Superior's Diesel Entry

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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. 

Comments (18)

Diesels - at least the ones that burn Jet-A - may well become more popular in the US, in the face of one possible trend that caught me a bit by surprise. I was looking at the AirNav entry for KAPA a couple of days ago, and saw one ad there for Jet-A at $3.03 a gallon and 100LL at $5.50. If that kind of price differential holds up, diesels suddenly become a heck of a lot more attractive.

Posted by: Jay Maynard | April 23, 2015 5:44 AM    Report this comment

Diesels aren't accepted (yet) in the US for a very simple reason: Upfront cost.

Last I looked, aircraft diesel engines have a five-figure price premium over gasoline engines; even the cars available here with diesels are priced several thousand dollars higher than gas models (and many require one to buy the highest trim level, too). A quick check of diesel options for my RV-7, for example, shows a price premium of about $30,000 for the diesel option (yes, thirty thousand dollars) over a 180HP IO-360 with EFII. That $30k will buy an entire IFR glass panel, or 8-10 years of gas money, or the entire rest of my airplane, or a nice car for the wife, or... well, you get the idea.

A much faster and easier route to cutting fuel cost, increasing efficiency, and even improving safety would be to adopt and certify an existing, proven electronic ignition and fuel injection package. It's a simple retrofit to the engine, and the required changes to the electrical system also make it ideal for use with advanced avionics. As long as the FAA doesn't keep piling on more and more conditions for certification, and keep moving the goalposts further and further (even though the system's reliability already exceeds mag-and-carb by a healthy margin), it would be a far cheaper option than a diesel engine, with nearly the same fuel efficiency, the ability to run E10 mogas, and no need to fiddle with a mixture knob, carb heat, priming, etc.

Posted by: Bob Martin | April 23, 2015 6:09 AM    Report this comment

This is good news. Having deep pockets that are not concerned with next quarter earnings, will allow a sufficient level of funding to develop the product for market. Not sure if it will take off in the US but it will add competitive pressure on all engine makers. The scalability of this design should give a boost to the larger bore market as well.

As Bob Martin said, if and that is a big if, the FAA doesn't complicate the certification, we may get another option for our bug bashers. If it does not work out that is one of the risks of the free market.

Posted by: Leo LeBoeuf | April 23, 2015 8:40 AM    Report this comment

Bob - you're right that the upfront cost differential has until now been the single biggest reason for slow diesel sales in the USA.

However, note that the Superior Gemini engine has only a 20% cost differential between it and the Rotax 912iS (about $4,000). That cost differential is, in practical terms, next to nothing, well within the noise level for a total new aircraft cost.

Considering the 25% fuel consumption difference and the price differential between jet A and 100LL (a difference that is likely to increase once the new 100LL replacement fuels get approved and distributed), and the fuel savings over a 2,000 hour TBO, net of the engine price differential, starts to look pretty darn good.

Using the numbers Jay quoted above, which are fairly representative (but with huge variations airport to airport) of $3.03/g for jet A vs. $5.50/g for 100LL and a 5.0 gph consumption by the Rotax, the total fuel cost for 2,000 hours for the Rotax would be $55,000 and for the Gemini would be $22,725. Therefore the total fuel savings from the diesel would be $32,275!

That's a whopping big number even on the very small scale of 100 hp engines. Multiply that on larger birds with bigger engines, and the fuel savings become a huge cost of flight factor, providing a lifetime benefit-cost ratio, for the slightly higher initial purchase cost diesel, on the order of 8 to 1.

If Superior can maintain the cost differential on their promised bigger versions of the Gemini at around 20% over equivalent power avgas engines, they're going to do very, very well, even here in the USA.

The weight differential of the liquid cooled diesels that Paul cites is only a minor issue, if any issue at all ... effectively wiped out by the higher fuel efficiencies of FADEC diesel engine technology. Fuel weight savings effectively wipe out the engine weight increase on diesels.

The principal advantage of FADEC and liquid cooling is longer and more reliable engine life, being not subject to poor pilot management of mixture and power. Which has been the bane of early top end overhauls and outright engine failures that causes many if not most gas engines to not make it to TBO without costly engine repairs. A modern diesel beats avgas engines in virtually every important factor on a total cost of ownership and flying safety basis. As long as the initial purchase costs are comparable (within 20%) the diesel will virtually always be a better economic choice than avgas.

Posted by: Duane Truitt | April 23, 2015 8:49 AM    Report this comment

As for the overall performance of diesels, you have to look at the entire package of airframe and engine.

A great example of new technology airframe (lightweight/strong composite with relatively low drag), engine (diesel, 155 hp FADEC), and avionics (Garmin G3X touchscreen) in a high performance, low cost package, just compare the numbers for the Flight Design C4 to the Cessna Skylane, both being fully capable relatively fast four place fixed gear singles:

Cessna Skylane (230-hp non-turbo) - cruises at about 139 kts, carries a full-fuel payload of about 700 pounds (three sizeable adults plus baggage), and has a nominal range of about 580 nm with standard (55 gal) tanks. The fuel burn at max cruise is about 10.6 to 11 ghp; fuel cost is $58.30/hr at $5.50/g.

