Soloy’s Mark II is not your “typical” bolt-on conversion. From the aerodynamically clean cowling to the new engine mounts and the crimped wiring connectors, every detail of the conversion is created using the latest in computer-aided design and manufacturing techniques, so the Mark II stands up to the harsh, off-airport and on-water operations its owner/pilots demand.
There’s something that’s both a little primeval and 21st century about starting a turbine engine. The rising whine of a turboprop beginning to spool up, turning to a deep roar when fuel is introduced, then screaming up to idle, seems somehow the proper sound for a machine designed to flail the sky into submission.
Take, for instance, the Allison/Rolls-Royce 250, long a stalwart of the helicopter industry. In various iterations, Allison/Rolls-Royce turbines have been installed in production Bell, Enstrom, Eurocopter and Sikorsky helicopters for nearly a half century.
Turbines are, in many respects, the simplest possible power plants, especially in contrast to piston engines. Like a piston mill, a turbine develops power by internal combustion, but in a logical, circular direction rather than slamming a six-pack or more of pistons up and down. Turbines also don’t rely on air cooling to keep temperatures in check during low speed or hovering flight. Better still, turbines have only a dozen or so moving parts, compared to several hundred in a piston power.
For all those reasons, turbine engines have proven, by far, the most reliable method of powering rotary-wing aircraft. The Rolls-Royce features a TBO of 3,500 hours, versus a 2,000-hour interval overhaul on a standard 300 hp Lycoming IO-540.
That’s perhaps only appropriate, as helicopters often must operate outside normal safety parameters. They can sometimes autorotate to land in a tiny space in the event of an engine failure, but by definition, rotorcraft often extend the normal safety envelope, sometimes pushing the limits of the height-velocity curve in order to accomplish their mission.
In more recent years, the Rolls-Royce 250 turbine has made major inroads into the fixed-wing market, mostly decorating the nose of traditional piston aircraft. These have included the Tradewinds Bonanza, O&N P210 and upcoming 340, Maule M7, Cessna 185, the upcoming production Extra 500 and several other models.
The benefits of a turboprop transplant are well established—more power, a dramatic reduction in engine weight, improved reliability, simpler and smoother operation, more useful load and easier, less frequent maintenance. The negatives are significant but fewer: increased fuel burn, often less friendly noise level, and the big one—higher cost.
The Cessna 206 is another model that lends itself to turboprop conversion. The Stationair has been a stalwart of the Cessna line for nearly a half century, and the type has earned its place as perhaps the most popular utility airplane still in production. Prior to the shutdown of all Cessna piston products in 1986, the stretched eight-seat Cessna 207 was the top of the company’s piston utility line, and the six-place 206 was the king of piston freighters.
After a long history of upgrading helicopters and airplanes, Soloy Aviation Solutions of Olympia, Wash., has been installing the Allison/Rolls-Royce 250 into a variety of Cessnas for nearly 30 years, starting with the 185 and, more recently, the 206/207 Stationairs. If you can’t afford the big jump to a Caravan, the larger series 200 piston Cessnas are popular machines for hauling pretty much anything to pretty much anywhere.
The Cessna 206 flies behind a nosewheel, and that limits the airplane’s operation to relatively smooth, semi-improved strips. They’re nevertheless popular machines in the world’s outback destinations.
Though the most common applications of turbine upgrades are for enhanced climb and cruise performance, Soloy’s goals are slightly different, especially on the 206 and 207 (the latter now long out of production), where utility operation is more the rule than the exception. For the Stationair, the mission is often where you can go and how much you can carry, rather than how quickly you can get there.
Soloy built some 85 of the initial Mark I conversions that utilized the Rolls-Royce 250-C20S turboshaft engine, pumping out 418 shaft hp. That represents nearly a 40% power increase, with the obvious implications.
In October 2008, Soloy received approval for the follow-on Mark II conversion, specifically designed for the 1999, and later, Cessna 206H/T206H. This upgrade uses a Rolls-Royce 250-B17F fitted with Soloy’s Turbine-Pac gearbox-drive system. The engine is rated for 450 shaft hp, roughly a 150 hp increase over the original Lycoming IO-540/TIO-540. Dual vacuum pumps, digital engine instruments and a Shadin fuel computer are standard, as is a bleed air heater in place of the standard muff-type system. Electrically deiced propeller and air inlet heater also are standard features of the Mark II conversion.
Soloy has redefined the applications of the 206 to make turbine Stationairs even more attractive for applications such as skydiving, law enforcement, fish and game, pipeline and powerline patrol. To help facilitate those tasks, the Soloy conversion realizes a payload increase of roughly 170 pounds, a function of the lightweight turbine engine (since gross weight remains unchanged at 3,600 pounds). Balancing the CG with a lighter engine demands extending the nose forward, improving the airplane’s lines and lengthening the fuselage by at least a foot.
