The X-4 was developed for the study of flight characteristics of swept wing, semi-tailess aircraft at transonic speeds. Northrop built two X-4s. After the aircraft completed, both aircraft were turned over to NACA for further testing. They proved to be unsuitable at transonic speeds and were retired. Aircraft one is on display at the Air Force Academy. Number two resides at the NMUSAF and is pictured here. NMUSAF
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