Bell X-1-2
Bell X-1-2

The X-planes are a series of experimental United States aircraft and rockets, used to test and evaluate new technologies and aerodynamic concepts. They have an X designator within the US system of aircraft designations, which denotes the experimental research mission.

Not all US experimental aircraft have been designated as X-planes; some received US Navy designations before 1962,[1] while others have been known only by manufacturers' designations,[N 1] non-'X'-series designations,[N 2] or classified codenames.[N 3] This list only includes the designated X-planes.


The X-planes concept officially came into being in 1944, as a joint programme between the National Advisory Committee for Aeronautics (NACA), the US Navy (USN) and the US Army Air Force (USAAF), in order to pursue research into high-speed aircraft.[2] NACA later became the National Aeronautics and Space Administration (NASA) and the USAAF became the United States Air Force (USAF). Other organizations such as the Defence Advanced Research Projects Agency (DARPA) and the US Marine Corps (USMC) have also since sponsored X-plane projects.

The first experimental aircraft specification, for a transonic rocket plane, was placed in 1945, and the first operational flight of an X-plane took place when the Bell X-1 made its first powered flight nearly three years later at Muroc Air Force Base, California, now known as Edwards Air Force Base.[3] The majority of X-plane testing has since taken place there.[4]

X-planes have since accomplished many aviation "firsts" including breaking speed and altitude barriers, varying wing sweep in flight, implementing exotic alloys and propulsion innovations, and many more.[5]

New X-planes appeared fairly regularly for many years until the flow temporarily stopped in the early 1970s. A series of experimental hypersonic projects, including an advanced version of the Martin Marietta X-24 lifting body, were turned down. Eventually issues with the Rockwell HiMAT advanced UAV led to a crewed X-plane with forward sweep, the Grumman X-29, which flew in 1984.[6]

Some of the X-planes have been well publicized, while others, such as the X-16, have been developed in secrecy.[7] The first, the Bell X-1, became well known in 1947 after it became the first aircraft to break the sound barrier in level flight.[8] Later X-planes supported important research in a multitude of aerodynamic and technical fields, but only the North American X-15 rocket plane of the early 1960s achieved comparable fame to that of the X-1.[citation needed] X-planes 8, 9, 11, 12, and 17 were actually missiles[9] used to test new types of engines, and some other vehicles were unoccupied or UAVs (some were remotely flown, some were partially or fully autonomous).

Most X-planes are not expected to go into full-scale production; one exception was the Lockheed Martin X-35, which competed against the Boeing X-32 during the Joint Strike Fighter Program, and has entered production as the F-35 Lightning II.[10]


In the list, the date is that of the first flight, or of cancellation if it never flew.

