WASHINGTON — The Defense Advanced Research Projects Agency has taken a major step forward toward creating an experimental airplane that can be maneuvered without traditional ailerons or other mechanical devices, instead using short bursts of air.
DARPA announced Tuesday it had selected Aurora Flight Sciences to start detailed design of an aircraft that uses a technology called active flow control to direct it, as part of the Control of Revolutionary Aircraft with Novel Effectors, or CRANE, program. Aurora is a subsidiary of Boeing headquartered in Manassas, Virginia, that specializes in developing advanced innovative designs for aircraft and uncrewed systems.
“Over the past several decades, the active flow control community has made significant advancements that enable the integration of active flow control technologies into advanced aircraft,” CRANE program manager Richard Wlezien said in a statement. “We are confident about completing the design and flight test of a demonstration aircraft with AFC as the primary design consideration. With a modular wing section and modular AFC effectors, the CRANE X-plane has the potential to live on as a national test asset long after the CRANE program has concluded.”
A typical aircraft has mechanical components such as ailerons on its wings and a rudder and elevators on its tail that its pilot uses to control the plane’s roll, pitch and yaw.
That general principle has remained largely unchanged and guided aircraft design for more than a century, former CRANE program manager Alexander Walan said in a November 2021 interview with Defense News.
But DARPA hopes the active flow control concept, if successful, could prompt a major rethinking of how planes are built and maneuver.
Active flow control technology would use small bursts of air from a wing or other air foil surface to shift the aircraft’s position or direction. The burst itself is not pushing the wings under this concept, he said, the way a spacecraft uses thrusters to nudge it into position in orbit or during re-entry.
Instead, an active flow control burst creates something of a speedbump that alters the way air flows over the wings, which then causes the aircraft to shift.
“It’s very energy-efficient,” Walan said. “Because I’m using the natural way the air wants to move, I’m injecting just a little bit of energy into it to get a big effect out of it. We’re not actually pushing the vehicle with air, we’re using it to tailor how the air is flowing over the wing.”
The aerospace community has considered this concept for at least three decades, he said, and tried laboratory experiments and some small-scale flight demonstrations. In 2015, NASA and Boeing teamed up to successfully fly a 757 aircraft modified with a vertical tail that used active flow control technology for increased aerodynamic efficiency.
So far, Walan said, no one has tried to control an entire airplane using this technology.
In recent years, he said, DARPA felt the technology — including supercomputers and advanced fluid dynamics tools, and drone aircraft that could make demonstrating active flow control much cheaper and safer than testing it on manned planes — had developed to a point where “the time was right to try to see if we could design an airplane around this.”
DARPA also had to show this technology isn’t just something that “sounds cool,” he said, but could yield tangible benefits over the traditional system.
In its Tuesday statement, DARPA said this technology could improve how aircraft fly in several ways, including by eliminating moving surfaces to control the plane, reducing drag, thicker wings for structural efficiency and increased fuel capacity, and simplified systems to improve an aircraft’s lift. Walan said in 2021 that it could also lead to lower costs and increased aircraft agility.
DARPA launched the CRANE program in 2019, and organizations such as Aurora, Lockheed Martin and the Georgia Tech Research Corporation took part in its earlier stages.
Aurora has now completed the project’s Phase 1, a preliminary design phase that yielded what DARPA described as “an innovative testbed aircraft” that successfully used active flow control in a wind tunnel test.
Aurora will now move into Phase 2 under the $42 million contract, where it will create a detailed engineering design for its plane and develop flight software and controls. This will end with a critical design review of an “X-plane” demonstrator, that will be able to fly without traditional moving flight controls on its wings or tail.
DARPA’s award also has the option to move Aurora into Phase 3 of the program, in which it would build a full-scale, 7,000-pound uncrewed aircraft that relies on active flow control for DARPA to test fly. This test aircraft would have modular wing configurations that would allow DARPA or other organizations to easily swap in advanced technologies in the future.
“Given all that we have learned about AFC and its application to tactical aircraft in prior phases of CRANE, the next step is to prove out these learnings in flight,” Graham Drozeski, Aurora’s vice president of government programs, said in a company statement. “The CRANE X-plane is designed specifically to explore the effectiveness of AFC technologies at mission relevant scale and Mach numbers.”
The company said it would build this X-plane, which would have a wingspan of 30 feet, at its facilities in Virginia, West Virginia and Mississippi, and it would fly at up to Mach 0.7. Aurora hopes to conduct flight tests in 2025.
It will be many years — if ever — before this kind of technology lands in an Air Force plane or other military aircraft. Walan said in 2021 this is an experimental project intended to show whether this kind of innovative technology can work, not to improve something already in operation.
If the concept does work, Walan said, it could be a “disruptive” technology — and even upend how future aircraft are designed.
“Because we’re DARPA, we can kind of push the envelope a little bit,” Walan said. “I don’t have to have a system out there that needs this.”
“What we’re trying to do on this program is open up the toolbox that airplane designers have, so future systems have new tools and new approaches they can take and consider,” Walan continued. “This is really the art of the possible.”
Stephen Losey is the air warfare reporter for Defense News. He previously covered leadership and personnel issues at Air Force Times, and the Pentagon, special operations and air warfare at Military.com. He has traveled to the Middle East to cover U.S. Air Force operations.