Small, Cheap, Fast

With turbine engines, those adjectives don't come to mind. Innodyns ambitious light turboprop seeks to rewrite the equation.

by Paul Bertorelli

When Charlie Taylor finally figured out how to wring 12 horsepower out of four cylinders for the Wright Flyer, he was unwittingly writing the first rule of the new century of flight: if you don’t have an engine, you don’t have squat. Progress has always been driven by powerplant technology and we define progress as faster, higher, farther and perhaps more efficient. In this first of a series of articles, we’ll examine how emerging small turbine technology may change the rules in light aircraft general aviation.


Applying the acid test of higher, faster, and farther, the spanking new Cessna 172s rolling off the line at Independence could be considered poster children for arrested development. Other than tarted up avionics, they havent changed much since 1956.

And neither have the engines that power them. There have been gains in available horsepower and improvements in subsystems such as fuel injection, ignition and propellers, but the market has remained steadfastly rooted in the ancient performance and efficiency rules with nothing in sight that promises to fundamentally change that.

In fairness, a tip of the hat to aerodiesels which appear to be at least more efficient than their gasoline brethren even if they arent faster and a nod to emerging FADEC technology, which might wring a little more efficiency from gasoline engines and allow the use of alternative fuels.

But if the next big leap is upon us, it appears that it will be driven by engines that burn Jet-A in a hot section, not atop a piston slapping around in a cylinder. And although those engines may came from the usual suspects-Pratt & Whitney, Williams International and perhaps Allison/Rolls Royce-they may also emerge from unlikely sources that Charlie Taylor would surely recognize.

Innodyn may be one of those sources. Its an upstart company thats trolling the bottom of the turbine pond with turboprops in the under-300-HP range. We recently visited the companys factory near State College, Pennsylvania and, frankly, we find this project one of the more intriguing initiatives weve seen in quite some time.

Grass Roots
Factory may too generous a term to describe Innodyns current digs, for these turbines are emerging out of whats essentially a well-equipped, industrial-grade machine shop that trades in all kinds of specialized machine work, mostly contract parts for other manufacturers. Modest though it is, big things came out of a simple bicycle shop in Ohio a century ago so looks can be deceiving. Innodyn grew out of a machine shop business started by Charlie Nearhoof and his son, Chuck, who has become the driving force in the turbine project. Both Nearhoofs are intimately involved in the business.

Chuck Nearhoof is a self-confessed low-time pilot with an interest in engines, specifically turbine engines. Curiously, while most of us look at turbine engines as a means of propelling airplanes, Nearhoof appears to view them through the prism of manufacturability; they are essentially challenging machining projects that yield-economically-to the wonders of modern CNC technology. More on this later but its a theme we are hearing from everyone in the jet business: the economics of manufacturing are suddenly making a game-changing shift in the direction of affordability for buyers below the bizjet strata.

Students of the engine arts may recall seeing the Nearhoof turbine at Oshkosh two years ago, where it appeared in an RV-4. It drew notice but so do a lot of other wacky projects that flash up, make the cover of the slicks and then sink without a trace. While Innodyns turbine engines are far from established, theyre looking like theyll have legs, given how the company appears to be proceeding.

These engines first appeared under the flag of a company called Affordable Turbine Power, essentially an offshoot of the Nearhoof machine shop business. Realizing that he had a potential tiger by the tale, Chuck Nearhoof hired a professional manager, Jeff Davidson, and the company was renamed Innodyn for marketing reasons.

The new company then set about seeking the lifeblood of every start-up: working capital. Davidson wouldnt say how much money Innodyn has raised but he says it has enough funding from private and government sources to carry it through the first phase of the business.

And that will be production engines for the experimental market and possible forays into the military segment, specifically turbines for UAVs, which now rely almost entirely on piston engines. Nearhoof told us Innodyn has capacity to build about 500 engines a year for the experimental market.

What about certified engines for new aircraft or retrofits for existing airplanes, for which the market might be vast? Imagine the demand for a 250-HP turbine to replace a clanky O-540 Lycoming. Yes, says, Davidson, we have heard that. I cant count the times Ive been asked by a Cessna 172 owner, what do I have to do to have turbine in my airplane?

