The world of light aircraft engines is defined by The Big Two: Lycoming and Continental. Although the powerplants produced by these two companies are outwardly similar, the engineering cultures couldnt be more different.
Continental has always had a flare for engineering creativity and experimentation, both in entirely new products and improvements to engines already in production. (The quotes are intentional; TCMs taste for innovation hasnt always had happy outcomes for customers.)
Lycoming, on the other hand, at least for the decade of the 1990s, has followed a developmental path as staid as the gray paint used on its new engines. Even as the company geared up for Cessnas re-entry into the market five years ago, it continued to downsize the workforce at Williamsport, eschewing serious new product development.
It did hire on some additional engineering help but even at that, Cessnas sport Lycoming engines that have changed only incrementally over the previous two decades.
Like every other manufacturer, however, Lycoming is listening to the rumble of customers who say they want better engine technology, specifically the aviation equivalent of the electronic fuel and ignition systems that have been standard on cars for decades.
Curiously, at some point in the recent past, the idea of electronic ignition systems for aircraft piston engines evolved from the not likely to the inevitable seemingly overnight.
Having accepted engine high-tech as a given, the question becomes: How to get there?
When we visited Lycoming recently for a progress report on the companys electronic fuel and ignition systems, we were as interested in what we didnt hear as what we did hear.
Absent from the Lycoming lexicon is the acronym FADEC, or full-authority digital engine controller. Instead, Lycoming uses the generic term EEC or electronic engine control. (The official proprietary name for this system is EPiC or electronic propulsion integrated control.)
Thats a mouthful and calling it something different than a FADEC may seem like a difference without distinction. However, Lycomings approach is fundamentally different than Continentals and, depending on how these systems perform in the field, it could conceivably give one company an advantage over the other.
Continentals system-an evolution of the electronic controls developed by Aerosance, a tiny start-up company bought by TCMs parent company-will eventually be available to all comers, including Lycoming customers. The Lycoming system, on the other hand, is designed specifically only for Lycoming engines. Presently, there are no plans to certify it for TCM engines.
The difference between a true FADEC-which the Continental system is-and Lycomings EPiC lies primarily in how the two designs approach the issue of reliability. Traditionally, modern jet-engine FADECs run the entire show and without them, the engine will run poorly, if at all. Jet FADECs are thus multi-channel affairs with redundant electronic back-up.
This is essentially how Continental has designed its piston-engine electronic control, with redundant electronics and a back-up electrical power source; a second conventional aircraft battery. The Lycoming system relies entirely on mechanical reversion, including a back-up fuel distribution system and magnetos capable of generating spark via electronic means or conventional coil and mechanical breaker points.
LASAR Mags
While Continental bought its partner in the electronic control biz, Lycoming has teamed up with Unison Industries, which manufactures Slick magnetos and pioneered the first baby step into electronic engine controls, the LASAR magneto system.
Certified in 1995, the LASAR added automatic spark advance to the magnetos traditional fixed timing. In theory, this allowed faster starting-the addition of higher spark energy during cranking helped-smoother idling and modest fuel economy gains in cruise, provided the engine was leaned correctly.
But leaned correctly has always been elusive for pilots and so were the economy gains of LASAR mags. Although the LASARs have proven relatively reliable in the field, among the major manufacturers, only Diamond Aircraft has opted for LASAR mags in its new DA40 Star and then only as an option. Our interviews with LASAR owners and engine shops selling the system indicate that its performance gains havent been dramatic, other than quicker starting.
Recent engine research seems to support the view that aggressive advanced ignition timing isn’t, of itself, enough to produce worthwhile economy or power gains. Lycoming hopes that the EPiC system will add the missing ingredient: Leaning appropriate to both the state of flight (climb, cruise) and ignition advance.
Fuel Control
Like the Continental system, the EPiC design is closed loop, meaning it uses input from engine sensors and then adjusts the fuel-air ratio and timing to achieve optimum performance. In this case, optimum performance is defined as the most power for the least fuel, but remaining within programmed limits, such as CHTs.
Eventually, the system will have accelerometer-based knock sensing so it should be able to handle lower-octane unleaded fuel, if the stuff ever becomes a reality.