List of X-planes
Image Type Manufacturer Agency Date Role Notes
Bell X-1 46-062 (in flight).jpg
X-1 Bell USAF, NACA 1946 High-speed and high-altitude flight First aircraft to break the sound barrier in level flight. Proved aerodynamic viability of thin wing sections.[11]
Bell X-1A.jpg
X-1A X-1B X-1C X-1D Bell USAF, NACA 1951 High-speed and high-altitude flight
Joe Walker X-1E.jpg
X-1E Bell USAF, NACA 1955 High-speed and high-altitude flight
X-2 After Drop from B-50 Mothership - GPN-2000-000396.jpg
X-2 Bell USAF 1952 High-speed and high-altitude flight First aircraft to exceed Mach 3.[12]
Douglas X-3 NASA E-17348.jpg
X-3 Stiletto Douglas USAF, NACA 1952 Highly loaded trapezoidal wing Titanium alloy construction; Underpowered, but provided insights into inertia coupling.[13]
X-4 Bantam Northrop USAF, NACA 1948 Transonic tailless aircraft[14]
X-5 Bell USAF, NACA 1951 variable geometry First aircraft to fly with variable wing sweep.[15]
NB-36H producing contrails in flight.jpg
X-6 Convair USAF, AEC 1957 Nuclear Propulsion Not built. The Convair NB-36H experiment, a B-36 modified to carry (but not powered by) a nuclear reactor, flew from 1955 to 1957.[16][17]
X-7 USAF.jpg
X-7 Lockheed USAF, USA, USN 1951 Ramjet engines.[18]
X-8 Aerobee Aerojet NACA, USAF, USN 1949 Upper air research[19] Later models used as sounding rockets.
Bell X-9 trailer.jpg
X-9 Shrike Bell USAF 1949 Guidance and propulsion technology Assisted development of GAM-63 Rascal missile.[20]
North American X-10 runway.jpg
X-10 North American USAF 1953 SM-64 Navajo missile testbed.[21]
Convair XSM-65A launch.jpg
X-11 Convair USAF 1957 SM-65 Atlas missile testbed.[22]
Convair XSM-65B launch.jpg
X-12 Convair USAF 1957 SM-65 Atlas missile testbed.[23]
Ryan X-13.jpg
X-13 Vertijet Ryan USAF, USN 1955 Vertical takeoff and landing (VTOL) tailsitting VTOL flight.[24]
Bell X-14 colour ground.jpg
X-14 Bell USAF, NASA 1957 VTOL Vectored thrust configuration for VTOL flight.[25]
X-15 in flight.jpg
X-15 North American USAF, NASA 1959 Hypersonic, high-altitude flight First crewed hypersonic aircraft; capable of suborbital spaceflight.[26]
X-15A2 NB-52B 3.jpg
X-15A-2 North American USAF, NASA 1964 Hypersonic, high-altitude flight Major Pete Knight flew the X-15A-2 to a Mach 6.70, making it the fastest piloted flight of the X-plane program.
Bell X-16.jpg
X-16 Bell USAF 1954 High-altitude reconnaissance[27] "X-16" designation used to hide true purpose.[28] Canceled and never flew.
Lockheed X-17 horizontal.jpg
X-17 Lockheed USAF, USN 1956 High Mach number reentry.[29]
Hiller X-18 testplatformLarge.jpg
X-18 Hiller USAF, USN 1959 Vertical and/or short take-off and landing (V/STOL) Evaluated the tiltwing concept for VTOL flight.[30]
