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February 26, 2013

DARPA VTOL X-Plane is pushing for a novel mix of fixed and rotary design to get to efficiently double the speed of helicopters

One of the greatest challenges of the past half century for aerodynamics engineers has been how to increase the top speeds of aircraft that take off and land vertically without compromising the aircraft's lift to power in hover or its efficiency during long-range flight.

The versatility of helicopters and other vertical take-off and landing (VTOL) aircraft make them ideal for a host of military operations. Currently, only helicopters can maneuver in tight areas, land in unprepared areas, move in all directions, and hover in midair while holding a position. This versatility often makes rotary-wing and other VTOL aircraft the right aerial platform for transporting troops, surveillance operations, special operations and search-and-rescue missions.

"For the past 50 years, we have seen jets go higher and faster while VTOL aircraft speeds have flat-lined and designs have become increasingly complex," said Ashish Bagai, DARPA program manager. "To overcome this problem, DARPA has launched the VTOL X-Plane program to challenge industry and innovative engineers to concurrently push the envelope in four areas: speed, hover efficiency, cruise efficiency and useful load capacity."

"We have not made this easy," he continued. "Strapping rockets onto the back of a helicopter is not the type of approach we're looking for. The engineering community is familiar with the numerous attempts in the past that have not worked. This time, rather than tweaking past designs, we are looking for true cross-pollinations of designs and technologies from the fixed-wing and rotary-wing worlds. The elegant confluence of these engineering design paradigms is where this program should find some interesting results."





Helos and other VTOL aircraft typically max out at 170 knots. Bagai wants the X-Plane to do 300 knots (345 mph). “We want to fly at improved efficiencies, both in hover and at forward flight,” he said, “and we want to demonstrate this is possible without sacrificing the ability to do useful work. And to do this concurrently is a very big challenge.”

The VTOL Xplane project is targeting a flight test in 42 months. Ten months later, when the program ends, “we want to have demonstrated all our key objectives and have a flying aircraft available,” he said. If it fails, helicopters, jump jets and tilt-rotors won’t be any worse off. If it succeeds, the VTOL X-Plane pretty much represents their next generation.

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