Napier Cub

The Napier Cub was an unusual and very large experimental 1,000 horsepower (750 kW) 16-cylinder 'X' pattern liquid-cooled aero engine built by the British engine company D. Napier & Son. The Cub was the only Napier 'X' engine design. First flown on 15 December 1922 in an Avro Aldershot biplane bomber aircraft, the only other application was in the Blackburn Cubaroo. Only six engines of this type were ordered and produced.[1]

Napier Cub rear view.
Type Piston aero engine
Manufacturer D. Napier & Son
First run 1919
Major applications Avro Aldershot
Blackburn Cubaroo
Number built 6


The four banks of four cylinders were arranged in a flattened 'X' when viewed from the front. The angle between the upper cylinders was 52.5 degrees, the lower cylinders 127.5 degrees, which gave an angle of 90 degrees between the outer cylinder banks. The cylinders consisted of separate individual steel forgings with welded steel water cooling jackets. The carburettor was situated below the propeller reduction gear at the front of the engine and fed the inlet valves through four inlet manifolds. The valve drive gear, magnetos and pumps were fitted to the rear of the crankcase.

Specifications (Cub)

Data from Lumsden[2]

General characteristics


  • Valvetrain: Single overhead camshaft with four poppet valves per cylinder
  • Fuel system: Updraught carburettor
  • Fuel type: Petrol
  • Cooling system: Liquid cooled
  • Reduction gear: Spur geared, reduction ratio 0.489:1, left hand tractor


See also

Comparable engines

Related lists



  1. Lumsden 2003, p.171.
  2. Lumsden 2003, p.170.


  • Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.
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