North American X-15

X-15
275px
Type	Rocket-powered aircraft
Manufacturer	North American Aviation
Maiden 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, including also 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. It could be considered the first manned suborbital spacecraft ever flown.

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 km) and the pilots were accordingly awarded astronaut status by the USAF. Three X-15 pilots also qualified to receive NASA astronaut wings.

Some respected aerospace researchers have placed the threshold of space at lower altitudes than the USAF and NASA, so many X-15 pilots could also be considered as astronauts. The "aeropause" region, where space-equivalent conditions are first encountered, starts at an altitude of 19 miles (30 km., 100,320 ft.) above the Earth. Many X-15 pilots traveled through, and far above, the aeropause.

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 62.1 mile (100 km., 328,084 ft.) mark.

Design and development

File:X-15 launched bw.jpg

X-15 just after release.

File:NorthAmericanX-15600.jpeg

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 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 cockpit near Randsburg, California. 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.

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 10,620 km/h or 2.95 km/s) at 95,000 ft (29 km) 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
• NB-52A - 52-003 (retired October 1969)
• NB-52B - 52-008 (retired November 2004)

File:Boeing NB-52A carrying X-15.jpg

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.

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 (18,000 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 km) or more. However the FAI set the limit of space at 100 km. Thirteen X-15 flights went higher than 50 miles (80 km) and two of these reached over 60 miles.

X-15 flights higher than 50 miles (80 km)

Flight	Date	Top speed	Altitude	Pilot
Flight 62	17 July 1962	3,831 mph	59.6 miles	Robert M. White
Flight 77	17 January 1963	3,677 mph	51.4 miles	Joe Walker
Flight 87	27 June 1963	3,425 mph	53.9 miles	Robert Rushworth
Flight 90	19 July 1963	3,710 mph	65.8 miles	Joe Walker
Flight 91	22 August 1963	3,794 mph	67.0 miles	Joe Walker
Flight 138	29 June 1965	3,431 mph	53.1 miles	Joseph H. Engle
Flight 143	10 August 1965	3,549 mph	51.3 miles	Joseph H. Engle
Flight 150	28 September 1965	3,731 mph	55.9 miles	John B. McKay
Flight 153	14 October 1965	3,554 mph	50.4 miles	Joseph H. Engle
Flight 174	1 November 1966	3,750 mph	58.1 miles	Bill Dana
Flight 190	17 October 1967	3,856 mph	53.1 miles	Pete Knight
Flight 191	15 November 1967	3,569 mph	50.3 miles	Michael J. Adams†
Flight 197	21 August 1968	3,443 mph	50.6 miles	Bill Dana

^† fatal

Fastest flights

X-15 10 fastest flights

Flight	Date	Top Speed	Altitude	Pilot
Flight 45	9 November 1961	4,092 mph	19.2 miles	Robert M. White
Flight 59	27 June 1962	4,104 mph	23.4 miles	Joe Walker
Flight 64	26 July 1962	3,989 mph	18.7 miles	Neil Armstrong
Flight 86	25 June 1963	3,910 mph	21.7 miles	Joe Walker
Flight 89	18 July 1963	3,925 mph	19.8 miles	Robert Rushworth
Flight 97	5 December 1963	4,017 mph	19.1 miles	Robert Rushworth
Flight 105	29 April 1964	3,905 mph	19.2 miles	Robert Rushworth
Flight 137	22 June 1965	3,938 mph	29.5 miles	John B. McKay
Flight 175	18 November 1966	4,250 mph	18.7 miles	Pete Knight
Flight 188	3 October 1967	4,519 mph	36.3 miles	Pete Knight

X-15 Pilots

Pilot	Organization	Total Flights	USAF space flights	FAI space flights	Max Mach	Max speed (mph)	Max altitude (miles)
Michael J. Adams†	U.S. Air Force	7	1	0	5.59	3,822	50.3
Neil Armstrong**	NASA	7	0	0*	5.74	3,989	39.2
Scott Crossfield	North American Aviation	14	0	0	2.97	1,959	15.3
Bill Dana	NASA	16	2	0	5.53	3,897	58.1
Joseph H. Engle**	U.S. Air Force	16	3	0*	5.71	3,887	53.1
Pete Knight	U.S. Air Force	16	1	0	6.70	4,519	53.1
John B. McKay	NASA	29	1	0	5.65	3,863	55.9
Forrest S. Petersen	U.S. Navy	5	0	0	5.3	3,600	19.2
Robert A. Rushworth	U.S. Air Force	34	1	0	6.06	4,017	53.9
Milt Thompson	NASA	14	0	0	5.48	3,723	40.5
Joe Walker*	U.S. Air Force	25	3	2	5.92	4,104	67
Robert M. White††	U.S. Air Force	16	1	0	6.04	4,092	59.6

^† Killed on Flight 191.

^†† Capt Iven Kincheloe had been selected in September 1957 as the Air Force's project test pilot for the X-15 program (with Capt Bob White as his alternate), but was killed the following year in an F-104 crash before the X-15 ever flew.

* Crossed the 60 mi mark during the X-15 program.

** These two pilots crossed the 60 mi mark after leaving the X-15 program, Armstrong in Gemini, Engle in the Shuttle.

See Also

• List of X-15 flights

References

Bibliography

• American X-Vehicles: An Inventory X-1 to X-50, SP-2000-4531 - June 2003; NASA online PDF Monograph
• Flight experience with shock impingement and interference heating on the X-15-2 research airplane 1968 - NASA (PDF)
• Godwin, Robert, ed. X-15: The NASA Mission Reports. Burlington, Ontario: Apogee Books, 2001. ISBN 1-896522-65-3.
• Hallion, Dr. Richard P. "Saga of the Rocket Ships," AirEnthusiast Six March-June 1978. Bromley, Kent, UK: Pilot Press Ltd., 1978.
• Hypersonics Before the Shuttle: A Concise History of the X-15 Research Airplane - NASA report (PDF)
• Thermal protection system X-15A-2 Design report 1968 - NASA report (PDF format)
• Thompson, Milton O. and Armstrong, Neil. At the Edge of Space: The X-15 Flight Program. Washington, DC: Smithsonian Institution Press, 1992. ISBN 1-56098-107-5.
• Tregaskis, Richard. X-15 Diary: The Story of America's First Space Ship. Lincoln, Nebraska: iUniverse.com, 2000. ISBN 0-595-00250-1.
• X-15 research results with a selected bibliography - NASA report (PDF)

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)

See also

Comparable aircraft

• X-20 Dyna-Soar

Related lists

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

See also

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North American X-15

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