Davidson and Nearhoof are evasive on committing to a certification program but were confident in reading between the lines. If these engines prove successful in the experimental realm and are as affordable to buy as Innodyn hopes, the clamor for certified versions will be deafening. If Innodyn doesnt, someone else will.

Not that making these engines marketable is a lead-pipe cinch. Heretofore, turbines have been both too expensive to buy and too thirsty for fuel to make them practical in anything smaller than a six-place airplane weighing 4500 pounds or more. Chuck Nearhoof believes he has solved-or is on the way to solving-both of these deal breakers.

Fewer Parts, Cheaper Parts
Nearhoof believes-and so do a lot of other people who have been in the turbine business longer than he has-that a confluence of technological shifts will radically reduce the cost of building turbines. One is that sophisticated, high-output CNC machinery costs a fraction of what it did a decade ago and it does better work more quickly. Second, there have been incremental improvements in metallurgy and materials and the emergence of competition in the materials field has driven down prices. Third, computer-aided design is now a desktop tool thats widely available, making it possible to produce multiple iterations of a design with progressive improvements all before ever cutting metal.

For the four-decades that small turbines have been around, the barriers for entry by competitors were so high, Nearhoof believes, that few companies already in the field saw much need to improved manufacturing efficiency to make turbine engines more affordable. Volume was low but margins were high so why cast off a good thing?

The Allison 250 may be the best case in point. Its design dates to the 1950s, its complex with many parts and is so expensive to buy that it hasnt made significant inroads into the single-engine, light aircraft field. The fact that its fuel specifics are poor compared to the best piston engines have to offer hasnt endeared it to the light GA market. (Thats a problem Innodyn will have to address, too.)

In contrast, Innodyns engines-there are four models-are the essence of simplicity. Not counting accessories, they have only 12 moving parts, most of which are in the gear reduction box, which also accounts for much of the engines 188-pound dressed weight. If that sounds too fantastic to be true, its in keeping with emerging trends in the industry. The PW610F Pratt & Whitney is building for Eclipse has half the parts of previous engines Pratt has built and its assembly time will be about one eighth that of the nearest most economical engine.

Chuck Nearhoof explained the scale shift this way: The price has come down so much in the machine tool market…in the 1970s, an NC [numerical control sans computer] cost $500,000. Now I can buy a machine 100 times as sophisticated for $150,000. That means guys like us can get into this market.

Not Invented Here
Nearhoof and Innodyn stake no claims on having invented, to steal a phrase from Eclipse CEO Vern Raburn, disruptive technology. They do claim to have brought together certain design elements from existing engines and married them with more efficient manufacturing methods. Innodyns engines owe their design inspiration to a line of small turbines made by Solar, specifically the Solar T62, which has found wide application as an APU and ground power unit in the 60- to 150-HP range. Charlie Nearhoof told us at least one homebuilder had adapted a Solar engine to an experimental airplane with results best described as mixed. But, says Nearhoof, Innodyn has no relationship with Solar, nor are the Innodyn engines exactly derivatives.

The two engine types share a common design element in that both have single-stage centrifugal inflow compressors and a single turbine wheel, rather than the more complex axial-flow or mixed centrifigal/axial designs found in other engines, including the Allison 250. Unlike Pratt & Whitneys turboprops, which have a free turbine design, the Innodyn engines are direct shaft, meaning there’s little spool-up delay when the pilot commands thrust. It also means they screech like banshees on the ground, due to constant high RPM.

In a tour of the shop, Nearhoof showed us the turbine build-up and it looks for all the world like a piston turbocharger and, at 6 1/2 inches in diameter, it isn’t much larger. The compressor wheel and turbine are machined out of house and are made of Inconel, both are mounted on a single common shaft which is carried forward into a planetary gear reduction unit which, in two stages, reduces the shafts 60,000 RPM to prop speeds. The engines will be geared for output speeds ranging from 2000 to 3600 RPM, with 2750 RPM as the recommended speed. As explained in the sidebar, thrust is largely modulated by prop pitch control.

In any turbine, air inflow is critical. In the Innodyn engines, the intake is immediately behind the gearbox and is shaped by five vanes which also serve to separate the back of the gearbox from the front of the turbine section.

