Gallery: Boom! NASA Wants to Bring Back Supersonic X-Planes
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The Bell X-1, NASA's first "x-plane," was the first aircraft to break the supposed sound barrier (or Mach 1) on Oct. 14, 1947, piloted by Chuck Yeager.
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In 1956, the Bell X-2 Starbuster broke Mach 3 and flew above 125,000 feet.
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Manufactured by the Douglas Aircraft Company, the X-3 was made to investigate the design features suited to sustained supersonic speeds, including the first use of titanium in major airframe components.
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The X-5 was the first plane with a variable swept wing design, so the planes could change position based on the needs of the moment.
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The X-15 took NASA from supersonic to hypersonic, setting unofficial records for speed (Mach 6.7) and altitude 354,200 feet.
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The X-24B was one of a series of planes designed to investigate how spacecraft could handle reentry into Earth's atmosphere.
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One of the crazier-looking x-planes, the X-29 featured a swept wing design, but with the wings swept forward instead of backward.
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The X-31 program tested the idea of using thrust vectoring—directing engine exhaust as a form of steering.
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The Lockheed Martin-built X-56A Multi-Utility Technology Testbed (MUTT) is an unmanned aircraft designed to how long, flexible airfoils can better handle wind gusts and turbulence.