The EPiC system samples manifold pressure, RPM, induction temperature and pressure, fuel pressure and temperature and cylinder head and exhaust gas temperatures and fuel flow and is thus able to calculate optimum performance based on local density altitude conditions.
Optimum operation, however, is still determined by fixed values written into the software. Other than economy versus performance leaning, the pilot has no control over it.
Leaning is done electronically, through a single pulsed valve. From the fuel injectors backward, the fuel system is stock Lycoming, including the fuel distribution spider. Forward of that, however, the electronically controlled valve is a variable duty solenoid whose pulse width can be precisely varied to meter fuel according to what the systems computer thinks is optimum. (The TCM system uses pulsed/timed injectors instead and can conceivably meter fuel on an individual cylinder basis, which the Lycoming system cannot do. It thus depends on good air distribution.)
Using input from its sensors, the computer also controls ignition timing, using a maximum advance of just under 30 degrees in the economy cruise mode. Where the LASAR mag marched to its own tune called only by manifold pressure and RPM then set timing against a fixed performance map, leaving the pilot on his own for leaning, EPiC automatically draws all the parameters together, setting leaning and timing for best performance.
How lean? As currently construed, the EPIC system will have two modes-performance and economy-both controlled by the pilot via a selector switch. In power mode, the system will lean to Lycomings recommended best power setting. This is generally 100 degrees rich of peak EGT, but it varies by engine and aircraft. If the switch is left in performance mode, the engine will run no leaner than that setting.
In economy mode, the system leans to peak EGT, although this may vary somewhat by aircraft installation. Lycoming generally approves peak-EGT operation for all of its engines but has no official view on lean-of-peak EGT operations. In any case, says senior engineer Scott Armish, there are currently no plans to program lean-of-peak engine operation.
Should a ham-fisted pilot attempt to takeoff in economy lean mode, EPiC will automatically compensate, enriching the mixture to remain within CHT limits.
Failure Modes
In keeping with its conservative engineering philosophy, Lycoming has designed the EPiC system with mechanical rather than electronic reversion. Where a traditional FADEC has one or more back-up channels, the EPiC system is best thought of as a two-mode system: Electronic and mechanical, either of which will run the engine.
Should aircraft power fail, the LASAR mags revert to their fixed-timing mechanical mode while the fuel simply bypasses the electronically controlled pulse valve and is piped through a component that essentially performs the task of the Bendix/RSA fuel servos found in Lycomings injected engines.
In electronic mode, the fuel unit serves as the engines throttle body. In mechanical mode, it also distributes fuel to the injection system. What about leaning in back-up mode? It depends. Initially, the EPiC system will be three-lever, meaning engines will have conventional throttle, prop and mixture controls. As the system evolves, Lycoming will develop an electronic prop control, eliminating the blue knob. But the mixture control will likely remain.
In electronic mode, the mixture control will have no effect, other than shutting the engine off when moved to idle cutoff. (Youll also have to select manual leaning mode during shutdown. )
In reversion mode, the mixture will control the back-up fuel system, allowing conventional leaning. In engines eventually equipped with electronic prop governors, the prop will revert to max RPM in the event of a failure.
Although both EPiC and Continentals FADEC may eventually reduce pilot workload, both of these systems may initially increase it somewhat, requiring a basic understanding of how the systems work in order to respond to any failures.
In the TCM failure scenario, a system failure may or may not require an expedient landing. The FADEC is equipped with a mode annunciator that gives the pilot general information on health status; itll be up to the pilot to interpret that. An electrical system failure puts the entire TCM FADEC on the back-up battery, making an expedient landing advisable. (Future TCM systems may be designed with dual alternators but the initial certifications will be dual-battery.)
Lycomings EPiC, on the other hand, will run in mechanical mode for as long as the fuel lasts and you could, conceivably, even take off in limp home mode. The most significant limitation may be loss of RPM control on engines equipped with electronic prop governors. EPiC will also eventually include a turbocharger controller and it too would revert to wastegate open, zero boost in the event of electronic failure.
In addition to the performance/economy switch, the EPiC system will also have a simple warning annunciator system. The prototype we were shown had three lights; green for normal, yellow for caution-indicating some form of unspecified failure-and red for complete system failure. Lycomings Randy Jenson told us the annunciator design may change by aircraft type and customer.
