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Flight Reports

June 2015 Issue




Turbine-Powered RV-10

New light turboprop engines are coming to Experimental/Amateur-Built aviation.

Just like Dorothy in Oz, I knew this demo flight would be altogether different. This revelation hit me the moment that Deland, Florida-based Turbine Solutions Group CEO and test pilot Peter Pierpont pointed to the engine start switch in the center of the instrument panel, just above the single power lever resting at idle position and just below the Garmin 650 GNS tucked into the panel for IFR. He said, "Now flip that switch."

Peter Pierpont, CEO of Turbine Solutions Group, in his favorite role as a test pilot.

I did, and with a soft whoosh of fuel, a whispering whir of spinning blades, and a subtle pop of ignition, the FADEC on the TP 100 turboprop engine under the long, raked cowling out front fired itself up. There was just the slightest aroma of Jet A from the exhaust blowing by the fuselage, but the powerful air conditioning (another single-switch activation) quickly washed it away.

The big 80-inch purpose-built three-blade metal Hartzell prop, dragged along by the free turbine PT-6 style, began to turn, and with oil pressure applied, it came out of feather. Amazingly, there was no vibration. No shudder on engine start or prop swing, not even the slightest shimmer sensed by the soles of my feet on the floorboards. And it was quiet, relatively speaking (that relativity being in relation to the growly Lycoming IO-540 on the front of my RV-10).

The aircraft throttle quadrant is simple: just one lever to move.

Within a minute we were at 53% power with the lever at idle, as displayed on the 10.4-inch Advanced Flight Systems 5600 PFD/MFD in front of us. There are two in this panel, as there are two of just about everything except the Garmin 650 GNS, the engine, and Hartzell prop on this proof-of-concept factory demonstrator RV-10 from Turbine Solutions Group (TSG). My job that day was not just to see it fly, but to fly in it, see how it worked, and feel what it felt like to fly an RV-10 with a modern engine burning Jet A.

With oil temperatures in the green, I released the brakes and the airplane began to roll at just about the right pace to preclude the need for either power or any more than a light tap on the brakes to round corners (the RV-10 has a free-castering nosewheel, so some braking is necessary for turns). By the time we reached the departure end of the runway, we'd completed our cockpit checks and the engine—which, unlike a piston engine, needs no runup—was ready to go.

Rob Hickman, founder of Advanced Flight Systems, worked with Turbine Solutions Group to interpret the CAN data from the TP 100 and display it properly on the AFS 5600 screens in the aircraft.

In the Air

Takeoff was a straightforward procedure. Turn the air conditioning off momentarily. Apply power to 85% N1, watch for 2158 rpm on N2, then, with everything in the green on the engine instruments displayed along the bottom of the AFS screen, we released the brakes and advanced the power lever to the forward stop. The FADEC-equipped engine control unit then gave us 100% power for the ISA +15° F conditions, and we felt a nice press back into the seat from the acceleration. Rotation took less back pressure than for my Lycoming-powered beast (mine is noticeably nose heavier with just two front-seat passengers—the TP 100 machine felt nicely balanced at the same loading).

Flying—one glance lets you know that this is no ordinary RV-10. Turbine Solutions Group's concept demonstrator is a full 10 inches longer than an IO-540 piston-powered RV-10. The stretch was necessary to keep the airplane in CG with the lightweight TP 100 turboprop engine out front.

Pierpont held the airspeed at 103 knots in the climb, producing 1700 fpm of up, up, up! If I did that in my Lycoming-powered RV-10 for more than about three minutes on anything other than a chilly morning, I'd see my CHTs begin to glow. The TP 100 RV-10 can hold that attitude and power setting for its full five-minute 100%-power limitation, then continue at 97.5% power and 1500 fpm right on up through whatever altitude you set for it. Exhaust gas temperatures and turbine inlet temperatures stayed in the green. The big scoops out front were doing their jobs—cooling is not an issue with this installation.

The FADEC and engine control unit is housed on the back of the engine. A certified version of the TP 100 will require dual FADEC—the component is ready for the addition of one more computer.

Now, for the pleasure of that rapid climb, you will go through a lot of highly refined dead dinosaurs, I must warn you. Not that my Lycoming is such a teetotaler at full power (it burns 25 gph at sea level full throttle). The TP 100 slurps 32 gph of Jet A at 100% power.

