History of X-Planes
X-planes are a series of experimental airplanes, helicopters, and rockets used to test and evaluate new technologies and aerodynamic designs. Most of the X-planes have been operated by the National Aeronautics and Space Administration (NASA) and its predecessor National Advisory Committee for Aeronautics (NACA), often in conjunction with the United States Air Force.
X-37b returning in September 2014 after a 2-year, classified mission (unmanned).
After WWII, experimental aircraft experienced a golden era as new designs and technology combined with cold war urgency. The United States was the only country at the time to possess the funds and technical talent for such an aggressive experimental program. The X-1, for instance, was the first piloted aircraft to break the sound barrier.
But X-planes were not the only driving force on the frontier of aeronautical innovation. Six months after the X-1 success, in April 1948, test pilot George Welch flew the swept-wing XP-86 beyond the sound barrier in stable flight. Much the same happened at Mach 2. The test pilot Scott Crossfield was the first to reach this mark, flying the experimental Douglas Skyrocket in November 1953. Simultaneously, Alexander Kartveli of Republic Aviation was well along in crafting the XF-105. In June 1956 an F-105 reached Mach 2.15. It too was an operational fighter, in contrast to the Skyrocket.
Beginning in the 1950s, ramjet-powered craft excelled beyond jet engine limitations. The Navaho cruise missile flew near Mach 3. An even more far-reaching prospect was in view at Republic Aviation, where Alexander Kartveli was working on the XF-103. It was designed to fly at Mach 3.7 with its own ramjet, nearly 2,500 miles per hour (mph), with a sustained ceiling of 75,000 feet. While not an official x-plane, the XF-103 demonstrates the important contributions made by designers working on practical, manned aircraft.
The Bell X-2 proved to be the fastest and highest-flying of the "round one" X-planes and the most tragic, with the two X-2s logging only 20 glide and powered flights between them. Nevertheless, Captain Iven C. Kincheloe, Jr., managed to take one of the airplanes to 126,200 feet on 7 September 1956. Twenty days later, Captain Milburn G. Apt was killed during his first X-2 flight after he reached Mach 3.196 (1,701 mph), becoming the first person to fly at three times the speed of sound, albeit briefly.
The first combat type designed from the start as a supersonic fighter—Kartveli's XF-91 "Thunderceptor"—made its maiden flight only 19 months after Yeager's flight. How much the X-1 experience contributed to Alexander Kartveli's design is unknown. Kartveli continued to design interceptors capable of reaching Mach 3+ speeds as the lead designer at Republic Aircraft.
Here is a list of all the x-planes.
Bell Aircraft
USAF, NACA
January 19, 1946High-speed and high-altitude testing.
First aircraft to break the sound barrier in level flight.
Proved aerodynamic viability of thin wing sections.
Bell Aircraft
USAF
June 27, 1952High-speed and high-altitude testing.
First aircraft to exceed Mach 3.
X-3 Stiletto
USAF, NACA
October 27, 1952
Titanium alloy construction; low aspect ratio wings.
Planned to test long-duration high-speed flight.
Incapable of reaching design speed, but provided insights into inertia coupling.
Northrop
USAF, NACA
December 15, 1948
Evaluated handling characteristics of tailless aircraft in the transonic speed region.
Bell Aircraft
USAF
April 1949
Guidance and propulsion technology testbed.
Assisted development of GAM-63 Rascal missile.
X-11 Convair
USAF
June 11, 1957
Testbed for SM-65 Atlas missile.
Ryan Aeronautical
USAF, USN
December 10, 1955
Vertical takeoff and landing (VTOL) testbed.
Evaluated tailsitting configuration for VTOL flight.
Bell Aircraft
USAF, NASA
February 19, 1957
VTOL testbed.
Examined the vectored thrust configuration for VTOL flight.
North American Aviation
USAF, NASA
June 8, 1959
Hypersonic (Mach 6.7), high-altitude (350,000 feet (110,000 m)) testing.
First manned hypersonic aircraft; capable of suborbital spaceflight.
Bell Aircraft
USAF
Never flew - High-altitude reconnaissance aircraft project.
"X-16" designation used as cover story.
Hiller Aircraft
USAF, USN
November 24, 1959
VTOL/Short take-off and vertical landing (STOVL) testbed.
Evaluated the tiltwing concept for VTOL flight.
Curtiss-Wright
Tri-serviceNovember 1963Tandem tiltrotor VTOL transport testbed.
XC-143 designation proposed.
Martin Marietta
USAF
December 21, 1966
Maneuvering atmospheric reentry effects testbed.
Designation never officially assigned.
Martin Marietta
USAF, NASA
August 1, 1973
Low-speed lifting body handling testbed.
Lifting body aerodynamic shape trials.
X-26
Frigate Schweizer
DARPA, US Army, USN
1967
Training glider for yaw-roll coupling
Quiet observation aircraft testbed.
Lockheed Martin
NASA
Prototype never completed. Half-scale reusable launch vehicle prototype.
Boeing
USAF, NASA
April 7, 2006 (drop test)
April 22, 2010 (orbital flight). Reusable orbital space plane.
Piasecki Aircraft
US Army
July 29, 2007
Compound helicopter
Vectored Thrust Ducted Propeller (VTDP) testbed.
X-52
Number skipped to avoid confusion with B-52.
Lockheed Martin Skunk Works
USAF
June 2, 2009
Advanced Composite Cargo Aircraft (ACCA).
Molded composite fuselage and empennage testbed.
Lockheed Martin Skunk Works
USAF/NASA
2012
Active flutter suppression and gust load alleviation technology for potential use in future high-altitude, long-endurance (HALE) reconnaissance aircraft
SOURCES:
Wikipedia
"The X-15: Extending the Frontiers of Flight" by Dennis Jenkins 2009