Part 6 of 12
Although there is some debate about what type of engines will power future airplanes—lightweight turbines, turbocharged diesels, or both—there is little debate about how these powerplants will be controlled. Electronics will tailor the fuel-air mixture and ignition timing of these future engines. Gone will be the magneto. Also gone will be the three engine controls that adorn today’s complex light airplane cockpits. They will be replaced by a single lever that will control the rpm, mixture, ignition, and more.
Computer control can manage an engine far more efficiently than the typical general aviation pilot can. In the future, stories of ritualistic starting techniques and hangar tales about proper engine management will be bantered about by us, the old-timers of tomorrow. Newer pilots may well be baffled by terms such as hot start or lean-of-peak operation. All the pilot will have to do is decide whether he wants to go fast and burn a lot of gas or go slow and sip the fuel. The computer will determine the most advantageous combination of manifold pressure, rpm, and mixture for the desired profile.
The industry buzzword for this computerized engine control is FADEC, which stands for full-authority digital engine control. FADEC has been around on turbine engines for some time. Recently, however, the technology has trickled down to general aviation and promises to make magnetos, mixture, and prop controls—as well as carburetors—a thing of the past. In other words, the pilot no longer will have to think much about engine management, leaving him to concentrate on simply flying. (In the late 1980s, Mooney’s PFM had electronic ignition and single-lever control, but production ceased after about 50 were built.)
Side benefits to FADEC will be increased efficiency, lower fuel burn, and the ability to accurately diagnose and troubleshoot engine problems. For the engine manufacturers, FADEC will make warranty claims more cut-and-dried because the computer will store previous flights in memory, pinpointing the cause of problems as operator error or as a genuine manufacturing defect. FADEC systems could also be the missing link to enable current engines to use the unleaded fuels of tomorrow.
Since 100LL avgas contains a healthy amount of lead, its future looks bleak. Currently, the highest pump octane that can be achieved without the addition of lead is about 92. That octane number, unfortunately, won’t provide adequate detonation margin for high-power or turbocharged engines using current fixed-timing ignition systems. But if dithering with the engine’s timing, optimizing the fuel-air ratio, or moving the cylinder’s peak pressure pulse can allow today’s engines to run on tomorrow’s unleaded fuels, it will save owners from having to scramble to reengine their airplanes with new, unproven powerplants.
FADEC systems are emerging today from Teledyne Continental Motors (TCM), Lycoming/Unison, and General Aviation Modifications Inc. (GAMI). The Lycoming/Unison and TCM FADEC systems are flying on test airplanes, while the folks at GAMI have logged about 50 hours of use in a sophisticated engine test cell. Each system has a unique way of simplifying engine control. Here’s a brief look at each system and its current state of progress.
TCM’s FADEC
TCM, along with its Aerosance Control division in Connecticut, is currently flying a Cessna 172, Beech Baron, and Diamond Katana equipped with FADEC. A Cessna 210 will be flying shortly and will be the first airframe to receive a supplemental type certificate for installation of a FADEC system. The first aftermarket installations of the system will be performed at TCM’s Fairhope, Alabama, facility and TCM’s recently purchased overhaul shop, Mattituck Airbase on New York’s Long Island.
TCM’s FADEC monitors the EGT and CHT of each cylinder, the pressure and temperature of the air in the intake manifold, and engine timing (see "Airframe and Powerplant: Bag of Chips," January Pilot). Based on that information, it will request that a measured amount of fuel be sent to each cylinder according to its individual need. A properly timed spark will also be sent to that cylinder based on current demands, whether it’s takeoff power or starting. TCM estimates a 12- to 15-percent fuel savings with its FADEC system installed, compared to the current magneto and continuous-flow injection setup. Above 65-percent power, the system shoots for a best-power fuel mixture. Below 65-percent power, the system can operate the engine as far as 50 degrees lean of peak. TCM’s FADEC is powered by the aircraft’s electrical system, but a dedicated independent battery will keep it working in the event of a power failure. In testing, a four-cylinder engine was able to continue running for three hours on the battery.
On the OEM side, Diamond will likely incorporate the TCM FADEC system into new DA20-C1s, which are powered by the Continental IO-240. It’s expected that the rest of the OEMs installing Continental engines at the factory will soon be incorporating the technology in their respective airplanes’ type certificates. All engines incorporating FADEC, from the factory or not, will change designators too; for example, IOF-240, IOF-360, IOF-550, etc. TCM estimates that the cost to retrofit an engine with FADEC will be in the range of $5,000 to $7,000. Given the cost of fuel these days and the potential fuel savings, the system will come close to paying for itself over a 1,700-hour TBO cycle of an IO-550, for example.
Although it’s too early to tell, Continental hopes to increase engine life through proper engine operation, narrower temperature extremes, and cleaner operation, thanks to optimized mixture management. Look for these systems to begin emerging on new airplanes and Mattituck overhauls by the end of the year.
