DARPA has awarded a contract to Aurora Flight Sciences to build a full-scale aircraft called the X-65. It will test a new technology that replaces moving control surfaces with Active Flow Control (AFC) actuators that use jets of air for control.
If you've ever sat in the wing seat of a plane, you probably noticed that there's a lot of activity going on out there. Flaps, slats, ailerons, spoilers all go into motion, while unseen on the tail of the plane the elevators and rudder play their part. It's all very dramatic, but it also involves a complex symphony of machinery and control systems to make it all work.
Using AFC actuators, DARPA hopes to one day replace all these expensive, weighty control surfaces with a much simpler system that depends on jets of air to do the same thing. Instead of moving control surfaces, an AFC system uses an array of nozzles installed on the following edges of the airfoils. By shooting compressed air out of these nozzles, they can change the air pressure in the vicinity and alter the air flow over the airfoil. In this way, the system can change the roll, pitch, and yaw of the aircraft.
According to DARPA, the robotic X-65 will have a distinct diamond-shaped design for greater strength. However, it will not be controlled solely by AFC actuators. Instead, it will have both an AFC system and a conventional mechanical control system. The purpose of this setup is to ensure the safety of the experimental craft, and to provide a means of building up a baseline of data that engineers can use to compare the two systems. As the tests proceed, the mechanical controls will be locked down and replaced selectively until the AFC system has full control.
Part of DARPA's Control of Revolutionary Aircraft with Novel Effectors (CRANE) program, the X-65 has a modular design for quick modifications, operates without a crew, weighs in at over 7,000 lb (3,175 kg) and has a 30-ft (9-m) wingspan. When airborne, it's expected to reach speeds of about Mach 0.7. These specifications make it similar to a military training jet, which means the test data can easily relate to the real world.
DARPA says that Aurora flight systems has already begun construction of the X-65, which is expected to roll out early next year.
If successful, the implications of the AFC technology are considerable. By reducing weight and simplifying systems, it will be possible for engineers to greatly improve aircraft by using the savings to make airframes lighter and sturdier. This could lead to thinner, longer wings with much greater efficiency and perhaps, one day, the technology could be expanded from airfoils to the entire aircraft, allowing it to be sheathed in a frictionless layer of air that will let the craft slip through the air with greatly reduced drag.
"It’s thrilling to be able to say, 'we’re building an AFC X-plane,'" said Dr. Richard Wlezien, DARPA’s program manager for CRANE. "I came to DARPA in 1999 to work on a program called Micro Adaptive Flow Control, which help (sic) pioneer the foundational understanding of fluid dynamics that eventually led to CRANE. I left DARPA in 2003 after managing MAFC, and it’s the chance of a lifetime to come back and help see that early work come to fruition in a full-scale physical aircraft. Aerospace engineers live to see their efforts take flight."
Source: DARPA