Curtiss-Wright X-19 flying.jpg
X-19 Curtiss-Wright Tri-service 1963 Tandem tiltrotor VTOL[31] XC-143 designation proposed.[32]
NASA Color Dyna Soar.jpg
X-20 Dyna-Soar Boeing USAF 1963 Reusable spaceplane Intended for military missions.[33] Canceled and never built.
X-21A Northrop USAF 1963 Boundary layer control[34]
X-22a onground bw.jpg
X-22 Bell Tri-service 1966 Quad ducted fan tiltrotor STOVL[35]
X-23 PRIME Martin Marietta USAF 1966 Maneuvering atmospheric reentry[36] Designation never officially assigned.[37]
X-24A Martin Marietta USAF, NASA 1969 Low-speed lifting body[38]
X-24B Martin Marietta USAF, NASA 1973 Low-speed lifting body[39]
X-25 Bensen USAF 1955 Commercial light autogyro for downed pilots.[40]
X-26 sailplane.jpg
QT-2PCs in STAAF, RVN Hangar c1968.jpg
X-26 Frigate Schweizer DARPA, US Army, USN 1967 Training glider for yaw-roll coupling Quiet observation aircraft[41]
X-27 mockup.jpg
X-27 Lockheed None 1971 high-performance research aircraft. High-performance fighter[42] Proposed development of Lockheed CL-1200 Lancer Canceled and never flew.
X-28 on ground.jpg
X-28 Sea Skimmer Osprey USN 1970 Low-cost aerial policing seaplane[43]
X-29 Grumman DARPA, USAF, NASA 1984 Forward-swept wing[44]
X-30 NASP 2.jpg
X-30 NASP Rockwell NASA, DARPA, USAF 1993 Single-stage-to-orbit spaceplane[45] Canceled and never built.
Rockwell-MBB X-31 landing.JPG
X-31 Rockwell-MBB DARPA, USAF, BdV 1990 Thrust vectoring supermaneuverability[46]
X-32A Boeing USAF, USN, USMC, RAF 2000 Joint Strike Fighter[47]
USAF X32B 250.jpg
X-32B Boeing USAF, USN, RAF 2001 Joint Strike Fighter[47]
X-33 Venture Star in Orbit.jpg
X-33 Lockheed Martin NASA 2001 Half-scale reusable launch vehicle prototype.[48] Prototype never completed.
Orbital Sciences X34.jpg
X-34 Orbital Sciences NASA 2001 Reusable pilotless spaceplane.[49] Never flew.
X-35A Lockheed Martin USAF, USN, USMC, RAF 2000 Joint Strike Fighter[50]
X-35B Steven F. Udvar-Hazy Center.tif
X-35B Lockheed Martin USAF, USN, USMC, RAF 2001 Joint Strike Fighter[50] First in family to use VTOL. Also used unconventional mode of lift engine (lift fan).
Lockheed F-35 Joint Strike Fighter.jpg
X-35C Lockheed Martin USAF, USN, USMC, RAF 2000 Joint Strike Fighter[50]
X-36 McDonnell Douglas NASA 1997 28% scale tailless fighter[51]
Boeing X-37B inside payload fairing before launch.jpg
X-37 Boeing USAF, USSF, NASA 2010 Reusable orbital spaceplane[52] Drop test performed in 2006. Six flights since 22 April 2010. (Five launches on Atlas V; one on Falcon 9.)
ISS Crew Return Vehicle.jpg
X-38 Scaled Composites NASA 1998 Lifting body Crew Return Vehicle[53]
X-39 Unknown USAF Future Aircraft Technology Enhancements (FATE) program.[54] Designation never officially assigned.[37]
Boeing X40A.jpg
