Fighter flies with most of wing gone

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If you can think fast enough and act fast enough, perhaps you, too, could fly an F-15 fighter with 60 percent of its right wing blown off.

A lot of pilots couldn’t, said David Vos, senior director of Control Technologies at Rockwell Collins.

But a computer algorithm that he helped create can. It piloted a scaled-down F/A-18 this spring, and then kept it aloft and under control even after most of the right wing was intentionally blown off in midflight.

The computer succeeded where many human pilots would undoubtedly fail because it was able to react about 20 milliseconds after the wing was damaged and because it “knows everything there is to know about the plane,” Vos said.

A human pilot, if he’s very sharp and very ready, can react in about 200 milliseconds, Vos said.

In that time, the computer made 10 more adjustments to keep the F/A-18 from falling out of the sky.

There are rare examples in which human pilots have been able to nurse critically damaged aircraft safely to the ground. In 1983, for instance, an Israeli pilot landed his F-15 after a midair collision tore a wing off.

But such incidents are famous because there are so few.

In multiple tests in April, a computerized flight control system called Automatic Supervisory Adaptive Control was able to quickly stabilize the wounded F/A-18, fly it to an airstrip and land it safely. First, 40 percent of the wing was “ejected,” then 60 percent.

Vos and his colleagues at Rockwell were amazed the plane could sustain that much damage and still fly.

“We had no idea [it] would get to 60 percent. We thought it would be uncontrollable long before that,” Vos said.

‘Maybe we didn’t push it far enough’
“My direction was to push this to the limit to see how far the technology went,” said Air Force Lt. Col. Jim McCormick, manager of the Damage Tolerant Controls project at the Defense Advanced Research Projects Agency. “Maybe we didn’t push it far enough — the aircraft recovered pretty easily.”

DARPA’s aim was to give aircraft a sort of artificial intelligence — what McCormick calls “air sense” — that would enable them to react to unexpected events the way a human pilot might.

Initially, at least, the damage-tolerant flight controls are intended for use on UAVs. Eventually, though, they could be built into manned aircraft.

That need for smarter UAVs arose while DARPA was working on the Joint Unmanned Combat Air System, an Air Force and Navy UAV designed to attack targets. J-UCAS was expected to rely heavily on stealth for survivability, but DARPA scientists also wanted the UAV to be able to save itself if it suffered damage. The J-UCAS program ended in 2006, but the need for UAVs to survive damage remains, McCormick said.

The plane used in the April test was a fully autonomous, 8-foot-long, 50-pound jet-powered model of an F/A-18. Vos said that a full-size F/A-18 equipped with the same damage-tolerant controls would react the same way. “The fundamentals of it are mathematics,” he said.

The computer runs an algorithm that understands the dynamics of the aircraft. That is, the computer understands why the plane flies and how one change — say the loss of part of a wing — will change the aerodynamics of the aircraft.

Based on that information, the computer calculates how to compensate for the change.

The algorithm is “based on fundamental, pure mathematical control theory,” Vos said. Control theory is a merger of engineering and math that explains how dynamic systems operate.

So after the F/A-18 lost most of its wing, the adaptive flight control system “reacted to the airplane’s new configuration.” The first thing the control system did was try to compensate by adjusting the plane’s control surfaces, Vos said.

But with 60 percent of the wing gone, the control surfaces alone couldn’t keep the plane in stable flight. So the computer began to “manipulate the whole plane,” using the entire aircraft as a control surface, Vos said.

It turned the plane slightly so that the damaged wing was pointed partially into the air stream, creating more lift. Consequently, the undamaged wing trails slightly, creating less lift. The new configuration brings the plane back into balance.


Article: http://www.militarytimes.com/news/20...ngless_070508/
Video: http://www.rockwellcollins.com/news/...tolerance.html