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The Airco DH.4 was a British two-seat biplane day bomber of World War I. It was designed by Geoffrey de Havilland (hence "DH") for Airco, and was the first British two-seat light day-bomber to have an effective defensive armament. It first flew in August 1916 and entered service with the Royal Flying Corps (RFC) in March 1917. The majority of DH.4s were actually built as general purpose two-seaters in the United States, for service with the American forces in France. The DH.4 was tried with several engines, of which the best was the 375 hp (280 kW) Rolls-Royce Eagle engine. Armament and ordnance for the aircraft consisted of one 0.303 in (7.7 mm) Vickers machine gun for the pilot and one 0.303 in (7.7 mm) Lewis gun on a Scarff ring mounting for the observer. Two 230 lb (100 kg) bombs or four 112 lb (51 kg) bombs could be carried. The DH.4 entered service on 6 March 1917 with No. 55 Squadron in France. ==Design and development== The DH.4 was designed by Geoffrey de Havilland as a light two-seat day bomber powered by the new BHP engine. The prototype first flew in August 1916, powered by a prototype BHP engine rated at 230 hp (170 kW).〔Jackson 1987, p. 53.〕 While the DH.4 trials were promising, the BHP engine required major redesign before entering production, and the Rolls-Royce Eagle engine was selected as the DH.4's powerplant. The first order for 50 DH.4s, powered by 250 hp (186 kW) Eagle III engines was placed at the end of 1916.〔 The aircraft was a conventional tractor two bay biplane of all-wooden construction. The crew of two were accommodated in widely spaced cockpits, separated by the fuel tank.〔 It was armed with a single forward-firing synchronised Vickers machine gun and one or two .303 in (7.7 mm) Lewis guns fitted on a Scarff ring fired by the observer. A bomb load of 460 lb (210 kg) could be fitted to external racks. While the crew arrangement gave good fields of view for the pilot and observer, it caused communication problems between the two crew members, particularly in combat, where the speaking tube linking the cockpits was of limited use.〔Bruce 1952, p. 507.〕 As production continued, DH.4s were fitted with Eagle engines of increasing power, settling on the 375 hp (280 kW) Eagle VIII, which powered the majority of frontline DH.4s by the end of 1917. Because of the chronic shortage of Rolls-Royce aero engines in general, and Eagles in particular, alternative engines were also investigated, with the BHP (230 hp/170 kW), the Royal Aircraft Factory RAF3A (200 hp/150 kW), the Siddeley Puma (230 hp/170 kW) and the 260 hp (190 kW) Fiat, all being used in production aircraft.〔 None of these engines could match the Rolls-Royce Eagle; however, there were simply not enough Eagles available. In American production, the new Liberty engine proved suitable as a DH.4 powerplant, although the engine produced a slightly inferior performance to the Eagle. The Liberty was also to eventually power the British DH.9A. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Airco DH.4」の詳細全文を読む スポンサード リンク
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