North American X-15

X-15
Role	Rocket-powered aircraft
Manufacturer	North American Aviation
First flight	8 June 1959
Introduced	17 September 1959
Retired	December 1968
Status	Museum piece
Primary users	U.S.Air Force NASA
Number built	3

The North American X-15 rocket-powered aircraft was part of the X-series of experimental aircraft, initiated with the Bell X-1, that were made for the USAF, the NASA, and the USN . The X-15 set speed and altitude records in the early 1960s, reaching the edge of outer space and returning with valuable data used in aircraft and spacecraft design. It currently holds the world record for the fastest speed ever reached by an aircraft.^[1]

During the X-15 program, 13 flights (by eight pilots) met the USAF spaceflight criteria by exceeding the altitude of 50 miles (80.47 km), thus qualifying the pilots for astronaut status; some pilots also qualified for NASA astronaut wings. ^[2][3]

Of all the X-15 missions, two flights (by the same pilot) qualified as space flights, per the international FAI definition of a spaceflight by exceeding a 100 kilometer (62.137 mi, 328,084 ft) altitude.

Design and development

X-15 just after release.

X-15 touching down on its skids. Compare jettisoned lower ventral fin with color picture, top.

The X-15 based on a concept study from Walter Dornberger for the NACA for a hypersonic research aircraft. ^[4] The requests for proposal were published on 30 December 1954 for the airframe and on 4 February 1955 for the rocket engine. The X-15 was built by two manufacturers: North American Aviation was contracted for the airframe in November 1955, and Reaction Motors was contracted for building the engines in 1956.

The first X-15 flight was an unpowered test flight by Scott Crossfield, on 8 June 1959; he also piloted the first powered flight, on 17 September 1959, with his first XLR-99 flight on 15 November 1960.

Like most X-series aircraft, the X-15 was designed to be carried aloft, under the wing of a B-52 bomber plane. The X-15 fuselage was long and cylindrical, with rear fairings that flattened its appearance, and thick, dorsal and ventral wedge-fin stabilizers. Parts of the fuselage were heat-resistant nickel alloy (Inconel-X 750).^[4] The retractable landing gear comprised a nose-wheel carriage and two rear skis. The skis did not extend beyond the ventral fin, which required the pilot to jettison the lower fin (fitted with a parachute) just before landing. The two XLR-11 rocket engines for the initial X-15A model delivered 72kN (16,000 lbft) of total thrust; the main engine (installed later) was a single XLR-99 rocket engine delivering 254kN (57,000 lbft) at sea level, and 311 kN (70,000 lbft) at peak altitude.

Before 1958, USAF and NACA, (later NASA), officials discussed an orbital X-15 spacecraft — the X-15B — for launching to outer space atop an SM-64 Navajo missile, that was cancelled when the NACA became the NASA, and Project Mercury was approved. By 1959, the X-20 Dyna-Soar space-glider program became the USAF's preferred means for launching military manned-spacecraft into orbit; the program was cancelled in the early 1960s.

Operational history

Three X-15s were built, flying 199 test flights, the last on 24 October 1968. Twelve test pilots flew the X-15, among them were Neil Armstrong (first man on the moon) and Joe Engle (a space shuttle commander). In July and August 1963, pilot Joe Walker crossed the 100 km altitude mark twice, thus joining the NASA astronauts and Soviet Cosmonauts as the only men to have crossed the barrier into outer space (Alan Shepard was the first American in space, while Soviet Yuri Gagarin was the first human being in space).

U.S. Air Force Test pilot Maj. Michael J. Adams was killed, on 15 November 1967, in X-15 Flight 191 when his craft (X-15-3) entered a hypersonic spin while descending, then oscillated violently as aerodynamic forces increased after re-entry. As his craft's flight control system operated the control surfaces to their limits, the craft's acceleration built to ±15 degrees vertical and ±8 degrees lateral. The airframe broke apart at 60,000 ft altitude, scattering the craft's wreckage for 50 square miles. On 8 June 2004, a monument was erected at the cockpit's locale, near Randsburg, California. ^[5] Maj. Adams was posthumously awarded astronaut wings for his final flight in craft X-15-3, which had reached 266,000 ft (81.1 km, 50.4 mi.) of altitude. In 1991, his name was added to the Astronaut Memorial monument, Kennedy Space Center, Florida.

