@ Washington, D.C.
August 2018
This ultimate X-plane hangs in the Boeing Milestones of Flight Hall at the National Air & Space Museum. Drop launched from a B-52, the North American X-15 flew faster and higher than any other airplane. After completing its initial test flights in 1959, the X-15 became the first winged aircraft to attain velocities of Mach 4, 5, and 6 (four, five, and six times the speed of sound). The highest speed, 4,520 mph (Mach 6.7), was achieved on 3 October 1967, when William J. Knight flew at an altitude of 102,100 feet (19.34 miles). This set the official world record for the highest speed ever recorded by a crewed, powered aircraft, which remains unbroken. Three X-15 research aircraft were built and flown, completing a total of 199 research flights by the time the program ended in 1968. Eight X-15 pilots flew higher than 50 miles above the Earth and earned their astronaut wings. The National Air and Space Museum has the historic X-15 #1, Air Force serial 56-6670, which flew 81 free flights. This X-15 would be the only one to survive without incident, #2 was rebuilt after a landing accident and #3 broke up at 60,000 ft after entering a hypersonic spin.
This provides a good view of the thick wedge tail, designed for hypersonic stability. Two panels at the base could be extended to increase the surface area, when deployed outward they functioned as air brakes. The Reaction Motors XLR99 rocket engine, provided 57,000 lbs of thrust, using anhydrous ammonia and liquid oxygen as propellant, and hydrogen peroxide to drive the high-speed turbopump that delivered propellants to the engine. It could burn the 15,000 pounds of propellant in 80 seconds of powered flight.
