Development of new high-end aircraft—kitbuilt or production line, your choice—might leave you thinking that everybody has come down with a bad case of Turbine Fever. Why is that? They (turbines) don’t smell better. They don’t have better fuel economy. They’re not cheaper to buy or to maintain.
The prop is an 80-inch Hartzell Scimitar with blended airfoil technology and an aggressive blade twist to optimize performance at higher speeds.
So, what’s the big deal with turbines, and why does everybody want to fly one?
You may already know the answers, or at least the justifications: Turbine engines enjoy a reputation for being powerful, reliable and comparatively low maintenance—though, as suggested earlier, this doesn’t mean they’re inexpensive to keep. They don’t need tending quite as often as a high-power piston engine, but when they do, the costs are greater. Just ask the guy down the hangar row with the King Air.
A rapid and sustained transition from big piston engines to turbines in transport aircraft in the middle of the last century paints a detailed picture. Suddenly, maintenance needs went down as speed went up—way up—at the cost of fuel consumption (which we didn’t care as much about when fuel was cheap). The airlines never looked back.
That was then. In today’s world, turbines are often employed to give existing designs a substantial performance boost. Taking a high-performance piston engine from, say, 350 to 500 horsepower is a huge undertaking, particularly if you have durability in mind. But the difference between a 500-shaft-horsepower Pratt & Whitney and a 750-shp version is very little in weight along with extra fuel burn and a hike in purchase price—in fact, the larger the turbine, the more efficient it is. Reliability doesn’t suffer a bit. With modern controls, turbines are easy to operate and dead reliable at power levels that would eat a piston engine alive and leave a trail of oily debris.
It’s a short and easy climb onto the wing thanks to the step.
What if there was a piston engine that had the power you needed for, say, a pressurized four-place traveling machine, that was even easier to manage, far less expensive to buy than a turbine and potentially just as reliable? And how about notably more fuel efficient at the same time?
Pipe dream? Hallucination?
Not according to Lancair and Lycoming. Together, they are developing what the engine manufacturer hopes could be watershed technology for piston engines, called IE2. (The official spelling is “iE2,” but we’ll spare you the squinting.) This system, which we’ll describe in detail shortly, amounts to truly advanced electronic engine control of an otherwise conventional engine. Lycoming shies away from the FADEC—full authority digital engine control—moniker because, technically, the system doesn’t control everything electronically; the throttle plate is mechanically manipulated by the pilot.
The motivation for Lycoming is to highlight this technology in a demanding environment: a turbocharged, pressurized, go-fast machine that needs to have power for speed and, at the very same time, acceptable fuel efficiency for cross-country travel.
That’s Lycoming’s angle. The motivation for Lancair is to broaden the market for its amazing Evolution kit aircraft, which was introduced with a Pratt & Whitney PT6A that’s just as capable of clicking off trouble-free hours at 750-shp as it is at running your bank account down in six-figure chunks.
The G900X package keeps the panel uncluttered. The center-mounted keyboard allows alphanumeric data entry, or the traditional rotary knobs on the displays can be used. Subsequent airplanes will have only a single power lever in the quadrant.
About That Engine
Lycoming started with an engine close to the TIO-540-AE2 found in a Piper Mirage. It’s the big-case, angle-valve-cylinder engine nominally good for 350 horsepower with twin turbos and intercoolers. The final IE2 engine will be called a TEO-540-A1A, and it will be an FAA-certified product. The mechanical differences between the TIO-540 and the TEO beyond the control system are minor, just slight changes in the head castings to accommodate the IE2’s knock sensors.
For the Evo, ahead of the firewall it’s all new stuff; aft, more familiar. We flew Lancair’s Turbine Evolution as a prototype at AirVenture 2008, and we found it to be a remarkable airplane (See the November 2008 issue). Converting a purpose-built turbine to a piston engine is not the normal pathway. Most often, the turbine follows the piston model by quite some distance, and it usually isn’t as well developed. Starting your design intending to use a comparatively fuel-efficient piston of a certain power is one thing; making the design actually work well with 50% more power (or even more) at substantially higher fuel flows often results in a fast, short-legged, highly compromised aircraft.
In a sense, Lancair did the right thing by starting with a turbine and working “backward” from there. This means both Evolution models have a healthy amount of fuel capacity (168 gallons max) and high airspeed limits (Vne is 255 knots indicated), just right for the turbine and quite generous for the piston version.
Beyond cost, why would you want the piston over the turbine? Efficiency. Among turbines, there are fantastic claims of ultra-low specific fuel consumption, but in the real world turboprops burn more than 0.6 pounds/horsepower/hour and pistons burn less than 0.5 pounds/horsepower/hour. Add the second decimal place, and the difference is nearly always 30%.