Level at 6500 msl and 97% power, the fuel flow settled to 21.7 gph to display 173 knots TAS (data downloaded from the airplane later showed we achieved 175 knots TAS). My Lycoming will burn 11.5 gph to produce 170 knots TAS when leaned out. The TP 100-powered RV-10 carries twice the fuel I do because it is going to burn more. Its wing tanks (four) are designed for a simple L/R operation. Gravity feeds fuel from custom fiberglass outer tanks to the stock metal inner tanks. Redundant fuel pumps ensure that the gas turbine up front never lacks for juice.

At low cruise, 95% N1, the airplane burned 19 gph for 162 TAS. Note: this is an unpainted airframe. It may go faster later on in development. As it stands now, the company picked up several knots from refining the exhaust stack shape and angle. The sleek design of the nose cowling certainly did not hurt, either. Pierpont noted that most operators will take advantage of the turboprop's ability to fly high and be rewarded with fuel flows closer to 15 gph between 12,000 and 18,000 msl, and higher true airspeeds, plus the possibility of picking up more favorable winds should increase actual operator efficiency even further. The engine has been flown in a pressure chamber to 29,000 msl without adverse effect. At this point, there is more concern over how a wing such as that on the RV-10 will perform above 18,000 msl than how the engine will perform, Pierpont said.

Seem a little long in the snout to you? TSG's engine is significantly lighter than a Lycoming IO-540. Its mount attaches to the original Van's motor mount and levers the engine several inches farther forward.

The Same—But Different

In-flight handling was nominal. It is an RV-10, after all, and if properly constructed, that airframe is known for its docile behavior. Looking out over the long, raked cowl wrapping the turboprop engine in front of me, I had the impression that we were flying along at a slightly nose-down attitude—but it was just an illusion. To the tip of the prop cone, the TP 100-powered RV-10 cowling is nearly 10 inches longer than standard.After a couple of 360-degree turns, I was sighting the horizon properly and appreciating the better view and lighter pitch-feel (as compared to my airplane). Stall speed clean at this altitude was around 57 knots IAS and straightforward, with no wing dip.

Christian Skoppe's handiwork with composites is evident in the unique nosebowl and air scoops of Turbine Solution Group's test RV-10.

This airframe had no rudder trim, and no need for it. Perhaps it was the way the airframe was constructed, or perhaps it was the slight angle tweaked into the engine and cowl that helped it fly straight. The long nose was a necessary modification, I learned later, designed to help compensate for the super-light weight of the engine, which is just 156 pounds wet. Dual batteries, the metal three-blade prop, and that powerful air conditioning system were all set up front to help make the CG work.

With the lighter engine, the weight of 120 gallons of fuel (heavier fuel at that) doesn't detract much from the generous useful load for the airplane because TSG kept its test bed airframe light: empty weight is just 1560 pounds. The double tanks in each wing should provide more than adequate range for TP 100-equipped machines. My airplane carries half that fuel, but then, in cruise at altitudes below 10,000 msl, it is consuming avgas at just over half the rate at which the TP 100 burns its Jet A.

The TSG concept airplane seems a bit slicker than mine with its long, skinny nose. By the time we were on base leg for landing, the power was essentially off and we trimmed nose up to make flap speed. We set up for a landing with airspeed around 60 knots as we settled over the fence. Even without beta mode (reversing the prop blades to make them push instead of pull), the airplane slows to a taxi easily from the low touchdown speed. Beta mode will come, Pierpont told me, as will an additional FADEC brain for redundancy, once Czech Republic-based PBS Velká Bíteš, the engine's manufacturer, goes for EASA and FAA certification. It is all in the plans.

A singular portrait of a unique aircraft: an RV-10 powered by a Czech-built TP 100 241-shp turboprop engine.

TP 100 Details

The venerable PBS Velká Bíteš developed the TP 100 as part of a European Union Efficient Systems and Propulsion for Small Aircraft (ESPOSA) project, a four-year partnership spanning 15 countries that includes 18 companies, 11 development centers and 10 universities, with a total budget of EUR 37.7 million ($45.93 million). PBS was recruited for the project because of its decades-long history manufacturing engines and engine components for aerospace, as well as its large and experienced workforce and reputation for producing quality products. The engine, one of two developed for the project, develops 241 shp plus 9 thrust horsepower in this incarnation and is currently being tested in a Polish tandem pusher single-engine fixed-wing aircraft in addition to the RV-10.

"This is the kind of engine that really demands a purpose-built aircraft around it," Pierpont told me while we sat in the cockpit on the ramp after engine shutdown, watching the AFS as it showed the small engine cooling unit kicking in to run its five-minute cooling cycle. He's got a design in mind, and even a customer. "It is so simple to install," he explained back in the hangar, pointing out the one fuel and two electrical connections running through the firewall. On the RV-10 installation, TSG chose to stick with the Van's factory engine mount and mount the lightweight TP 100 in its own mount, directly to the stock mount. "Two people should be able to install this kit in the field in a couple hours, the way we've rigged it," smiled Pierpont.

