see widespread use, powering many aircraft in the mid-World War II time frame. The rationale behind the single sleeve valve design was two-fold: to provide optimum intake and exhaust gas flow in a two-row radial engine, improving its volumetric efficiency; and to allow higher compression ratios, thus improving its thermal efficiency.

General characteristics

  • Type: 14-cylinder, two-row, supercharged, air-cooled radial engine
  • Bore: 5.75 in (146mm)
  • Stroke: 6.5 in (165mm)
  • Displacement: 2,360 in (38.7 L)
  • Length: 53.15 in (1,350mm)
  • Diameter: 55 in (1,397mm)
  • Dry weight: 1,929 lb (875kg)


  • Power output:
    • 1,272hp (949 kW) at 2,800rpm for takeoff
    • 1,356hp (1,012 kW) at 2,750rpm at 4,000 ft (1,220 m)
  • Specific power: 0.57hp/in (26.15 kW/l)
  • Compression ratio: 7.0:1
  • Specific fuel consumption: 0.43 lb/(hph) (261 g/(kWh))
  • Power-to-weight ratio: 0.7hp/lb (1.16 kW/kg)


  • Valvetrain: Gear-driven sleeve valves with five ports per sleeve three intake and two exhaust
  • Supercharger: Single-speed centrifugal type supercharger
  • Fuel system: Claudel-Hobson carburettor
  • Fuel type: 87 Octane petrol
  • Cooling system: Air-cooled
  • Reduction gear: Farman epicyclic gearing, 0.44:1