Superior's Diesel Entry
When Superior Air Parts told us that it was announcing a new engine product for Sun 'n Fun, I figured it would be one of two things: another gasoline variant in the experimental or certified line or a resurrection of the three-cylinder diesel that Tim Archer was involved with back in 2008. He had left Superior at the time and was running a company called Powerplant Developments, a U.K. firm developing this unique engine. They were far enough along with it that at least one company, Tecnam, was interested in trying it in a P92 light sport. Although we don't hear about this sort of thing much, companies are always trying new engines that never see the light of day. Cirrus has flown everything that can swing a prop.
So will Superior's new Gemini be an also ran or something that finds a little market traction? To judge that, take off your U.S.-centric hat and put on your global market hat with a gaze toward China. Since Superior is Chinese-owned and China is bullish on aviation investment without the typical ROI constraints expected of U.S. businesses, I suspect the project isn't construed to turn big numbers or big profits--or maybe any profits--for the near term. Ironically, if that's true, it's a business plan similar to what Rotax envisioned for its 912 iS; a 20-year product cycle. I'll get back to that in a moment.
So in considering whatever appeal the Gemini has, it may enjoy some competitive advantage in China for being both a homegrown engine and one with a years-long product cycle. (It's homegrown in the sense that Superior is a Chinese-owned company.) Engine nerds will recognize the design of the Gemini as a reiteration of the famed Junkers Jumo 205, of pre-war and World War II fame. The 205 was a six-cylinder design with 12 pistons and up to 886 HP. It was considered a successful design and was used in the Junkers Ju 86 and a couple of Blohm & Voss long-range maritime designs, including an airliner. However, when the combat demands of World War II pushed development toward high-output gasoline engines, the Jumo was less competitive.
As explained in our video on the engine, the Gemini update of this design is also a two-cycle engine. Supercharging is required to start it, since it's otherwise incapable of flowing the incoming charge sufficiently to compress and ignite. That means the engine has no valve gear--good--but it does have the supercharger and potentially a turbocharger as well, so that hits the weight budget. It's also watercooled, which means it has radiators and the associated plumbing and complexity. While the Jumo had mechanical injection, the Gemini will be FADEC-controlled with pulse injection, which promises to squeeze out a little more fuel efficiency. Superior says the Gemini is now running at about 0.38 lbs/hr BSFC, which puts it between the best diesels and best gasoline engines in terms of efficiency. For what it's worth, a Continental IO-550 running lean of peak can do nearly as well on gasoline, but no commercially important small gasoline engines that I know of do that well.
Well, maybe one does. Rotax's new 912 iS and the Sport variant of that engine has proven to be exceptionally efficient; more so than the company originally promised. I haven't run those calcs recently, but I wouldn't be surprised if it's running at 0.40 BSFC, if not a little better. And that's what Rotax had in mind when it developed this engine. It could see potential disruption from diesels in the small-engine market and, among other things, wanted to remain competitive. Rotax considered diesel, but Francois Tremblay, head of the BRP Powertrain division, told me last summer that it demurred. "Not our thing," he said. Rotax took a long look at buying Thielert, but passed.
Compared to a Rotax, Superior says the Gemini will be price competitive, but will give up 20 pounds in installed weight to the Rotax. Frankly, I'll be surprised if the weight Delta is that small in actual installations. But even at 20 pounds, isn't that a deal killer in an LSA that's already challenged to maintain an empty weight against a hard gross weight of 1320 pounds in the U.S.? Not really. Kitfox is able to install both a Lycoming O-233 or a 912 iS in the same airframe and the Lycoming is quite a bit heavier. This will vary by airframe, of course, but some light sport airframes can accommodate heavier engines.
In return, the diesels return lower fuel burn and lower costs and potentially better range, if that happens to matter to an LSA operator. It might or might not or it might not matter enough to tolerate the weight hit and teething pains of a new engine package. A Remos engineer once told me that small diesels in very light aircraft weren't worth the trouble. Diesel economy is directly scalable, which is why the numbers really tilt toward them being a better choice for large-displacement engines. A 20-percent fuel savings on 17 gallons an hour is a lot more meaningful than the same savings on 4.5 GPH.
In those parts of the world where avgas is hard to get, the ready availability of Jet A or even low-grade kerosene will be a much big driver than it is in the U.S in a preference for diesel. That describes a developing aviation market in China and Africa and an evolving market in Europe. It doesn't describe the U.S., where there's still a detectable bias against diesel aircraft engines.
The world diesel aircraft engine market continues to advance like straight-weight oil on a cold morning. Continental is making progress selling conversions, but we're not seeing huge numbers here. Diamond continues to sell diesel singles and twins, which constitute the majority of its business. Cessna has two diesel models and it has taken a very un-Cessna-like glacial pace to certify the diesel Skylane. I don't know why this is so, but part of it might be that Cessna has a similar long-term view of the market as the Chinese seem to, which is to say it's going to remain viable, but isn't going to explode in the near term.
Nothing about Superior's introduction seems likely to change any of this, in my view. If it can find sufficient offshore demand for this engine to support a modest business plan with a very long timeline, I can see it working. Diesels or not, light sport production numbers have been modest and will probably remain so. And guess what? Gasoline development doesn't stand still against diesel competition, which is what Rotax demonstrated with the 912 iS. More competition from diesel will keep that kettle boiling.