page_title: Boeing B-47 Stratojet
section_title: Overview
hierarchical_section_title: Boeing B-47 Stratojet / Design / Overview
caption_attribution_description: The first Boeing XB-47 built (S/N 46-065), taken on Dec. 1, 1947, before its first flight.
context_page_description: The Boeing B-47 Stratojet 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 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.
context_section_description: 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 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) IAS 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. The wings were fitted with a set of Fowler flaps that extended well behind the wing to enhance lift at slow speeds. The flight control surfaces were powered, augmenting the pilot's inputs and reducing the exertion required to overcome the forces involved.
  The XB-47 was designed to carry a crew of three in a pressurized forward compartment: a pilot and copilot, in tandem, in a long fighter-style bubble canopy, and a navigator/bombardier in a compartment in the nose. The copilot doubled as tail gunner (using a remotely controlled, radar-directed tail gun), and the navigator as bombardier. The bubble canopy, which provided a high level of visibility to the pilots, pitched up and slid backward; as the cockpit was high off the ground, the crew entered via a door and ladder on the underside of the nose. The extreme front of the nose was initially glazed for visual navigation and bomb sighting, but this requirement was soon deleted together with the glazing. Most production versions had a metal nose with no windows. A K-series bombsight provided integrated radar navigation and visual navigation, the optical portion extending through the nose in a small dome. For greater comfort, both heaters and refrigeration systems were present in the cockpit to manage the cockpit environment. There was little vibration compared to prior bombers powered by reciprocating engines.
caption: The first Boeing XB-47 built (46-0065) on 1 December 1947
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