Airplanes are great, but they can't hover without crashing. And helicopters are great, but they can't fly very fast. Attempts to tie the two together, such as the Harrier jump jet, V-22 tiltrotor or Sikorsky X-2 are aerodynamic compromises that end up doing neither especially well.
Aircraft need air moving fast over the wing to create enough lift to support the plane's weight, and since the wings are fixed in position it needs to keep moving. Helicopter rotors work like wings, they're spinning fast enough to generate enough lift to let the helicopter hover, but the rotor needs to be pointed upwards, otherwise nothing is generating lift.
But the Defense Advanced Research Projects Agency aims to change that, and they've just started handing out money for a new X-plane program. DARPA wants the airplane to fly at least 350mph -- faster than most small general aviation planes, but not as fast as an airliner -- while carrying up to 12,000 pounds. It's harder than it might seem. To do so, you need to step away from conventional airplanes and helicopters.
Aurora Flight Sciences, a relatively small Virginia-based company, just got $14 million to build a scale model prototype of their system, whatever it is. Aurora is known for its innovation, doing unusual things with experimental one-offs or low-production drones; their most prominent programs to date are large experimental airplanes meant to stay airborne for days or years at a time. Just what they are pitching to DARPA we don't yet know -- the company did not immediately return phone calls. But it may look a lot like some other recently-introduced entries, and nothing like what's in the skies today.
One proposal is Boeing's Phantom Swift, which uses a winged fan-in-body configuration, with two rotors inside the fuselage of the aircraft itself and two ducted fans on either wing to hover. The ducted fans tilt forwards to act as propellers, and the internal rotors help take the load off so they don't have to be especially powerful. For forward flight the ducted fans tilt forward to become propellers, while the wings -- and crucially, the fuselage -- can generate lift. Other companies are using some or all of the same ideas.
"We're looking at doing this in an elegant fashion, we're not looking for brute force," DARPA program manager Ashish Bagai said when the program was announced. "There is a lot of technology now available to directly address shortcomings" of previous designs, he added.
The first phase of the contract involves a few competitors, flying scale models and making their best pitches for the real thing. The second phase, starting in 2015, will downselect to a single competitor to build a full-scale airplane.
Nobody is expecting this to happen quickly -- X-planes are built to test ideas, not work operationally -- but the potential benefits to aviation are huge.