On the morning of November 20, 1953, A. Scott Crossfield became the first pilot to fly at Mach 2, twice the speed of sound. He accomplished this feat in the experimental air-launched, rocket-propelled Douglas D-558-2 Skyrocket number 2. The swept-wing research aircraft attained Mac 2.005 (1,291 mph) at 62,000 feet while in a shallow dive. Seconds afterwards, the airplane's XLR-8 rocket engine exhausted its fuel supply and shut down. Crossfield glided earthward to a smooth dead-stick landing on Muroc Dry Lake at Edwards Air Force Base in southern California.
D-588-2 number 2 would go on to make a total of 105 research flights, setting several records in the process. In 1961, the aircraft was transferred from the U.S. Navy to the Smithsonian Institution, where it underwent at 10-month restoration, completed in 1973, to arrest and repair patches of rust and corrosion and to drain water trapped in the magnesium alloy fuselage. The Skyrocket has been on display at the National Air and Space Museum since it opened in 1976.
Number 2 was one of six D-588 research airplanes ordered by the U.S. Navy from the Douglas Aircraft Company for obtaining aerodynamic information at transonic and supersonic speeds. The Navy issued a letter of intent to Douglas on June 22, 1945, for construction of six D-588 aircraft, all possessing straight and thin wing and tail surfaces and turbojet propulsion. Development of the aircraft began under the direction of chief engineer Edward H. Heinemann. Subsequent analysis of captured data on wartime German swept-wing research, combined with swept-wing studies by U.S. scientist Robert T. Jones, pushed Douglas and the Navy to modify the D-588 contract by canning three of the planned aircraft and replacing them with three swept-wing vehicles powered by both turbojet and rocket engines. The first three aircraft, each powered by a single General Electric TG-180 turbojet, became known as D-588-1 Skystreaks. The last three, powered initially by a Westinghouse J-34 turbojet for low-speed flight plus a Reaction Motors XLR-8 rocket engine for high-speed research, became known as D-588-2 Skyrockets.
The D-588-1 and D-588-2 greatly differed from each other in detail design, and there was little commonality between them, although both took off from the ground. Because of its engine type and airframe design, the D-588-1 was limited to approximately Mach 1. The more powerful D-588-2, using a 6,000-pound-thrust rocket engine fueled with liquid oxygen and diluted ethyl alcohol, could easily exceed Mach 1. The safety hazards of operating a heavily loaded rocket-propelled airplane from the ground later caused Douglas to modify D-588-2 numbers 2 and 3 for air modify D-588-2 numbers 2 and 3 for air launching from the bomb bay of a converted Boeing P2B-1S (U.S. Navy B-29) Superfortress. As the same time, Douglas modified number 2 for all-rocket propulsion, storing additional fuel in the space formerly taken by its turbojet engine. Thus modified, number 2 was flown in a high-speed flight research program run by the National Advisory Committee for Aeronautics (NACA).
The D-588-1 and D-588-2 were of mixed aluminum and magnesium construction. Both types featured nose sections that could be jettisoned to serve as emergency escape capsules, and both were designed to carry heavy instrument loads for flight research. The first two D-588-1 Skystreaks were bright glossy red overall, but D-588-1 number 3 and later D-588-2 Skyrockets were glossy white, which provided more desirable optical tracking purposes.
The first D-588-2 Skyrocket, bureau number 37973 (NACA 143), completed its initial flight on February 4, 1948, piloted by John F. Martin. The second Skyrocket, bureau number 37974 (NACA 144), was used by the NACA to investigate the behavior of swept wings. During this program, before its conversion to all-rocket propulsion, D-588-2 number 2 revealed that swept-wing aircraft tend to pitch up under certain aerodynamic conditions.
The NACA used the third D-588-2, bureau number 37975 (NACA 145), in a program evaluating the effectiveness of wing slats and leading edge devices, and examined its behavior with external stores mounted beneath its wings. All three Skyrockets were retired from flight operations in 1956. At one point, Douglas considered developing a D-588-3 hypersonic research aircraft, upon request of the Office of Naval Research, but this aircraft remained a paper study.
—Richard P. Hallion
Adapted from Aircraft of the National Air and Space Museum, edited by F. Robert van der Linden, Smithsonian Institution Press, 1998.