Image courtesy of Aurora Flight Sciences
Aurora Flight Sciences’ XV-24A LightningStrike subscale vehicle demonstrator has completed its planned flight test program, Aurora said Tuesday during Navy League’s Sea Air Space. Tests included outbound and inbound transition fight. The full-scale demonstrator is currently in production, with the flight test program slated for late 2018.
This project is part of the Defense Advanced Research Projects Agency’s (DARPA) X-Plane program and is funded by DARPA. The subscale model weighs 325 pounds and is designed to 20% scale of the full-size aircraft. It flies completely autonomously on programmed routes, without a human in the loop. The small model runs on lithium battery with an endurance of five minutes. But the full-scale model would be 12,000 pounds with a 61-foot wingspan, powered by hybrid-electric propulsion, significantly extending the endurance. The full-scale XV-24A would use three Honeywell megawatt generators with one Rolls-Royce AE 1107C turboshaft engine — the same engine used on the Bell Boeing V-22.
Although the program was recently designated the XV-24A by DARPA and the Air Force, DARPA did not specify a mission set to which the full-scale aircraft is to comply. There are performance hopes, though, that have been in mind since the beginning:
- Achieve a top sustained flight speed of 300 kt to 400 kts
- 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 to 6
- Carry a useful load of at least 40% of the vehicle’s projected gross weight of 10,000-12,000 pounds
Does DARPA think the program can meet those lofty aspirations? Not without putting in some more work.
“Behind closed doors, you can see the performers sweat because they're not easy,” said Ashish Bagai, DARPA’s program manager for this project. “If they were easy, we would have seen them done a long time ago. We really struggle some times to see to make every single thing converge, enabling those four to happen. Do we feel strongly that we will meet every single one of them? I think we'll get very close to them; I think it will be significantly better than what we've seen in the past. So the confidence that we will get you a very sophisticated machine, new design spaces that meet those performance parameters is high. We have some work to do to make sure we get to the point that we want to.”
Bagai noted that since there were no specified mission capabilities, design evolution could dictate exactly how those performance hopes are adjusted.
The technology in this project, especially the hybrid-electric propulsion, has implications for future technology. After the XV-24A, an electric-powered tail rotor for a helicopter is simple, joked Bagai. Electric gearboxes is something that Rolls-Royce is exploring, said Mark Wilson, COO for Rolls-Royce North American Technologies Inc. (LibertyWorks). And Tom Konicki, director of business development for Honeywell, said that the company’s megawatt generator was designed from a clean sheet. The challenge it is very close to overcoming is one that Rolls-Royce is facing too — how to make the power source lightweight and small in size.
In the future, Aurora can imagine the XV-24A as an armed escort for the V-22. Or, just as the Bell Helicopter XV-15 was an experimental aircraft that paved the way for the V-22, the full-scale LightningStrike could be a test bed for future aircraft.
“When we first set up the program, the government asked performs to step out of their comfort zones and to step away from them to see what other design spaces could actually materialize,” Bagai said. “I think this is a program that actually took that upon itself, took that challenge to heart and demonstrated it.”
The test program for the full-scale V-24A is planned for Naval Air Station Patuxent River in Maryland.