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 USAF/NASA/USN X-series of experimental aircraft, initiated with the Bell X-1. The X-15 set numerous speed and altitude records in the early 1960s, reaching the edge of space and bringing back valuable data that was used in the design of later aircraft and spacecraft.

During the X-15 program, 13 flights (by eight pilots) met the USAF's criteria for a spaceflight by passing an altitude of 50 miles (80.47 km) and the pilots were accordingly awarded astronaut status by the USAF. Three X-15 pilots also qualified to receive NASA astronaut wings.^[1][2]

Out of all the X-15 missions, two flights (by the same pilot) also qualified for the international FAI definition of a spaceflight by passing the 100 kilometre (62.137 mi., 328,084 ft.) mark.

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 original Request for Proposals was issued for the airframe 30 December 1954, and for the rocket engine on 4 February 1955. North American received the airframe contract in November 1955, and Reaction Motors contracted in 1956 to build the engines.

As with many of the X-aircraft, the X-15 was designed to be carried aloft under the wing of a B-52. The fuselage was long and cylindrical, with fairings towards the rear giving it a flattened look, and it had thick wedge-shaped dorsal and ventral fins. Parts of the fuselage were made of a heat-resistant nickel-based alloy (Inconel-X 750). The retractable landing gear consisted of a nose wheel and two skids — to provide sufficient clearance part of the ventral fin had to be jettisoned before landing. The two XLR-11 rocket engines of the initial model X-15A delivered 36 kN (8,000 lbf) of thrust; the "real" engine that came later was a single XLR-99 that delivered 254 kN (57,000 lbf) at sea level, and 311 kN (70,000 lbf) at peak altitude.

Prior to 1958, USAF and NACA (later NASA) officials discussed an orbital X-15, called the "X-15B", to be launched into space atop a Navajo missile. The idea was scrapped after NASA was formed out of NACA and Project Mercury was approved for manned orbital spaceflight. By 1959, the X-20 Dyna-Soar space-glider program became the USAF's preferred means to launch a military manned spacecraft into orbit. The X-20 program was cancelled in the early 1960s.

The first X-15 flight was an unpowered test made by Scott Crossfield on 8 June 1959, who followed up with the first powered flight on 17 September. The first flight with the XLR-99 was on 15 November 1960.

Operational history

Three X-15s were built in all, and they made a total of 199 test flights, the last one on 24 October 1968. Plans were made for a 200th X-15 flight to be launched over Smith Ranch, Nevada. It was scheduled for 21 November 1968 with William J. Knight as the pilot. Various technical and weather delays caused the planned launch to slip at least six times until late December, 1968. Finally after a cancellation on 20 December 1968 due to weather, it was decided there would not be a 200th flight. The X-15 ground crew de-mated the aircraft from the NB-52A, and prepared it for indefinite storage. X-15 #1 was sent to the National Air and Space Museum in Washington, DC. X-15 #2 is on display at the National Museum of the United States Air Force at Wright-Patterson Air Force Base near Dayton, Ohio. X-15 #3, 56-6672, was destroyed in a crash on 15 November 1967.

Twelve test pilots flew the plane, including Neil Armstrong, later the first man on the Moon, and Joe Engle, who went on to command Space Shuttle missions.

In July and August 1963, pilot Joe Walker crossed the 100 km altitude mark twice, becoming the first person to enter space twice.

Air Force Test pilot Major Michael J. Adams was killed on 15 November 1967 in X-15 Flight 191 when his X-15-3 entered a hypersonic spin on descent, then experienced violent oscillations as aerodynamic forces increased after reentry. As the X-15-3's adaptive flight control system drove control surfaces to their limits, acceleration built to plus or minus 15 g vertically and plus or minus 8 g laterally. The airframe broke up as its descent neared 60,000 feet, scattering wreckage over 50 square miles. On 8 June 2004, a memorial monument was erected at the location of the cockpit near Randsburg, California.^[3] Maj. Adams was posthumously awarded astronaut wings for his last flight in the X-15-3, which had attained an altitude of 266,000 ft (81.1 km, 50.4 mi.). In 1991, Adams' name was added to the Astronaut Memorial at the Kennedy Space Center in Florida.

NB-52A (s/n 52-003) permanent test variant, carrying X-15. Notice mission markings, horizontal X-15 silhouettes indicating glide flights, near-vertical ones recording powered ones.

The second X-15A was rebuilt after a landing accident. It was lengthened by about 2.4 ft (0.74 m), received a pair of auxiliary fuel tanks slung under the fuselage, and was given a heat-resistant surface treatment, the result being called the X-15A-2. It first flew 28 June 1964, and eventually reached a speed of 7,274 km/h (4,520 mph or 2,021 m/s).

The altitudes attained by the X-15 remained unsurpassed by any piloted aircraft except the Space Shuttle until the third spaceflight of SpaceShipOne in 2004. The speeds and altitudes have, also, frequently been exceeded by unpiloted air-launched rockets, such as the Pegasus rocket which has carried several satellites all the way into orbit. The widely reported record achieved by the diminutive X-43A scramjet testbed on 16 November 2004 of nearly Mach 10 (6,600 mph or 10,622 km/h or 2.95 km/s) at 95,000 ft (29 km, 17.99 mi) is only a record for an air-breathing jet engine.

Five main aircraft were involved in the X-15 program: The three X-15s and two B-52 carrier aircraft.

• 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 crash)
• NB-52A - 52-003 (retired October 1969)
• NB-52B - 52-008 (retired November 2004)

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

Wikimedia Commons has media related to:

North American X-15

• 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

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