Flight Design C4 (155-hp diesel) - cruises at about 145 kts (75% power), carries a full-fuel (70 gal jet A) payload of about 840 pounds (four sizeable adults plus baggage), and has a full-fuel range of 1,700 nm (!!!). The fuel burn at max cruise is 7.9 gph; fuel cost is $23.94/hr at $3.03/g (less than half the fuel cost of the gas Skylane).

So the modern tech airframe and engine combo delivers a greater payload at a faster airspeed with a fuel cost less than half of the old tech airframe/engine combo. And likelier also with a much higher reliability.

Oh, and by the way, the target price of the (to be) certified C-4 is $250K for the gas version, while Flight Design hasn't yet published the price for the diesel (safe to assume it will be higher) ... vs. about $440K for the gas Skylane (and about $520K for the diesel version).

What's not to like about the diesel C4 when compared to any comparable performance avgas bird?

Posted by: Duane Truitt | April 23, 2015 10:22 AM    Report this comment

"What's not to like about the diesel C4 when compared to any comparable performance avgas bird?"
For the flight training lot, I think it still goes like this. What's not to like? Initial cost, hull insurance cost, power plant maintenance cost, TBR and/or TBO cost, down time cost, transition to other aircraft cost, flight training cost, rental cost. COST vs VIABLE MARKET maintains the pilot decline rate we've had for decades - a steady loss of 10,000 pilots per year. A $300K or even $250K unit price is largely unaffordable. What maintains some sort of balance is the $60K to $30K training or rental aircraft fleet that's not going away. Refurbs and retrofits are the down line solution. Keep pricing down and keep it simple.

Posted by: Rafael Sierra | April 23, 2015 11:29 PM    Report this comment

Rafael - A C4 is not a trainer, just as a Skylane is not a trainer, so you're making entirely the wrong comparison.

You may as well compare a 50 year old C150 to a brand new Cirrus SR20. The C-4 is a serious transportation bird with its speed, range, and true four place payload, just like the Skylane, only better and a whole lot cheaper. And a C4 is enormously more capable than a still-higher-priced G1000 Skyhawk.

If you want to compare and contrast trainers, then argue trainer birds.. In any event, flight schools are already in a transition from legacy birds to new advanced aircraft, with many offering both types to their students. Those more economy minded can go for the old legacy aircraft and those more attuned to modern aviation technology (mainly in the form of avionics and glass panels) or simply don't want to fly an old, tired, smelly bird that is riddled with squawks.

Posted by: Duane Truitt | April 24, 2015 7:42 AM    Report this comment

The Flight Design C4 would be as much a trainer as the C172 as it is comparable and its designers intend it to swing both ways. If ultimately available with the O-360 then I would go with this power plant alternative as Diesels are more expensive to operate, period. My concern is, independent of power plants, that the higher the initial cost the higher it drives the operating costs making "old, tired, smelly birds" an attraction. As I said before, Refurbs and retrofits are the down line solution. Keep pricing down and keep it simple.

Posted by: Rafael Sierra | April 24, 2015 9:34 AM    Report this comment

Further, I'm sure that Flight Design considers the flight training market as primary in importance. The C4 could be an investment with a bearing on flight school or aeroclub lease-back deals augmenting affordability, not just for personal purposes. I would think that Flight Design is planning on a wide market acceptance and use of their C4s.

Posted by: Rafael Sierra | April 24, 2015 10:15 AM    Report this comment

Sorry, Rafael, but no - the C172 is in no way comparable to the C4, unless by "comparable" you mean that it is 34 knots slower, carries little more than half the full-fuel payload, and has one third the full fuel range, but is still "comparable". No, not even close.

Can Flight Design sell some C4s as trainers? Sure ... just as some training schools use Cirrus SR-22s to train Cirrus pilots .. but nobody would ever call a SR-22 a "trainer". It would be a big waste of the customer's money and time to do primary flight training in a serious cross country traveler when a C-150 or Piper Warrior would do the same thing at far lower hourly cost.

Even the C182 Skylane - which no knowledgeable pilot would call a "trainer" or "comparable to a C-172", comes up far short of the performance capabilities of the diesel C4, as I detailed above, on speed, range, and payload.

And no .... diesels are not more expensive to operate than avgas engines... quite the contrary. Aside from the fuel cost - which is about half the fuel cost of equivalent avgas engines, as I detail above - the maintenance cost is also far less. No plugs to replace or foul, no valves to burn (on the 2-stroke models like the Gemini), no periodic top end overhauls due to mis-managed manual power and mixture control (instead, everything is controlled by the FADEC computer). Certified TBO on the Gemini is the same 2,000 hours as most avgas engines have, and in the real world, the diesel engine will likely lase far longer.

Posted by: Duane Truitt | April 24, 2015 2:06 PM    Report this comment

Shhh...is Truitt still in the vicinity?

