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The Napier Dagger Aircraft Engine

Frank Halford designed the Dagger in the the early 1930's and Napier built a prototype which first ran in 1934. The Napier Dagger is an air-cooled aero-engine which has 24-cylinders placed in a H-pattern, this resulted in a very compact and high reving engine. An important advantage of Halford's "H" design is each cylinder bank is in phase with an opposite cylinder bank and is nearly perfectly balanced, vibration is low resulting in a very smooth running engine.

Napier Dagger Aircraft Engine


The Dagger's compact design did not come without disadvantages, cooling was not easily achieved, manufacturing and routine maintenance were difficult and time consuming, also while the engine was compact for it's capacity and power output it weighed as much, or even more than conventional designs of a similar performance.

In service the Napier Dagger was impractical in hot climates due to overheating, although the engine was smooth running, 24 cylinders running at four thousand rpm (800 detonations per second) was very noisy compared to a 12 cylinder engine running at 3,000 rpm (300 detonations per second) and was unpleasant for the aircrew. The Napier Dagger's complex design resulted in a lot of potential for things to go wrong and fixing them was a nightmare for the ground crew. Having two Dagger engines in an aircraft, as used on the RAF's Handley Page Hereford doubled all the engine's negative attributes for all concerned. These problems were addressed  with the later Napier Sabre

Napier Dagger III MS Specifications:

  • Type: Twenty-four-cylinder supercharged air-cooled H engine with two poppet valves per cylinder
  • Bore: 3.813 in (96.8 mm)
  • Stroke: 3.75 in (95.25 mm)
  • Displacement: 1,027 in (16.8 L)
  • Length: 80 in (2,032 mm)          Width: 22.5 in (584 mm)      Height: 45.125 in (1,146 mm)
  • Dry weight: 1,358 lb (616 kg)
  • Supercharger: Single-speed centrifugal type supercharger, 5.04:1 reduction
  • Fuel system: Napier-Claudel-Hobson carburettor
  • Fuel type: 87 Octane petrol
  • Cooling system: Air-cooled
  • Reduction gear: Spur, 2.69:1

Aircraft that were powered by the Napier Dagger

Handley Page HerefordHawker Hart
Hawker Hector 

Power output:

  • 725 hp (541 kW) at 3,500 rpm for takeoff
  • 794 hp (592 kW) at 4,000 rpm at 5,000 ft (1,520 m)
  • Specific power: 0.77 hp/in (35.13 kW/l)
  • Compression ratio: 7.75:1
  • Specific fuel consumption: 0.43 lb/(hph) (261 g/(kWh))
  • Oil consumption: 0.18-0.35 oz/(hph) (7-13 g/(kWh))

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