For IFR the aircraft is equipped with a touchscreen Garmin GTN 650.

He is confident that if the engine is certified, it will find many comfortable cowlings to nestle into among the aging piston aircraft fleet around the world. "The Seneca is a perfect platform, ready for re-engining with a light turboprop," he said. Mooneys, Cessnas and Pipers, anything currently sporting 210 to 250 hp and decent-sized gas tanks would work.

Of course, with avgas in a downward price spiral, it is hard to imagine the need to re-engine in order to burn less expensive Jet A here in the U.S. It's not so difficult to imagine, however, in Europe, Asia, Africa, the Pacific, or even Central America and the Caribbean. Ask a world-rounder or a ferry pilot. Ask anyone who has had to have a drum of avgas delivered and staged in a remote outpost before he arrived there. They will tell you that pretty much everywhere else in the world avgas is difficult, ridiculously expensive, or simply impossible to come by. If the TP 100 is certified, there is a market for it as a retrofit for aging piston engines all over the world. And if it is sold to those markets in quantity, you can bet the cost of production, and ultimately the cost of acquisition and, with a good reliability record, the cost of maintenance will go down.

The TP 100 is a lightweight, compact way to get 241 shp onto an RV-10.

But right now it is an engine in R&D, and that shows up in the conservative inspection and replacement limits dictated by its operation manual. "We expect those to be lengthening rapidly, now that the engine has more than 1600 hours on the test cell in the Czech Republic," said Pierpont. Other than its required inspections once a year or at pre-determined cycles, the engine requires little in the way of regular servicing. Check the oil, change the oil, and borescope it at manufacturer-prescribed intervals, and it should run flawlessly, according to Pierpont.

Being a turbine engine, all of this, right down to the powerplant's overhaul time and ultimate life limits, will be spec'd out for you to follow meticulously in your Experimental aircraft's FAA-approved operations limitations, should you choose to fly behind (or in front of) one. Yes, this is different than the way the FAA handles Experimentals with piston engines. Want turbine power on your Experimental aircraft in the U.S? You'll comply.

The innards. Compressor section for a Walter engine undergoing maintenance at TSG.

And you'll be returning to Deland, Florida, for all your servicing needs as a part of that deal. "We will be the factory-certified service center for the TP 100 engine here in North America," explained Christian Skoppe, president of Turbine Solutions Group (TSG). "Once the TP 100 is FAA certified, we will also become an FAA-certified repair station for the engine," he continued.

It won't be the first turbine that TSG repairs and reconditions. As Dimech Turbines, Skoppe has been working on GE Walter 601 turboprop engines since 1991, and he currently repairs and overhauls those engines and their accessories. The facility includes an engine test cell, extensive hangar space, sophisticated turbine balancing equipment, parts inventory, fuel control unit troubleshooting, AVIA prop overhaul and conditioning, and experienced technicians available for both on-site and in-field support.

How Much Will It Cost?

What does TSG want for the firewall-forward package it is developing on the RV-10 (come on, I know you want to know)? "We are hoping to offer it for between $168,000 and $175,000 USD," said Skoppe. This particular project is Skoppe's baby, and his handiwork is evident in the clean lines of the cowling, the shape and twist of the carbon-ceramic exhaust stacks, and the overall straightforward installation of the package. Skoppe knows that many of his customers will be from far-flung destinations, some with little maintenance support on site. He wanted plug-and-play as much as possible. That goal is close at hand.

While the company waits for the engine to finish R&D and receive EASA and FAA certification, it is poised to sell the Experimental version. "We have interest in three engines for a Velocity project that we hope to finalize early in 2015, and there are a few others interested in putting it on RV-10s. Skope has already negotiated a favorable price for five more engines from PBS and hopes that price will hold for others. "The PBS plant is big and has 750 employees. It takes two of them about a week to assemble, test, disassemble, inspect, and reassemble an engine for shipment," he continued.

"The R&D money already invested in this project and the EU commitment to light turbine technology as a replacement for piston engines makes me confident that this engine will be put forward for certification," said Pierpont. The EU push toward cleaner skies and the total elimination of avgas in the confines of its airspace, with its lead component, points toward a rosy future for light turbine engines such as the TP 100.

Yet certification bureaus such as EASA and FAA take their time. As we roll into the middle of the second decade of the 21st century, we can only hope that advances in certification processes can keep up with the inspired innovations of our engineers.

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