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Flight Reports

November 2014 Issue

Same Fun, Less Fuel

Glasair Aviation leads the way with new Diesel Sportsman 2+2.

Glasair Aviation has introduced the first diesel-powered airplane kit on the market. After a disappointing attempt to develop a diesel package with Delta-Hawk, Glasair has joined forces with Continental to bring their 2.0-liter diesel engine to amateur builders. As one would expect when working with a company with Continental's stature, the engine package works, and it works well. This is the same firewall-forward package that Continental offers for retrofit on Cessna 172s, so it is well developed, complete, and proven in the field. Continental wanted to expand this portion of their business into the Experimental market, and Glasair wanted to get a diesel engine package that was ready to go right now. The two came together to deliver an impressive, if admittedly rather expensive, alternative to traditional Lycoming-based engine packages.

The Diesel Sportsman currently features a three-blade MT prop. It performs well and is amazingly quiet, but Hartzell plans to give the Germans some competition in the very near future with their own composite prop.

The Sportsman airplane hardly needs an introduction to KITPLANES® readers. Hundreds of these kits have been sold to both traditional builders and through the ever-popular Two-Weeks-To-Taxi program. It is a versatile utility airplane that will fill the needs of a broad range of pilots. The design has been refined and improved over the years to make it one of the best all-around traveling machines you can build. Such features as four seats, a sub-50 knot power-off stall speed, and 135 to 145 knot cruise speeds, combined with a useful load of 1000 pounds makes the Sportsman a very capable airplane. When one can be built in a mere two weeks, it becomes a viable alternative to Cessna products costing twice as much or more.

The Continental diesel engine package makes the Sportsman even more capable by giving it unbelievable range with very few sacrifices in performance. It also makes the airplane useful to the large number of pilots in the world who are challenged to find avgas at a reasonable price or, in some cases, at any price. In the U.S. we take for granted that avgas is readily available at something approaching a reasonable price. In the rest of the world this is far from typical, and in many third world countries it is almost unobtainable. With the new Chinese owners of Glasair looking far beyond the American market, they see a need for a plane that will not be dependent on the availability of avgas. With this broader view in mind, it made perfect sense to Glasair to embrace diesel technology at the earliest opportunity.

The Diesel Sportsman markings on the prototype are distinctive but utilitarian. They will likely give way to something with a little more artistic flair when customer planes start getting built.

The Engine

The Diesel Sportsman uses the 2.0-liter (121 cubic inch) geared, turbocharged powerplant now made by Continental. The engine is an outgrowth of the original Thielert Centurion 1.7-liter engine installed in Diamond aircraft. That engine had many problems, leading Thielert to redesign and improve the engine, resulting in the current 2.0-liter powerplant. By the time the dust settled, Diamond had given up on Thielert and developed its own diesel engine. Thielert was then stuck with a good engine, but a terrible reputation and no customer. Continental bought them out of bankruptcy and started working on an engine package for the Cessna 172. This is the engine package that Glasair installed in their Sportsman. This gave them a fully developed engine package with the latest digital technology, and it gave them an engine with a proven history of working well in the field.

The fuel rail atop the Continental diesel engine carries a pressure of 19,000 psi when the engine is running.

The engine itself is relatively small in displacement, but uses a turbocharger to extract 155 hp out of a four-cylinder, 2.0-liter mill. Full FADEC controls and an MT three-blade propeller complete the firewall-forward package that produces 100% power up to 9000 feet msl. A maximum recommended cruise power setting of 85% can be delivered up to 14,000 feet. Climbs at 100% power are allowed, giving the Sportsman a 900 foot per minute rate of climb up to at least 9000 feet. Fuel flow at 100% power is about 8.0 gallons per hour. If 155 hp sounds a bit anemic, consider that an IO-390 produces 153 hp at 9000 feet wide open, and an O-360 only produces 131 hp. At 14,000 feet the diesel is making 131 hp versus 104 for the O-360 and 122 for the IO-390.

The alternator is tucked away low and towards the rear of the engine on the pilot side. Blue hoses go to the cabin heat radiator that is yet to be fully installed.

How Does the Diesel Perform?

The Lycoming IO-390 and O-360 are currently the most popular engine choices for Sportsman builders. The IO-390-powered Sportsman will out-climb the new diesel to 10,000 feet, but the diesel will easily out-climb the smaller 180-hp O-360. At low altitudes the IO-390 will climb out at 1500 feet per minute, something the diesel simply will not do. Long climbs come out about the same, because very few pilots are going to sustain climbs to 9000 feet or so at maximum power, whereas this is easily done with the diesel. This means the diesel and the IO-390 will climb to 10,000 feet in just about the same amount of time.

In the test for this article, we were loaded to 2170 pounds, well under the Sportsman's 2500-pound gross weight. At this weight we were able to take off with a ground roll of just under 500 feet. A Sportsman at the same weight with an IO-390 engine should be able to beat that number by about 150 feet, with an O-360-powered Sportsman somewhere in between. This means that the diesel is not your best choice for ultra-short backcountry strips, but as the altitude increases the advantage of the IO-390 begins to disappear. Remember, at 9000 feet they are making exactly the same horsepower.

