Volume 10, Number 1 • January/February 2002 • Aerospace Technology Development

Dryden Engineers Receive Emergency Flight Control Patent

Engineers at NASA’s Dryden Flight Research Center in Edwards, California have received a patent on an emergency flight control system using only one engine and fuel transfer.

Engineers Frank Burcham, John Burken and Jeanette Le designed the software and the emergency control scheme entitled Emergency Flight Control System Using One Engine and Fuel Transfer.

The patent provides pilots with another method of landing an aircraft in emergency conditions, such as total hydraulic pressure loss and engine failure on one side. The Propulsion-Controlled Aircraft (PCA) project at Dryden in the early 1990s provided the first reliable method for dealing with such large-scale failures in flight. Results from testing the emergency control system in simulators show an increase in the chances of safely landing a crippled airplane.

“Normally, the damage that results in a total loss of the primary flight control of a transport airplane, including all the engines on one side, would be catastrophic,” says John Burken. “In response to this type of failure, Dryden has conceived a fix. The emergency controller uses the engines still working, along with a lateral center-of-gravity shift from transferring fuel,” Burken said.

The alternative remedy addressed by the patent provides for the control of a troubled aircraft by shifting its lateral center of gravity via fuel transfer and by coordinating the thrust of only one engine in conjunction with the fuel transfer. In transferring fuel out of the wing with the failed engine(s), the weight of that fuel added to the other wing helps balance the off-center thrust condition caused by the failed engine(s). Autonomous fuel transfer can then be used to affect the pitch and roll of an aircraft. The patent serves primarily multi-engine aircraft with multiple fuel tanks.

Emergency flight control system software programmed into an aircraft’s flight control computer is linked to existing autopilot knobs in the cockpit. The software automatically commands the required fuel transfer and engine thrust variances to accommodate the pilot’s inputs, while compensating for whatever caused the emergency, such as a failed engine.

This changing of an aircraft’s center of gravity and thrust situation is much too complicated for a pilot, thus requiring computer control. It also frees the pilots to perform other functions during an emergency, rather than having to concentrate on transferring fuel quickly and accurately while continually adjusting the throttles of good engines.

Lateral center-of-gravity shifting in the transport airplanes studied (MD-11, C-17 and B-747) ranges from four to six feet. On the MD-11, the fuel shift moves the weight to the left or right at about three inches per minute. Wings-level flight can be maintained immediately, but approximately five to eight minutes is required to achieve level flight. The control system may provide for a survivable landing if the original control failure is not too severe and occurs at a sufficiently high altitude to allow time for the fuel shift.

Burcham, Burken and Le all participated in the previously related PCA project at Dryden, which resulted in the successful landing of MD-11 and F-15 research aircraft using only throttle control. None of the usual flight controls, such as ailerons, flaps or stabilizers, were used. Q

For more information, contact Frank Burcham at NASA Dryden Flight Research Center, 661/276-7979, Frank.burcham@dfrc.nasa.gov. Please mention you read about it in Innovation.

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