Posted by: Rafael Sierra | April 25, 2015 8:25 PM    Report this comment

You fuel numbers are not realistic. It so happens APA is the exception with a $2 delta since they're waging a Jet-A price war between FBO's. $1 difference is more like it on average.

Posted by: Robert Goubitz | April 25, 2015 8:27 PM    Report this comment

I did more research and the average difference in the USA is between 50 and 70 cents/gallon between Avgas and Jet-A. You can forget about running any comparisons at $2, let's be fair. One of the main advantages of Jet-A will be availability, not pricing.

Posted by: Robert Goubitz | April 25, 2015 8:56 PM    Report this comment

It's a misnomer to attribute maintenance savings as much of a reason for having a FADEC-controlled aircraft engine, unless you limit your thinking to legacy design air-cooled engines. There are really only two examples of these, the Continental Powerlink and Lycoming's IE2. Neither has been fielded in significant quantities to prove the theoretical claim that taking the pilot out of the engine control loop saves dollars on wrenching it. Nice idea. Unproven reality.

As for water-cooled engines like the Rotax and diesels, the larger order savings, by far, come from fuel economy. A true FADEC allows two things: variable ignition timing and electronically controlled fuel injection. In the 912 iS, for example, BSFC improves enough to save $14,000 in fuel costs (or more) over the TBO run. That's a much larger number than any maintenance savings related to what a pilot might or might not do when flying this relatively thermally stable engine.

Rotax engines typically don't have many chronic maintenance issues reaching TBO related to pilot operation. The best thing you can do is run them on unleaded auto fuel, not avgas. That avoids fouling the oil with lead, which can lead to gearbox/clutch issues. This is what Rotax told me when I spent three days at the factory last summer. The acid test will be how the iS compares to the ULS. My guess is they will have similar maintenance costs and patterns. One advantage of the FADEC in the iS is electronic diagnostics. That will save some bucks, but probably not a huge difference against the ULS.

Same thing for diesel, but more so. The major gains in diesel economy have come almost entirely from electronic control, specifically pulse injection that allows very precise pulse width and shaping of the fuel charge. Mechanical injection can't do that very well, if at all. Rotax had this option with the iS; they could have used direct gasoline injection, as many cars do today. They decided the gains were not worth the investment, so they stuck with port injection.

Anyone who is honest with the numbers comparing gas with diesel will realize the costs in the U.S. are not a slam dunk yet, although they are trending positive. Diesel costs are still high upfront, still high to overhaul and they still have short TBOs. In Europe, however, diesel enjoys a huge advantage because Jet A so much cheaper than avgas.

Posted by: Paul Bertorelli | April 26, 2015 8:37 AM    Report this comment

Paul, thanks for the explanation. And what are your thoughts about using the C4 as a trainer? Also, which engine would the U.S. flight training market most likely prefer?

Posted by: Rafael Sierra | April 26, 2015 10:14 AM    Report this comment

OK then, IMO the C4 with the G1000, A/P, ADS-B Out, and the carbureted O-320, 50 gal. fuel cap., at $200K would be a good choice as a trainer and for the personal use market.

Posted by: Rafael Sierra | April 26, 2015 1:49 PM    Report this comment

Raf, I don't think the C4 will come in at $200K with the G1000. They've been saying around $250K with Dynon avionics, or the equivalent. In other words, avionics not certified in the traditional way.

Also, that price envisions the Continental IO-360AF, not a diesel, which would be more expensive to install. And we don't yet know if Flight Design will hit its price point. Institutional buyers have not been historically very sensitive to price of new trainers, hence they're willing to buy $400,000 Skyhawks. The big drivers for them are predictable costs, maintenance reliability and pot sweeteners from Cessna or Diamond.

At some point, this could change however. After all, Cessna is promising diesel Skyhawks so two or three years hence when Flight Design is ready to sell in volume, the market may look a little different. Smaller schools and private buyers, who do tend to be price sensitive, may like what they see in the C4.

For training, It's not night/day against the 172, but claims to be 20 or 30 knots faster and with as much as 1300 pounds of useful load. Can flight schools really put both of those things to work? Maybe, especially it it really is $150,000 cheaper.

Diesel or gas, the C4 has real potential, for sure. We'll have to see if it delivers. Looks great so far.

Posted by: Paul Bertorelli | April 27, 2015 12:28 PM    Report this comment

It seems we aviation types are so like poor old Charlie Brown; no matter how many times the football is pulled away we are ready at the drop of a promise to give it our all one more time.

Example: Herein we see elaborate and detailed comparisons of the Skyhawk, whose plusses and minuses have been demonstrated for decades, with the Flight Design C4, a bird whose actual flight, much less actual performance and even actual cost, are all as yet evidenced only in the manufacturer's press releases.

And to further muddy the waters, the C172 / C4 comparisons add to the C4 Diesel power imbued with wonderful - but similarly unproven - life cycle costs. This in spite of the fact the manufacturer says its C4 will fly behind the IO-360AF.

Oh well, if not this time then surely next time.

Posted by: John Wilson | April 28, 2015 12:35 PM    Report this comment

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