The turbocharger and intercooler fit into the right side of the engine compartment. It is hard to see the turbocharger behind the other components.

In cruise the diesel cannot match the speed of the IO-390 if you are willing to burn the fuel necessary to achieve that speed. The Sportsman with the big Lycoming will easily exceed 140 knots at 9000 feet, but at a cost of around 13 gallons per hour. The Diesel Sportsman will cruise at 85% power at that altitude at 133 knots while burning only 7.3 gallons per hour. That extra eight to ten knots will cost you about $30 per hour in fuel at current U.S. prices. In Europe where the price and price differential are both much higher, the savings could easily be twice that or more.

If you are willing to slow down a bit to 128 knots (75% power) then fuel flow will drop to 6.3 gallons per hour. At 65% power the speed drops off to 117 knots, but fuel flow also drops to a miserly 5.2 gallons per hour, giving the Sportsman an endurance of nine hours and a range of just over 1000 nautical miles with reserves. This range will allow the Diesel Sportsman to fly non-stop from Glasair's headquarters in Arlington, WA to the author's home base of Chino, CA. It is hard to say who might want to actually do this, but it is noteworthy that it is possible, if you did. By the way, don't forget to bring an empty bottle with you. You are going to need it.

Long climbs at maximum power did not produce any excessive coolant temperatures on a standard day. A second Diesel Sportsman prototype based in Las Vegas is seeing some higher temperatures during 100% power climbs with their 100° F weather. The cowling is being modified to solve this problem, with the goal of eliminating all power restrictions, even on such hot days. Of course, climbing out of Las Vegas on a 100° day with an IO-390 at full power is likely to produce some pretty warm cylinder head temperatures, too.

A rather small flange protrudes from the gear reduction unit on the front of the engine and connects to a specially made prop hub on the MT constant-speed prop.

How Does It Fly?

The new Diesel Sportsman flies like a Sportsman, which is to say pretty well. A complete flight test can be found in a back issue of KITPLANES®, but to summarize, it is very benign and predictable with well-coordinated controls and a powerful rudder that is seldom needed, unless you are dealing with a crosswind or wish to deliberately slip the plane to steepen your approach. Stalls are mild and straightforward if you are coordinated going in. Spinning is all but impossible, which is a deliberate design feature carried over from the GlaStar. It is a stable IFR platform that will make you look like a better pilot, and it will not embarrass you unless you really force it. It is a good short-field airplane, especially in the taildragger configuration, and it is equally well-suited for a long cross-country. It is comfortable and roomy, even for a pretty big guy. There are faster planes in cruise, just as there are those that will land shorter, but it is hard to find a better compromise between those two opposite requirements in one plane.

The prototype panel features a two-screen setup by Advanced Flight Systems. Right now engine instruments are not incorporated into the AFS displays, but there are plans to do so soon. Note the single FADEC power lever. Engine management couldn't be any simpler.

The Diesel Sportsman does have its own unique handling compared to the Lycoming-powered versions. It is a bit heavier, with the prototype weighing in at 1560 pounds empty. Glasair hopes to get this down to 1500 pounds in the final production version, but the engine is just heavier than either the IO-390, or its smaller brother, the O-360. The Diesel Sportsman will be standard with the carbon fiber fuselage, which saves weight, but does add cost. The weight is not really felt in most situations since the center of gravity is just about exactly the same as the IO-390 version. With two up front and power off, there was just enough elevator authority to get a break at the stall. This is important for an airplane that has the potential to land on short, rough strips.

The Lycoming-powered Sportsman is well-known for developing a pretty good sink rate when full flaps are applied for landing. In fact most Sportsman pilots will delay going to full flaps until they are almost ready to land. This is desirable when a steep approach is needed, but it initially takes a little bit of adjustment for most pilots who prefer long, flat approaches. The Diesel Sportsman differs in this regard because of the residual thrust the engine provides at idle. A power-off approach in the Diesel Sportsman is not quite the same as a power-off approach with a Lycoming engine where a windmilling constant-speed prop produces a lot of drag and virtually no thrust. This will not be an issue for most operations, but for serious short-field work it will need to be taken into account, unless Glasair can find a way to eliminate it.

Nuts and Bolts

The Continental diesel engine is a turbocharged engine with an intercooler. This helps to reduce engine temperatures and produce more power. It takes up a fair bit of space in the engine compartment, but presumably it is worth it. Liquid cooling creates the need for a radiator, but it stabilizes engine temperatures much better than air cooling, allowing for tighter tolerances and better performance, but at the cost of some added weight. There is a separate small radiator just for cabin heat that was not hooked up on the prototype, but should be very effective once completed. This will be especially nice for pilots in cold country where ordinary cabin heaters just don't get the job done.

