AirVenture: The Diesel Dance

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To say that aviation development and market uptake moves glacially is an insult to glaciers everywhere, or at least the piles of dirty snow that pass for glaciers in a world where average summer temperatures make Venus look temperate. I can develop a fairly long list, but let’s consider diesel engines for the moment.

These make perennial appearances at AirVenture and like the pixel-addled zombies that we are, we dutifully troop off to the press conferences, write down what the people say and then stumble off to the hangars to recover in one of those Magic Fingers chairs while the guy in next booth flogs copper-bottom pots. Yeah, I did it last year and never even got the massage.

This year, the Wisconsin-based startup, EPS, had a press conference and so did DeltaHawk. Remember them? EPS showed; DeltaHawk didn’t, although they were on the field. You can hear about EPS’s latest progress in this podcast

Cutting to the chase, the EPS engine is a high-output diesel capable of up to 450 HP, so it targets high-performance singles and twins, utility aircraft and the UAV market. The company claims to have provisional orders for more than 1000 engines, without saying who the customers are. It’s an innovative 180-degree V-8 configuration with one crankpin sharing two rods, so the engine is shorter. But at 657 pounds installed, it’s still heavier than a gasoline engine on a power-to-weight basis. If the company’s numbers are accurate, it has stunning fuel specifics: 0.32 BSFC compared to 0.35 for the diesels already out there and 0.42 for typical gasoline engines. 

Without occupying the minds of the people who buy these engines—and that’s OEMs, not aircraft owners—it’s hard to know how much such sunny numbers sway them, if at all. Consider Cessna’s on-again-off-again but mostly off-again flirt with diesel. It pulled the plug on a Skyhawk diesel in 2007 just as Thielert was about to sink. Then it announced the 182 JT-A in 2012 with the SMA SR305-230 diesel, only to flatline that project in 2015. This spring, Cessna killed the diesel Skyhawk using Continental’s CD-155.

Piper is hanging in with its CD-155-powered Archer DX, but it doesn’t appear to be a strong seller. We know Cirrus has flown various diesels in the SR22; we don’t know if they’re remotely interested in offering a diesel model. My guess would be … maybe, but probably no. Mooney has its diesel M10 trainer project in limbo, if not abandoned entirely.

Along with a few conversions, Diamond still owns what there is of the diesel market, which by my estimation, is about 7 to 9 percent of total new GA piston aircraft. Like the EPS engine, the Austro four-cylinders Diamond developed have impressive fuel specifics and are, bar none, the smoothest running powerplants in piston GA. But they’re heavy and more expensive than gasoline engines. But this may not matter to a buyer who can afford a $1.4 million DA62.

And this gets me to the wrong-assumption stage of the discussion. With the exception of Diamond, airframers are not exactly risk takers. Volumes and margins on GA airplanes are thin at best and a clean sheet innovative airplane that tanks—always a good chance that it will—takes the P&L with it. Ask Diamond about that after the DA42 teething pains with the original Thielert engines.

Sure, OEMs want performance and economy to juice the ad copy, but they just as desperately want to avoid a turd of an engine that may suffer from infant mortality and a vaporous supply chain and support structure. You can practically get parts for a Lycoming at NAPA, but a new-age diesel? Not so much.

And that’s where I think innovative powerplant developers run off the rails. It’s not enough to have great performance, impressive fuel specifics and single-lever control; OEMs also want companies that appear to have legs and staying power in the commercial sense. That, more than anything, makes breaking in with a new engine daunting as best, improbable at worst. 

Fears about the extinction of leaded avgas were once driving this, especially in the U.S., but even as the FAA has all but surrendered on an unleaded replacement, I don't sense much concern. Owners aren't asking us what we think is going to happen. Not that I have a clue in hell anyway. But diesels—especially new, unestablished ones—will have a steep uphill slog to gain market share. Technical excellence or lack thereof may have nothing to do with it; market inertia may drive it. And evidently, except for a small niche, pilots love gasoline.

