by The US Defense Advanced Research Projects Agency (DARPA) says it’s time for some planes to ditch elevators, flaps and rudders for flight control.
DARPA’s new X-plane concept would remove these movable external control surfaces to reduce aerodynamic drag and increase fuel efficiency, contrary to a century of standard aviation design practice. But the Advanced Technology Division of the US Department of Defense says it has a viable option for maintaining control in the air at high speeds.
Aurora Flight Sciences received a design contract (opens in a new tab) from DARPA on Tuesday (Jan. 17) under the Control of Revolutionary Aircraft with Novel Effectors (CRANE) program, which seeks to fly an experimental aircraft without moving joints.
The Boeing subsidiary “will design a full-scale X-plane that relies solely on changes in airflow for in-flight maneuvers,” DARPA wrote in a Tuesday tweet (opens in a new tab) of Aurora’s price. Should the concept succeed, officials added, the design would be “a new phase in the creation of an aircraft.”
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Moving aircraft parts has been a necessary inconvenience for more than a century. On the one hand, control surfaces create drag and reduce fuel efficiency. However, pilots must move the aircraft around safely, and elevators, flaps and rudders have been tried, tested and improved for decades.
DARPA is by no means the first to consider removing parts previously considered essential to flight operations. In 2018, a team at the Massachusetts Institute of Technology flew what they called (opens in a new tab) the “first ever aircraft with no moving parts”, but that term referred more to propulsion. MIT used an electric charge on the plane to stay aloft, an effect known as “ionic wind” — not traditional propellers or engine turbines.
However, some previous aircraft have dispensed with one or more traditional moving surfaces. “Tailless flight,” for example, incorporates pitch and roll into the main wing, but usually still requires a rudder. Such aircraft have been around since at least the 1910s, with the now-retired supersonic Concorde aircraft being perhaps the most prominent example.
Few details are available now about how CRANE will stay stable in the air, but tantalizing hints are available via a 2021 presentation (opens in a new tab) by Alexander “Xander” Walan, program manager for DARPA’s Tactical Technology Office.
Active flow control (AFC) uses a variety of methods such as air jets or even electrical discharges to shape or shape the airflow over the aircraft, the presentation notes. DARPA seeks to use commercial parts where possible to provide low-cost alternatives and to “fully explore the AFC trade space,” meaning seeking technologies that can provide viable alternatives.
Although no further details about the AFC are available on DARPA’s laconic CRANE website (opens in a new tab)The Aurora announcement (opens in a new tab) suggests that their design will use “modular wing configurations that enable future integration of advanced technologies” to achieve AFC.
There’s not much to go on, but in the 2021 presentation, Aurora’s bid promised to model several conceptual wing designs to find the best one. Based on available images, it appears that the X-plane will use a type of “coplanar joined wing”, which includes two front wings and two tail wings instead of the traditional V-shaped wing of most commercial and military aircraft.
The next part of CRANE, known as Phase 2, will involve the design and development of the controls and flight software. It will be complemented by a critical design review of the X-planet. DARPA may request a Phase 3 to fly a 7,000-pound (3,175 kg) X-plane demonstrator with AFC technology. No financial or timeline details were released.
Elizabeth Howell is the co-author of “Why am I taller? (opens in a new tab)?” (ECW Press, 2022; with Canadian astronaut Dave Williams), a book about space medicine. Follow her on Twitter @howellspace (opens in a new tab). Follow us on Twitter @Spacedotcom (opens in a new tab) or Facebook (opens in a new tab).
