by Paul Bertorelli
Two thousand years from now, after mankind has incinerated itself with weapons yet to be invented, only two things will remain: cockroaches and magnetos. And we wouldnt be at all surprised if theyre the fixed timing variety, not the sort with electronic advance. (Repetitive 500-hour inspection ADs will, no doubt, still apply.)
Three years ago, when we first began reporting on the emergence of full-authority digital engine controls, we confidently predicted that by 2003, youd have your choice of at least a couple of systems with more choices waiting in the wings. This technology has a certain inevitably to it and we expected buyers to be won over in onesies and twosies, if not in droves.
Well take our crow with a side order of onion rings and a cold Sam Adams, thanks. In reality, FADEC isnt happening at anything like the modest pace its designers seem to have hoped for. Only one system-Aerosance/Continentals PowerLink is flying, with limited certifications and a handful of installations. A second, the Lycoming EPiC, has been temporarily parked pending a sniff of interest from the market and a third, GAMIs PRISM, churns away on the test stand but hasnt flown yet. (Given buyer indifference, were not sure thats a bad thing.)
Why arent these systems being snapped up or at least nibbled at? A half-dozen reasons come to mind: Item one: the shrill, sky-is-falling press reports on the demise of 100LL-yes, we did our share-seem to have been premature by, say, 20 years. Item two: without the crying need to burn lower-octane, lead-free gas, the advantage of an expensive FADEC may appear elusive at best, invisible at worst. Item three: none of the major OEMs have jumped on the FADEC bandwagon and until that happens, FADEC may not get the marketing push it needs to get off the dime. Item four: the much vaunted single-lever power control may be turning out to be a yawner. Item five: diesels are making gains. In Europe, they may edge out interest in FADEC for gasoline engines. Item six: power gains possible with FADEC controls through the use of higher-compression ratios havent yet materialized.
What follows is a status report on the state of piston-engine FADEC and a brief technical comparison of the three systems.
• Company: Aerosance/Teledyne Continental
• System name: PowerLink
• Type: Dual-channel FADEC
• Flight status: 30 systems flying
• Certified: Yes; approvals list is growing.
• OEM takers: Three
• Cost: $10,000, minimum
• Technical plusses: Eventually, a true single-lever system requiring minimal pilot input; allows selection of power or economy settings, at least in some aircraft.
• Technical minuses: Complex, sensor-rich system; electrical reversion only; no options for pilot selection of novel operating modes, such as unique RPM or mixture settings.
In keeping with its philosophy to experiment freely with new engine technology, Teledyne Continental has led the current movement toward electronic engine controls. In 1998, it bought a small start-up company called Aerosance, which had been specifically launched to develop FADEC.
The engineering talent came in part from Hamilton-Standard, a company familiar with the multi-channel FADECs typically used in jets and turboprops.
The Aerosance-developed system is called PowerLink and has been certified to one degree or another since 2000. Its a dual-channel closed-loop FADEC but unlike the Lycoming and GAMI systems, the design impetus has been toward less rather than more pilot control options. In its most refined iteration, PowerLink is a true single-lever system.
PowerLink is best thought of as FADEC on the automotive paradigm, relying on pulsed fuel injection and variable timing to achieve the multiple goal of better fuel economy, lower octane requirement, thermal stability and ease of operation.
Of the three systems, we consider it to be the most complex and intrusive to install, since it requires opening up the engine accessory case to install sensors and the engine room itself must accommodate largish units called MPCs or master power controllers.
Theres one of these for every two cylinders. The MPCs house the spark generation apparatus-automotive-type CDI-and the control brains for the pulsed fuel injection system for each of the two cylinders it controls.
The Aerosance design is sensor rich with quite a bit of wiring, in our view. It has a Hall effect sensor behind the cam gear for crank position sensing, manifold pressure and temperature sensors, fuel pressure, EGT and CHT sensors and RPM sensing. Flight critical sensors are duplicated and although there are provisions for knock sensors, they havent been used yet.
All of this data is plugged into a closed-loop system whose overall goal is maximum efficiency with minimal thermal spiking. In other words, it aims to keep temperatures as stable as possible.
How does it do that? It manages each cylinders power output and mixture through a combination of sequential fuel injection and variable timing. From what were able to determine, PowerLinks control laws-which are embedded in fixed look-up tables or maps -are similar to the Lycoming EPiC. At idle, climb or max cruise, it leans to essentially best-power, which is 75 to 125 degrees rich of peak EGT.
