“I was always afraid of dying. It was my fear that... kept me...always alert in the cockpit."
Chuck Yeager
Supersonic airplanes fly faster than the velocity of sound, this being about 770 miles per hour (1,230 kph) at ground level. During World War II certain fighter planes, such as the Mitsubishi Zero and the Supermarine Spitfire could approach this speed in a dive but the near supersonic air passing over the plane produced disruptive shockwaves and turbulence. The propellers became much less efficient and chaotic effects amplified pressure, perturbations, producing an increase in drag and a loss of lift and control. These effects became known as the "sound barrier," which was "broken" by introducing the much more powerful jet engine and by strengthening the airframes and wings. Fortunately, flight became smooth again when the aircraft moved faster than the speed of sound.
There is still a slight controversy over who flew the first supersonic airplane. Chuck Yeager broke the sound barrier on October 14, 1947, over the Mojave Desert in his rocket-powered Bell X-1 plane, by flying at Mach 1.06. But shortly before that, ground witnesses saw George Welch, testing the prototype of the F-86 Sabre jet fighter, go into a steep dive and heard the ba-boom of the sound barrier being broken.
