If there was a competition for the oddest looking aircraft, then DARPA's VTOL Experimental Plane (VTOL X-Plane) would have to be in the running for the main prize. With a modularized, cellular wing design that looks like a flying set of cupboards, the unmanned aircraft is a hybrid of fixed-wing and rotary wing technologies designed to create a vertical take-off and landing (VTOL) aircraft that boasts greater range and speed capabilities.
VTOL aircraft have been around in one form or another for over a century, but even the best of them have been notorious for their inferior payload, stability, range, and speed capabilities when compared to traditional fixed wing aircraft. DARPA's VTOL X-Plane program is looking to overcome this problem with a new modular design that it's claimed will provide radical improvements in both vertical and horizontal flight capabilities.
The goal is to build a demonstrator aircraft that can reach a top sustained speed of 300 to 400 knots (345 to 460 mph, 555 to 740 km/h), hover with an efficiency of at least 75 percent instead of the current 60 percent, reduce the cruise lift-to-drag ratio from five or six to 10, and carry a payload equal to 40 percent of the X-Plane's 10,000 to 12,000 lb (4,536 to 5,443 kg) gross weight.
The VTOL X-Plane is the result of Aurora Flight Sciences Corporation's Phase 2 design contract for the program and is aimed at addressing both vertical and horizontal flight requiements. DARPA says that by calling on over half a century of advanced air vehicle and aeromechanics design and testing, adaptive and reconfigurable control systems, and highly integrated designs, the VTOL X-Plane does away with conventional mechanical drive systems in favor of a modular approach.
What this means is that instead of a single powerplant directly powering one or two rotors by way of a shaft, the VTOL X-Plane has two large rear wings and two smaller front canards. These are made up of cells carrying 24 ducted fans – nine integrated in each wing and three in each canard. These each have their own electric motor and all 24 are powered by a turboshaft engine off a V-22 Osprey tiltrotor aircraft, which cranks out 4,000 hp (3 MW) of electrical power.
To control this arrangement, the VTOL X-Plane has power distribution systems for multiple fans in a "transmission-agnostic air vehicle design." That means no gearbox, so the flight control system must be able to alter the thrust of each fan independently for efficiency as well as for changing from vertical to horizontal flight and back.
"This VTOL X-plane won't be in volume production in the next few years but is important for the future capabilities it could enable," said Ashish Bagai, DARPA program manager. "Imagine electric aircraft that are more quiet, fuel-efficient and adaptable and are capable of runway-independent operations. We want to open up whole new design and mission spaces freed from prior constraints, and enable new VTOL aircraft systems and subsystems."
Flight tests are scheduled for 2018 and DARPA says that the VTOL X-Plane technology is also suitable for manned aircraft.
The animation below shows the DARPA VTOL X-Plane in action.