X-40A Boeing USAF, NASA 1998 80% scale Space Maneuver Vehicle X-37 prototype.[55]
Early CAV concept 1997-98 NSSRM.jpg
X-41 Unknown USAF Maneuvering re-entry vehicle.[56]
X-42 Unknown USAF Expendable liquid propellant upper-stage rocket.[57]
X-43 NASA.jpg
X-43 Hyper-X Micro-Craft NASA 2001 Hypersonic Scramjet[58]
X-44 Manta artistic impression.JPG
X-44 MANTA Lockheed Martin USAF, NASA 2000 F-22-based Multi-Axis No-Tail Aircraft thrust vectoring[59] Canceled, never flew.
Boeing X-45A UCAV.jpg
X-45 Boeing DARPA, USAF 2002 Unmanned combat air vehicle (UCAV)[60]
X-46 Boeing DARPA, USN 2003 Unmanned combat air vehicle (UCAV).[61] Naval use. Canceled, never flew.
X-47A rollout.jpg
X-47A Pegasus Northrop Grumman DARPA, USN 2003 Unmanned combat air vehicle (UCAV)[62] Naval use.
X-47B operating in the Atlantic Test Range (modified).jpg
X-47B Northrop Grumman DARPA, USN 2011 UCAV Naval use.
X-47C Northrop Grumman DARPA, USN UCAV Naval use. Design only.
X-48 Boeing NASA 2007 Blended Wing Body (BWB)[63]
Piasecki X-49A.jpg
X-49 SpeedHawk Piasecki US Army 2007 Compound helicopter Vectored Thrust Ducted Propeller (VTDP) testbed.[64]
X-50 Dragonfly Boeing DARPA 2003 Canard Rotor/Wing[65]
X-51 Waverider Boeing USAF 2010[66] Hypersonic scramjet[67]
X-52 Number skipped to avoid confusion with Boeing B-52 Stratofortress.[37]
X-53 Active Aeroelastic Wing NASA test aircraft EC03-0039-1.jpg
X-53 Boeing NASA, USAF 2002 Active Aeroelastic Wing[68]
X-54 Gulfstream NASA Low-noise supersonic transport[69] in development.
Lockheed Martin X-55 ACCA 001.jpg
X-55 Lockheed Martin USAF 2009 Advanced Composite Cargo Aircraft (ACCA)[70]
Lockheed Martin X-56A.jpg
X-56 Lockheed Martin USAF/NASA 2012 Active flutter suppression and gust load alleviation Part of the high-altitude, long-endurance (HALE) reconnaissance aircraft program.[71]
X-57 Maxwell ESAero/Tecnam NASA 2016 Low emission plane powered entirely by electric motors[72] Part of NASA's Scalable Convergent Electric Propulsion Technology Operations Research project[72] (SCEPTOR)
X-58 Number skipped; slot apparently assigned to Kratos XQ-58 Valkyrie.[73]
Low-Boom Flight Demonstrator.jpg
X-59 QueSST Lockheed Martin NASA 2018 Prototype quiet supersonic transport aircraft[74]
X-60 Generation Orbit Launch Services USAF 2018 Air-launched rocket for hypersonic flight research[75]
X-61 Gremlins Dynetics USAF 2019 Air-launched and air-recoverable reconnaissance unmanned air vehicle (UAV)[76][77]
X-62 VISTA.jpg
X-62 VISTA Lockheed Martin/Calspan USAF 2021 Variable In-flight Simulator Test Aircraft. First flew in 1993 as the NF-16D (for the MATV program). Designated the X-62A during a major research system upgrade in 2021. Assigned to the USAF Test Pilot School.[78]