However, the EPiCs controller will have provisions for system data output in serial form, so presumably some clever aftermarketer could design the mother of all engine monitors. (Insight and JPI, take note.)
Performance
Thus far, the EPiC system has accumulated some 79 hours in the test cell and has flown for about three hours. Lycoming is cagey about whos flying the system but did allow as how it was a customer in a IO-540 equipped airplane of some sort. Just guessing here, we would say there’s a Cessna 206 out there tooling around with a prototype EPiC aboard.
We didnt see any performance specs on the system but Lycomings Armish reports that initial tests revealed no surprises and fuel economy improvements in the 10 percent range. This is consistent with results TCM has achieved with its FADEC.
Interestingly, when we first flew the LASAR system in 1996 in an instrumented Cessna 172, we observed the performance gains-chiefly an 8 percent reduction in fuel flow at the same apparent power-that Unison claimed for the LASAR system. Lacking any confirmed data, we think Lycomings initial modest claims are credible and we wont be surprised if theyre able to better them a bit.
Off to Market
Although Lycoming announced EPiC nearly two years ago at Oshkosh, the product is only now entering its certification trials. Actually, given the scale of the developmental task, thats not a bad showing, if the system makes it to market later this year or early next year in some form. By years end, Lycoming expects to have 25 systems flying in trials.
Wisely, Lycoming plans to significantly exceed the FAAs minimum 150-hour test cell certification run. This conservative approach is one reason the new Cessna 206 was certified with the IO-540 engine, not the IO-580 as originally planned.
Lycoming says there were too many unknowns in the initial test runs of the larger engine and Cessna was talked into sticking with the proven 540. (Pure speculation, of course, but 206 owners should be forever grateful.)
In our view, Lycoming is also doing the right thing in certifying EPiC on large displacement engines first, since its likely to be a somewhat pricey add-on whose benefits wont be as attractive to owners whose engines burn a mere 10 gallons per hour. Unisons initial certification of the LASAR on small displacement engines may have hampered its market entry.
When it announced EPiC, Lycoming said it would be competitive with-but not necessarily cheaper-than a conventional fuel and ignition system. Bottom line, then, there is no bottom line on price just yet.
Economics and competition being what they are in the little airplane market-which is to say intense-our blue sky guess is that the EPiC system will be comparable in price to the TCM FADEC, which will cost $5000 for four-cylinder engines and $7000 for six-cylinder powerplants.
Unlike the TCM system, which requires an additional power controller for the extra set of cylinders, the EPiC system varies little between four- and six-cylinder models, needing only an extra pair of ignition leads and fuel lines.
It is thus somewhat lighter than the TCM FADEC and adds only a slight weight gain over conventional fuel and ignition systems.
In our March 2000 flight report on TCMs FADEC, we noted that if any or all of these systems perform as claimed-or even close, for that matter-the economics are compelling, at least for high-performance aircraft.
At 150 owner-flown hours a year, fuel savings on a large-displacement engine could total between $500 and $600, paying back the cost of the system during a typical TBO run of 2000 hours.
There are other potential-but as yet unproven-benefits. Lower magneto maintenance may be one of them, although with its moving parts and conventional points, the LASAR mag may not be a strong player in this regard. (The TCM system may have the advantage in potential lower maintenance, if its all-electronic master power controllers prove to be reliable.)
One of the hoped-for-but as yet unproven-benefits of electronic engine controls is improving the odds of making TBO. If we can keep the engine from overtemping, keep too much fuel from washing down the cylinder walls and operate the engine optimally, thats good, say Lycomings Randy Jensen.
But we don’t have any data on that and we arent making any claims, he adds. As we reported in the March 2000 issue, electronic engine controls represent risky development for Lycoming and Continental. The research is expensive and the payoff is hardly assured.
A third company, General Aviation Modifications, is pursuing its own system, which relies on variable timing to control the engines peak pressure pulse. At least two of these systems will be certified for both Lycoming and Continental engines very soon after they emerge, although Lycomings system seems destined only for its engines at the moment.
Although all three systems get to the same place-fuel economy and thermal control-each does it via different means.
To us, this represents genuine market choice and were looking forward to a flyoff in the next year or two.
Contact- Textron Lycoming; 652 Oliver St.; Williamsport, PA 17701; 570-327-7045; www.lycoming.textron.com.