Lycoming/Unison EPiC
Lycoming and Unison’s entrant to the FADEC playing field is called EPiC, which stands for electronic propulsion integrated control. Like the TCM system, EPiC is currently in the flight-test stage. EPiC is intended for OEM use on airplanes powered by Lycoming engines. Someday the system may be available for aftermarket installation but, for now at least, the Lycoming/Unison team is focusing on new aircraft. Unison’s Lasar is a simpler electronic-ignition system that is currently available on an aftermarket basis for about $2,500.
EPiC monitors manifold pressure, inlet-air pressure and temperature, cylinder-head temperature, exhaust-gas temperature, fuel flow, and outside-air temperature, and manipulates the ignition timing, rpm, and fuel flow to optimize efficiency (see "Airframe and Powerplant: Bag of Chips," January Pilot). Not wanting to remove too much control from the pilot, EPiC-equipped aircraft will have a flight mode switch that allows the pilot to select between performance optimized for speed or economy flight regimes.
Unlike TCM’s FADEC, EPiC relies on traditional mechanical systems for backup, thereby negating the need for an independent electrical power source. Besides simplicity, this makes the system competitive in terms of installed weight. While the TCM FADEC system is expected to add many pounds to an airplane’s empty weight, EPiC will not. Dual-mode magnetos will continue to supply the sparks, and fuel delivery will be handled by a mechanical mixture control. When operating, EPiC controls overall fuel flow to all cylinders and doesn’t individually tailor fuel amounts for each cylinder. Since EPiC’s propeller governor is to be electronic, it will simply revert to the full takeoff power value if the electrics go out.
For turbocharged applications, EPiC will provide an electronic automatic wastegate actuator that will compensate for altitude and provide protection from overboost. If the system fails, the wastegate will default to a predetermined position.
EPiC is progressing through a 150-hour endurance test and is scheduled to be certified by the end of the year.
GAMI’s Prism
Finally, there are the folks at GAMI, makers of the GAMIjector replacement fuel injector nozzles. GAMI’s pressure-reactive intelligent spark management (Prism) system looks at pressure pulses within an engine’s cylinders via a fiber-optic cable, which sends the information back to a computer (see "Airframe and Powerplant: Heat, Light, and Sparks," February Pilot). The computer will alter ignition timing as necessary to optimize the combustion pressure event.
Unlike the other systems, which make engine management a no-brainer, Prism allows the pilot to have complete control of rpm and mixture to provide a very wide range of operating parameters. In other words, if the pilot wants to run the engine at lean-of-peak power settings, the computer will optimize the timing for such an operation while increasing the already-improved fuel economy. What’s more, the system can recover much of the horsepower lost in normally aspirated engines by operating on the lean side when manifold pressure is limited by altitude.
This combustion pressure control also offers the potential to allow an engine to use higher-compression pistons to improve power at altitude without busting the maximum cylinder pressures during takeoff or high-power operation. Another side benefit is that if unleaded fuels become mandated, Prism simply adjusts the timing to allow the engine to run on whatever is in the tanks while still guaranteeing detonation protection.
Prism will be powered by the GAMI Supplenator, a self-exciting minialternator that will mount on one of the vacated magneto pads on the engine. The aircraft’s electrical system becomes the backup system. A side benefit of this setup is that the Supplenator will have enough surplus power to run both Prism and take over some of the aircraft’s load in the event that the ship’s power fails. Prism has the potential to increase engine life by keeping peak cylinder pressures at bay.
Prism will appeal to those pilots who don’t want to lose the freedom to operate their engines at a seemingly infinite combination of power settings. Prism isn’t flying on an airplane yet, but GAMI recently opened a high-tech dynamometer test facility in which a Continental TSIO-520 has logged more than 50 hours under Prism control. A two-cylinder test engine logged hundreds of hours under the control of Prism.
GAMI is pushing for joint certification of Prism and the ability for Prism-controlled engines to use 100LL and 100LL with the lead additives removed, which is capable of about 91 to 92 octane. The advantage to the no-lead 100LL is that it is already compatible with rubber fuel system components. If all goes well, certification could come by the second quarter of 2001. At that point we may see Prism offered as an STC available for retrofit on existing aircraft and an option on factory-new airplanes. GAMI says the cost will be compatible with other FADEC systems.
FADEC systems are born of both necessity and the need to bring aircraft engine technology out of the World War II era. Not only will these systems bring fresh technology and increased efficiency to our flying, but they will also will also reduce pilot work load and smooth the transition to unleaded fuels.
Next month’s "Future Flight" will explore tomorrow’s airframes. Links to other articles about future engine controls can be found on AOPA Online ( www.aopa.org/pilot/links/links0006.shtml ).
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