Aerosances Steve Smith sounds vaguely fed up with endless arguments about lean-of-peak versus rich-of-peak. He insists that PowerLink runs the engine at the most efficient settings for the phase of flight, regardless of lean state.
He tells us most installations have included a power/economy selection switch which gives the pilot some control of the leaning fuel schedule but nothing approaching what you get with the mixture knob. In fixed-pitch applications, the selection switch is linked to the power lever. At 95 percent of full throttle movement, the system commands best-power leaning. If the lever is backed off, the PowerLink leans and times according to RPM. At higher speed, its best power and at lower speed, its best economy, which can be lean-of-peak EGT.
As with the EPiC system, leaning is done electronically by varying the pulse width of the injected fuel at the injector, just as is done in the typical mainstream car engine. In true single-lever systems, RPM control is thrown into the closed loop mix but the pilot has control of only slow-or-go with the throttle.
Theres no means of selecting novel RPM or mixture settings unless the OEM demands a two-lever system. (The electronic prop governor is still a developmental item.) Back-up is electric, using two alternators and/or a dedicated battery to run the system
Weve flown the Aerosance system twice-in a Cessna 210 and a Liberty XL2-and talked to both an owner and a shop who have installed it. The engine shop we interviewed, Penn Yan Aero, had some beefs about technical support during installation-it left much to be desired-but reported that the system worked as claimed once installed. We also spoke with Ken Bartoo, who installed a PowerLink system on the O-360 in his RV-6 experimental and has flown it some 500 hours.
Bartoo validated Continentals claims of 10 to 15 percent fuel savings and he reports longer spark plug life and, apparently, cleaner oil. He has experienced no sensor failures, which is a worry in a system this complicated.
Personally, I dont see why you wouldnt want the FADEC. Im going with it again, he said, as he considers building another airplane.
Bottom line: the Aerosance system seems to deliver on its claims but even though it has been available for more than two years, it hasnt found many takers. Reliability appears good but flight experience is limited.
• Company: Lycoming
• System name: EPiC
• Type: Single-channel FADEC
• Flight status: Test only
• Certified: No
• OEM takers: None
• Cost: Unknown
• Technical plusses: Somewhat of a modular, customizable system depending on OEM/customer desires; moderately sensor-intensive; mechanical magneto reversion mode; could be a one or two-lever system.
• Technical minuses: Complex compared to PRISM; some sensors are critical; requires a modified intake manifold and back-up fuel delivery.
Lycoming has traditionally been less adventurous in fielding new technology to what has essentially been a stagnant market for the past three decades. Indeed, it has proposed various initiatives-a joint venture with John Deere in the 1980s to pursue a rotary engine and, more recently, a diesel project with Detroit Diesel-only to abandon these efforts in the face of lackluster market interest.
And once again, Lycoming is pulling in its horns or, more accurately, putting developmental work on hold until the market decides what it wants. With considerable fanfare in 1998-five years ago-Lycoming announced another joint venture, this time with Unison, which makes the LASAR magneto system, to produce an electronic engine control. Lycomings technology is called EPiC for electronic propulsion integrated control.
By the summer of 2000, Lycoming and Unison had developed a prototype system which had been run for 79 hours in the test cell and had flown for 79 hours in a Cessna. (See the July 2000 issue of Aviation Consumer for more detail.)
Since then, the company has continued to refine the EPiC system, accumulating more flight and test cell hours and advancing development to the point that its ready to proceed into certification. The hardware is nearly production ready but Lycoming tells us the project has essentially been shelved, awaiting indications that anyone is interested in having more than one or two electronic engine controls.
Lycomings Mike Wolf told us that EPiC has been shopped to the major aircraft manufacturers who have thus far shown no interest. Until one does, says Wolf, Lycoming wont pursue certification. Lycoming and Unison continue to search for viable applications or for STC installations that would justify the expenditure of limited resources, Wolf told us. At this time, it is on hold as we pursue other product development options, he added.
Given the short history of electronic controls for piston aircraft engines, Lycoming and Unison can hardly be blamed for their reticence. Eight years ago, Unison introduced the LASAR magneto, which garnered favorable press reports even from us. The LASAR system-for limited authority spark advance- applied modest electronic control to a conventional magneto to allow variable timing according to a fixed performance map. According to our tests, it delivered measurable but hardly dramatic fuel savings over conventional magnetos and higher spark energy at start-up. But buyers have found the LASARs benefits to be elusive and it has not been a strong seller for Unison.
