The Sopwith Cobham was a British twin-engined

triplane A triplane is a fixed-wing aircraft equipped with three vertically stacked wing planes. Tailplanes and canard foreplanes are not normally included in this count, although they occasionally are. Design principles The triplane arrangement may ...

bomber aircraft designed and built by the

Sopwith Aviation Company The Sopwith Aviation Company was a British aircraft company that designed and manufactured aeroplanes mainly for the British Royal Naval Air Service, the Royal Flying Corps and later the Royal Air Force during the First World War, most famously ...

during the

First World War World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...

. The only twin-engined aircraft built by Sopwith, the Cobham did not fly until after the end of the war, and was unsuccessful due to the failure of its engines, only three

prototypes A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and software programming. A prototype is generally used to ...

being built.

Design and development

The Sopwith Cobham was designed to meet a June 1918 requirement for a twin-engined long-range medium bomber to equip the

Royal Air Force The Royal Air Force (RAF) is the United Kingdom's air and space force. It was formed towards the end of the First World War on 1 April 1918, becoming the first independent air force in the world, by regrouping the Royal Flying Corps (RFC) and ...

(to meet RAF Type IV, VI and VII specifications). The design, by

Herbert Smith Herbert Smith LLP was a multinational law firm headquartered in London, United Kingdom. The firm was founded in the City of London in 1882 by Norman Herbert Smith and merged with the Australian law firm Freehills on 1 October 2012, forming Herber ...

was a twin-engined

with a wooden box-girder fuselage with fabric and

plywood Plywood is a material manufactured from thin layers or "plies" of wood veneer that are glued together with adjacent layers having their wood grain rotated up to 90 degrees to one another. It is an engineered wood from the family of manufactured ...

covering, while the wings, which were of equal span, each had two

spruce A spruce is a tree of the genus ''Picea'' (), a genus of about 35 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal (taiga) regions of the Earth. ''Picea'' is the sole genus in the subfami ...

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and fabric covering. It was designed to be powered by two of the new

ABC Dragonfly The ABC Dragonfly was a British radial engine developed towards the end of the First World War. It was expected to deliver excellent performance for the time and was ordered in very large numbers. It proved, however, to be extremely unreliable ...

radial engine The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is ca ...

s, which promised high power for low installed weight, and had been ordered in large numbers to equip most of the prospective types planned to equip the RAF.Mason 1994, p. 121. It had a crew of three, with a pilot sitting in a cockpit just forward of the leading edge of the wings, while gunners sat in nose and dorsal positions, each armed with Lewis guns on

Scarff ring The Scarff ring was a type of machine gun mounting developed during the First World War by Warrant Officer (Gunner) F. W. Scarff of the Admiralty Air Department for use on two-seater aircraft. The mount incorporated bungee cord suspension in eleva ...

s.Lewis 1980, pp. 110–111. Three 250 lb (114 kg) bombs could be carried vertically in the fuselage. Three prototypes were ordered, the only twin-engined aircraft to be built by Sopwith.Bruce 1957, pp. 635–637. The first prototype was completed in December 1918, but no Dragonfly engines were available, so it was fitted with 240 hp (179 kW)

Siddeley Puma The Siddeley Puma was a British aero engine developed towards the end of World War I and produced by Siddeley-Deasy. The first engines left the production lines of Siddeley-Deasy in Coventry in August 1917, production continued until December 1 ...

engines to allow flight testing, making its maiden flight in April 1919. It was later re-engined with more-powerful, high compression Pumas, rated at 290 hp (220 kW), being tested at

RAF Martlesham Heath Royal Air Force Martlesham Heath or more simply RAF Martlesham Heath is a former Royal Air Force station located southwest of Woodbridge, Suffolk, England. It was active between 1917 and 1963, and played an important role in the development of ...

in March 1920. Flight-ready Dragonfly engines were delivered during 1919. As they were heavier than expected, the design had to be modified with the engines mounted further back and the stagger on the wings adjusted. The Dragonfly powered aircraft were also fitted with a larger rudder as a result of experience with the Puma powered aircraft. The two Dragonfly powered prototypes, designated Cobham Mk I (with the Puma-powered first prototype designated Cobham Mk II), flew in January and February 1920. The Dragonfly proved to be extremely unreliable, and development of the engine was stopped in September 1920, leading to the two Dragonfly powered prototypes being discarded. The first prototype did not last much longer, being last flown on 27 January 1921 at the

Royal Aircraft Establishment The Royal Aircraft Establishment (RAE) was a British research establishment, known by several different names during its history, that eventually came under the aegis of the Ministry of Defence (United Kingdom), UK Ministry of Defence (MoD), bef ...

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Variants

;Cobham Mk I :Version powered by 360 hp (269 kW) Dragonfly IA engines. Two built. ;Cobham Mk II :First prototype, powered by Siddeley Puma engines. One built.

Specifications (Cobham II)

Notes

References

*Bruce, J.M. ''British Aeroplanes 1914-18''. London:Putnam, 1957. *Lewis, Peter. ''The British Bomber Since 1914''. London:Putnam, Third edition, 1980. . *Mason, Francis K. ''The British Bomber since 1914''. London:Putnam, 1994. . *Robertson, Bruce. ''Sopwith-The Man and his Aircraft''. Letchworth, UK:Air Review, 1970. .

External links