65 years since the first flight at a speed more than four times faster than the speed of sound

March 7 marked the 65th anniversary of the first manned flight at a speed more than four times faster than the speed of sound. On that day in 1961, test pilot Robert White reached a speed of 4,675 km/h at an altitude of 23,600 m in an X-15 aircraft, which was 4.43 times the speed of sound.

The X-15 was a purely experimental aircraft developed by the American company North American Aviation. Its first flight took place on June 8, 1959. The aircraft was designed to study the characteristics of hypersonic flight at high altitudes, up to the boundary between the atmosphere and space. The results were to be used in the creation of reusable spacecraft and new generations of combat aircraft. The flights were performed exclusively by test pilots – military and NASA.

The aircraft had many features, here are just a few. The main structural material was Inconel, an alloy of nickel, chromium, and iron, which allowed it to withstand significant heating from friction with the air. The aircraft was equipped with a liquid rocket engine (several versions of this power plant were tested). The X-15 had a wedge-shaped tail, optimized for hypersonic flight, but at subsonic speeds it created too much aerodynamic drag. The X-15 was not designed to take off from the ground on its own – it was lifted into the air by a specially modified B-52 bomber suspended under its wing. The landing gear, whose rear supports were equipped with small skis, was used for landing. The aircraft was not supposed to land at a regular airfield, but on the surface of a dry salt lake.

A total of three X-15s were built, each with its own characteristics. One of them went into a hypersonic spin and crashed on November 15, 1967. Test pilot Michael J. Adams was killed.

By the end of 1968, 199 X-15 flights had been completed. During these flights, speed and altitude records for manned aircraft were set that remain unbroken to this day. On August 22, 1963, Joseph Walker set an absolute altitude record of 108 km, and on October 3, 1967, William Knight set an absolute speed record of 7,274 km/h (6.07M).