In early 1917, the Sopwith chief engineer, Herbert Smith, began designing a new two-bay, single-seat biplane fighter (internal Sopwith designation 5F.1). In an effort to give pilots an improved field of view.
The upper wings were attached to an open steel cabane frame above the cockpit and there was no centre section in the upper wing.
The pilot’s head was positioned above the upper wing, with the fuselage filling the gap between the wings.
To maintain the correct centre of gravity, the lower wings were positioned 13 inches forward of the upper wings, creating the Dolphin’s distinctive negative wing stagger.
The first Dolphin prototype was powered by a geared 150 hp Hispano-Suiza 8 and featured a deep "car-type" frontal radiator. Test pilot Harry Hawker carried out the maiden flight on 23 May 1917.
On 13 June, the prototype flew to Saint-Omer, France where it was evaluated by several front line pilots, including Billy Bishop of No. 60 Squadron, all reported favourably on it. On 28 June 1917, the Ministry of Munitions ordered 200 Dolphins from Hooper & Co. Shortly thereafter, the Ministry ordered a further 500 aircraft from Sopwith and 200 aircraft from Darracq Motor Engineering Company.
Only one prototype had been completed, two more were soon to follow with a number of revisions. The main change was the cowling was streamlined further, providing an even greater field of view. The radiators were moved around in an attempt to provide better cooling for the engine. The third prototype proved to solve the radiator issue, and gave the Dolphin another of its eccentric features, the two radiators, each mounted on the side of the cockpit. This arrangement kept the cockpit warm and comfortable as the cooling pipes pipes ran alongside the cockpit walls to the two side-mounted radiators. Pilot adjustable shutters in front of each radiator core allowed control of engine temperature.
Despite early problems, the Dolphin proved to be a formidable fighter and generally popular with pilots. The aircraft was fast, manoeuvrable and easy to fly. When functioning properly, the Hispano-Suiza afforded the Dolphin excellent performance at high altitude and the Dolphin was often sent against German reconnaissance aircraft such as the Rumpler C.VII, which routinely operated at altitudes above 20,000 ft.
As the end of the war drew closer, Sopwith started looking at updating the Dolphin design. the most impressive of these improvements became known as the Dolphin II and featured a 300hp Hispano Suiza, which gave very impressive performance figures for the time. The RAF were uninterested in this upgrade, but the United States ordered around 2000 of them, though ultimately the armistice came in before they could be delivered.
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