Nearhoof claims-and has patented-significant improvements to the Solar engine idea. One is FADEC control of pulsed-width fuel injection of the sort found on state-of-the-art automobile engines. Although Innodyn is careful not make any fuel economy claims before additional test data is available, it believes the application of pulsed injection will significantly reduce fuel consumption, the bane of all small turbine engines and a principal reason theyve found no wide application in light aircraft. As in a piston engine, the fuel is carefully metered to suit operating conditions and the injectors are is fast enough, says Nearhoof, to pulse as much 46 times per second at peak power demands.

Innodyn has brought this technology together to offer four engine models: the 165E at 165 HP, the 185TE at 185 HP, the 205TE at 205 HP and the 255TE at 255 HP. They are geared for use with manual, variable pitch props, although constant speed props using a governor are under consideration.

Whats most eye opening about these powerplants-other than their light weight and small size-are the proposed prices. At the low power end of the line, the 165-HP 165TE will retail at an introductory price of $26,500 while the top of the line-255 HP-will sell for $34,500. For a homebuilder shopping for an engine in the 200-HP range, say a Lycoming IO-360, the Innodyn price is competitive; in fact, at $29,500, its about two thirds of the $49,500 Lycoming asks for a new IO-360.

Few homebuilders worthy of the name would pay that much for a piston engine-many buy salvage engines-but the numbers are, nonetheless, intriguing. Not surprisingly, Innodyn has been overwhelmed with interest from the homebuilt market. At the top of the line, Innodyns 255-HP turbine will carry a $34,500 price, compared $55,000 to $60,000 for an equivalent new piston engine in the same power range.

For Real?
Predictably, the piston guys all but look with derision on the Innodyn initiative as being an airball that will flameout when the true economics clarify. Cant be done has been the standard response to market demand for a small turbine, to which Innodyn would reply that the only reason to say it cant be done is because it hasnt been done. Clearly, Innodyn is riding the crest of the same wave that Pratt & Whitney and Williams International are to design light, simple and relatively cheap turbines.

All of these companies are focusing the same emerging technology-CAD design, order of magnitude improvements in machining economics and quick assembly methods-to expand the market downward. The principal difference for Innodyn is that this work is being done in a machine shop in Pennsylvania instead of a clean room in Walled Lake or Montreal and the FAA isn’t around to muck up development and cost the inventors money. Unless we really mess this up, Chuck Nearhoof says, we are going to be around. We are going to have a position in the market.

There are good reasons to believe him. For one, Innodyn has this market segment to itself. Pratt and Williams are fully engaged in turbofans for the personal jet market and Allisons 250 is too complex to be competitively re-tooled and re-marketed.

In our view, Innodyn is doing some things right. Davidson and Nearhoof have an almost pathological aversion to even discussing a certification program for this engine, something we see as a good thing at this stage of the companys development.

Aviation start-ups seem given to inflated performance claims and unachievable delivery promises. Innodyn is a refreshing example of the opposite. By focusing on the experimental market, Innodyn can learn to do business in the world of turbine engines and can prove out its idea without the distraction of unrealistic deliveries and certification goals.

And it has plenty yet to prove. Thus far, the engines have relatively little total flight time, on the order of 100-plus hours with another 400 or 500 hours in the test cell. Innodyn is projecting engine life of at least 5000 hours, with the only maintenance being oil changes at 500 hours and igniter/plug replacement every two years.

That sounds nice on paper but Innodyn needs to get dozens of engines flying so it can learn what breaks and what doesnt in the rough-and-tumble of daily flight ops. Second, Innodyn will have to prove that the theoretical gains in manufacturing efficiency arent just that, theories. If prices escalate dramatically, the engines may miss gaining a foothold.

Last, fuel efficiency. Again, Innodyn is making no claims yet-at least those with numbers on them-and although any sophisticated buyer will grasp the immutable physics that a turbine will never be as efficient as a piston engine, there’s an acceptable Delta in there somewhere. To a homebuilder, a specific fuel consumption of .58 or higher might not matter; homebuilders buy a turbine to have a turbine, not to set range/endurance records.

But if market demand puts these engines on the road to certification, theyll need better fuel specifics than small turbines have thus far achieved. Innodyn will have to demonstrate that this efficiency sweet spot exists and that it can be delivered in an affordable engine. we’ll be watching this project closely to see if they succeed.

Contact – Innodyn, 877-466-1200,

Also With This Article
“The Quest for Efficiency”
“Flying the Innodyn”