Dryden Engineers Receive Emergency Flight Control Patent

Engineers at NASA’s Dryden Flight Research Center, Edwards, Calif.,
have received a patent on an emergency fuel 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 documented in U.S. Patent #
6,126,111 entitled Emergency Flight Control System Using One Engine
and Fuel Transfer.

The patent provides pilots 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 still working engines 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 or engines. 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 an autopilot knob in
the cockpit. The software automatically commands the required fuel
transfer and engine thrust variances to adjust for whatever caused
the emergency, such as an inoperative engine.

This automatic changing of an aircraft’s center of gravity and thrust
situation is slow enough and complicated enough to require computer
control. It also frees the pilots to fly an aircraft during an
emergency rather than having to concentrate on transferring fuel
quickly and accurately while readjusting 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. The fuel shift
moves the weight of the airplane to the left or right at about three
inches per minute, demonstrating that wings-level flight can be
maintained. The control system may provide for a survivable landing
if the original control failure is not too abrupt.

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.

– NASA –

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