Lycoming IE2: Incremental Technology

Its as close to a clean-sheet engine as youre likely to see in the current market. But what it really does is adapt mainstream auto technology to airplane engines.

The modern car engine-even a cheap one-is such a marvel that you can turn the key without thinking about its once-in-a-million failure-rate ECU, its direct-fire coils and fuel injectors that can paint the Mona Lisa in 93-octane pulses. Oh, and if you cant get 93 octane, no worries, the ECU will adjust the timing to burn 91.

Were it so simple with aircraft engines. And not that Lycoming and Continental havent tried to make it that simple and they

are still trying. Lycomings latest and most sophisticated attempt is the new IE2 for integrated electronic engine. Integrated means electronically customized for the airframe and dancing cheek to cheek with the airplanes EFIS and it also means full-bore electronic control of nearly everything. Lycoming has been at this awhile, some three years, but the project only recently came out of the ground in Lancairs new flagship Evolution, a behemoth of a pressurized 230-knot kit airplane. The IE2 will be the Evos centerpiece and Lycoming plans to move smartly forward with certification for other aircraft requiring high-horsepower engines. Its not impossible to imagine this engine in certified form in a year to 18 months and we wouldnt be surprised to see Piper offer it on the Mirage or some other manufacturer to offer an airframe molded around the IE2. The timing on that just feels right.

Its not that the IE2 is such a spectacular leap forward in aircraft propulsion. It isn’t. What it is is a thorough application of automotive-type technology to yield an evolutionary improvement in the pilots ease of use and measurable improvements in performance and economy. Lycoming is not rewriting the laws of physics here, but simply bringing aircraft internal combustion into the 21st century. Lycoming is betting that the market timing is right, what with the high-octane fuel worry overhanging the sales like the grim reapers scythe and with more owners plainly saying that they want engines that are easier to operate and more economical. (Then again, theyve always said that.)

Maintenance reliability plays into the marketing attraction, too. Theoretically, with the engines built-in protective algorithms against overtemping and overrevving, the engine wont be subjected to abuse by a ham-fisted pilot. Further, the ECUs are sucking up and storing a lot of data, transmitting some directly to the cockpit for the pilots real-time analysis and storing a lot more for use by techs to diagnose maintenance issues, using a code-type system similar to modern cars.

No Magic Bullet

While the IE2 promises to be several things, it is not a panacea for the lack of 100-octane fuel. As we reported in the July issue of Aviation Consumer, Lycoming general manager Michael Kraft is clear about one thing: No matter how clever or how effective, electronic controls wont address the loss of six to nine octane points. As far as octane management, FADEC-type

controls are adequate around the margins, but in Lycomings view, they wont allow a 350-HP engine to run on 94-octane unleaded fuel.

While this idea was a prime mover for Teledyne Continentals work on its own FADEC, the PowerLink system, Lycoming says it has a different agenda for the IE2. Specifically, it sees the octane issue as part of the picture, but the IE2 is intended to be core technology to make Lycomings entire line of engines easier for pilots to fly, more economical to operate while taking weight and cost out of the airframe.

We get the weight part, but does Lycoming really think electronic controls will be less expensive than iron magnetos? It does. Recurrent maintenance on magnetos and traditional fuel systems-mostly the mags-piles up the bucks on the way to TBO. The electronics, although more expensive to install, are expected to lower to-TBO mainteance costs, plus provide some fuel economy. Lycoming views the IE2 not as a bolt-on FADEC, but a leap beyond first-gen piston electronics. True clean-sheet engines don’t come often from either Lycoming or Continental, but the IE2 may very we’ll be a practical example of just that.

No Surprises

When we pored over the IE2 at Lycomings test hangar in Williams-port recently, we saw more or less exactly what we expected to see: an iteration of state-of-the-art automotive electronic technology adapted to a 350-HP TIO-540 to morph into the TEO-540. But its not an off-the-shelf 540. The crankcase and cylinders are purpose-made for the electronic controls and the accessory case and gearing would be unrecognizable to a mechanic whos wrenched a 540.

