North American X-15

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The North American X-15 is a hypersonic rocket-powered aircraft formerly operated by the United States Air Force and the National Aeronautics and Space Administration (NASA) as part of the X-plane series of experimental aircraft. The X-15 set speed and altitude records in the 1960s, crossing the edge of outer space and returning with valuable data used in aircraft and spacecraft design. The X-15's highest speed, Script error: No such module "convert".,[1] was achieved on 3Script error: No such module "String".October 1967,[2] when William J. Knight flew at MachScript error: No such module "String".6.7 at an altitude of Script error: No such module "convert"., or 19.34Script error: No such module "String".miles. This set the official world record for the highest speed ever recorded by a crewed, powered aircraft and remains unbroken.[3][4]

During the X-15 program, 12Script error: No such module "String".pilots flew a combined 199Script error: No such module "String".flights.[1] Of these, 8 pilots flew a combined 13Script error: No such module "String".flights which met the Air Force spaceflight criterion by exceeding the altitude of Script error: No such module "convert"., thus qualifying these pilots as being astronauts; of those 13Script error: No such module "String".flights, 2 (flown by the same civilian pilot) met the FAI definition (Script error: No such module "convert".) of outer space. The 5Script error: No such module "String".Air Force pilots qualified for military astronaut wings immediately, while the 3Script error: No such module "String".civilian pilots were eventually awarded NASA astronaut wings in 2005, 35Script error: No such module "String".years after the last X-15 flight.Template:Sfn[5]

Design and development

File:X-15 in flight.jpg
X-15 after igniting rocket engine

The X-15 was based on a concept study from Walter Dornberger for the National Advisory Committee for Aeronautics (NACA) of a hypersonic research aircraft.Template:Sfn The requests for proposal (RFPs) were published on 30Script error: No such module "String".December 1954 for the airframe and on 4Script error: No such module "String".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.

Like many X-series aircraft, the X-15 was designed to be carried aloft and drop launched from under the wing of a B-52 mother ship. Air Force NB-52A, "The High and Mighty One" (serial 52-0003), and NB-52B, "The Challenger" (serial 52-0008, also known as Balls 8) served as carrier planes for all X-15 flights. Release of the X-15 from NB-52A took place at an altitude of about Script error: No such module "convert". and a speed of about Script error: No such module "convert"..[6] 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 (the outer skin[7]) were heat-resistant nickel alloy (Inconel-XScript error: No such module "String".750).Template:Sfn The retractable landing gear comprised a nose-wheel carriage and two rear skids. The skids did not extend beyond the ventral fin, which required the pilot to jettison the lower fin just before landing. The lower fin was recovered by parachute.

Cockpit and pilot systems

File:North American X-15A-2 cockpit 2 USAF.jpg
Cockpit of an X-15

The X-15 was the product of developmental research, and changes were made to various systems over the course of the program and between the different models. The X-15 was operated under several different scenarios, including attachment to a launch aircraft, drop, main engine start and acceleration, ballistic flight into thin air/space, re-entry into thicker air, unpowered glide to landing, and direct landing without a main-engine start. The main rocket engine operated only for a relatively short part of the flight but boosted the X-15 to its high speeds and altitudes. Without the main rocket engine thrust, the X-15's instruments and control surfaces remained functional, but the aircraft could not maintain altitude.

As the X-15 also had to be controlled in an environment where there was too little air for aerodynamic flight control surfaces, it had a reaction control system (RCS) that used rocket thrusters.[8] There were two different X-15 pilot control setups: one used three joysticks, the other, one joystick.[9]

The X-15 type with multiple control sticks for the pilot placed a traditional center stick between a left 3-axis joystick that sent commands to the Reaction Control System,[10] and a third joystick on the right used during high-G maneuvers to augment the center stick.[10] In addition to pilot input, the X-15 "Stability Augmentation System" (SAS) sent inputs to the aerodynamic controls to help the pilot maintain attitude control.[10] The Reaction Control System (RCS) could be operated in two modes – manual and automatic.[9] The automatic mode used a feature called "Reaction Augmentation System" (RAS) that helped stabilize the vehicle at high altitude.[9] The RAS was typically used for approximately three minutes of an X-15 flight before automatic power off.[9]

File:X-15A2 NB-52B 3.jpg
X-15A-2, with sealed ablative coating, external fuel tanks, and ramjet dummy test

