The Napier Dagger was a 24-cylinder H-pattern ''(or H-Block)'' air-cooled engine designed by

Frank Halford Major Frank Bernard Halford CBE FRAeS (7 March 1894 – 16 April 1955) was an English aircraft engine designer. He is best known for the series of de Havilland Gipsy engines, widely used by light aircraft in the 1920s and 30s. Career Educate ...

and built by Napier before World War II. It was a development of the earlier

Napier Rapier The Napier Rapier was a British 16-cylinder H pattern air-cooled aero engine designed by Frank Halford and built by Napier & Son shortly before World War II. Design and development The Rapier was the first of Napier's H cylinder engines. The ...

Design and development

The H-Block has a compact layout, as it essentially consists of two vertically opposed, flat-twelve inline engines lying side-by-side and driving side-by-side crankshafts. Another advantage is that since the cylinders are opposed, the motion in one is balanced by the opposite motion in the one on the opposite side, leading to very smooth running. The Dagger was remarkable for its fast rotation, running at up to 4,000

rpm Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or r⋅min−1) is a unit of rotational speed (or rotational frequency) for rotating machines. One revolution per minute is equivalent to hertz. Standards ISO 80000-3:2019 def ...

but unlike the later

Napier Sabre The Napier Sabre is a British H engine, H-24-cylinder, coolant, liquid-cooled, sleeve valve, piston aircraft engine, aero engine, designed by Frank Halford, Major Frank Halford and built by D. Napier & Son during World War II. The engine evolv ...

, it had conventional

poppet valve A poppet valve (also sometimes called mushroom valve) is a valve typically used to control the timing and quantity of petrol (gas) or vapour flow into or out of an engine, but with many other applications. It consists of a hole or open-ended ch ...

s. Although considered a masterpiece of engine design by

, there were problems with cooling, maintenance, manufacturing and weight, which were not solved during the Dagger's lifetime and went unresolved well into the lifetime of the

, its successor. The Dagger powered the

Hawker Hector The Hawker Hector is a British biplane army co-operation and liaison aircraft of the late 1930s; it served with the Royal Air Force and saw brief combat in the Battle of France in May 1940. Some Hectors were later sold to Ireland. It was named ...

army co-operation aircraft and the Handley Page Hereford, a variant of the Hampden bomber. The operational usefulness of the Hector was restricted by engine cooling problems, which made it unsuitable for operations in the tropics and the Hereford was found to be unsuitable for combat, because its Dagger VIII engines were noisy and unreliable. The Dagger was also used in the experimental

Martin-Baker MB 2 The Martin-Baker MB 2 was a British private-venture fighter prototype based on a simple basic structure that had been developed in the earlier MB 1 civil aircraft. Although briefly evaluated as a fighter by the Royal Air Force, the MB 2 was li ...

fighter.

Variants

;Napier-Halford Dagger I 1934 – 650 hp. ;Dagger II 1938 – 755 hp ;Dagger IIIM 1938 – 725 hp ;Dagger VIII 1938 – 1000 hp, intermediate altitude supercharger, initially known as E.108

Applications

Some of these aircraft were test beds only. *

Fairey Battle The Fairey Battle is a British single-engine light bomber that was designed and manufactured by the Fairey Aviation Company. It was developed during the mid-1930s for the Royal Air Force (RAF) as a monoplane successor to the Hawker Hart and Ha ...

testbed only * Handley Page Hereford - a few aircraft used for training only *

Hawker Hart The Hawker Hart is a British two-seater biplane light bomber aircraft that saw service with the Royal Air Force (RAF). It was designed during the 1920s by Sydney Camm and manufactured by Hawker Aircraft. The Hart was a prominent British aircraf ...

- single private venture prototype

Engines on display

A preserved Napier Dagger is on display at the

Royal Air Force Museum London The Royal Air Force Museum London (also commonly known as the RAF Museum) is located on the former Hendon Aerodrome, in North London's Borough of Barnet. It includes five buildings and hangars showing the history of aviation and the Royal Air ...

Specifications (Napier Dagger III MS)

References

* Jane's All the World's Aircraft 1942

Notes

Bibliography

* * Gunston, Bill. ''World Encyclopedia of Aero Engines: From the Pioneers to the Present Day''. 5th edition, Stroud, UK: Sutton, 2006. * Lumsden, Alec. ''British Piston Engines and Their Aircraft''. Marlborough, UK: Airlife Publishing, 2003. . * White, Graham. ''Allied Aircraft Piston Engines of World War II: History and Development of Frontline Aircraft Piston Engines Produced by Great Britain and the United States During World War II''. Warrendale, Pennsylvania: SAE International, 1995.

External links

Napier Power Heritage Trust site

{{Napierengines

Dagger A dagger is a fighting knife with a very sharp point and usually one or two sharp edges, typically designed or capable of being used as a cutting or stabbing, thrusting weapon.State v. Martin, 633 S.W.2d 80 (Mo. 1982): This is the dictionary or ...

1930s aircraft piston engines H engines