The rear seats have comfortable head, leg and elbow room for the long flights made possible by the low fuel burn of the Lycoming IE2 piston engine.
Examining the IE2
Lycoming fully understands the turbine/piston arguments, and is set to leverage the piston engine’s greatest asset, efficiency, through electronic integration. The TEO-540 is controlled by a single power lever mechanically connected to the throttle plate. Everything else is controlled by the computer—everything. That includes but is not limited to ignition timing, mixture, wastegate position and propeller speed. These items are not just controlled by the computer, they are controlled to the individual cylinder. This means fuel is metered individually to each cylinder, and the ignition is timed to each spark plug. The timing can be staggered if needed to achieve desired performance, and individual cylinder fuel delivery can be altered to balance power, improve smoothness and efficiency, and to prevent detonation or thermal runaway.
To safely control all of these aspects of the engine, everything must be monitored by the computer. This includes, among others, manifold pressure, oil pressure, fuel pressure, induction pressure, exhaust-gas temperature, cylinder-head temperature, turbine-inlet temperature, camshaft position, oil pressure, oil temperature, ignition voltage, ship’s voltage, knock sensors that sense detonation before it becomes destructive and more parameters that Lycoming would not talk about. (Believe us, we asked…).
Knock sensing is the “killer application” here, a technology used widely in cars but thought impossible to implement in piston aircraft engines. Why? Acoustic knock sensing “listens” for detonation; in comparatively smooth, quiet car engines, this isn’t difficult. In fact, you can often hear engine ping from the driver’s seat. But an aircraft engine is, mechanically speaking, much noisier. Lycoming, however, says it has developed the right computer algorithms to detect detonation from the rest of the mechanical din.
Controlling the mixture and timing to each cylinder means these parameters must be monitored individually at each cylinder. Bill Weeks, the Lycoming engineer responsible for installing and integrating the engine and airframe, showed a graph of a data download from a previous flight with the engine. The amount of data available was nearly beyond comprehension.
Sensors feed two computers, each kept alive by two independent power supplies that are powered by a PMA (permanent magnet alternator) and backed up by ship’s power. The computers start on battery power then run on the PMA unless it fails, when it reverts to the ship’s battery. Obviously, electrical-system design will have to be top notch, along with its execution, in an airplane so dependent on electricity to keep the engine running.
Having two computers to control the engine is great until they disagree. When they do, the tough question is: Who gets to break the tie? Instead of installing a third computer, and to save money as well as identify sensor failures, both computers feed the engine parameters into a simulator that predicts what every sensor should be seeing for the current conditions. When there is disagreement, the simulator breaks the tie or highlights a possible sensor error.
As I was listening to the explanation of how the system works, my mind started to wander, and I began to realize all the options and capabilities that become available to make the engine more bulletproof and reliable. All of these channels create numerous possibilities for failures, but they also offer redundancy that is almost beyond calculation. For instance, should an ignition coil fail, the engine will sense the problem and adjust the fuel flow and ignition timing to that cylinder to protect it from detonation. If the governor fails and the prop runs away, the engine will use its rev limiter to cut spark to cylinders to control engine speed.
In automotive applications, electronic controls with knock sensing have gradually allowed an increase in compression ratio and power without requiring ever greater octane fuel. And while electronic controls for aircraft promise to add detonation margin across the board, it’s Lycoming’s view that such technology needs to be used to improve power and increase efficiency, not make up for lower-octane fuels. (See “Around the Patch: Unlead by example.”)
The Evolution’s high-aspect-ratio wing and smooth finish render excellent flying qualities across its airspeed envelope.
Tech, Schmeck. Is It a Good Airplane?
Appreciating the nuances of the IE2 system guarantees a fast-curing bout of mind boggle, it’s true. A more compelling question is: How does it fly? The piston Evolution airframe we flew at Sun ’n Fun this year was much more complete than the prototype turbine we had flown previously. It was outfitted with a luxurious interior, a Garmin G900X EFIS and an Electronics International MVP-50 engine monitoring system, a TruTrak Sorcerer autopilot and an ACES cabin-pressurization system. In this category of kit-built aircraft, it’s safe to assume that most will be lavishly equipped.
The walk-around is straightforward. The fit and finish of the airplane is excellent. The engine cowling looks good on the airplane, but it is a prototype, a work in progress. Lancair Director of Marketing Doug Meyer says it will change. I suspect it will get smaller, with detail improvements to balance drag and cooling capacity.
In general terms, the Evolution has a 37-foot wingspan, but it seems larger. It sits high off the ground on a robust trailing-link main landing gear. Unless you dislike the round cabin windows that are reminiscent of a Rutan design, it looks good.
Too often kit airplane designers trim the size of the tail to maximize the airspeed. Lancair got the tail size compromise on this airplane just right.