The alternative control setup used the MH-96 flight control system, which allowed one joystick in place of three and simplified pilot input.[11] The MH-96 could automatically blend aerodynamic and rocket controls, depending on how effective each system was at controlling the aircraft.[11]

Among the many controls were the rocket engine throttle and a control for jettisoning the ventral tail fin.[10] Other features of the cockpit included heated windows to prevent icing and a forward headrest for periods of high deceleration.[10]

The X-15 had an ejection seat designed to operate at speeds up to Script error: No such module "convert". and Script error: No such module "convert". altitude, although it was never used during the program.[10] In the event of ejection, the seat was designed to deploy fins, which were used until it reached a safer speed and altitude at which to deploy its main parachute.[10] Pilots wore pressure suits, which could be pressurized with nitrogen gas.[10] Above Script error: No such module "convert". altitude, the cockpit was pressurized to Script error: No such module "convert". with nitrogen gas, while oxygen for breathing was fed separately to the pilot.[10]

Propulsion

File:NASM-SI-2008-5570.jpg
X-15 tail with XLR-99

The initial 24 powered flights used two Reaction Motors XLR11 liquid-propellant rocket engines, enhanced to provide a total of Script error: No such module "convert". of thrust as compared to the Script error: No such module "convert". that a single XLR11 provided in 1947 to make the Bell X-1 the first aircraft to fly faster than the speed of sound. The XLR11 used ethyl alcohol and liquid oxygen.

By November 1960, Reaction Motors delivered the XLR99 rocket engine, generating Script error: No such module "convert". of thrust. The remaining 175Script error: No such module "String".flights of the X-15 used XLR99 engines, in a single engine configuration. The XLR99 used anhydrous ammonia and liquid oxygen as propellant, and hydrogen peroxide to drive the high-speed turbopump that delivered propellants to the engine.[8] It could burn Script error: No such module "convert". of propellant in 80Script error: No such module "String".seconds;[8] Jules Bergman titled his book on the program Ninety Seconds to Space to describe the total powered flight time of the aircraft.[12]

The X-15 reaction control system (RCS), for maneuvering in the low-pressure/density environment, used high-test peroxide (HTP), which decomposes into water and oxygen in the presence of a catalyst and could provide a specific impulse of Script error: No such module "convert"..[9]Template:Sfn The HTP also fueled a turbopump for the main engines and auxiliary power units (APUs).[8] Additional tanks for helium and liquid nitrogen performed other functions; the fuselage interior was purged with helium gas, and liquid nitrogen was used as coolant for various systems.[8]

Wedge tail and hypersonic stability

File:X-15 and B-52 Mother ship.jpg
X-15 attached to its B-52 mother ship with a T-38 flying nearby

The X-15 had a thick wedge tail to enable it to fly in a steady manner at hypersonic speeds.[13] This produced a significant amount of base drag at lower speeds;[13] the blunt end at the rear of the X-15 could produce as much drag as an entire F-104 Starfighter.[13]

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A wedge shape was used because it is more effective than the conventional tail as a stabilizing surface at hypersonic speeds. A vertical-tail area equal to 60 percent of the wing area was required to give the X-15 adequate directional stability.

— Template:Comma separated entries

Script error: No such module "Check for unknown parameters". Stability at hypersonic speeds was aided by side panels that could be extended from the tail to increase the overall surface area, and these panels doubled as air brakes.[13]

Operational history

File:Inside the X-15 NASAs Revolutionary Rocket Plane 1959.webm
"Inside the X-15: NASA's Revolutionary Rocket Plane" (1959) Official NASA promotional film reel.

Before 1958, United States Air Force (USAF) and NACA officials discussed an orbital X-15 spaceplane, the X-15B that would launch into outer space from atop an SM-64 Navaho missile. This was canceled when the NACA became NASA and adopted Project Mercury instead.

By 1959, the Boeing X-20 Dyna-Soar space-glider program was to become the USAF's preferred means for launching military crewed spacecraft into orbit. This program was canceled in the early 1960s before an operational vehicle could be built.Template:Sfn Various configurations of the Navaho were considered, and another proposal involved a Titan I stage.[14]

Three X-15s were built, flying 199Script error: No such module "String".test flights, the last on 24Script error: No such module "String".October 1968.