The airplane I flew for this evaluation was what Soloy calls the Sentinel, a dedicated law- enforcement version. The test airplane was fitted with a remotely mounted FLIR (Forward Looking Infra Red) system beneath the left wing, a specially adapted third seat aft of the pilot stations and a large vertical floor-to-ceiling observation window on the left side. The large aft left window can be purchased separately, and has proven extremely popular. Soloy has sold 150 conversions of the tall observation window.
All the modifications have little effect on aircraft control, though the heavy FLIR system halfway out on the wing does demand slight roll trim compensation.
I had flown the Mark I conversion many years ago in Washington, so I was eager to sample the new airplane’s talents. Soloy demo pilot Paul Haagland manned the right seat, and we taxied out for a short demo flight in the Los Angeles area.
Predictably, a third more power makes a remarkable difference in performance. If you’re leaping out of a short strip, you’ll appreciate the strong push when the power goes forward; then, you can watch the VSI do things you’ve probably never seen on a 206. At light weights, the Soloy Mark II will drive the needle up to 1,500 fpm or more. Better still, if the mission demands high-altitude operation, the Soloy Mark II can vault higher in a similar hurry.
Having extra power is especially welcome on waterbirds, and the new mod will undoubtedly find happiness on Stationair floatplanes and amphibians. Nearly a quarter of the original Soloy Mark I conversions were made to float-equipped Stationairs. Climbing up onto the step with a heavy load can be a struggle with the standard piston engine under even the best of conditions, but it’s far safer and more enjoyable with the Rolls-Royce 250 out front.
Cruise isn’t the province of the Soloy Mark II, but the airplane does pretty well for a draggy 3,600-pound utiliplane with struts and wheels hanging in the breeze. At a typical cruise setting two miles above the sea, the turbine Cessna will trip along at 170 knots, burning 25 gph. If you’re willing to climb to 18,000 feet, the Soloy Mark II should deliver 185 knots. When out-and-back range is more important than speed, you can reduce the torque to a more civilized level, see 140 knots and fly one-way legs of nearly 270 nm each direction.
Aside from the extra enthusiasm in climb, you’d be hard pressed to find much difference in handling qualities between the turbine and piston versions of the Stationair. The airplane flies through rough air with the stability of Amtrak, and maneuvering flight is equally controllable. It’s not hard to imagine chasing bad guys in a Soloy Mark II conversion at speeds as slow as 65 knots or as fast as 150 knots. Normal cruise rpm is only 2,030, so the tips of the standard 90.5-inch diameter prop are running at only about 545 mph or Mach .72.
Stall and approach speeds are straight out of the Stationair manual. Dirty stall remains 54 knots, and accordingly, approaches can be pretty much whatever you need, from 65 knots to sandwich into a short runway to 130 knots on an ILS into LAX to stay ahead of the 757 approaching the outer marker.
The big, 90.5-inch-diameter three-blade Hartzell is fully reversible, and that can make a major difference in stopping distance on miniature runways, provided there’s no FOD risk. It’s best to limit reverse thrust to those instances when you really need it.
After the flight, I sat down with Dave Stauffer, CEO and president respectively, of Soloy Aviation Solutions.
“We’ve targeted the law enforcement and aerial observation mission as one of the primary markets for this Sentinel conversion,” said Stauffer, “and we’ve had quite a bit of interest from Customs and Border Patrol, California Highway Patrol, Canada’s RCMP and a number of other agencies,” Stauffer continued. “The Mark II also works well at transporting other items too large for some other freighters.”
As with most modifiers, Soloy does considerably more than simply install a new engine. The modification includes what amounts to a full, ground-up rebuild, including paint. “If a client asks, we’ll even find a Stationair for him, do a full modification and configure the airplane to the customer’s specs,” says Stauffer.
The standard conversion is $615,000 uninstalled plus $85,000 for installation, and you can buy a reasonable 1998-2000 Cessna 206H for around $220,000. That puts your total investment in the airplane at roughly $920,000. Soloy offers a variety of options, everything from 30 to 50 gallons more fuel to Wipaire floats and the five-blade MT propeller.
The company is capable of producing between 10 and 20 conversions a year, but because the current poor economy makes it inefficient, Soloy won’t be building the Mark II on a production line basis.
The airplane I flew was number nine, and it garnered more than its share of attention just sitting on the ramp. Esthetically, the standard Soloy Cessna 206 Mark II conversion doesn’t look all that different in many respects, and perhaps for that very reason, you’re guaranteed to get everyone’s attention when you start the engine.