There is no difference, aft of the firewall, between the piston and turbine versions. The cabin is spacious for four, with a lot of rear legroom. The door opposite the pilot provides easy entry to the front and rear seats, and closes with a comfortable clunk that you would expect in a pressure vessel with a 5-psi differential. A reasonably large baggage door is on the opposite side of the fuselage behind the rear seats; it could be used to egress the airplane in an emergency.
My cockpit partner for the flight was Peter Zaccagino, president of High Performance Aircraft Training, the authorized factory training partner for Lancair. He provided a simple and concise checklist that was normal until we got to “Engine Start.” The checklist is basically this. Boost pump: Auto. Ignition switch: On. Starter switch: Push.
No priming, no mixture lever and no concern about hot starts—the TEO-540 starts like a car. Once running, everything proceeded normally until the runup, where things got interesting again. When the oil temp reaches 100°, advance the throttle to 1800 rpm and push the PFA button (PFA means pre-flight actions). The computer does everything. It will cycle the prop (the electric prop governor was not installed in this airplane), check the ignition, verify that everything is functioning normally and extinguish an annunciator light labeled NTO (no takeoff).
Should faults occur in flight, the NTO light will illuminate. There is also a TLD (time limited dispatch) light. Think of it as the check-engine light on your car—except don’t ignore it like you do in your leased Toyota, OK? If the engine senses a minor anomaly, it will illuminate the TLD light and start a timer allowing 20 hours of flight time for you to resolve the issue, at which point the NTO light would illuminate. Whatever fault triggered the light is stored by the engine computer for retrieval by your A&P, again just like your car. It’ll tell him what’s sick.
The horizontal stabilizer is a constant-chord design with a conventional elevator and an electrically actuated trimtab.
Hey, Ho. Let’s Go
Assuming those lights are clear, all that is required on takeoff is to push the power lever to the stop. The electro-hydraulic wastegate controller regulates the manifold pressure at 42 inches. The 350-hp Lycoming does not launch the Evolution like a 750-hp PT6A-135, but the acceleration is brisk, the rotation smooth, and again we were reminded that the Evolution is an airplane that is happy in the air. We joined with a Beech A-36 Bonanza and the combination of comfortable control pressures and wonderful handling characteristics made close formation flying a breeze.
The single-lever power control meant no need to worry about mixture, and the engine even protects the turbo from shock cooling by leaning aggressively when it senses rapid power reductions sometimes needed in a formation flight. This protects the engine and turbocharger from major and rapid temperature changes.
The pressurized baggage door and the baggage compartment are large enough to easily accept the biggest bags or a trade-show booth.
After loitering at the low power settings of the photo shoot, we pushed the lever up to 39 inches for our climb to altitude. For a moment I notice the slightest roughness, and then just as quickly it is gone, likely a result of the system fine-tuning itself on the fly, so to speak. Let’s remember too that this package is still very much in the development phase. Little quirks like this can be expected during the early flights, but they should be cleared before customers get this package.
Climbing through 5000 feet at 39 inches/2500 rpm the airplane was climbing 1050 fpm at 140 KIAS, burning 34.4 gph with CHTs below 400°. At 12,500 feet, nothing had changed but the CHTs, which had started to rise. They were, at this point, in the range of 413° to 446°, a spread that suggests an imbalance of cooling-air flow in the prototype aircraft’s cowling. It should go without saying that fine-tuning of an engine’s cooling is one of the most difficult tasks facing an engineering group, and it can be a moving target when software changes to systems like the IE2 introduce more variables.
The climb through FL180 at the same 140 KIAS—but at 36 inches MP—had the fuel flow down to 25 gph and a CHT range of 345° to 469°.
Do these temps seem high to you? Well, Lycoming says that the IE2 engine can operate and survive with much higher CHTs than we are accustomed to or comfortable with. The protection provided by the elaborate sensors and precise engine control allows operations at temperatures that would destroy a manually regulated engine.
The propeller speed will be set by an electrically controlled prop governor.
Again, the engine we flew was still very much a prototype. We had hoped to climb to the engine’s proposed certified ceiling of FL250, but at FL210 one cylinder started acting up, a malady attributed to a recent change in the IE2’s programming. All of the other cylinders were within acceptable limits, so we leveled at 21,000 feet and let the airplane accelerate.
With high cruise power of 38 inches/2500 rpm set, soon we were flying 163 KIAS for a TAS of 235 knots, burning 27.2 gph. CHTs were now in the range of 408° to 446°. At the maximum cabin differential of 5 psi, the cabin altitude was a comfortable 5000 feet. In an effort to determine the critical altitude of the engine, I pushed the power lever to the stop, and the manifold pressure went to 41 inches. It wasn’t possible to tell if that was all that was available, or the wastegate was regulating at 41 inches. Either way, the engine has lots of power available at altitude, and overall the system seemed more than capable of maintaining power and cabin pressurization.
