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X-Planes Explained

The Bell X-1 in flightOn a January day over 50 years ago, an unusual orange plane prepared for its first flight.  Carried aloft underneath a giant Boeing B-29 Superfortress bomber, the plane would be released to fly freely once the target altitude was reached.  With its then-cutting-edge aerodynamics, the rocket-powered plane was designed to go fast.  In fact, it was designed to fly faster than any plane had ever flown before, and faster than some people believed was even possible.  That plane was the X-1.   Manufactured by Bell Aircraft Company, the X-1 would go on to make history.  Less than 2 years after its first flight, an X-1 flown by Air Force pilot Captain Chuck Yeager would become the first plane to travel faster than the speed of sound.  But, that orange aircraft has another important legacy—it launched the era of the X-planes.

What is an X-plane?  An X-plane is completely unlike any other aircraft.  Some of the X-planes are not even airplanes at all.  The X-planes are a series of experimental vehicles sponsored by the U.S. government.  They are designed for a variety of purposes and are sponsored by several different government agencies, including NASA.  X-planes include everything from jets to cruise missiles to spacecraft.  The first X-plane, the X-1, first flew on January 25, 1946.  About 30 X-planes flew over the next 30 years, but then the program tapered off.  Between 1973 and 1997, only two new X-planes actually flew (though research was done on a handful of others).  During the late 1990s, the program saw resurgence, and the latest designation to be assigned (as of August 2003) is the X-50, an advanced rotorcraft being built by the Boeing Company.

The X-15The X-plane program predates NASA, but the agency’s predecessor, the National Advisory Committee for Aeronautics (NACA), was a sponsor of many of the early vehicles.  One of the first X-planes NASA was involved with is also one of the most famous—the X-15, which made 199 flights between June 1959 and October 1968.  A joint project involving the U.S. Air Force, Navy, NACA, and NASA, the North American Aviation-built X-15 rocket plane was designed for high-speed, high-altitude flight research.  In fact, the X-15 was the fastest, highest flying manned winged vehicle until the first Space Shuttle flight.  It was capable of flying to an altitude of over 100 kilometers (62.5 miles), which is considered to be the edge of space, earning a handful of its pilots Air Force astronaut wings.  (Among those astronaut pilots was Neil Armstrong, who later went on to become the first man on the Moon.)  The highest altitude reached by the X-15 was 67 miles, and it set a speed record of Mach 6.7 (4,520 miles per hour).  The plane was even used to carry many experiments, and contributed to the Mercury, Gemini, Apollo, and Space Shuttle programs.

Ironically, NASA was not involved in the first X-plane spacecraft, which never made it to the flight stage.  The Air Force’s X-20 Dyna-Soar, built by Boeing, was cancelled while still in the construction phase.  The Dyna-Soar was to be a manned space plane carried into orbit by a rocket booster.  The early development of the X-20 occurred prior to Yuri Gagarin making the first manned spaceflight in 1961, and the program was cancelled in 1963, after the completion of only one nonflying prototype.  Although the program was cancelled, the research conducted during the project had long-term benefits for the space program.

The X-29 in flightAnother NASA X-plane, the X-24, was used to demonstrate that it would be possible for the Space Shuttle to land precisely as an unpowered glider.  Martin Marietta Corporation created two versions of the X-24—the lifting-body design X-24A, and the X-24B, which was created by adding a new shell to the X-24A to make it longer and change its shape.  NASA was also involved in the only new flying X-plane of the 1980s, which was widely recognized because of its distinctive appearance.  The X-29 jet, built by Grumman Aerospace, was unusual because its wings were swept forward instead of aft.  It made 437 flights between December 1984 and September 1991, but demonstrated that the design did not produce the reductions in drag that the engineers had wanted.  Similar to the X-29 project for NASA was the X-36 project, which involved 25 flights of a Boeing-built unmanned tailless jet aircraft.  The agency is also involved in the X-44 program, for which Lockheed Martin is constructing a crewed tailless research aircraft.  The X-36 and X-44 are both part of research to create high-performance, highly maneuverable tailless stealth aircraft. (Although the program has not been cancelled, all funding for the X-44 program was halted in 2000.)

NASA’s next two X-planes never made it to the flight stage, and were designed to test concepts for reusable single-stage-to-orbit spacecraft.  The National Team’s X-30 was part of President Ronald Reagan’s National Aero-Space Plane concept, but never made it to the prototype stage.  Lockheed Martin’s X-33 program was designed to test concepts that would be used to develop a successor to the Space Shuttle.  While problems eventually led to the cancellation of the program, it let to substantial research into advanced spacecraft concepts.  NASA’s X-34 program, contracted to Orbital Sciences Corporation, was conceived as a way to test technologies intended to reduce the cost of space launches.  A prototype was flown in captive-carry flights under a larger plane, but no free flights were conducted.

As part of the International Space Station (ISS) program, NASA worked with scaled composites to create the X-38, which was a technology demonstrator for a planned crew rescue vehicle for the ISS.  The X-38 made it as far as unpowered drop tests, but was cancelled when NASA decided to pursue a new spacecraft, known as the Orbital Space Plane (OSP) that could carry astronauts both to and from ISS.  Currently, the agency is working with Boeing on the X-37 project, which is testing concepts that may be used for OSP.  A related project, the X-40A, involved eight flight tests of an 80-percent scale version of the X-37.An artist's version of the X-43 Hyper-X

Also currently ongoing for NASA is work on the X-43 Hyper-X program.  This program involves testing of a Microcraft, Inc.-built scramjet aircraft, created to use an air-breathing engine to reach speeds of Mach 7 and 10.  A flight test of the Hyper-X is currently scheduled for late 2003.  NASA is also currently working with Boeing on the X-48 blended-wing-body aircraft, which will produce a plane that is essentially one giant wing.  Flight tests are scheduled to begin in 2004.

Taken individually, the X-planes have very little in common with each other.  Even the ones NASA is involved with cover a wide spectrum.  Include the X-planes created by other agencies, and it’s quite an assortment indeed.  As a group, however, there are some shared traits of all the X-planes.  They are all high-tech, and attempt to do what no aircraft has done before.  All of them, even the “failures,” leave aerospace technology a little further along than when they started.  And, all of them are an attempt to bring about the future just a little bit faster.

Information in this article was accurate as of the publication date. For the latest updates about this project, visit the NASA homepage (