The first X-15 flight was an unpowered glide flight by Scott Crossfield, on 8Script error: No such module "String".June 1959. Crossfield also piloted the first powered flight on 17Script error: No such module "String".September 1959, and his first flight with the XLR-99 rocket engine on 15Script error: No such module "String".November 1960. Twelve test pilots flew the X-15. Among these were Neil Armstrong, later a NASA astronaut and the first man to set foot on the Moon, and Joe Engle, later a commander of NASA Space Shuttle missions.

In a 1962 proposal, NASA considered using the B-52/X-15 as a launch platform for a Blue Scout rocket to place satellites weighing up to Script error: No such module "convert". into orbit.[14][15]

In July and August 1963, pilot Joe Walker exceeded 100 km in altitude, joining NASA astronauts and Soviet cosmonauts as the first human beings to cross that line on their way to outer space. The USAF awarded astronaut wings to anyone achieving an altitude of Script error: No such module "convert"., while the FAI set the limit of space at Script error: No such module "convert"..

On 15Script error: No such module "String".November 1967, U.S. Air Force test pilot Major Michael J. Adams was killed during X-15 Flight 191 when X-15-3, AF Ser. No. 56-6672, entered a hypersonic spin while descending, then oscillated violently as aerodynamic forces increased after re-entry. As his aircraft's flight control system operated the control surfaces to their limits, acceleration built to Script error: No such module "convert". vertical and Script error: No such module "convert". lateral. The airframe broke apart at Script error: No such module "convert". altitude, scattering the X-15's wreckage across Script error: No such module "convert".. On 8Script error: No such module "String".May 2004, a monument was erected at the cockpit's locale, near Johannesburg, California.[16] Major Adams was posthumously awarded Air Force astronaut wings for his final flight in X-15-3, which had reached an altitude of Script error: No such module "convert".. In 1991, his name was added to the Astronaut Memorial.[16]

File:X-15 Crash at Mud Lake, Nevada - GPN-2000-000120.jpg
X-15-2 crash at Mud Lake, Nevada

The second plane, X-15-2, was rebuilt[17] after a landing accident on 9Script error: No such module "String".November 1962 which damaged the craft and injured its pilot, John McKay.[18] The new plane renamed X-15A-2, had a new Script error: No such module "convert". fuselage extension to carry liquid hydrogen.[1] It was lengthened by Script error: No such module "convert"., had a pair of auxiliary fuel tanks attached beneath its fuselage and wings, and a complete heat-resistant ablative coating was added. It took flight for the first time on 25Script error: No such module "String".June 1964. It reached its maximum speed of Script error: No such module "convert". in October 1967 with pilot William "Pete" Knight of the U.S. Air Force in control.

Five principal aircraft were used during the X-15 program: three X-15 planes and two modified "nonstandard" NB-52 bombers:

  • X-15-1 – 56-6670, 81 free flights
  • X-15-2 (later X-15A-2) – 56-6671, 31 free flights as X-15-2, 22 free flights as X-15A-2; 53 in total
  • X-15-3 – 56-6672, 65 free flights, including the Flight 191 disaster
  • NB-52A – 52-003 nicknamed The High and Mighty One (retired in October 1969)
  • NB-52B – 52-008 nicknamed The Challenger, later Balls 8 (retired in November 2004)

Additionally, F-100, F-104 and F5D chase aircraft and C-130 and C-47 transports supported the program.[19]

The 200th flight over Nevada was first scheduled for 21Script error: No such module "String".November 1968, to be flown by William "Pete" Knight. Numerous technical problems and outbreaks of bad weather delayed this proposed flight six times, and it was permanently canceled on 20Script error: No such module "String".December 1968. This X-15 (56-6670) was detached from the B-52 and then put into indefinite storage. The aircraft was later donated to the Smithsonian Air & Space Museum for display.

Aircraft on display

File:X-15 at the Mary Baker Engen Restoration Hangar.jpg
X-15-1 56-6670 in the Mary Baker Engen Restoration Hangar
File:17 14 083 X15.jpg
X-15 at the USAF Museum

Both surviving X-15s are currently on display at museums in the United States. In addition, three mockups and both B-52 Stratofortresses used as motherships are on display as well.

