American X-Vehicles: An Inventory, X-1 to X-45

For a while, it seemed the series of experimental aircraft sponsored by the Air Force and the National Aeronautics and Space Administration had run its course. Between the late 1940s and the late 1970s, almost thirty designations had been allocated to aircraft meant to explore new flight regimes or untried technologies. Then, largely, it ended. But there was a resurgence in the mid- to late-1990s, and as we enter the year 2000 the designations are up to X-45. Many have a misconception that X-Planes have always explored the high-speed and high-altitude flight regimes, something popularized by Chuck Yeager in the original X-1 and the exploits of the twelve men that flew the X-15. Although these flight regimes have always been in the spotlight, many others have been explored by X-Planes. The little Bensen X-25 never exceeded 85 mph, and others were limited to speeds of several hundred mph. There has been some criticism that the use of X designations has been corrupted somewhat by including what are essentially prototypes of future operational aircraft, especially the two JSF demonstrators. But this is not new-the X-11 and X-12 from the 1950s were going to be prototypes of the Atlas intercontinental ballistic missile, and the still-born Lockheed X-27 was always intended as a prototype of a production aircraft. So although this practice does not represent the best use of X designations it is not without precedent. This document is an inventory of the experimental aircraft starting with the X-1 aircraft and ending with the X-45 aircraft.