The Defense Advanced Research Projects Agency took one step further in building a radically different vertical take off and landing or VTOL aircraft that can fly fast and carry a big load.
Specifically DARPA awarded Aurora Flight Sciences the $89 million prime contract for Phase 2 of the agency’s Vertical Takeoff and Landing Experimental Plane (VTOL X-Plane) program which looks to:
- Achieve a top sustained flight speed of 300 kt-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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DARPA said 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—one used in V-22 Osprey tiltrotor aircraft—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,” DARPA stated.
Engineering an aircraft that can go fast, carry usable amounts of equipment and people and hover has always been one of aviation's greatest challenges. There are plenty of fast helicopters -- one of the world's fastest helicopters, the Eurocopter X3 can hit nearly 300 MPH -- but they are usually limited in the amount of weight they can carry. Jets with VTOL capability such as the F-35 but their mission is not to be hauling cargo.
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When it initially launched VTOL-X development DARPA program manager Ashish Bagai said: “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. "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.”
The Phase 2 design addresses in innovative ways many longstanding technical obstacles, 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 revolutionary design advances to be incorporated in the Aurora technology demonstrator:
- Electric power generation and distribution systems to enable multiple fans and transmission-agnostic air vehicle designs.
- Modularized, cellular aerodynamic wing design with integrated propulsion to enable the wings to perform efficiently in forward flight, hover and when transitioning between them.
- Overactuated flight control systems that could change the thrust of each fan to increase maneuverability and efficiency.
“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” Bagai said in a statement this week. “This is an extremely novel approach,” Bagai said of the selected design. “It will be very challenging to demonstrate, but it has the potential to move the technology needle the farthest and provide some of the greatest spinoff opportunities for other vertical flight and aviation products.”
The program has the goal of performing flight tests in the 2018.
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