Mockups

Stratofortress mother ships

File:Boeing NB-52B takeoff 061127-F-1234S-007.jpg
NB-52B Balls 8 takes off with an X-15
  • NB-52A (AF Ser. No. 52-003) is displayed at the Pima Air & Space Museum adjacent to Davis–Monthan AFB in Tucson, Arizona. It launched the X-15-1 30Script error: No such module "String".times, the X-15-2, 11Script error: No such module "String".times, and the X-15-3 31Script error: No such module "String".times (as well as the M2-F2 four times, the HL-10 11Script error: No such module "String".times and the X-24A twice).
  • NB-52B (AF Ser. No. 52-008) is on permanent display outside the north gate of Edwards AFB, California. It launched the majority of X-15 flights.

Record flights

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File:X15 speed altitude.jpg
Key speed and altitude benchmarks of the X-15

Highest flights

During 13 of the 199 total X-15 flights, eight pilots flew above Script error: No such module "convert"., thereby qualifying as astronauts according to the US Armed Forces definition of the space border. All five Air Force pilots flew above 50Script error: No such module "String".miles and were awarded military astronaut wings contemporaneously with their achievements, including Adams, who received the distinction posthumously following the flightScript error: No such module "String".191 disaster.[20] However the other three were NASA employees and did not receive a comparable decoration at the time. In 2004, the Federal Aviation Administration conferred its first-ever commercial astronaut wings on Mike Melvill and Brian Binnie, pilots of the commercial SpaceShipOne, another spaceplane with a flight profile comparable to the X-15's. Following this in 2005, NASA retroactively awarded its civilian astronaut wings to Dana (then living), and to McKay and Walker (posthumously).[21][22] Forrest S. Petersen, the only Navy pilot in the X-15 program, never took the aircraft above the requisite altitude and thus never earned astronaut wings.

Of the thirteen flights, only twoTemplate:TspTemplate:NdashTemplate:Tspflights 90 and 91, piloted by WalkerTemplate:TspTemplate:NdashTemplate:Tspexceeded the Script error: No such module "convert". altitude used by the FAI to denote the Kármán line.

X-15 flights higher than 50 milesEvans|2013b|p=12-23|[23]Template:Sfn
Flight Date Top speedTemplate:Efn Altitude Pilot
Flight 91 22 August 1963 Script error: No such module "convert". (Mach 5.58) Script error: No such module "convert". Joseph A. Walker
Flight 90 19 July 1963 Script error: No such module "convert". (Mach 5.50) Script error: No such module "convert". Joseph A. Walker
Flight 62 17 July 1962 Script error: No such module "convert". (Mach 5.45) Script error: No such module "convert". Robert M. White
Flight 174 1 November 1966 Script error: No such module "convert". (Mach 5.46) Script error: No such module "convert". William H. "Bill" Dana
Flight 150 28 September 1965 Script error: No such module "convert". (Mach 5.33) Script error: No such module "convert". John B. McKay
Flight 87 27 June 1963 Script error: No such module "convert". (Mach 4.89) Script error: No such module "convert". Robert A. Rushworth
Flight 138 29 June 1965 Script error: No such module "convert". (Mach 4.94) Script error: No such module "convert". Joe H. Engle
Flight 190 17 October 1967 Script error: No such module "convert". (Mach 5.53) Script error: No such module "convert". William J. "Pete" Knight
Flight 77 17 January 1963 Script error: No such module "convert". (Mach 5.47) Script error: No such module "convert". Joseph A. Walker
Flight 143 10 August 1965 Script error: No such module "convert". (Mach 5.20) Script error: No such module "convert". Joe H. Engle
Flight 197 21 August 1968 Script error: No such module "convert". (Mach 5.01) Script error: No such module "convert". William H. "Bill" Dana
Flight 153 14 October 1965 Script error: No such module "convert". (Mach 5.08) Script error: No such module "convert". Joe H. Engle
Flight 191 15 November 1967 Script error: No such module "convert". (Mach 5.20) Script error: No such module "convert". Michael J. Adams†

