X-5

The Bell X-5 was built to test the feasibility of changing the sweep angle of an aircraft's wings in flight. A pair of X-5s were built, serial numbers 50-1838 and 50-1839. They were similar in shape to the Messerschmitt P.1101 design captured by U.S. troops in April 1945, with a nose-mounted intake, a bubble canopy, an underslung engine, and a boom-mounted tail.

The wings pivoted from a 20 to 60 degree angle in flight. The mechanism used to swivel the wings was very complex. As the X-5's wings were swept back, its center of gravity and center of pressure changed. To compensate, the entire wing assembly simultaneously moved forward on rails inside the fuselage. Sweeping the wings from a 20 degree angle to the full 60 degree angle required that they also be moved about 27 inches forward from their starting position. The change from 20 to 60 degrees required about 20 seconds. In the event of an electrical failure, the pilot could hand crank the wings back into landing position. (The X-5 could not safely land with a sweep angle greater than 40 degrees.)

The first X-5 (50-1838) made its first flight on June 20, 1951. On January 8, 1952, the first X-5 was turned over to the NACA. The second X-5 (50-1839) had, by this time, also been delivered and was flown by the Air Force. The final NACA X-5 flight was made on October 25, 1955, by a new High-Speed Flight Station pilot, Neil A. Armstrong. In all, the first X-5 had made 122 NACA flights. The aircraft was sent to the Air Force Museum in March of 1958.

The results of the X-5 were mixed. It provided verification of wind tunnel predictions about drag reductions and performance improvements from variable sweep wings. The X-5 pilots also found that the variable sweep wings gave a tactical advantage over conventional aircraft. The poor stall/spin characteristics were due to the aircraft's design, rather than the variable wing sweep. But while the concept of changing the wings' sweep angle was shown to have promise, the mechanism itself, which required the wings move back and forth as their angle changed, was not practical. The solution to this, developed by NACA engineers at Langley, was to move the pivot points of the wings outside the fuselage.