By automotive standards, the IE2 is about on par sensor wise. But it doesnt need the oxygen sensor circuit nor the transmission conrols found on modern cars to improve fuel economy. The basic inputs are venturi pressure and temperature for mass airflow calculation, MAP, induction temperature, CHT, TIT and RPM. For crankshaft and top dead center reference, the IE2 has two magnetic position sensors, one on the crank and one on the cam. They sense crank position by magnetically detecting a missing tooth in the gear train, but unlike Hall-effect sensors, they arent powered, thus eliminating at least one failure point.

Speaking of power, its delivered to the engine via a dedicated dual-channel power box that can run the engine either from the aircraft bus or from the default position-a dedicated permanent magnet alternator installed on the accessory case. The engine is designed to run independently of aircraft electrics, although it doesnt have to. It has provisions for an additional alternators on the accessory case or via front-belt drive.

Starting with the air, gone is the traditional Bendix RSA throttle body and injector system. In its place is a throttle body that still has hard linkage to the power lever, but one thats equipped to measure mass airflow and temperature, with redundant temperature sensing capability, since air density and flow is such an important player in power setting. The engine control unit is housed in a single box the size of a thick netbook and is dual channel-either channel can run the engine. The ECUs use sensed throttle position as a target reference for the pilots power command, then the mass airflow data is used to fuel the engine accordingly by referring to a customizable look-up table and fine tuning that according to a feedback loop with programmed limits and protections.

The IE2 uses electronic pulse injectors whose reliability in automobile use has been raised to nearly failure-proof levels. These run from a common rail at a pressure of 3 bars or about 43 PSI.

This fueling option adds a measure of reliability because the

engine is set up to run each cylinder as an individual power unit-if one fails, either due to fuel or ignition, the other five will continue running as smoothly as the software can make them. The system is configured with return lines which circulate fuel as a hedge against vapor lock.

Ignition still terminates in two plugs per cylinder, but rather than mags or remote spark generation, each plug has its own direct-fire coil similar to the high-reliability type found on modern motorcycles. In automotive and motorcycle apps, direct-fire coils usually attach to the plug, but on the IE2, there’s no room for that. All of the coils-12 total-live in an array mounted on top of the engine where the fuel injection spider would otherwise be found. As youd expect, the ECU channels cross control, so if one fails, the other can still fire at least one plug in each cylinder.

Mechanically Different

Although the engines overall dimensions and its bore and stroke and combustion chambers havent changed, the IE2 gets its own purpose-manufactured cylinders, crankcase and accessory case design. The cylinders have been modified to accept both the pulse injectors and acoustic knock sensors, so these represent new production parts. Further, the crank and cam are fitted with magnetic position sensors and the accessory case has completely revised gearing, eliminating the mag drives entirely and providing space for the PMA and the fuel pump for the injector system.

When Continental pioneered its FADEC 15 years ago, it took baby steps-leaving prop governing and wastegate controls for future iterations. It used largish, remote ignition modules installed behind the engine. But Lycoming isn’t doing any of this, since its goal is simple, single-lever operation for the pilot right out of the box. The prop control is on the front of the engine and is an electro-hydraulic design controlled entirely by the ECUs. So is the wastegate, a single unit in the IE2 version we looked at. The engine has dual turbochargers.


When we probed about the IE2 operating strategy, we learned that Lycoming wants to change the conversation about lean-of-peak versus rich-of-peak operation, preferring instead to say that the IE2 runs at the best efficiency for whatever power level the pilot has commanded. In a nutshell, that means it fuels heavily for takeoff and climb, backs that off in high-power cruise and runs lean of peak when it senses the pilot has pulled the throttle back to improve economy.

