Rockwell Collins is preparing to begin test flying its damage tolerant flight control algorithms onboard an unnamed operational unmanned air vehicle (UAV) following the latest round of successful flight testing under phase three of a Defence Advanced Research Projects Agency (DARPA) contract.

"The next step is to port the technology to an operational UAV," says Dave Vos, senior director of Rockwell Collins Control Technologies and Unmanned Aircraft Systems. "It will be out there in the operational world shortly." Vos would not say which platform will be used.

In the latest testing at the Aberdeen Proving Ground in Maryland, engineers subjected a subscale F/A-18 jet-powered model to increasingly severe levels of structural and control system damage, all of which resulted in controllable outcomes with the aid of the adaptive control algorithms.

The patented control technologies, which are based on nonlinear multi-variable design solutions, use all available control means to attempt to follow a trajectory despite failure conditions. The design uses an inner control loop operating at 50-100Hz to manage aircraft attitude and an outer loop operating at 10-50Hz to control trajectory.

Vos says the design is 99% deterministic, which makes it predictable in terms of stability margins that aviation authorities would expect to see in a full civil aircraft certification program. The other 1% is an adaptive control method that does "fine tuning of the control system", says Vos. "We could very easily leave out the adaptive portion," he adds.

During various tests at Aberdeen, Rockwell Collins ejected 60% of the right wing, 30% of the right fin rudder and 30% of the right stabiliser. Other failure tests included locking the right aileron in neutral position to cause an uncontrolled roll. Despite the simulated failures and damage, the UAV remained steady in-flight and was able to land in each case. Another flight test demonstrated the ability for the aircraft to continue to fly a fixed trajectory and land safely after the engine was turned off. A final flight test involved ejecting 80% of the UAV's right wing and successfully landing. Previous testing had involved ejecting up to 60% of the wing. All flight tests included autonomous take off and landing.

"This latest flight test campaign is an important step toward our ultimate goal of offering our damage tolerance control software to the UAV market," says Vos. "Our solution improves the survivability of UAVs in theater, while simultaneously improving the reliability of UAVs flying in civilian airspace. By detecting and instantly and automatically compensating for failure or damage in flight, UAVs and manned aircraft can soon achieve coexistence."

Source: Flight International

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