See also


  1. ^ For example, the Piasecki PA-97
  2. ^ For example, the NASA AD-1 and Bell XV-15
  3. ^ For example, the Northrop Tacit Blue


  1. ^ "D-558-I" NASA Dryden Fact Sheets. NASA. Accessed May 8, 2010.
  2. ^ Miller 1983, p.9.
  3. ^ Miller 1983, pp.15-17.
  4. ^ "X-Planes Experimental Aircraft". Federation of American Scientists. Retrieved 2012-06-01.
  5. ^ Miller 1983, p.9.
  6. ^ Miller 1983, p.13.
  7. ^ Miller 2001, p. 209
  8. ^ First Generation X-1 (fact sheet), Dryden: NASA, retrieved May 8, 2010.
  9. ^ Jenkins, Landis & Miller 2003, p. 14,15,17,18,24.
  10. ^ A history of the Joint Strike Fighter Program, UK: Martin-Baker, January 2010, archived from the original on 2010-12-30.
  11. ^ Jenkins, Landis & Miller 2003, p. 5–7.
  12. ^ Jenkins, Landis & Miller 2003, p. 8.
  13. ^ Jenkins, Landis & Miller 2003, p. 9.
  14. ^ Jenkins, Landis & Miller 2003, p. 10.
  15. ^ Jenkins, Landis & Miller 2003, p. 11.
  16. ^ Jenkins, Landis & Miller 2003, p. 12.
  17. ^ Miller 1983.
  18. ^ Jenkins, Landis & Miller 2003, p. 13.
  19. ^ Jenkins, Landis & Miller 2003, p. 14.
  20. ^ Jenkins, Landis & Miller 2003, p. 15.
  21. ^ Jenkins, Landis & Miller 2003, p. 16.
  22. ^ Jenkins, Landis & Miller 2003, p. 17.
  23. ^ Jenkins, Landis & Miller 2003, p. 18.
  24. ^ Jenkins, Landis & Miller 2003, p. 19.
  25. ^ Jenkins, Landis & Miller 2003, p. 20.
  26. ^ Jenkins, Landis & Miller 2003, p. 21–22.
  27. ^ Jenkins, Landis & Miller 2003, p. 23.
  28. ^ "X-16". Global security, accessed 11 May 2010.
  29. ^ Jenkins, Landis & Miller 2003, p. 24.
  30. ^ Jenkins, Landis & Miller 2003, p. 25.
  31. ^ Jenkins, Landis & Miller 2003, p. 26.
  32. ^ Baugher 2007
  33. ^ Jenkins, Landis & Miller 2003, p. 27.
  34. ^ Jenkins, Landis & Miller 2003, p. 28.
  35. ^ Jenkins, Landis & Miller 2003, p. 29.
  36. ^ Jenkins, Landis & Miller 2003, p. 30.
  37. ^ a b c Parsch 2009, "Missing Designations"
  38. ^ Jenkins, Landis & Miller 2003, p. 31.
  39. ^ Jenkins, Landis & Miller 2003, p. 32.
  40. ^ Jenkins, Landis & Miller 2003, p. 33.
  41. ^ Jenkins, Landis & Miller 2003, p. 34.
  42. ^ Jenkins, Landis & Miller 2003, p. 35.
  43. ^ Jenkins, Landis & Miller 2003, p. 36.
  44. ^ Jenkins, Landis & Miller 2003, p. 37.
  45. ^ Jenkins, Landis & Miller 2003, p. 38.
  46. ^ Jenkins, Landis & Miller 2003, p. 39.
  47. ^ a b Jenkins, Landis & Miller 2003, p. 40–41.
  48. ^ Jenkins, Landis & Miller 2003, p. 42.
  49. ^ Jenkins, Landis & Miller 2003, p. 43.
  50. ^ a b c Jenkins, Landis & Miller 2003, p. 44–45.
  51. ^ Jenkins, Landis & Miller 2003, p. 46.
  52. ^ Jenkins, Landis & Miller 2003, p. 47.
  53. ^ Jenkins, Landis & Miller 2003, p. 48.
  54. ^ Jenkins, Landis & Miller 2003, p. 49.
  55. ^ Jenkins, Landis & Miller 2003, p. 50.
  56. ^ Jenkins, Landis & Miller 2003, p. 51.
  57. ^ Jenkins, Landis & Miller 2003, p. 52.
  58. ^ Jenkins, Landis & Miller 2003, p. 53.
  59. ^ Jenkins, Landis & Miller 2003, p. 54.
  60. ^ Jenkins, Landis & Miller 2003, p. 55.
  61. ^ Jenkins, Landis & Miller 2003, p. 56.
  62. ^ Jenkins, Landis & Miller 2003, p. 57.
  63. ^ Jenkins, Landis & Miller 2003, p. 58.
  64. ^ Parsch 2009, "DOD 4120.15-L"
  65. ^ Jenkins, Landis & Miller 2003, p. 60.
  66. ^ "X-51 Waverider makes historic hypersonic flight". US Air Force Public Affairs. 26 May 2010. Retrieved 27 May 2010.
  67. ^ "X-51 Scramjet Engine Demonstrator - WaveRider" Accessed 2010-05-11.
  68. ^ Jordan 2006
  69. ^ 412015-L
  70. ^ Kaufman 2009
  71. ^ Norris 2012
  72. ^ a b Harrington, J.D.; Kamlet, Matt; Barnstorff, Kathy (17 June 2016). "NASA Hybrid Electric Research Plane Gets X Number, New Name". NASA. Retrieved 17 June 2016.
  73. ^ The Air Force Valkyrie Drone, a Sidekick for Human-Piloted Planes, Will Fly This Year
  74. ^ Jim, Banke (27 June 2018). "NASA's Experimental Supersonic Aircraft Now Known as X-59 QueSST". NASA. Retrieved 28 June 2018.
  75. ^ "U.S. Air Force Designates GO1 Hypersonic Flight Research Vehicle as X-60A". 4 October 2018. Retrieved 4 October 2018.
  76. ^ "Earthquake damage delays Gremlins trial". Flight International. 24 September 2019. Retrieved 28 October 2019.
  77. ^ "Dynetics X-61A Gremlins makes first flight, but destroyed after parachute fails". Flight International. 17 January 2020. Retrieved 13 February 2020.
  78. ^ Giancarlo Casem (30 Jul 2021) NF-16D VISTA becomes X-62A, paves way for Skyborg autonomous flight tests