The XS-1 (renamed X-1 in 1962) is an experimental American aircraft powered by a rocket engine. It is famously known as the first aircraft to break the sound barrier in level flight on October 14, 1947. Specifically developed for this purpose under the X-Planes research program by the USAAF and NACA (predecessor of NASA), it was built by Bell Aircraft Corporation.
Resembling a bullet with tiny wings and a rocket engine, it was designed to be air-dropped from a B-29A Superfortress bomber.
To replace both the X-1A and X-1D, which exploded in flight in 1951, the
X-1-3 (serial number 46-063) was modified and renamed the X-1E. The
cause of these explosions, which had long remained a mystery, was
discovered. They were attributed to seals made of leather treated with
TCP used in the liquid oxygen system. In the presence of pure oxygen and
mechanical stress, TCP was found to be unstable and triggered the two
explosions. This error resulted in the loss of two pilots' lives.
