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Boeing B-47 Stratojet
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Boeing B-47 Stratojet
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.
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), becoming a mainstay of its bomber strength by the late 1950s. Over 2,000 were manufactured to meet the Air Force's 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 Boeing's own B-52 Stratofortress. 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 or within Soviet air space. The type remained in service as a reconnaissance aircraft until 1969. A few served as flying testbeds up until 1977.
The B-47 arose from an informal 1943 requirement for a jet-powered reconnaissance bomber, drawn up by the United States Army Air Forces (USAAF) to prompt manufacturers to start research into jet bombers. Boeing was among several companies to respond to the request; one of its designs, the Model 424, was basically a scaled-down version of the piston-engined B-29 Superfortress equipped with four jet engines. In 1944, this initial concept evolved into a formal request-for-proposal to design a new bomber with a maximum speed of 550 mph (480 kn; 890 km/h), a cruise speed of 450 mph (390 kn; 720 km/h), a range of 3,500 mi (3,000 nmi; 5,600 km), and a service ceiling of 45,000 ft (13,700 m).
In December 1944, North American Aviation, Convair, Boeing and the Glenn L. Martin Company submitted proposals for the new long-range jet bomber. Wind tunnel testing had shown that the drag from the engine installation of the Model 424 was too high, so Boeing's entry was a revised design, the Model 432, with the four engines buried in the forward fuselage. The USAAF awarded study contracts to all four companies, requiring that North American and Convair concentrate on four-engined designs (to become B-45 and XB-46), while Boeing and Martin were to build six-engined aircraft (the B-47 and XB-48). The powerplant was to be General Electric's new TG-180 turbojet engine.
In May 1945, the von Kármán mission of the Army Air Forces inspected the secret German aeronautics laboratory near Braunschweig. Von Kármán's team included the chief of the technical staff at Boeing, George S. Schairer. He had heard about the controversial swept-wing theory of R. T. Jones at Langley, but seeing German models of swept-wing aircraft and extensive supersonic wind-tunnel data, the concept was decisively confirmed. He wired his home office: "Stop the bomber design" and changed the wing design. Analysis by Boeing engineer Vic Ganzer suggested an optimum sweepback angle of about 35 degrees. Boeing's aeronautical engineers modified the Model 432 with swept wings and tail to produce the "Model 448", which was presented to the USAAF in September 1945. It retained the four TG-180 jet engines in its forward fuselage, with two more TG-180s in the rear fuselage. The flush-mounted air intakes for the rear engines were inadequate while the USAAF considered the engine installation within the fuselage to be a fire hazard.
The engines were moved to streamlined pylon-mounted pods under the wings, leading to the next iteration, the Model 450, which featured two TG-180s in a twin pod mounted on a pylon about a third of the way outboard on each wing, plus another engine at each wingtip. The Army Air Force liked this new configuration, so Boeing's engineers refined it, moving the outer engines further inboard to about 3⁄4 of the wingspan. The thin wings provided no space for tricycle main gear to retract so it would have needed a considerable bulge in the fuselage aft of the bomb bay for lateral stability. The only way to get a bomb-bay long enough for an A-bomb was to use a "bicycle landing gear", the two main gear assemblies arranged in a tandem configuration and outrigger struts fitted to the inboard engine pods. As the landing gear arrangement made rotation impossible, it was designed so that the aircraft rested on the ground at the proper angle for takeoff.
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Boeing B-47 Stratojet
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.
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), becoming a mainstay of its bomber strength by the late 1950s. Over 2,000 were manufactured to meet the Air Force's 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 Boeing's own B-52 Stratofortress. 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 or within Soviet air space. The type remained in service as a reconnaissance aircraft until 1969. A few served as flying testbeds up until 1977.
The B-47 arose from an informal 1943 requirement for a jet-powered reconnaissance bomber, drawn up by the United States Army Air Forces (USAAF) to prompt manufacturers to start research into jet bombers. Boeing was among several companies to respond to the request; one of its designs, the Model 424, was basically a scaled-down version of the piston-engined B-29 Superfortress equipped with four jet engines. In 1944, this initial concept evolved into a formal request-for-proposal to design a new bomber with a maximum speed of 550 mph (480 kn; 890 km/h), a cruise speed of 450 mph (390 kn; 720 km/h), a range of 3,500 mi (3,000 nmi; 5,600 km), and a service ceiling of 45,000 ft (13,700 m).
In December 1944, North American Aviation, Convair, Boeing and the Glenn L. Martin Company submitted proposals for the new long-range jet bomber. Wind tunnel testing had shown that the drag from the engine installation of the Model 424 was too high, so Boeing's entry was a revised design, the Model 432, with the four engines buried in the forward fuselage. The USAAF awarded study contracts to all four companies, requiring that North American and Convair concentrate on four-engined designs (to become B-45 and XB-46), while Boeing and Martin were to build six-engined aircraft (the B-47 and XB-48). The powerplant was to be General Electric's new TG-180 turbojet engine.
In May 1945, the von Kármán mission of the Army Air Forces inspected the secret German aeronautics laboratory near Braunschweig. Von Kármán's team included the chief of the technical staff at Boeing, George S. Schairer. He had heard about the controversial swept-wing theory of R. T. Jones at Langley, but seeing German models of swept-wing aircraft and extensive supersonic wind-tunnel data, the concept was decisively confirmed. He wired his home office: "Stop the bomber design" and changed the wing design. Analysis by Boeing engineer Vic Ganzer suggested an optimum sweepback angle of about 35 degrees. Boeing's aeronautical engineers modified the Model 432 with swept wings and tail to produce the "Model 448", which was presented to the USAAF in September 1945. It retained the four TG-180 jet engines in its forward fuselage, with two more TG-180s in the rear fuselage. The flush-mounted air intakes for the rear engines were inadequate while the USAAF considered the engine installation within the fuselage to be a fire hazard.
The engines were moved to streamlined pylon-mounted pods under the wings, leading to the next iteration, the Model 450, which featured two TG-180s in a twin pod mounted on a pylon about a third of the way outboard on each wing, plus another engine at each wingtip. The Army Air Force liked this new configuration, so Boeing's engineers refined it, moving the outer engines further inboard to about 3⁄4 of the wingspan. The thin wings provided no space for tricycle main gear to retract so it would have needed a considerable bulge in the fuselage aft of the bomb bay for lateral stability. The only way to get a bomb-bay long enough for an A-bomb was to use a "bicycle landing gear", the two main gear assemblies arranged in a tandem configuration and outrigger struts fitted to the inboard engine pods. As the landing gear arrangement made rotation impossible, it was designed so that the aircraft rested on the ground at the proper angle for takeoff.
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