The American X-planes were part of the romance of the heyday of post-war aviation with test pilots like Chuck Yeager breaking the sound barrier in the X-1 and a rival corps of astronauts flew into space in the X-15. As part of a 10-year plan proposed by the Obama administration, NASA Aeronautics' New Aviation Horizons program wants to revive the X-planes for the 21st century as demonstrators for emerging, greener flight technologies.

Part of President Obama's federal budget request for the next fiscal year, New Aviation Horizons is aimed at creating new technologies that will make aircraft more environmentally friendly, more fuel efficient and lower airline operating costs. The key to this is a new tranche of "X-plane" experimental technology demonstrator airplanes, similar to the ones that made so many American aviation breakthroughs from the 1940s onward.

If funding is approved, the first flights of these X-planes could take off sometime around 2020. The aircraft would be manned and typically scaled to about half the size of production aircraft. According to NASA, the purpose of the planes will be to test such things as lightweight composites, quieter, more advanced engines, quieter landing gear and flap mechanisms, shape-changing wing flaps, and bug-resistant coatings. The agency says that these have the potential to save the air industry US$225 billion dollars over a 25-year period.

This version of a hybrid wing body aircraft concept has turbofan engines on top of the back end, flanked by two vertical tails to shield people on the ground from engine noise(Credit: NASA / Boeing)

Beyond individual technologies, the X-planes will include novel designs, such as a truss-braced wing for subsonic flight, an aircraft propelled by a battery of small electric motors, and an aircraft featuring a blended-wing design with top-mounted engines that can fly at the same speed as a commercial transport. Other design features under study include a double-wide fuselage, very long and narrow wings, and engines installed inside the aircraft instead of mounted on pylons.

NASA says that the X-planes will also include a civilian supersonic aircraft. This business-sized jet would not only fly faster than the speed of sound, but would do so using bio-fuels and have a wing and fuselage design that would reduce sonic booms to an unnoticeable level on the ground.

This truss-braced wing concept could be another subsonic X-plane design(Credit: NASA Langley/Sandie Gibbs)

In addition, the new NASA plan would include a new effort to improve air traffic flow both in the air and on the ground as a way to not only save fuel, but also to decrease the noise associated with takeoff and landings.

"We're at the right place, at the right time, with the right technologies," says Jaiwon Shin, associate administrator for NASA's Aeronautics Research Mission Directorate. "The full potential of these technologies can't be realized in the tube-and-wing shape of today's aircraft. We need the X-planes to prove, in an undeniable way, how that tech can make aviation more Earth friendly, reduce delays and maintain safety for the flying public, and support an industry that's critical to our nation's economic vitality."

The federal budget request is for the fiscal year starting on October 1, 2016, with NASA's 10-year plan to kick off next year if the request is approved.

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