† fatal

Fastest recorded flights

X-15 ten fastest flights[24]Template:Sfn
Flight Date Top speedTemplate:Efn Altitude Pilot
Flight 188 3 October 1967 Script error: No such module "convert". (Mach 6.70) Script error: No such module "convert". William J. "Pete" Knight
Flight 175 18 November 1966 Script error: No such module "convert". (Mach 6.33) Script error: No such module "convert". William J. "Pete" Knight
Flight 59 27 June 1962 Script error: No such module "convert". (Mach 5.92) Script error: No such module "convert". Joseph A. Walker
Flight 45 9 November 1961 Script error: No such module "convert". (Mach 6.04) Script error: No such module "convert". Robert M. White
Flight 97 5 December 1963 Script error: No such module "convert". (Mach 6.06) Script error: No such module "convert". Robert A. Rushworth
Flight 64 26 July 1962 Script error: No such module "convert". (Mach 5.74) Script error: No such module "convert". Neil A. Armstrong
Flight 137 22 June 1965 Script error: No such module "convert". (Mach 5.64) Script error: No such module "convert". John B. McKay
Flight 89 18 July 1963 Script error: No such module "convert". (Mach 5.63) Script error: No such module "convert". Robert A. Rushworth
Flight 86 25 June 1963 Script error: No such module "convert". (Mach 5.51) Script error: No such module "convert". Joseph A. Walker
Flight 105 29 April 1964 Script error: No such module "convert". (Mach 5.72) Script error: No such module "convert". Robert A. Rushworth

Pilots

X-15 pilots and their achievements during the program
Pilot Organization Year assigned
to X-15[25][26] 		Total
flights 		USAF
space
flights 		FAI
space
flights 		Max
Mach 		Max
speed
(mph) 		Max
altitude
(miles)
Michael J. Adams† U.S. Air Force 1966 7 1 0 5.59 3,822 50.3
Neil A. Armstrong NASA 1960[27] 7 0 0 5.74 3,989 39.2
Scott Crossfield North American Aviation 1959 14 0 0 2.97 1,959 15.3
William H. Dana NASA 1965 16 2 0 5.53 3,897 58.1
Joe H. Engle U.S. Air Force 1963 16 3 0 5.71 3,887 53.1
William J. Knight U.S. Air Force 1964 16 1 0 6.7 4,519 53.1
John B. McKay NASA 1960 29 1 0 5.65 3,863 55.9
Forrest S. Petersen U.S. Navy 1958 5 0 0 5.3 3,600 19.2
Robert A. Rushworth U.S. Air Force 1958 34 1 0 6.06 4,017 53.9
Milton O. Thompson NASA 1963 14 0 0 5.48 3,723 40.5
Joseph A. Walker†† NASA 1960[28] 25 3 2 5.92 4,104 67.0
Robert M. White U.S. Air Force 1957 16 1 0 6.04 4,092 59.6

† Killed in the crash of X-15-3
†† Died in a group formation accident on 8 June 1966.

Gallery

Video resources

Specifications

File:North American X-15 3-view.svg
Three view drawing
File:North American X-15 Cutdrawing.jpg
X-15 cutdrawing

Other configurations include the Reaction Motors XLR11 equipped X-15, and the long version.

Template:Aircraft specs

In popular culture

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See also

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Aircraft of comparable role, configuration, and era

Related lists

Notes

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References

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  1. ↑ a b c Script error: No such module "citation/CS1".
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  5. ↑ Script error: No such module "citation/CS1".
  6. ↑ Script error: No such module "citation/CS1".
  7. ↑ Script error: No such module "citation/CS1".
  8. ↑ a b c d e Script error: No such module "citation/CS1".
  9. ↑ a b c d e Script error: No such module "citation/CS1".
  10. ↑ a b c d e f g h i Script error: No such module "citation/CS1".
  11. ↑ a b Script error: No such module "citation/CS1".
  12. ↑ Script error: No such module "Citation/CS1".
  13. ↑ a b c d Script error: No such module "citation/CS1".
  14. ↑ a b Script error: No such module "citation/CS1".
  15. ↑ Script error: No such module "citation/CS1".
  16. ↑ a b Script error: No such module "Citation/CS1".
  17. ↑ Script error: No such module "Footnotes".
  18. ↑ Script error: No such module "Footnotes".
  19. ↑ Script error: No such module "citation/CS1".
  20. ↑ Jenkins (2000), Appendix 8, p. 117.
  21. ↑ Script error: No such module "citation/CS1".
  22. ↑ Script error: No such module "citation/CS1".
  23. Evans|2013b|p=12_23-0|↑ Script error: No such module "Footnotes".
  24. ↑ Script error: No such module "Footnotes".
  25. ↑ Script error: No such module "citation/CS1".
  26. ↑ Script error: No such module "citation/CS1".
  27. ↑ Script error: No such module "citation/CS1".
  28. ↑ Script error: No such module "citation/CS1".

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Bibliography

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External links

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NASA

Non-NASA

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