North American X-15 Explained

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 a manned aircraft.[1]

During the X-15 program, 13 of the flights (by eight pilots) met the USAF spaceflight criteria by exceeding the altitude of 50 miles (80.47 km. 264,000ft.), 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

The X-15 is 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.

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:

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.


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).

X-15 flights higher than 50 miles (80 km)
FlightDateTop speedAltitudePilot
Flight 6217 July 19623,831 mph59.6 milesRobert M. White
Flight 7717 January 19633,677 mph51.4 milesJoe Walker
Flight 8727 June 19633,425 mph53.9 milesRobert Rushworth
Flight 9019 July 19633,710 mph65.8 milesJoe Walker
Flight 9122 August 19633,794 mph67.0 milesJoe Walker
Flight 13829 June 19653,431 mph53.1 milesJoseph H. Engle
Flight 14310 August 19653,549 mph51.3 milesJoseph H. Engle
Flight 15028 September 19653,731 mph55.9 milesJohn B. McKay
Flight 15314 October 19653,554 mph50.4 milesJoseph H. Engle
Flight 1741 November 19663,750 mph58.1 milesBill Dana
Flight 19017 October 19673,856 mph53.1 milesPete Knight
Flight 19115 November 19673,569 mph50.3 milesMichael J. Adams
Flight 19721 August 19683,443 mph50.6 milesBill Dana

Fastest flights

X-15 10 fastest flights
FlightDateTop SpeedAltitudePilot
Flight 459 November 19614,092 mph19.2 milesRobert M. White
Flight 5927 June 19624,104 mph23.4 milesJoe Walker
Flight 6426 July 19623,989 mph18.7 milesNeil Armstrong
Flight 8625 June 19633,910 mph21.7 milesJoe Walker
Flight 8918 July 19633,925 mph19.8 milesRobert Rushworth
Flight 975 December 19634,017 mph19.1 milesRobert Rushworth
Flight 10529 April 19643,905 mph19.2 milesRobert Rushworth
Flight 13722 June 19653,938 mph29.5 milesJohn B. McKay
Flight 17518 November 19664,250 mph18.7 milesPete Knight
Flight 1883 October 19674,519 mph36.3 milesPete Knight

X-15 pilots

X-15 pilots and their achievements during the program
Michael J. AdamsU.S. Air Force7105.593,82250.3
Neil ArmstrongNASA7005.743,98939.2
Scott CrossfieldNorth American Aviation14002.971,95915.3
Bill DanaNASA16005.533,89758.1
Joseph H. EngleU.S. Air Force16305.713,88753.1
Pete KnightU.S. Air Force16106.704,51953.1
John B. McKayNASA29005.653,86355.9
Forrest S. PetersenU.S. Navy5005.33,60019.2
Robert A. RushworthU.S. Air Force34106.064,01753.9
Milt ThompsonNASA14005.483,72340.5
Joe WalkerU.S. Air Force25325.924,10467.0
Robert M. WhiteU.S. Air Force16106.044,09259.6
Killed * White was backup for Capt. Iven Kincheloe



External links

Notes and References

  1. " | Aircraft Museum X-15".
  2. Jenkins, Dennis R. Space Shuttle: The History of the National Space Transportation System: The First 100 Missions, 3rd edition. Stillwater, Minnesota: Voyageur Press, 2001. ISBN 0-9633974-5-1.
  3. "NASA astronaut wings award ceremony".
  4. Käsmann 1999, p. 105.
  5. X-15A Crash site
  6. United States Air Force Museum 1975, p. 73.