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The Bell X-5 was the first aircraft capable of changing the sweep of its wings in flight. It was inspired by the untested war-time P.1101 design of the German Messerschmitt company. However, whereas the German design could only be adjusted on the ground, the Bell engineers devised a system of electric motors to adjust the sweep in flight.
Development
The X-5 had three sweep positions: 20°, 40°, and 60°. A jack screw assembly moved the wing's hinge along a set of short horizontal rails, using disc brakes to lock the wing into its inflight positions. Moving from full extension to full sweep took less than 30 seconds. The articulation of the hinge and pivots partly compensated for the shifts in center of gravity and center of lift as the wings moved. Even so, the X-5 had vicious spin characteristics, which in some wing positions led to an irrecoverable spin--this led to the destruction of the second aircraft and the death of a test pilot.
Operational History
Two X-5s were built (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 (12,200 m). On 14 October 1953 USAF Captain Ray Popson died in a crash at Edwards Air Force Base during spin testing. The other X-5 remained at Edwards until 1958, being used as a chase plane after its own research program had been completed in 1955. It is now on display in the National Museum of the United States Air Force at Wright-Patterson Air Force Base near Dayton, Ohio.
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 later successfully implemented in such aircraft as the F-111, F-14 Tomcat and B-1 Lancer.
Specifications (Bell X-5)
References
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