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Six times the Speed of Sound?

The North American X-15 (first flight: June 8, 1959, last flight: October 24, 1968) was a manned rocket-powered aircraft that broke record after record in the 1960's, flying at astonishing altitudes (328 084 ft) and hypersonic speeds (Mach 6.72). Mach 6.72 is actually 6.72 times the speed of sound!

The X-15 was part of the X-series of experimental aircraft, which the Bell X-1 was part of.

In the end, three X-15's were built and they flew a total of 199 flights (12 pilots):
  • X-15A-1 - 56-6670, 82 powered flights
  • X-15A-2 - 56-6671, 53 powered flights
  • X-15A-3 - 56-6672, 64 powered flights

How the plane was launched...

The X-15 did not launch from a runway. Instead, it was attached to a wing pylon on a specially designed B-52 that brought it to 45 000 feet where the plane was released. The B-52 was designated NB-52 and appropriately called the "mothership".

Two NB-52's were built, NB-52A ( (52-003) and NB-52B (52-008).


Of the three X-15's that were built, planes number 2 and 3 were destroyed in accidents (number 2 was repaired but never flew again). The pilot of the first accident (plane number 2), Jack McKay, survived the crash but was an inch shorter when he was pulled out from under the plane. Unfortunately, the pilot of the second accident (plane number 3), Mike Adams, was killed.

Record Breaking Flights...

  • Joseph Albert Walker broke the highest altitude record of the time three times, his last on August 22, 1963. He reached 328 084 ft on his X-15.
  • William J. "Pete" Knight broke the fastest speed record then on October 3, 1967. Knight reached a top speed of Mach 6.72 (6.72 times the speed of sound).
However, the records set by the X-15 have been broken today by new and more advanced planes.

Planes of the X-15 program on display...

  • X-15A-1 is on display in the National Air and Space Museum "Milestones of Flight" gallery
  • X-15A-2 is on display in the National Museum of the United States Air Force's Research and Development hanger alongside other "X-planes"
  • NB-52A is on display in the Pima Air and Space Museum
  • NB-52B is at the Dryden Flight Research Center

Interesting Facts...

  • Neil Armstrong (first person to set foot on the moon) was one of the X-15 pilots
  • The planned 200th flight of the X-15, piloted by William J. Knight was delayed six times due to technical problems and bad weather. It was eventually cancelled


General characteristics

  • Crew: one

  • Length: 50 ft 9 in (15.45 m)

  • Wingspan: 22 ft 4 in (6.8 m)

  • Height: 13 ft 6 in (4.12 m)

  • Wing area: 200 ft² (18.6 m²)

  • Empty weight: 14,600 lb (6,620 kg)

  • Loaded weight: 34,000 lb (15,420 kg)

  • Max takeoff weight: 34,000 lb (15,420 kg)

  • Powerplant: Thiokol XLR99-RM-2 liquid-fuel rocket engine, 70,400 lbf at 30 km (313 kN)


  • Maximum speed: Mach 6.72 (4,520 mph / 7,274 km/h)

  • Range: 280 mi (450 km)

  • Service ceiling: 67 mi (354,330 ft / 108 km)

  • Rate of climb: 60,000 ft/min (18,288 m/min)

  • Wing loading: 170 lb/ft² (829 kg/m²)

  • Thrust/weight: 2.07

This article was created with information from AcePilots

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