The prototype is currently fitted with a special MT three-blade prop, but Hartzell is also set to provide a composite prop that promises even better performance. Further testing will be needed to see which one makes the final cut.

The engine mount has been shortened to help set the heavier engine farther back towards the center of gravity. This was effective in keeping the weight where it needs to be, but there is precious little room between the engine and the firewall. It is not going to be the easiest engine to work on. The standard Sportsman cowl is being used now on the prototype, but a new cowl with better cooling especially designed for the diesel is in the works.

Right now, the engine gauges are separate from the Advanced Flight Systems displays on the panel. Dynon (owner of AFS) is working to develop a package that will allow the Continental engine management system to talk to the AFS displays. This will provide more detail than is currently available with the Continental displays. It is important to remember that this is a prototype, but if it never got any better than it is right now, that wouldn't be such a bad thing.

What Does It Cost?

The Diesel Sportsman will only be available through the Two-Weeks-To-Taxi program. This will give Glasair the control they feel they need over the engine installation process. It may be available to traditional builders in the future, but Glasair is not making any promises at this time. The Two-Weeks process adds a little under $20,000 to the cost of the components that go into the plane, but it does compromise the flexibility of the building process to some degree. Its continued popularity is a testament to how well it works. The diesel firewall-forward package—engine, mount, prop, carbon fiber cowling, etc.—costs $90,000, but Glasair is offering an introductory package at a $30,000 discount. The bottom line is that a complete Diesel Sportsman, after adding two weeks of your effort, will cost $249,000 with a VFR panel. More advanced instrument packages are available at an added cost. If you are looking for that elusive, affordable $50,000 kit airplane, you won't find it here. But if you compare this plane to a new Cessna 172, it starts to look like a real bargain. It is faster, hauls more, flies better, and is way cheaper than the competition from Wichita. And you can have it pretty much exactly the way you want it, with about four years' worth (in two weeks) of aviation education thrown in as a bonus.

The engine cooling radiator is on the left side of the engine and keeps temperatures well under control. The projection ahead of the alternator is the engine oil sump.

The Bar Is Set High

With about 1000 hours of experience in the Sportsman and its predecessor, the GlaStar, I had some definite preconceived notions of how the Diesel Sportsman should fly. The GlaStar is a pretty nice airplane, and the Sportsman is even better. Neither has ever disappointed me when I asked it to do something, and they have never given me one of those "Why the heck did it do that?" moments. Trike or taildragger, big engine or small, each did what I expected it to do when I expected it. No fuss, no drama; they just got it done. Sexy? Not so much. Comfortable and confidence-inspiring? You bet. So how is the Diesel Sportsman going to fit into all of this?

To be honest I expected to be disappointed. When I looked at 155 hp, I thought performance would be sub-par. When I considered the weight of the diesel engine, I thought of a forward center of gravity making the plane want to land on its nose like some lightly-loaded Cessna 206. I was wrong! And I am glad I was. I like the people at Glasair. I have known some of them for 15 years or more. And I like my Sportsman a lot. I just didn't think this diesel engine idea was going to work out, but it did.

The plane flies well and is very smooth. The turbocharger also does a good job of taming engine noise. The power management with the FADEC control is incredibly simple. One handle does it all. Just set the percent power you want and away you go. You never have to adjust anything until you want to change your power setting. I just don't know how it could be made any easier. It is a pleasure to fly from an engine-management standpoint—in fact from any standpoint. The engine package is refined and easy to operate. There are no odd vibrations or confusing controls or procedures to distract you from your flying. Everything works as it should. My expectation of how it should fly was pretty high, but my expectation of how it would fly was somewhat lower. My expectations were exceeded to say the least.

What do I like? I like the super simple engine management, especially never having to worry about mixture adjustments again. I like the smoothness of the engine, something I never expected. I like the climb performance. I like the miserly fuel consumption and never having to enrich the mixture to manage cylinder head temperatures. And I like that all of this is available on a Sportsman, one of my favorite airplanes.

OK, so there must be something I don't like, and there are a few things. I can't justify the added cost with the amount of flying I do. I don't like the smell of Jet-A exhaust when the plane is idling in place. Fortunately this disappears as soon as things get moving. I don't like how tightly things are packed in the engine bay; it doesn't look like it is going to be very easy to work on. And I don't like the previously mentioned residual thrust at idle, but I am hoping Glasair can make that go away. This is a small dislike to be sure, but one that I would like to see reduced or eliminated if possible. Lastly, I worry about some lineperson putting avgas in it when I'm not looking. I almost never let anyone fuel my plane when I'm not there, so I guess if I had a Diesel Sportsman, I would have to simply make that never instead of almost never.

It is important to remember that this is a prototype that will undoubtedly benefit from some further refinement. But even taking that into account, this is a pretty refined package as it stands today. If I could justify the added cost, I would not hesitate to buy a Diesel Sportsman.

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