Comments (18)

" ... pilots love gasoline. ". Pilots love lower costs.

Posted by: Rafael Sierra | July 27, 2018 12:09 PM    Report this comment

"Fears about the extinction of leaded avgas were once driving this..."

Exactly. That fear certainly has been the prime mover of MY enthusiasm for diesels. I still have that fear. But until the last drop of 100LL is burned in anger, aviators everywhere - well, at least in the U.S. - will extend their middle fingers at the prospect, much less the inevitability.

In 2018, diesels look a lot like a good idea whose time has not yet come. And never may.

Posted by: YARS (Tom Yarsley) | July 27, 2018 6:24 PM    Report this comment

"But they're heavy and more expensive than gasoline engines"

Understate things much? (Almost) nobody that's paying for their airplane out of their own pocket, rather than using it for business, is going to fork over the five-digit price premium for a diesel engine conversion. Even in the homebuilt market it's an uneconomic proposition. Last I checked that DeltaHawk would run me about $70k for my RV-7... I could built the entire airplane for that, and have money left over.

I'd love to have a diesel. But I'm not paying 2-3 times as much, or more, for the privilege of having one.

Posted by: Robert Gatlin-Martin | July 27, 2018 7:30 PM    Report this comment

Diesels ... smielsels ... I tromped up and down everywhere looking for a charging station for my electric airplane and all I could find was a couple of outlets behind the Hangar Cafe. NOW what do I do? I only have a 50' extension cord.

But OHHHHH ... did you see that carbon fibre looking "thing" that is a cross between ... I don't know what? Of course, it's a "prototype" so the finished product (available in 10 years) ought to be great. A $5K deposit will hold your position, though.

I swear ... you could sell flying carpets to millenials at OSH (sigh).

Posted by: Larry Stencel | July 28, 2018 9:19 AM    Report this comment

Perhaps the focus for the US at least should be on improving our spark ignition gasoline engines and getting the lead out of the fuel. A quick look at the automotive industry shows that modern electronics and technology can garner gobs of horse power out of small engines that do not have much sensitivity to the quality of fuel being burnt.

Granted air cooled engines will never reach the efficiency levels of water cooled designs, but any improvement in fuel flexibility and power output will be a big plus. Removing the lead will increase engine life. I am old enough to remember the maintenance problems of automotive engines and exhaust systems during the days of leaded automotive fuel. During the move away from leaded fuel, there were all sorts of predictions of doom and gloom about burnt valves, lost power, poor performance, starting troubles etc. etc. The reality is that today automotive engines are extremely reliable, tolerant of varying fuel quality and very efficient.

Diesel engines are more fuel efficient but due to the higher stresses, tend to be heavy. A 3000 + pound, 9 liter, 425 HP engine in a Keworth is not an issue, however, for an airplane every ounce counts. The diesel engines that we are seeing in aviation are either clean sheet designs or reworked automotive engines.

From a developmental stand point, I believe that improved spark ignition engines are much further along the development curve than are compression ignition engines. Granted aircraft engines live in a different environment than automotive engines, but many of the design features can be incorporated. I have flown behind the IOF-240 FADEC engine and was very impressed with its performance and economy. Unfortunately, Continental has chosen not to promote or improve upon this certified engine ignition/ fuel system improvement.

Will we see more diesel engines swinging props? I don't think that there will be a diesel on every airport in the foreseeable future. Would be nice to say "top it off with Jet-A with Prist" when giving a fuel order but i am not holding my breath.

Posted by: Leo LeBoeuf | July 28, 2018 9:36 AM    Report this comment

The catch 22 might indeed be the fuel supply. Roadable aircraft solve that and a lot of other problems. The other problem is that flight schools and other fleet operators are averse to anything new (and not without good reasons). Still, the idea of a parts network in GA is plane BS (sorry).

Ya gonna get stuck. Own it. Your part is almost always coming over night. I'd recommend EPS and others tell parts distributors to add more value to the chain, or good luck in their new venture. Own your distribution and contract someone worth a darn to run your operation.

