The Bell X-1 (XS-1) "Sound Barrier" October 14, 1947

From Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Bell_X-1
The Bell X-1, originally designated XS-1, was a joint NACA-U.S. Army Air Forces/US Air Force supersonic research project and the first aircraft to exceed the speed of sound in controlled, level flight. This resulted in the first of the so-called X-planes, an American series of experimental aircraft designated for testing of new technologies and usually kept highly secret.

On 16 March 1945, the United States Army Air Forces' Flight Test Division and the National Advisory Committee for Aeronautics (NACA) (now NASA) contracted Bell Aircraft to build three XS-1 (for "Experimental, Supersonic", later X-1) aircraft to obtain flight data on conditions in the transonic speed range. The XS-1 was the first high-speed aircraft built purely for aviation research purposes and was never intended for production.

The X-1 was in principle a "bullet with wings" that closely resembled the shape of the Browning .50-caliber (12.7 mm) machine gun bullet that was known to be stable in supersonic flight. The pattern shape was followed to the point of seating the pilot behind a sloped, framed window inside a confined cockpit in the nose. After the aircraft ran into compressibility problems in 1947, it was modified to feature a variable-incidence tailplane. An all-moving tail was developed by the British for the Miles M.52, and first saw actual transonic flight on the Bell X-1 that allowed it to pass through the sound barrier safely.

The rocket propulsion system was a four-chamber engine built by Reaction Motors, Inc., one of the first companies to build liquid-propellant rocket engines in America. It burned ethyl alcohol diluted with water and liquid oxygen. The thrust could be changed in 1500 lbf increments by firing one or more of the chambers. The fuel and oxygen tanks for the first two X-1 engines were pressurized with nitrogen and the rest with steam-driven turbopumps. The all-important fuel turbopumps, necessary to raise the chamber pressure and thrust, while lightening the engine, were built by Robert Goddard who was under Navy contract to provide jet-assisted takeoff rockets.

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