Two X-4s were built by the Northrop Corporation, but the first was found to be mechanically unsound and after 10 flights it was grounded and used to provide parts for the second. While being tested from 1950 to 1953 at the NACA High-Speed Flight Research Station (now Edwards Air Force Base), the X-4's semi-tailless configuration exhibited inherent longitudinal stability problems (porpoising) as it approached the speed of sound. It was concluded that (with the control technology available at the time) tailless craft were not suited for transonic flight. It was believed in the 1940s that a design without horizontal stabilizers would avoid the interaction of shock waves between the wing and stabilizers. These were believed to be the source of the stability problems at transonic speeds up to Mach 0.9. Two aircraft had already been built using a semi-tailless design—the rocket-powered Me 163 Komet flown by Germany in World War II, and the British de Havilland DH.108 Swallow built after the war. The United States Army Air Forces signed a contract with the Northrop Aircraft Company on 11 June 1946, to build two X-4s. Northrop was selected because of its experience with flying wing designs, such as the N-9M, XB-35 and YB-49 aircraft. The resulting aircraft was very compact, only large enough to hold two Westinghouse J30 jet engines, a pilot, instrumentation, and a 45-minute fuel supply. Nearly all maintenance work on the aircraft could be done without using a ladder or footstool. A person standing on the ground could easily look into the cockpit. The aircraft also had split flaps, which doubled as speed brakes General characteristics Crew: 1 Length: 22 ft 3 in (7.1 m) Wingspan: 26 ft 10 in (8.2 m) Height: 14 ft 10 in (4.5 m) Wing area: ft² (m²) Empty weight: 5,600 lb (2,540 kg) Max. takeoff weight: 7,820 lb (3,550 kg) Powerplant: 2 × Westinghouse J30 turbojet, 1,600 lbf (7.1 kN) each Performance Maximum speed: 640 mph (1,035 km/h) Service ceiling: 44,000 ft (13,400 m)

johnbr, Dec 5, 2012
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    Post-War Aircraft
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    Dec 5, 2012
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