Modern 4 cylinder gas power plants put out so much HP and torque. Also, they so rarely break. It's amazing. I don't know the numbers on these engines, but EPS isn't exactly proud of theirs, so I can't compare.

And why go to eight cylinders? Isn't six enough? Eight seems to be an issue unless the plan for overhaul involves melting the block.

Posted by: Eric Warren | July 28, 2018 10:58 AM    Report this comment

I think there's a gap between turboprop and piston at the 400hp mark that a diesel could neatly fill. Certainly based on the quoted numbers the EPS engine would be perfect for the airvan. I hadn't heard that it would be 657 lbs though, which is what 100kg heavier than the IO-540?

Posted by: Gareth Allen | July 28, 2018 11:01 AM    Report this comment

More than 70 years ago there were hundreds (possibly thousands) of diesel aircraft engines in service. These were primarily installed on patrol and reconnaissance flying boats operated by the Luftwaffe,

A major reason for their adoption was the limited availability of aviation-quality gasoline in Germany. If historical president holds, then fuel availability will drive the acceptance of diesel power plants, not their technical merits.

Just a data point to support statements made by previous posters.

Posted by: kim hunter | July 28, 2018 12:51 PM    Report this comment

I second Leo's comments. Why do we keep pursuing diesel engines when there are plenty of technologies from the automotive industry that could keep gasoline engines running for a long time. I don't know how many times I have been told by supposed aircraft engine "experts" that car engines are different and won't work in airplanes. If that is the case, then why do we think that diesel engines - mostly from truck and car technology - are so much better? The simple idea of electronic ignition and variable spark timing would go a long way to keeping the existing engine fleet running.

One reason I hear for switching to diesel is that it is available everywhere. But, I don't see mass orders for diesels coming from Europe or Africa where Avgas is very expensive and hard to obtain. In fact, the Europeans seem to be moving away from diesel in favor of electric or hybrid designs.

The biggest stumbling block to better engine technology seems to be industry reluctance to change, mostly because of the huge capital costs for certification and setting up a supply chain for the new designs. Diesel engines don't change that dynamic any more than updating piston engines does.

Posted by: John McNamee | July 28, 2018 6:46 PM    Report this comment

Per Leo: "Perhaps the focus for the US at least should be on improving our spark ignition gasoline engines and getting the lead out of the fuel. A quick look at the automotive industry shows that modern electronics and technology can garner gobs of horse power out of small engines that do not have much sensitivity to the quality of fuel being burnt. "

I add a third to Leo's take on it. A modernized plain vanilla gas engine with today's software-controlled ignition and individual cylinder fuel optimization, coupled with a compression ratio that tolerated 80-ish octane gas and topped with a suitable rules adjustment that allowed development & deployment without tripling the actual cost would basically solve the current engine/fuel problems.

To say it's just a paperwork problem wouldn't be all that far removed from reality.

Posted by: John Wilson | July 28, 2018 10:54 PM    Report this comment

New engines of ANY type "solve the fuel problem" ONLY for those who are looking for a REPLACEMENT for their existing powerplant(s). In almost all cases, the cost of any new engine installation (including applicable STCs) would exceed the value of a typical light GA aircraft.

Posted by: YARS (Tom Yarsley) | July 29, 2018 11:32 AM    Report this comment

Flogging a dead horse?

Posted by: Rafael Sierra | July 29, 2018 12:05 PM    Report this comment

Auto conversions get the reputation for being "not suitable" because in the majority of cases, they are one-off installations being done by amateurs. It's not the core engine (crank, case/cylinders/block, etc) that causes the problems, but the ancillary systems.

Cessna, Piper, Beech, et al, and even NACA/NASA spent a lot of time and money figuring out how to properly install air-cooled opposed engines. Most of Lycoming and Continental engines, and even Rotaxes and other purpose-designed airplane engines, copy the same installation practices used on certified airplanes with lots of testing behind them.

