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The Douglas Y1B-7 was a 1930s United States bomber aircraft. It was the first US monoplane given the ''B-'' 'bomber' designation. The monoplane was more practical and less expensive than the biplane, and the United States Army Air Corps chose to experiment with monoplanes for this reason. At the time the XB-7 was ordered, it was being tested by Douglas Aircraft as an observational plane. ==Design and development== In 1929–1930, the Douglas Aircraft Company designed a new twin-engined monoplane observation aircraft to compete with the Fokker XO-27, two prototypes of which had been ordered by the United States Army Air Corps in July 1929, as Douglas feared that the advanced Fokker would challenge Douglas's role as the major supplier of observation aircraft to the Air Corps. The Douglas proposals resulted in the Air Corps placing an order for two prototypes, the XO-35 and XO-36, on 26 March 1930. The two aircraft were to differ only in the engines fitted, with the XO-35 having geared Curtiss V-1570-29 Conqueror engines, while the XO-36 used direct-drive V-1570-23, which both produced each.〔Pelletier ''Air Enthusiast'' March/April 2002, pp. 30, 32.〕〔Francillon 1979, pp. 135–136.〕 The Douglas design had gull wings mounted high on the aircraft's fuselage, the engines being suspended in streamlined nacelles under the wings by bracing struts. A retractable tailwheel undercarriage was fitted, the mainwheels retracting into the engine nacelles. The fuselage was a semi-monocoque structure with corrugated duralumin covering, which housed the aircraft's crew of four: a nose gunner/observer, a pilot whose cockpit was situated ahead of the leading edge of the wing, an upper gunner who sat in a cockpit aft of the wing, and a radio operator housed within the fuselage. Armament was two .30 in machine guns.〔〔 The projected performance of the new twin-engined Douglas and Fokker observation aircraft was much greater than the Keystone biplanes (the Keystone B-3, B-4, B-5 and B-6) that equipped the Air Corps light bomber squadrons, and both Fokker and Douglas were instructed to complete one of their prototypes as a bomber, with the XO-36 being redesignated the XB-7, with provision to carry up to of bombs on racks under the fuselage added.〔Pelletier ''Air Enthusiast'' March/April 2002, p. 32.〕 The XO-36 made its first flight at the Santa Monica, California factory of Douglas in spring 1931.〔Francillon 1979, p. 137.〕 On 22 August 1931, the Air Corps placed an order for a small batch of service test aircraft, consisting of seven Y1B-7 bombers and five Y1O-35 observation aircraft. These differed from the prototypes by having smooth fuselage skins rather than the corrugated skins used on the prototype, while the fuselage was longer to adjust the aircraft's center of gravity. A revised fuel system was fitted, with more fuel carried in order to give the two-hour endurance specified by the Air Corps. More powerful Conqueror engines were fitted, with all aircraft using geared engines as used on the XO-35.〔 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「Douglas Y1B-7」の詳細全文を読む スポンサード リンク
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