The Defense Advanced Research Projects Agency (DARPA) has unveiled its design for a vertical takeoff and landing (VTOL) unmanned aircraft that would combine plane-like speed with helicopter-like agility. The VTOL Experimental Plane (X-Plane), designed by Aurora Flight Sciences, uses a combination of fixed- and rotary-wing technologies to boost vertical and cruising flight capabilities.

Aurora’s Phase 2 design for the VTOL X-Plane envisions an unmanned aircraft with two large rear wings and two smaller front canards—short winglets mounted near the nose of the aircraft. A turboshaft engine mounted in the fuselage would provide 3 megawatts (4,000 horsepower) of electrical power, the equivalent of an average commercial wind turbine. The engine would drive 24 ducted fans, nine integrated into each wing and three inside each canard. Both the wings and the canards would rotate to direct fan thrust as needed: rearward for forward flight, downward for hovering and at angles during transition between the two.

VTOL X-Plane combines fixed- and rotary-wing technologies for speed and maneuverability. Image credit: DARPA.VTOL X-Plane combines fixed- and rotary-wing technologies for speed and maneuverability. Image credit: DARPA.The design envisions an aircraft that could fly fast and far, hover when needed and accomplish diverse missions without the need for prepared landing areas. While the prototype to be built would be unmanned, DARPA says the technologies that VTOL X-Plane intends to develop could also apply to manned aircraft.

The Phase 2 design addresses many longstanding technical obstacles to VTOL flight, the biggest of which is that the design characteristics that enable good hovering capabilities are completely different from those that enable fast forward flight. Among the design advances to be incorporated in the demonstrator that will enable both capacities are:

· Electric power generation and distribution systems that enable multiple fans and transmission-agnostic air vehicle designs;

· Modularized, cellular aerodynamic wing design with integrated propulsion to enable the wings to perform efficiently during forward flight, while hovering and when transitioning between them;

· Overactuated flight control systems that could change the thrust of each fan to increase maneuverability and efficiency.

Ultimately, the program has the goal of developing a technology demonstrator in the 2018 timeframe that can:

· Achieve a top sustained flight speed of between 300 kt and 400 kt;

· Raise aircraft hover efficiency from 60% to at least 75%;

· Present a more favorable cruise lift-to-drag ratio of at least 10, up from 5-6;

· Carry a useful load of at least 40% of the vehicle’s projected gross weight of 10,000-12,000 pounds.

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