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Frank B. Halford was a talented independent British engine designer of the early and mid-twentieth century who worked for a number of manufacturers including de Havilland, Cirrus and Fiat. In 1928, he contracted with Napier for design of a series of air-cooled engines in a vertical H configuration having twin crankshafts geared together. There were two basic types, the 16-cylinder Rapier and the 24-cylinder Dagger. The Rapier, produced in small numbers, powered the Short Mercury seaplane. By 1935, the Dagger served a large military market, and the British Air Ministry ordered it in quantity. Both the lower powered Dagger I and Dagger II versions powered the Hawker Hart aircraft. The final version, the 712 kW (955 shp) Dagger VIII, powered the Fairey Battle I and Handley Page H.P.52 Hereford I.

Late in his career, with access to the work of Frank Whittle, Halford led the de Havilland Engine Co. where he designed turbine engines.

 Display Status This object is not on display at the National Air and Space Museum. It is either on loan or in storage.
Object Details
Date Circa 1938 Country of Origin United Kingdom Type PROPULSION-Reciprocating & Rotary Manufacturer Napier Aero Engines Ltd. Physical Description Type: Reciprocating, 24 cylinders, Air cooled, Supercharged Power rating: 470 kW (630 hp) at 3,500 rpm Displacement: 16.8 L (1,027 cu in) Bore and Stroke: 96.8 mm (3.8125 in.) x 95.3 mm (3.75 in.) Weight: 587 kg (1,295 lb) Dimensions Height 175.3 cm (69 in.), Width 99.1 cm (39 in.), Depth 223.5 cm (88 in.)
 Materials Steel, Paint, Aluminum, Magnesium, Wood, Stainless Steel, Rubber, Copper
 Inventory Number A19710930000 Credit Line Transferred from the U.S. Navy Data Source National Air and Space Museum Restrictions & Rights Open Access (CCO)
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