With VTOL X-Planes, DARPA aims for a futuristic lift

The Pentagon's purveyor of far-out ideas wants a new breed of aircraft that's good at both hovering and high-speed cruising.

Jon Skillings Editorial director
Jon Skillings is an editorial director at CNET, where he's worked since 2000. A born browser of dictionaries, he honed his language skills as a US Army linguist (Polish and German) before diving into editing for tech publications -- including at PC Week and the IDG News Service -- back when the web was just getting under way, and even a little before. For CNET, he's written on topics from GPS, AI and 5G to James Bond, aircraft, astronauts, brass instruments and music streaming services.
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Jon Skillings
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Sikorsky concept for DARPA VTOL X-Plane program
Sikorsky is pitching this concept for the VTOL X-Plane program at DARPA. Sikorsky Aircraft

The helicopters of the future may not look much like helicopters at all, at least in one scheme that DARPA is cooking up.

That's because DARPA, the arm of the Pentagon known for its fanciful and even sci-fi approach to military technology, wants "radical improvements" in aircraft that are capable, as helicopters are and fixed-wing planes are not, of vertical takeoff and landing, or VTOL.

The brainstorming agency has now moved a bit closer to realizing its vertical-lift ambitions. Through its VTOL X-Plane program, DARPA has awarded contracts to four companies -- heavyweights Boeing and Sikorsky, and lesser-known Karem Aircraft and Aurora Flight Sciences -- to flesh out their designs for futuristic flying machines. All four designs are for unmanned aircraft, though DARPA doesn't see any reason at this point that the technologies involved couldn't someday be applied to manned aircraft as well.

This program is separate from the Army-led Future Vertical Lift program, which has a somewhat more pragmatic goal and which also counts Sikorsky (teamed with Boeing) and Karem among its participants.

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DARPA is asking for rather a lot of its X-Plane hopefuls. Down the road, when a one-off "technology demonstrator" VTOL aircraft gets built, it will need to be able to hit all four of these points:

  • Fly fast, achieving a top sustained flight speed of between 300 and 400 knots, or significantly faster than what today's helicopters can achieve.
  • Hover well, boosting aircraft hover efficiency from 60 percent to at least 75 percent.
  • Fly efficiently, delivering a cruise lift-to-drag ratio of at least 10, up from between 5 and 6.
  • Be strong, carrying a "useful load" of at least 40 percent of the vehicle's projected gross weight of 10,000 to 12,000 pounds.

Historically, DARPA said, VTOL designs have been "unable to increase top speed without sacrificing range, efficiency or the ability to do useful work." The X-Plane program, then, is looking to stimulate "innovative cross-pollination" between the worlds of fixed-wing aircraft and rotary-wing machines -- that is, helicopters.

"The proposals we've chosen aim to create new technologies and incorporate existing ones that VTOL designs so far have not succeeded in developing," Ashish Bagai, VTOL X-Plane program manager, said in a statement Tuesday.

Karem Aircraft concept for DARPA VTOL X-Plane program
This is how Karem Aircraft envisions its VTOL X-Plane. Karem Aircraft

Where Karem's concept aircraft has the gangly wings and fuselage of a glider, albeit with a pair of engine nacelles and oversize propellers, Boeing's gives the impression of a shark that swallowed the Batmobile. Sikorsky's design concept looks most like a conventional aircraft at first glance, though on closer examination it seems like it might want to land by sitting upright on its tail, with its nose to the sky.

Aurora, meanwhile, has given a name to its X-Plane, calling it LightningStrike, but did not supply an image and, in response to a query from CNET, said that at this time it is not discussing the program publicly.

Boeing has actually already built a working small-scale version of its entry, the Phantom Swift. That design incorporates a pair of lift fans in the fuselage, which would be covered when the aircraft is in airplane-like cruise mode, while the wingtips sport smaller ducted fans that would, among other things, deliver forward thrust.

But getting to DARPA's goals won't be easy.

"Designing an aircraft to perform a vertical takeoff, while maintaining adequate low-speed control, is challenging. Sustaining efficient hover is also difficult, and adding a high cruising speed is even more challenging," Dan Newman of Boeing's Phantom Works said in a statement Wednesday.

It's all still in the very early stages. Preliminary designs aren't due till late 2015. After that, DARPA will select who gets to build the technology demonstrator, with test flights expected sometime around 2017 or 2018.

Boeing concept for DARPA VTOL X-Plane program
Boeing's VTOL X-Plane concept is heavy on the fans. Boeing