Bell X-5

The Bell X-5 was a research aircraft developed by the United States in the early 1950s to investigate the effects of variable sweep wings on aircraft performance. It was the first aircraft capable of changing its wing sweep in flight. The design was heavily influenced by the German Messerschmitt P.1101, a late-World War II design that was never completed but extensively studied by the Allies after the war.

Two X-5 aircraft were built. They were used by the National Advisory Committee for Aeronautics (NACA), the predecessor to NASA, to gather data on how wing sweep affected lift, drag, stability, and control at different speeds and altitudes. The X-5 could vary its wing sweep from 35 degrees to 60 degrees.

The aircraft proved to be a valuable tool for understanding the complexities of variable geometry wings. However, it also suffered from some stability problems, particularly at high sweep angles. One of the two aircraft was lost in an accident in 1953, resulting in the death of its pilot. Despite this setback, the X-5 program provided important data that contributed to the development of later variable-sweep wing aircraft, such as the F-111 and the B-1.