We didnt get a detailed look at the fueling map, but engineer Jim Morris explained that the fueling schedule-as least the version developed thus far-is designed to compromise between the best efficiency and acceptable temperatures. At high-power cruise, it appears to be running rich of peak, based on the fuel flows we were quoted. But when the pilot pulls the throttle back, the ECU smoothly adjusts RPM and fuel accordingly until, at some point, it fuels around the peak CHT spike just rich of peak and transitions to lean of peak operation. The prop RPM change is a smooth enough ramp not to be noticed by the pilot, although the fueling happens almost instantaneously. But unlike the Cirrus approach of running Continental engines lean of peak at high power, the IE2 goes lean only at lower power settings, probably around 65 percent or lower.

Morris declined to say what brake specific fuel consumption Lycoming is expecting with the IE2, but he noted that initial data shows that the Evolution can run at nearly 200 knots on 12 GPH at altitude. Without knowing the power output or much about the Evos drag, we cant calculate a BSFC, but our

bluesky guess is around .4 to .41, which is an efficiency improvement over the typical 540-series engine.

Limits and Protections

Following the automotive paradigm, the IE2 has various limits and protections built into it. Obviously, traditional aircraft engines limit revs through the prop governor, albeit somewhat crudely. The IE2 has a hard electronic rev limiter, just like a car does. This value can presumably be set by the engine installer or OEM for different engine setup, but if the engine gets outside the governors range, it backs off the fuel first, then interrupts the ignition. The pilot would notice this a brief burble, if it were noticed at all.

CHT is also an automatic operational limitation. The upper end limit is 450 degrees F, but normal operation is allowed up to 420 degrees F. When the limit is reached, the ECU adjusts first with fueling-richer or leaner, presumably based on throttle position-followed by slightly retarded timing. For starting, by the way, the IE2 retards to 5 degrees BTDC from its base advance of 23 degrees BTDC. This results in reliable, car-like starting whether the engine is hot or cold. It also figures out starting fueling based on engine temperature.

In our view, the most intriguing aspect of the IE2 is its individual acoustic knock sensors. These are obviously a play toward allowing lower octane or, as Lycoming says, to make the engine not limited to 100LL. But that doesnt mean mogas and it doesnt mean 94UL. It does mean a few octane points under 100. Lycomings corporate view is that the industry needs to move toward a 100-octane solution to the loss of 100LL.

Acoustic knock detection has been a difficult nut to crack for air-cooled aircraft engines because their inherent vibration signatures make pinging difficult to extract from the hash of background noise. But knock sensors have gotten better and there’s more processing horsepower available to separate the wheat of pinging from the chaff of banging valve trains and the whirr of gears. In any case, with individual cylinder knock detection, the IE2 suppresses detonation the same way it handles high CHTs-first with fueling, then with timing adjustments.


If you were hoping Lycoming would produce a radical, watercooled and super-efficient engine that would turn the aircraft industry on its ear, the IE2 is not that. In our view, if Lycoming had launched such a project, we would view it as running off a cliff. Such an engine would require vastly more investment than the IE2 will, OEMs don’t seem to be clamoring for it and even if they were, we doubt if it would ignite sufficient demand to justify the cost of developing it in the current market. In a few years, maybe.

Lycoming (and Continental) have to be mindful of the 100,000-plus engines each of it continues to support in the legacy fleet. While those engines represent a millstone of sorts, they also represent a profitable installed base. New airframes-including TAA models like the Cirrus-still tilt toward conventional powerplants that don’t require liquid cooling systems and heavy investment in a retooled service network.

In this context, we like what we see thus far in the IE2. It appears to be a logical, well-engineered incremental step toward improved performance and economy on what are, in the end, relatively efficient and reliable base engines.

Some years ago, a watercooled engine Continental developed for Dick Rutans Voyager project became known as the Voyager engine. If the IE2 is successful and becomes known as the Evolution engine, we think Lycoming will have hit just the resonant note it seems to be aiming for.