An X-15 experimental aircraft parked on a dry lakebed in 1960. Despite the extreme dangers involved with the X-15 program, it only recorded one fatality during a mid-air breakup in 1967. (NASA)

Why the North American X-15 Was One of the Most Dangerous Planes Ever Built

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Built to test aerodynamics at hypersonic speed, the X-15 had more in common with a rocket than a conventional aircraft, making it extremely difficult to fly and land.

The X-15 remains one of the most remarkable experimental aircraft ever built, nearly 70 years after its first flight. Completing 199 flights between 1959 and 1968, the X-15 was a monumental success—reaching Mach 6.70 (roughly 4,520 miles per hour) and 354,200 feet altitude, to establish the program’s speed and altitude records.

At those extremes, the X-15 encountered problems conventional aircraft obviously did not: things like hypersonic heating, rocket-engine hazards, underpowered landings, and the fact that aerodynamic controls became useless in near-space. Yet, despite operating at the edges of human engineering performance, the program suffered only one fatal flight, though there were a handful of close calls.

About the X-15 Rocket Plane

Year Introduced: 1959

Length: 49 ft 2 in (15 m)

Wingspan: 22 ft 4 in (6.81 m)

Weight (Gross): 33,500 lb (15,195 kg)

Propulsion: One Reaction Motors XLR99-RM-2 liquid-fueled rocket engine; 70,400 lb thrust

Top Speed: ~4,520 mph (7,270 km/h); approx. Mach 6.7’

Range: ~280 mi (450 km)

Service........

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