Bomber NB-52A (s/n 52-003), permanent test variant, carrying an X-15, with mission markings; horizontal X-15 craft silhouettes denote glide flights, diagonal silhouettes denote powered flights.

The second X-15A was rebuilt after a landing accident. It was lengthened 2.4 ft (0.74 m), a pair of auxiliary fuel tanks attached under the fuselage, and a heat-resistant surface treatment applied. Re-named the X-15A-2, it first flew on 28 June 1964, reaching 7,274 km/h (4,520 mph, 2,021 m/s).

The altitudes attained by the X-15 aircraft do not match that of Alan Shephard's 1961 NASA spacecapsule flight (116 miles), nor subsequent NASA spacecapsules and space shuttle flights. However, the X-15 flights did reign supreme among rocket-powered aircraft until the third spaceflight of Space Ship One in 2004. The widely-reported record achieved, by the small X-43A scramjet testbed, on 16 November 2004, of approximately Mach 10 (6,600 mph, 10,622 km/h, 2.95 km/s) at 95,000 ft (29 km, 17.99 mi) is an air-breathing jet engine record.

Five aircraft were the X-15 program: three X-15s, two B-52 bombers:

• X-15A-1 - 56-6670, 82 powered flights
• X-15A-2 - 56-6671, 53 powered flights
• X-15A-3 - 56-6672, 64 powered flights (destroyed in a crash)
• NB-52A - 52-003 (retired in October 1969)
• NB-52B - 52-008 (retired in November 2004)

A 200th flight over Nevada was slated for 21 November 1968, piloted by William J. Knight. Technical problems and bad weather delayed the flight six times, and on 20 December 1968, the 200th flight was finally cancelled. The X-15 was unfastened from the wing of bomber NB-52A, and prepared for indefinite storage.

Survivors

• X-15-1 (s/n 56-6671) is on display at the National Air and Space Museum, in Washington, D.C.
• X-15-2 (s/n 56-6671) is at the National Museum of the United States Air Force, Wright-Patterson Air Force Base, near Dayton, Ohio. It was retired to the Museum in October 1969.^[6]
• X-15-3, (56-6672), crashed and burned on 15 November 1967.

Specifications (X-15)

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

Performance

• Maximum speed: Mach 6.70 (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

Record flights

Highest flights

In the United States there are two definitions of how high a person must go to be referred to as an astronaut. The USAF decided to award astronaut wings to anyone who achieved an altitude of 50 miles (80.47 km) or more. However the FAI set the limit of space at 100 km. Thirteen X-15 flights went higher than 50 miles (80.47 km) and two of these reached over 62.137 miles (100 km).

^† fatal

Fastest flights

X-15 pilots

See also

Comparable aircraft

• X-20 Dyna-Soar
  

Related lists

• List of rocket planes
• List of X-15 flights
• List of space disasters
  

References

Notes

Bibliography

External links

• NASA's X-15 website
• X-15 Research Results With a Selected Bibliography (NASA SP-60, 1965)
• "Transiting from Air to Space: The North American X-15" (1998)
• "Proceedings of the X-15 First Flight 30th Anniversary Celebration, 8 June 1989"
• (PDF) Hypersonics Before the Shuttle: A Concise History of the X-15 Research Airplane (NASA SP-2000-4518, 2000)
• A Field Guide to American Spacecraft - Locations of X-15 aircraft
• unofficial X-15 website
• X-15 Research Results (1964)
• X-15 photos at Dryden
• Encyclopedia Astronautica's X-15 chronology
• Major Michael Adams Monument
• X15 site in French, with detailed flight reports
• Aerospace Legacy Foundation
• X-15, X-15A-2 • Dimensional references, plans and images (Primary source: NASA Technical Reports)
• Fly the X-15 in Flight Simulator.
• Interview with Neil Armstrong about his experience in the X-15
• X-15 at the Internet Movie Database
• Scott Crossfield Foundation - Promoting aerospace education

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