The Boeing B-47 Stratojet (Boeing company designation Model 450) is a retired American long-range, six-engined, turbojet-powered strategic bomber designed to fly at high subsonic speed and at high altitude to avoid enemy interceptor aircraft. The primary mission of the B-47 was as a nuclear bomber capable of striking targets within the Soviet Union.
Development of the B-47 can be traced back to a requirement expressed by the United States Army Air Forces (USAAF) in 1943 for a reconnaissance bomber that harnessed newly developed jet propulsion. Another key innovation adopted during the development process was the swept wing, drawing upon captured German research. With its engines carried in nacelles underneath the wing, the B-47 represented a major innovation in post-World War II combat jet design, and contributed to the development of modern jet airliners. Suitably impressed, in April 1946, the USAAF ordered two prototypes, designated "XB-47"; on 17 December 1947, the first prototype performed its maiden flight. Facing off competition such as the North American XB-45, Convair XB-46 and Martin XB-48, a formal contract for 10 B-47A bombers was signed on 3 September 1948. This would be soon followed by much larger contracts.
During 1951, the B-47 entered operational service with the United States Air Force's Strategic Air Command (SAC), quickly becoming a mainstay of its bomber strength by the late 1950s. Over 2,000 were manufactured to meet the Air Force's extensive demands, driven by the tensions of the Cold War.
The B-47 was in service as a strategic bomber until 1965, at which point it had largely been supplanted by more capable aircraft, such as the Boeing B-52 Stratofortress. However, the B-47 was also adapted to perform a number of other roles and functions, including photographic reconnaissance, electronic intelligence, and weather reconnaissance. While never seeing combat as a bomber, reconnaissance RB-47s would occasionally come under fire near to or within Soviet air space. The type remained in service as a reconnaissance aircraft until 1969; a handful served as flying testbeds up until 1977.
The XB-47, which looked nothing like contemporary bombers, was described by Boyne as a "sleek, beautiful outcome that was highly advanced". The 35-degree swept wings were shoulder-mounted, the inboard turbojet engines mounted in twin pods, at about a third of the span, and the outboard engines singly near the wing tip. This arrangement reduced the bending moment at the wing roots, saving structural weight; the engines' mass also acted as counter-flutter weights.
The wing airfoil was identified by Boeing as the BAC 145, also known as the NACA 64A(.225)12 mod airfoil. Wing flexibility was a concern, flexing as much as 17.5 ft (5.3 m) at the tip; major effort was expended to ensure that flight control could be maintained as the wing moved up and down; these worries proved to be mostly unfounded. Its maximum speed was limited to 425 kn (787 km/h) to avoid control reversal, where aileron deflections would cause the wings to twist and produce a roll in the opposite direction to that desired by the pilot. More details
Development of the B-47 can be traced back to a requirement expressed by the United States Army Air Forces (USAAF) in 1943 for a reconnaissance bomber that harnessed newly developed jet propulsion. Another key innovation adopted during the development process was the swept wing, drawing upon captured German research. With its engines carried in nacelles underneath the wing, the B-47 represented a major innovation in post-World War II combat jet design, and contributed to the development of modern jet airliners. Suitably impressed, in April 1946, the USAAF ordered two prototypes, designated "XB-47"; on 17 December 1947, the first prototype performed its maiden flight. Facing off competition such as the North American XB-45, Convair XB-46 and Martin XB-48, a formal contract for 10 B-47A bombers was signed on 3 September 1948. This would be soon followed by much larger contracts.During 1951, the B-47 entered operational service with the United States Air Force's Strategic Air Command (SAC), quickly becoming a mainstay of its bomber strength by the late 1950s. Over 2,000 were manufactured to meet the Air Force's extensive demands, driven by the tensions of the Cold War.
The B-47 was in service as a strategic bomber until 1965, at which point it had largely been supplanted by more capable aircraft, such as the Boeing B-52 Stratofortress. However, the B-47 was also adapted to perform a number of other roles and functions, including photographic reconnaissance, electronic intelligence, and weather reconnaissance. While never seeing combat as a bomber, reconnaissance RB-47s would occasionally come under fire near to or within Soviet air space. The type remained in service as a reconnaissance aircraft until 1969; a handful served as flying testbeds up until 1977.