Credit: NASA Photo / USAF photo by Lt. Robert A. Hoover
The Bell Aircraft Corporation X-1-1 in flight with the shock wave pattern in the exhaust plume visible. The X-1 series aircraft were air-launched from a modified Boeing B-29 or a B-50 Superfortress bombers. Lasting from 1946 to 1958, the project’s goal was breaking the sound barrier, which was achieved on Oct. 14, 1947.
2 of 26
Maj. Arthur 'Kit' Murray with X-1A
Credit: NACA/NASA
The Bell X-1A was similar to the Bell X-1, except for having turbo-driven fuel pumps , a new cockpit canopy, longer fuselage and increased fuel capacity. Testing began on Jan. 7, 1953 but after a few short flights the aircraft suffered an explosion. This image shows U.S. Air Force test pilot Maj. Arthur "Kit" Murray in front of the plane.
3 of 26
X-1B
Credit: NACA/NASA
The Bell X-1B was a second-generation X-1 used by the U.S. Air Force for pilot familiarization before being turned over to NACA in December 1954. This aircraft completed a total of 27 glide and powered flights. This image was taken April 9, 1958.
4 of 26
X-1E
Credit: NASA/Les Teal
The X-1E, the last of the X-1 aircraft series, made 26 flights to obtain in-flight data at twice the speed of sound, with particular emphasis placed on investigating the improvements achieved with the high-speed wing. This image was taken in February 1996.
5 of 26
Douglas X-3
Credit: NACA/NASA
The Douglas X-3, known as the Stiletto, was built to investigate the design of an aircraft suitable for sustained supersonic speeds. It first flew in October 1952 and has 20 flights between 1954 and 1956. This image was taken in 1956.
6 of 26
X-4
Credit: NACA/NASA
The X-4 was designed to obtain in-flight data on the stability and control of semi-tailless aircraft at high subsonic speeds. The X-4 flew 82 research flights from 1950 to 1953 before being retired from service. This image was taken in 1950.
7 of 26
X-5
Credit: NACA/NASA
The X-5 was flight tested at the NACA High-Speed Flight Research Station from 1952 to 1955 to test variable sweep wings. The aircraft completed 133 test flights during three years of service. This image was taken in 1957.
8 of 26
X-15
Credit: NASA
The X-15 research aircraft was developed to provide in-flight information and data on aerodynamics, structures, flight controls, and the physiological aspects of high-speed, high-altitude flight. Flown over a period of nearly 10 years, June 1959 to Oct. 1968, the vehicles completed a total of 199 flights.
9 of 26
X-2
Credit: NASA/USAF
The X-2 was a swept-wing, rocket-powered aircraft designed to fly faster than Mach 3 (three times the speed of sound). Two aircraft completed a total of 20 flights from June 1952 to September 1956. This image was taken in 1956.
10 of 26
X-24
Credit: NASA
The X-24 was one of a group of lifting bodies flown from 1963 to 1975. The X-24 was flown 28 times in the program that validated the concept that a Space Shuttle vehicle could be landed unpowered. This image was taken Sep. 5, 1975.
11 of 26
X-29
Credit: NASA
Two X-29 aircraft, featuring one of the most unusual designs in aviation history, flew from 1984 to 1992 to test several new technologies. During its flight history, the X-29 aircraft flew 422 research missions and a total of 436 missions. This image was taken in November 1990.
The X-31 Enhanced Fighter Maneuverability Demonstrator was used to test the newest technology in highly maneuverable fighters. The X-31 program logged an X-plane record of 580 flights during the program, 559 research missions and 21 in Europe for the 1995 Paris Air Show. This image was taken in March 1998.
13 of 26
X-33 Advanced Technology Demonstrator
Credit: NASA
However, due to technical problems with the composite liquid hydrogen tank, the X-33 program was cancelled in February 2001.
