Design of x 15

The X-15 was a follow-on research aircraft to the early X-planes, which had explored the flight regime from just below the speed of sound (Mach 1) to Mach 3.2. In 1952 the NACA had begun preliminary research into space flight and associated problems. Two years later, NACA's Research Airplane Projects Panel discussed the need for a new research airplane to study hypersonic and space flight. The NACA established the characteristics of what became the X-15 and presented them to the Air Force and Navy in July 1954. The two services and NACA signed a memorandum of understanding for the joint project in December 1954, and the Air Force selected North American to develop three X-15 research aircraft in September 1955.

A North American team headed by Chief Project Engineer Charles Feltz designed the aircraft, with technical guidance from the NACA's Langley Aeronautical Laboratory (later NASA's Langley Research Center), Hampton, Va., and High-Speed Flight Station (as Dryden was then called).

Although the number two aircraft was later modified, the basic X-15 was a single-seat, mid-wing monoplane designed to explore the areas of high aerodynamic heating rates, stability and control, physiological phenomena, and other problems relating to hypersonic flight (above Mach 5). Because the Reaction Motors Division of Thiokol Chemical Corp. did not have the throttleable XLR-99 engine ready for the early flights of the aircraft, the X-15 initially flew with two XLR-11 engines, producing a thrust of 16,380 lb. Once the XLR-99 was installed, the thrust became 57,000 lb.

The X-15 used conventional aerodynamic controls for flight in the dense air of the usable atmosphere. The controls consisted of rudder surfaces on the vertical stabilizers to control yaw (movement of the nose left or right) and canted horizontal surfaces on the tail to control pitch (nose up and down) when moving in synchronization or roll when moved differentially.

For flight in the thin air outside the Earth's atmosphere, the X-15 used a reaction control system. Hydrogen peroxide thrust rockets on the nose of the aircraft provided pitch and yaw control. Those on the wings furnished roll control.

The outer skin of the X-15 consisted of a nickel-chrome alloy called Inconel X, employed in a heat sink structure to withstand the results of aerodynamic heating when the aircraft was flying within the atmosphere. The cabin was made of aluminum and was isolated from the outer structure to keep it cool.