Pilots keep control

Engineers at NASA’s Dryden Flight Research Centre have received a patent on an emergency fuel control system using only one engine and fuel transfer.

The patent, granted to Frank Burcham, John Burken, and Jeanette Le, provides pilots another method of landing an aircraft in emergency conditions, such as total hydraulic pressure loss and engine failure on one side.

In the early 1990’s the Propulsion Controlled Aircraft (PCA) project 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 aeroplane.

‘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,’ said 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 centre-of-gravity shift from transferring fuel,’ Burken said.

The alternative remedy addressed by the patent is said to provide for the control of a troubled aircraft by shifting its lateral centre of gravity via fuel transfer, and by co-ordinating 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-centre 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 centre 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 centre-of gravity shifting in the transport aeroplanes studied – MD-11, C-17 and B-747 – ranges from four to six feet. The fuel shift moves the weight of the aeroplane 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.

On the web