On the other hand, Unisons LASAR mags do serve as the basis for the EPiCs spark and they alone provide mechanical reversion for back-up, if the electronics fold up or the power fails.
EPiC is similar to the Aerosance system in that it uses input from multiple sensors-EGT, CHT, manifold pressure, RPM, induction pressure and temperature and fuel flow-to adjust engine performance to a set of fixed parameters.
The system has acoustic knock sensors and is programmed to maintain pre-determined CHTs by manipulating spark timing and fuel flow. Technically, says Unison, EPiC is not a closed-loop system, since it relies on performance maps.
Fuel is handled essentially by the stock Lycoming Bendix/RSA injection system but with one important distinction: Like automotive systems, EPiC has electronically controlled pulsed fuel injectors whose pulse width can be precisely metered to control fuel flow and thus leaning.
In the EPiC system, leaning is continuous and automatic to one of two settings: best power or best economy. Applying CHT limits and EGT sensing, the system will lean automatically at high power settings and in climb. Best power is Lycomings standard, 100 degrees rich of peak EGT while best economy is at peak EGT.
With no mixture control, how do you select one leaning mode over the other? Possibly using a two-position switch, as the Aerosance system does, says Lycomings Rick Moffett. Possibly doesnt mean that Lycoming hasnt figured out how to do it but that the decision is in limbo, pending specifications by airframers. Moffett says there are many ways to configure EPiC and Lycoming sees no point in further experimentation until the airframers declare an interest. He says the system can be configured as a single-lever power-control set-up or a two-lever system, according to customer wishes.
Interestingly, Moffett reports that when the single-lever idea was shopped to OEMs, at least one noted-correctly-that a single-lever system makes compromises that preclude owners from operating the engines in certain ways, say a high-RPM, high-power cruise into a strong headwind. The same OEM allowed as how that might be a hard sell, especially if the system sells for a premium over magnetos, as Lycoming says it will.
Moffett says EPiC has demonstrated faster, easier starting-especially hot starts-and fuel economy in the 10 to 15 percent range, which it achieves primarily by automatic control of fuel scheduling and not more efficient combustion. Beyond that, no other claims are made in terms of reliability over magnetos, cost effectiveness or improved maintenance reliability.
Bottom line: the system has test-cell hours and some flight testing behind it. The claims appear plausible based on tests described to us but not demonstrated. Although EPiC could be market ready, it isnt, since it lacks certification. OEM interest-or lack of it-seems to hold sway.
• Company: General Aviation Modifications, Inc.
• System name: PRISM
• Type: Pressure reactive spark control
• Flight status: Hasnt flown
• Certified: No
• OEM takers: None announced
• Cost: Unknown
• Technical plusses: Simple system with only one type of sensor; minimally intrusive, bolt-on installation; allows novel operating modes; no current option for single lever, meaning youre on your own for setting RPM and mixture.
• Technical minuses: The entire show rides on pressure sensors; no current option for single lever, meaning youre on your own for setting RPM and mixture.
No, we didnt mistakenly print the above sentence twice. Flying in the face of conventional if unproven wisdom, GAMIs electronic ignition system wont be a single-lever design and, in fact, it isnt even a FADEC, since it has full authority over only one thing: spark timing.
Fuel and RPM settings are up to the pilot. If you like fiddling with the red and blue knobs, PRISM is the system for you. If you dont, shop elsewhere.
GAMI has established its reputation with a line of balanced fuel injectors for Continental and Lycoming engines and it has become a think tank of sorts for advanced engine research. That research is-slowly-yielding the PRISM or pressure reactive intelligent spark management system, whose operating concept couldnt be simpler, despite requiring some hairy software to make it work.
GAMIs George Braly told us he unearthed non-proprietary engine research dating to the 1970s which describes how manipulating the position of the peak pressure in each cylinder relative to the piston travels top dead center-by spark timing-can dramatically effect power output, torque and efficiency.
Essentially, in PRISM, the spark is set to ignite the mixture at a point in piston travel that will allow it to do the most work for the least fuel burned. The desirable byproduct is lower peak pressures and, necessarily, lower CHTs, both of which should cause less wear and tear on the engine and increase detonation margin.
Pressure-based engine control has been well understood enough for Toyota and Nissan, among others, to have experimented with the technique but it hasnt been practically fielded in the automotive field. One reason for this may be that pressure-based control is computationally intensive and, second, with efficiency and emissions control as their holy grail, automotive engineers have favored closed-loop systems dominated by oxygen sensing to reduce unburned hydrocarbons in the exhaust.
