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.
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.
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.
June 27, 1952High-speed and high-altitude testing.
First aircraft to exceed Mach 3.
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.
December 15, 1948
Evaluated handling characteristics of tailless aircraft in the transonic speed region.
June 20, 1951First aircraft to fly with variable geometry wings.
Guidance and propulsion technology testbed.
Assisted development of GAM-63 Rascal missile.
USAF, USN, RAF
Joint Strike Fighter prototype.
April 7, 2006 (drop test)
April 22, 2010 (orbital flight). Reusable orbital space plane.
Classified - Unknown Purpose
August 11, 1998
26 May 201
Hypersonic scramjet demonstrator.
Number skipped to avoid confusion with B-52.
"The X-15: Extending the Frontiers of Flight" by Dennis Jenkins 2009