One-lever control
Juggling engine management tasks such as monitoring — and adjusting — their engine's mixture, prop rpm, and power settings while manipulating the flight controls and airplane speed to keep the localizer and glideslope needles centered during a low-ceiling and -visibility ILS approach is a challenge for general aviation pilots. So, to those experienced in this dance, the idea of an automatic one-lever engine control system seems too good to be true. And, until very recently, it has been.
Full authority digital engine control (FADEC) systems automatically control the engine's power setting, fuel flow, propeller pitch, and mixture setting for all flight regimes. A FADEC system removes engine management struggles from a pilot's workload, thus enabling him to devote the lion's share of his attention to flying the airplane.
Although turbine-powered-aircraft pilots have been controlling their powerplants with FADEC systems for more than 40 years, this workload-reducing device has only recently been installed in a few new production piston-powered airplanes, and is available for retrofit (by supplemental type certificate) on a handful of airplane models already in the fleet.
The sad fact is that today's pilot flying a piston-powered airplane is manipulating the same engine management controls that his grandfather used back in 1945. Until very recently just about the only arrow the piston pilot could add to his quiver of engine management tools has been a digital engine monitor. These monitors provide a flood of data such as fuel flow and cylinder head and exhaust gas temperatures (EGTs). These data are of little use unless the pilot can correctly interpret the information and take the appropriate action.
The task of developing a system for controlling the power delivered to the propeller by a piston engine is not easy or inexpensive. Operating parameters must be established, data-gathering networks must be designed, fuel-delivery systems must be developed and optimized. Software to crunch the data and deliver operating instructions to the variables — ignition spark timing, flow and timing of fuel injection, propeller rpm, and in some cases, the turbocharger wastegate position — must be developed and tested.
Questions must be answered, such as how much power — 65 percent? 75 percent? — and what mixture setting — 50 degrees rich of peak? 30 degrees lean of peak EGT? — best balance economy and engine life for takeoff, climb, and cruise conditions. Software that automatically adjusts ignition and fuel mixtures to maintain ideal cylinder head temperatures (CHTs) must be flexible enough to let go of the CHT limits, thus preventing FADEC from overriding the pilot's command when CHTs drop rapidly in the event the pilot decides that a power-off emergency descent is required.
Redundancy is the law in aviation. This mandates a parallel or backup system. System components must withstand environmental hazards such as high levels of vibration and exposure to corrosive fluids and high temperatures while complying with certification rules for both hardware and software.
Competitive systems, most likely from a European or Australian or New Zealand company, will soon arrive on the market. These will drive down prices, and more owners will trust FADEC systems enough to remove their propeller and mixture controls and turn over their engine management tasks to FADEC. It's inevitable. Only those few who embrace the good old days will insist on continuing to debate the virtues of various techniques for starting a hot fuel-injected engine — the rest of us will just turn the key and FADEC will automatically take care of our engine business.— Steven W. Ells, Associate Editor
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