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Bell X-1

The Bell X-1 is a rocket-engine–powered aircraft, designated originally as the XS-1, and was a joint National Advisory Committee for Aeronautics–U.S. Army Air Forces–U.S. Air Force supersonic research project built by Bell Aircraft. Conceived during 1944 and designed and built in 1945, it achieved a speed of nearly 1,000 miles per hour (1,600 km/h; 870 kn) in 1948. A derivative of this same design, the Bell X-1A, having greater fuel capacity and hence longer rocket burning time, exceeded 1,600 miles per hour (2,600 km/h; 1,400 kn) in 1954. The X-1, piloted by Chuck Yeager, was the first manned airplane to exceed the speed of sound in level flight and was the first of the X-planes, a series of American experimental rocket planes (and non-rocket planes) designed for testing new technologies.
Swept wings were not used because too little was known about them. As the design might lead to a fighter the XS-1 was intended to take off from the ground, but the end of the war made the B-29 Superfortress available to carry it into the air. After the rocket plane experienced compressibility problems during 1947, it was modified with a variable-incidence tailplane following technology transfer with the United Kingdom.
The story of Yeager’s 14 October flight was leaked to a reporter from the magazine Aviation Week, and The Los Angeles Times featured the story as headline news in their 22 December issue. The magazine story was released on 20 December. The Air Force threatened legal action against the journalists who revealed the story, but none ever occurred. The news of a straight-wing supersonic aircraft surprised many American experts, who like their German counterparts during the war believed that a swept-wing design was necessary to break the sound barrier. On 10 June 1948, Air Force Secretary Stuart Symington announced that the sound barrier had been repeatedly broken by two experimental airplanes.
After NACA started its high-speed testing with the Douglas Skyrocket, culminating in Scott Crossfield achieving Mach 2.005 on 20 November 1953, the Air Force started a series of tests with the X-1A, which the test pilot of the series, Chuck Yeager, named "Operation NACA Weep". These culminated on 12 December 1953, when Yeager achieved an altitude of 74,700 feet (22,800 m) and a new airspeed record of Mach 2.44 (equal to 1620 mph, 724.5 m/s, 2608 km/h at that altitude). Unlike Crossfield in the Skyrocket, Yeager achieved that in level flight. Soon afterwards, the aircraft spun out of control, due to the then not yet understood phenomenon of inertia coupling. The X-1A dropped from maximum altitude to 25,000 feet (7,600 m), exposing the pilot to accelerations of as much as 8g, during which Yeager broke the canopy with his helmet before regaining control.
The X-1E first flew on 15 December 1955, a glide-flight controlled by USAF test pilot Joe Walker. Walker left the X-1E program during 1958, after 21 flights, attaining a maximum speed of Mach 2.21 (752 m/s, 2,704 km/h). NACA research pilot John B. McKay took his place during September 1958, completing five flights in pursuit of Mach 3 (1,021 m/s, 3,675 km/h) before the X-1E was permanently grounded after its 26th flight, during November 1958, due to the discovery of structural cracks in the fuel tank wall.