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Three levers in one
By Mark Allan Gottschalk; Anna Allen -- Design News, September 6, 1998
Aurora Flight Sciences Corp. has applied knowledge gained in developing full-authority digital engine controls (FADEC) for the company's Perseus unmanned aerial vehicle to create what is said to be the first all-digital single-lever power control (SLPC) for general aviation. Unlike the single gas pedal in a car, current piston engine aircraft have three controls to govern air speed: one for the throttle, one for the fuel-to air mixture, and one for propeller pitch control. An SLPC integrates a FADEC with a single power lever interface, greatly simplifying the pilot's job while simultaneously improving engine efficiency, decreasing emissions, and even extending engine life. "The SLPC increases safety and decreases pilot workload," says Benjamin Russ, SLPC project manager. "In a single-engine aircraft, our test pilot estimates that it cuts his workload by about 50%." The single-lever power command input is interpreted into optimal engine speed and inlet manifold pressure commands for the given flight condition. These commands are met by the real-time control laws running on the FADEC. As with the electronic engine-management system found on most new automobiles, the FADEC processes numerous engine parameters such as manifold air pressure, engine speed, cylinder head temperature, oil temperature, exhaust gas temperature, flight speed, and altitude to determine the best engine settings for a given power lever setting. "The pilot sets the power lever to a relative value--say half power--and the system determines the best way to develop half power given the current conditions," says Russ. Given today's sensor and processing technology--and Aurora's system leverages many automotive components--the SLPC seems like a straightforward product. However, safety is a paramount concern, and engineers have initially had to find ways to integrate the SLPC into the Cessna O-2A test aircraft without disabling the conventional mechanical fuel injection and magneto spark system. The result is player-piano like, with the manual engine-control levers moving in harmony to the SLPC's commands. OEM installations would probably be more elegant but still retain a mechanical backup for limping home.
