20 June 1951 – “The Bell X-5 was the first aircraft capable of changing the sweep of its wings in flight. It was inspired by the untested wartime P.1101 design of the German Messerschmitt company. In contrast with the German design, which could only have its wing sweepback angle adjusted on the ground, the Bell engineers devised a system of electric motors to adjust the sweep in flight…
Two X-5s were built (serial numbers 50-1838 and 50-1839). The first was completed 15 February 1951, and the two aircraft made their first flights on 20 June and 10 December 1951. Almost 200 flights were made at speeds up to Mach 0.9 and altitudes of 40,000 ft (12,000 m). One aircraft was lost on 14 October 1953, when it failed to recover from a spin at 60° sweepback. Air Force Captain Ray Popson died in the crash at Edwards Air Force Base. The other X-5 remained at Edwards and continued active testing until 1955, and remained in service as a chase plane until 1958.
The X-5 successfully demonstrated the advantage of a swing-wing design for aircraft intended to fly at a wide range of speeds. Despite the X-5’s stability problems, the concept was developed to an outboard rather than inboard hinge,[4] and was later successfully implemented in such aircraft as the General Dynamics F-111 and Grumman F-14 Tomcat, the Mikoyan Gurevich MiG-23 and MiG-27, the Sukhoi Su-17/20/22 and Su-24, the Tupolev Tu-22M and Tu-160, the Panavia Tornado and the Rockwell B-1 Lancer.”(1)