14 of 26
X-34 Technology Testbed Demonstrator
Credit: NASA/Tom Tschida
The unpiloted X-34 is a technology testbed demonstrator that is designed to demonstrate key vehicle and operational technologies applicable to future low-cost reusable launch vehicles. This image was taken July 20, 2000.
15 of 26
X-36 Tailless Fighter Agility Research Aircraft
Credit: NASA/Carla Thomas
The X-36 was built as a prototype remotely-piloted fighter jet without traditional tail surfaces. It first flew in 1997 and had 31 research flights since then. This image was taken on Oct. 30, 1997.
16 of 26
X-37 Advanced Technology Demonstrator
Credit: NASA
This artist's conception shows the X-37 Advanced Technology Demonstrator in the Shuttle Payload Bay. The aircraft is designed to test technologies for NASA's space plane program.
17 of 26
X-38 Crew Return Vehicle
Credit: NASA/Carla Thomas
The X-38 Crew Return Vehicle (CRV) research project is designed to test a prototype emergency crew return vehicle for the International Space Station. Flight research with the X-38 at Dryden began in 1997 and the aircraft has since completed eight flights. The program was terminated in 2002. This image of a drop test was taken Dec. 13, 2001.
18 of 26
X-40A Space Manuever Vehicle
Credit: NASA/ Tony Landis
The unpowered X-40A, a space maneuver vehicle, proved the capability of an autonomous flight control and landing system in a series of glide flights at NASA's Dryden Flight Research Center in California. The image was taken May 5, 2001.
19 of 26
X-43A Hypersonic Experimental Vehicle
Credit: NASA/Tom Tschida
The X-43A Hypersonic Experimental (Hyper-X) Vehicle hangs suspended in the cavernous Benefield Aenechoic Facility at Edwards Air Force Base in January 2000. The X-43A was developed to flight test a dual-mode ramjet/scramjet propulsion system at speeds from Mach 7 up to Mach 10.
20 of 26
X-45 Unmanned Combat Air Vehicle
Credit: NASA / Jim Ross
The Boeing X-45A is being tested by the Joint Unmanned Combat Air Systems (J-UCAS) program as a weaponized unmanned vehicle. This image was taken on April 18, 2004 during a GPS-guided weapon demonstration flight.
21 of 26
X-48B in Flight
Credit: NASA/ Tony Landis
A joint NASA/Boeing team tested the X-48B Blended Wing Body aircraft at NASA's Dryden Flight Research Center. The team completed the 80th and last flight of the project's first phase on March 19, 2010.
22 of 26
Rotor Systems Research Aircraft/X-Wing
Credit: NASA
The Rotor Systems Research Aircraft/X-Wing, a vehicle that was used to demonstrate an advanced rotor/fixed wing concept called X-Wing, is shown here on Nov. 4, 1986. The vehicle was rolled out in 1986 and made several taxi tests before the program was terminated in 1988.
23 of 26
XB-70 Valkyrie
Credit: NASA
The XB-70A, capable of flying three times the speed of sound, was the world's largest experimental aircraft in the 1960s. The plane was built to test stability and handling of large delta-wing aircraft at high speeds.
24 of 26
Republic XF-91 Thunderceptor
Credit: NASA
The Republic XF-91 Thunderceptor, created as a Prototype fighter, sits at the South Base ramp at Edwards Air Force Base. The image was taken in March 1951.
25 of 26
XF-92A
Credit: NACA/NASA
This photograph of the XF-92A was taken at Edwards Air Force Base in January 1953. The plane was designed as the prototype of a delta-wing fighter. A brief series of 25 flights were made in 1953 which showed the aircraft had violent pitch-up tendencies during turns.
26 of 26
XV-15 Tilt Rotor
Credit: NASA
This photo shows the unique XV-15 Tiltrotor aircraft in vertical flight at the NASA Dryden Flight Research Center. The aircraft was involved in limited research in 1980 and 1981 in order to improve design and efficiency of rotorcraft using tilt rotors. The image was taken on Oct. 3, 1980.
