Northrop X-4

From the placard:
The X-4 was developed for the study of flight characteristics of swept wing, semi-tailess aircraft at transonic (about Mach .85) speeds. Northrop built two X-4s. The No. 1 aircraft was first flown by Northrop on December 16, 1948, and the second X-4 made its initial flight on June 7, 1949. The No. 1 aircraft was grounded after its 10th flight to provide spare parts for the No. 2 aircraft. Northrop's part of the test program ended on February 17, 1950, with the 20th flight of the remaining X-4. Although both aircraft were turned over to the Air Force and then to the National Advisory Committee for Aeronautics (NACA) in May 1950, only the No. 2 X-4 was used in the joint USAF/NACA to explore stability problems near the speed of sound. The program ended in September 1953 with the 102nd and last flight of this, the No. 2 aircraft, after proving that swept wing aircraft without horizontal tails were not suitable for transonic flight. Both aircraft survived the test program without serious incident. The No. 1 X-4 (S/N 46-676) is displayed at the Air Force Academy. The No. 2 aircraft (S/N 46-677) was transferred to the Museum shortly after the program ended. It was restored by the Western Museum of Flight, Hawthorne, California, and the U.S. Air Force Museum, Wright-Patterson AFB, Ohio.

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