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.

History

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. 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]

List

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
	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]
	X-1A X-1B X-1C X-1D	Bell	USAF, NACA	1951	High-speed and high-altitude flight
	X-1E	Bell	USAF, NACA	1955	High-speed and high-altitude flight
	X-2	Bell	USAF	1952	High-speed and high-altitude flight	First aircraft to exceed Mach 3.[12]
	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]
	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	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.
	X-9 Shrike	Bell	USAF	1949	Guidance and propulsion technology	Assisted development of GAM-63 Rascal missile.[20]
	X-10	North American	USAF	1953	SM-64 Navajo missile testbed.[21]
	X-11	Convair	USAF	1957	SM-65 Atlas missile testbed.[22]
	X-12	Convair	USAF	1957	SM-65 Atlas missile testbed.[23]
	X-13 Vertijet	Ryan	USAF, USN	1955	Vertical takeoff and landing (VTOL)	tailsitting VTOL flight.[24]
	X-14	Bell	USAF, NASA	1957	VTOL	Vectored thrust configuration for VTOL flight.[25]
	X-15	North American	USAF, NASA	1959	Hypersonic, high-altitude flight	First crewed hypersonic aircraft; capable of suborbital spaceflight.[26]
	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.
	X-16	Bell	USAF	1954	High-altitude reconnaissance[27]	"X-16" designation used to hide true purpose.[28] Canceled and never flew.
	X-17	Lockheed	USAF, USN	1956	High Mach number reentry.[29]
	X-18	Hiller	USAF, USN	1959	Vertical and/or short take-off and landing (V/STOL)	Evaluated the tiltwing concept for VTOL flight.[30]
	X-19	Curtiss-Wright	Tri-service	1963	Tandem tiltrotor VTOL[31]	XC-143 designation proposed.[32]
	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-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 Frigate	Schweizer	DARPA, US Army, USN	1967	Training glider for yaw-roll coupling Quiet observation aircraft[41]
	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 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	Rockwell	NASA, DARPA, USAF	1993	Single-stage-to-orbit spaceplane[45]	Canceled and never built.
	X-31	Rockwell-MBB	DARPA, USAF, BdV	1990	Thrust vectoring supermaneuverability[46]
	X-32A	Boeing	USAF, USN, USMC, RAF	2000	Joint Strike Fighter[47]
	X-32B			2001
	X-33	Lockheed Martin	NASA	2001	Half-scale reusable launch vehicle prototype.[48]	Prototype never completed.
	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			2001		First in family to use VTOL. Also used unconventional mode of lift engine (lift fan).
	X-35C			2000
	X-36	McDonnell Douglas	NASA	1997	28% scale tailless fighter[51]
	X-37	Boeing	USAF, USSF, NASA	2010	Reusable orbital spaceplane[52]	Drop test performed in 2006. Seven flights to space since 22 April 2010
	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]
	X-40A	Boeing	USAF, NASA	1998	80% scale Space Maneuver Vehicle X-37 prototype.[55]
	X-41	Unknown	USAF		Maneuvering re-entry vehicle.[56]
	X-42	Unknown	USAF		Expendable liquid propellant upper-stage rocket.[57]
	X-43 Hyper-X	Micro-Craft	NASA	2001	Hypersonic Scramjet[58]
	X-44 MANTA	Lockheed Martin	USAF, NASA	2000	F-22-based Multi-Axis No-Tail Aircraft thrust vectoring[59]	Canceled, never flew.
	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 Pegasus	Northrop Grumman	DARPA, USN	2003	Unmanned combat air vehicle (UCAV)[62]	Naval use.
	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]
	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	Boeing	NASA, USAF	2002	Active Aeroelastic Wing[68]
	X-54	Gulfstream	NASA		Low-noise supersonic transport[69] in development.
	X-55	Lockheed Martin	USAF	2009	Advanced Composite Cargo Aircraft (ACCA)[70]
	X-56	Lockheed Martin	USAF/NASA	2013	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	2023	Low emission plane powered entirely by electric motors[72]	Part of NASA's Scalable Convergent Electric Propulsion Technology Operations Research project[72] (SCEPTOR). Cancelled in 2023, never flew.
—	X-58	—	—	—	—	Number skipped; slot apparently assigned to Kratos XQ-58 Valkyrie.[73]
	X-59 Quesst	Lockheed Martin	NASA	2024	Prototype quiet supersonic transport aircraft[74]
	X-60	Generation Orbit Launch Services	USAF		Air-launched rocket for hypersonic flight research[75]
	X-61 Gremlins	Dynetics	DARPA	2020	Air-launched and air-recoverable reconnaissance unmanned air vehicle (UAV)[76][77]
	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]
—	X-63	—	—	—	—	Number skipped
—	X-64	—	—	—	—	Number skipped
	X-65 CRANE	Aurora Flight Sciences	DARPA	2025	Control of Revolutionary Aircraft with Novel Effectors[79]
	X-66	Boeing	NASA	2028	Transonic Truss-Braced Wing[80]

See also

• Experimental aircraft
• List of experimental aircraft
• List of military aircraft of the United States

Notes

References

Bibliography

External links

• Media related to Experimental aircraft of the United States at Wikimedia Commons
• Early X-planes
• X-15 Videos by NASA