The PRISM system has none of that. It has a single sensing mode-cylinder pressure-which it uses to adjust spark timing to plant the peak cylinder pressure 15 degrees past top dead center. Braly tells us that this allows the engine to make maximum torque for any arbitrary combination of fuel volume, octane, air and RPM.
In other words, you set the throttle, RPM and mixture where you want, the PRISM system times the ignition to optimize the pressure pulse at 15 degrees past TDC. As Braly sees it, theres nothing the pilot could do to harm a PRISM-equipped engine short of plowing it into the rocks.
Mechanically, as currently construed, PRISM will have a fiber optic pressure sensor for each cylinder fitted into a custom-designed Champion sparkplug. Although fewer sensors might eventually be used, until certification trials are complete, we dont yet know how many sensors PRISM will need to dispatch.
PRISM is powered by its own dedicated alternator, with the aircraft bus and battery as secondary and tertiary back-up. Spark comes from CDI packs bolted into the existing magneto pads and these units also contain a rotor which informs the system of crank position. Ignition reversion comes from the CDI coils; reversion is not software based but is variable timed.
Hardware wise, PRISM is minimalist. It has the smart box for the electronics, the two coil packs which bolt into the mag pads and the add-on alternator, with a control panel. Cost is unknown at this point, although Braly says it will cost more than magnetos and less than a full-blown FADEC.
Bottom line: although PRISM is inching through certification, it appears more distant from approval than the other systems and it hasnt flown yet.
Conclusion
In researching this article and talking to the various players involved, we were acutely struck by one overwhelming impression: FADEC development is bumping along but this technology isnt ready yet.
And the market is certainly not ready to accept it in a broad way. There currently is no choice in the market. Aerosance is out in front with certified systems but it hasnt fielded many, in our view, and it still lacks the electronic prop control and turbocharger controls that will complete the system to its full single-power-lever potential.
It seems to us that the strongest market for single-lever FADEC will be among large-displacement turbocharged engines with high-octane requirements.
As far as the single-lever idea is concerned, we wonder if the industry has sold itself a bill of goods on this concept. Its an appealing idea but in practice, if you cant fiddle to find an RPM sweet spot or set the mixture where you want it, will you be a happy customer? We have growing doubts about this and, apparently, so do Lycoming, Honda and, obviously, GAMI. (We would want to retain the blue knob, at least.)
One reason FADEC isnt generating a hot response is that theres a distinct lack of buzz about it. Potential buyers are aware of the systems, especially the Aerosance PowerLink, but they appear unaware or doubtful of potential benefits.
Aerosance, for instance, claims improved fuel economy in the 10 to 15 percent range, smoother operation and perhaps improved longevity due consistent temperature control. Well buy the fuel economy argument and the smoothness but the longevity claim remains unproven and it may be a long time before it is proven, if it ever is.
Longer TBOs and/or sweet warranty deals from the factory on FADEC-equipped engines might help stir some demand. So will some serious OEM interest from the likes of a Cessna, a Mooney, Cirrus or Diamond. STCs for FADECs on these airplanes are contemplated or underway but-and this is important-the factories arent yet involved. STCs dont carry the gravitas of factory standard equipment.
The OEMs believe the market is too price-sensitive to tolerate the add-on cost of FADEC. They want it for the same price as magnetos. The FADEC guys say this misses the point; you have to examine the long-term benefits of a better-running, more thermally stable engine, not to mention eliminating magneto failure and maintenance.
Thats nice boilerplate but owers still have to justify the cost. Running the numbers on the Aerosance system, were not convinced of the cost/benefit just yet. For a Bonanza, the system cost is typically $10,000, if installed at overhaul; add another $3000 to $4000 if its installed mid-stream. Three years ago, the numbers were estimated at $8000.
Allowing for a generous 15 percent fuel savings over a TBO run of 2000 hours, the net savings on a large-displacement engine might just pay for the system and that assumes it will need no major maintenance through TBO, something yet to be demonstrated. FADEC should be more reliable than magnetos-and require less routine maintenance. Again, neither notion has been convincingly demonstrated, thus buyer reticence is understandable.
Against this backdrop, Lycomings wait-and-see strategy with its EPiC system may make sense. We would like to the company field it into the experimental or STC market, however, just so the system can get some flight experience behind it. The same applies to GAMIs PRISM system. Weve visited the companys Ada, Oklahoma test cell and seen the real-time dancing graphs. We would like to see the system flying at least experimentally so the market will have a chance at generating what it now seems to lack: genuine excitement.
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