Go High to Go Fast
Turbine engines are naturally aspirated. Making them perform better at higher altitudes requires either a higher-power engine and flat-rating it to a lower horsepower, or installing an oversized compressor to increase the critical altitude, which reduces the efficiency of the engine at lower altitudes. Turbochargers recover some of the wasted heat energy in the exhaust and convert it to manifold pressure. There is some lost efficiency in operating a turbocharged airplane below its optimum altitude, but not nearly as much as is lost when a turbine is operated at low altitudes when strong headwinds dictate flying low.
The side-stick control is mounted in a comfortable location and has well-balanced stick forces appropriate to a cross-country cruising airplane.
When the engine-control program is resolved and a new cowling is complete, the power that is available at altitude will easily take the Lycoming IE2-powered Evolution beyond 250 KTAS at FL250. Achieving the 270 KTAS in the Lancair literature might be a stretch. It will require going to FL280—the highest altitude available without RVSM approval and above the certified ceiling of the engine—but that’s not a legal limitation in an Experimental aircraft.
The Evolution enjoys a 220 KIAS Vno (top of the green), which makes descending easy. At 24 inches of manifold pressure we were descending nearly 2000 fpm at 200 KIAS. The engine monitor showed that the IE2 kept all of the temperatures toasty warm, even at what most would consider an excessive descent rate in a piston-powered airplane. Traditionally, turbines carry the advantage in rapid descents from high altitude, but the Piston Evolution does fine, thanks very much.
The high-aspect-ratio wing flexes a little and rides comfortably even at high indicated airspeeds, and the pressurized cockpit is quiet, which necessitates careful attention to the airspeed indicator. The ACES cabin altitude controller is automatic and totally transparent. Never once did the cabin bump or the rate become noticeable.
The trailing-link landing gear is machined from billet aluminum and disguises the small high-pressure maingear tire. Smooth landings are the norm in the Evolution.
The conversion from a turbine to a piston was accomplished without any perceptible compromises to the handling or operation of the airframe. Meyer reported that the piston version weighs about 200 pounds more than the turbine, but it will seldom need all 164 gallons of fuel (146 is standard, but most will opt for the extra capacity), so the extra engine weight will nearly always be offset by the reduced fuel requirement.
As with the turbine Evo, I was amazed by how comfortable the airplane feels at what seemed like ridiculously slow speeds in the pattern. The airplane is rock solid with glorious handling characteristics in all regimes, and Evolution landings are just the icing on the cake. The trailing-link gear disguises the high pressure maingear tires. Greasers are the norm with the nose comfortably in the air and adequate elevator authority to let it down smoothly as the speed bleeds off.
Flying the turbine or piston Evolution will make you smile. What remains to be determined is the price of the engine. Lycoming and Lancair are still crunching the numbers, but the same basic engine is offered through the Thunderbolt aftermarket arm at $85,000. Hard to say if the firewall-forward package with the IE2 will come in closer to $100,000 or $120,000. Add $495,000 for the Lancair airframe, including avionics and builder assistance. That’s white-fingernail territory for most of us, but still well below the cost of the airplane with a turbine up front.
A simple dropped-hinge design creates a slot in the flap without the complexity normally required. The hinges are cleanly faired to reduce drag.
Today and Tomorrow
Lycoming has dedicated substantial resources to this project, reflecting the fact that it sees IE2 as the future. Lycoming General Manager Michael Kraft said, “We have lots of excess I/O capacity.” This means that the IE2 architecture was designed to have applications beyond the TEO-540. Kraft added, “The platform needs to last a couple of decades. That sounds like a long time until you consider that our current architecture has been in service for nearly seven decades.” He’s right, electronics technology moves faster than engine technology; you have to plan way ahead to stay ahead. Plus, as difficult as certification has become, you don’t want to do it any more often than you absolutely have to.
If electronic integration of monitoring and control can do for aircraft engines what it has done for auto engines in terms of reliability and low maintenance, it may be possible to quash Turbine Fever in this power class. Then maybe Lycoming will build an IE2-controlled, 1500-hp liquid-cooled V-12. And Lancair could build a two-seat, tandem, pressurized taildragger that looks like a Mustang, flies like an Evolution and goes like a jet. That would cure Turbine Fever for good.
And it would smell better!
For more information, call 541/923-2244 or visit www.lancair.com.
Doug Rozendaal’s pilot certificate requires two cards and includes ratings in business jets, WW-II bombers, transports and fighters, as well as seaplanes, gliders and the coveted “All Makes and Models of Single and Multi Engine Piston Powered” endorsement. He holds a low altitude aerobatic waiver and flies airshows in the P-51, T-6, Rocket, and RVs.