North
American X-15
North American X-15. Among the most famous planes is the X-15. Part airplane and part spacecraft, the X-15 was used to provide data about heating, stability, control and problems of re-entry into the atmosphere. It has flown higher and faster than any other airplane, achieving a speed of Mach 6.72 (4534 MPH) and an altitude of 354,200 feet. After 199 flights the X-15 program was terminated in 1968.
