BOEING FRONTIERS / SEPTEMBER 2013 13 The rocket-powered X-15 blazed new trails in hypersonic flight and aerospace research By Mike Lombardi It’s an icon of the X-planes, one that took highly skilled pilots past the edge of space at unprecedented speeds—and pioneered aerospace research that was needed to take explorers to the moon. North American Aviation’s X-15 was one of the most successful and productive flight research programs of all time. A team effort of bold and innovative engineers and courageous pilots, the X-15 program rocketed again and again into the unknown, achieving amazing results while fulfilling its primary purpose of accelerating the manned the rocket plane as it glided back to the dry lake bed at Edwards Air Force Base, Calif., where all X-15 flights would take place. Later, on Sept. 17, Crossfield flew the X-15 under power for the first time. Originally the X-15 was designed to fly up to Mach 6, or six times the speed of sound, but after the second X-15 was damaged in a landing accident it was not only repaired but fitted with external fuel tanks and lengthened 29 inches (74 centimeters), reborn as the X-15A-2 and capable of Mach 8. On Oct. 3, 1967, Pete Knight flew the X-15A-2 to Mach 6.7—an unofficial speed record for winged aircraft that would stand until the Space Shuttle Columbia first returned from space in 1981. Earlier, in August 1963, NASA pilot Joseph Walker set an altitude record of 354,200 feet (more than 65 miles, or 100 kilometers), a record broken in 2004 by SpaceShipOne, ington, D.C., and the X-15A-2 is in the collection of the National Museum of the United States Air Force in Dayton, Ohio. Their structures, made of titanium covered by black Inconel-X, a nickel-steel alloy capable of withstanding temperatures of 1,200 degrees (650 degrees Celsius), show the result of being battered by extreme aerodynamic forces and superheated temperatures—a testament to the exploration of the unknown by the X-15, and the pilots who flew it. n michael.j.lombardi@boeing.com PHOTOS: (Above) The X-15 research aircraft on its first powered flight on Sept. 17, 1959. NASA (Insets, from left) A view of the X-15 from the observation port of the B-52 mother ship. NASA The X-15 is launched from its B-52 mother ship for its second powered flight. Boeing archives This photo of a free-flight model of the X-15 being fired into a wind tunnel shows the shock-wave patterns for airflow at Mach 3.5. NASA U.S. spaceflight program that culminated in the first human footprints on the moon. “The X-15 was to snoop out and lay bare the problems and dangers of manned space travel so that those coming behind us might profit,” North American’s X-15 project pilot Scott Crossfield would say in a Saturday Evening Post interview. Crossfield had been the first to go twice the speed of sound, in the Douglas D-558-II, following in the footsteps of famed test pilot Chuck Yeager, who first broke the sound barrier in the Bell X-1 in October 1947. The X-15 would go much further in gathering data and understanding about the unknown regions of hypersonic speeds (five times the speed of sound and above) while reaching the limits of Earth’s atmosphere. And it would set long-lasting records for speed and altitude. Much more than a platform to break records, the X-15 had an important purpose of exploring the aerodynamic and thermodynamic forces that would be encountered during flight in and out of Earth orbit in support of the effort to put U.S. astronauts into space. The program officially began in December 1955, when the National Advisory Committee for Aeronautics (the forerunner to NASA) awarded North American Aviation, a Boeing heritage company, a contract to build three rocket-powered X-15s. Under the leadership of North American’s top engineer, Harrison Storms, and X-15 project engineer Charles Feltz, the first X-15-1 was rolled out from North American’s Los Angeles plant on Oct. 15, 1958. On June 8, 1959, the X-15-1 was deployed from its Boeing B-52 mother ship for the first time and Crossfield tested the handling and landing characteristics of the first privately funded manned spacecraft. After nearly 10 years of productive research, the X-15 program ended in October 1968. Twelve pilots had flown a combined 199 flights; 108 of those flights exceeded Mach 5 and four exceeded Mach 6. Those pilots flew into an environment that was filled with unknowns and tremendous risks, underscored by an accident that destroyed the third X-15 and claimed the life of Air Force pilot Mike Adams. Five Air Force pilots earned astronaut wings by exceeding an altitude of 264,000 feet (50 miles, or 80 kilometers), the altitude recognized by the Air Force as crossing into space. Later, in 2005, NASA awarded three civilian X-15 pilots with their astronaut wings. Today, the X-15-1 is displayed at the National Air and Space Museum in Wash
Frontiers September 2013 Issue
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