Most auto conversions, though, are installed as one-offs. Each one is different, often drastically so, and reduction drives (if fitted) often don't get the full vibration analysis they really need. There's also the added complication that most light airplanes are designed for air-cooled opposed engines; packaging a liquid-cooled inline engine plus its radiators into that space requires a lot of changes. Look at a P-51 vs. a Corsair for extreme examples.

There's no reason an auto-derivative engine couldn't be successful in an aircraft application, provided that the installation is properly engineered and tested. However, the costs of doing so are high. Even for the experimental market, such an engineered "FWF package" would take a large upfront investment and require pricing in the same ballpark as traditional engines just to make a long-term payback. You can forget the certified market, because the FAA would have an anyeurism over buying the engines straight off the line, and setting up a dedicated production line would kill the economics.

Posted by: Robert Gatlin-Martin | July 29, 2018 2:04 PM    Report this comment

Let's give Diamond more credit in this space: They've been successfully producing and shipping their Austro turbodiesel engines in their planes for 9 years now.

I've owned a pair in my DA42 twin for 4 years, and now in a DA62 twin. Yes, they each weigh an extra 100 lbs compared to a Lycoming avgas engine, but so what in a carbon fiber aircraft with a max gross weight of over 5000 lbs. I burn only 15 gph (7.5 gph per side) in cruise doing 180 knots.

These engines are unbelievably quiet and smooth, with push-button start, no need for winter preheat, and with single-lever FADEC throttles with no mixture or prop controls. I only need to change the oil (synthetic since there's no lead in JetA) every 100 hours, and never have to add more than one quart/liter between oil changes. IMHO basing these engines on Mercedes diesel car engines (of which Mercedes built more than a million) was pure genius.

I've flown the Austro diesel DA40 NG back-to-back with the Lycoming DA40, and the avgas plane feels like flying in a cement mixer compared to the smooth, quieter diesel. (Check out this month's Flying magazine's cover story.)

Posted by: DAVE PASSMORE | July 29, 2018 4:02 PM    Report this comment

" ... the avgas plane feels like flying in a cement mixer compared to the smooth, quieter diesel."

I've told you a million times not to exaggerate!

Posted by: Rafael Sierra | July 30, 2018 11:33 AM    Report this comment

Diesel powered Diamond DA40 NG price: $500,000 ? I'll buy two, dos, low time SR22s for the same amount.

Posted by: Rafael Sierra | July 30, 2018 6:09 PM    Report this comment

Betamax was better than VHS.
Macintosh was better than Windows 3.0.
Diesels are better than gas engines.

Point is that there are a LOT of reasons why "better" is not necessarily getting adopted.
Wanna ask the EU how it NOW feels about Diesel engines?

Posted by: Mark Fraser | July 31, 2018 9:03 AM    Report this comment

Yars comments: "New engines of ANY type "solve the fuel problem" ONLY for those who are looking for a REPLACEMENT for their existing powerplant(s). In almost all cases, the cost of any new engine installation (including applicable STCs) would exceed the value of a typical light GA aircraft"

Not precisely sure what your point is, but the problem I am looking at is, in fact, the replacement engine one. There are doubtless many others in my position. I would prefer to replace my high-time IO-520 with a zero-time reman, but hate the idea of paying that sort of big-bucks (and yes, in my case, it would indeed be a significant fraction of the bird's value), only to get hit with some fuel availability fiasco before the engine cost was even fractionally amortized.

What I am envisioning wouldn't be a whole new engine development, just a makeover. Six new cylinders engineered for the sensors needed for real-time electronic spark and mixture control, and the automotive-style spark/injection systems to match. I don't expect this to happen, of course, because by the time engineering costs are recomputed by the FAA-mandated cost multipliers and divided by the limited production run....well, we all know the math. But it's a way forward I might try if I ran the entire zoo.

Posted by: John Wilson | July 31, 2018 2:35 PM    Report this comment

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