The Diesel Dilemma

Jet-A engines are hot in Europe so why arent they here yet? You wont like the answer: Gas is still too cheap and service is non-existent.

For years-about 25, to be exact-we have been writing sky-is-falling stories about the looming fuel crisis in general aviation. And while weve been patiently waiting for it to happen, it has, in fact, been right under our noses all along. Leaded avgas is simply too cheap and there’s too much of it available to stir even mild market interest in new engine technologies.

This may sound absurd if-as we have-youve paid as much as $3.50 a gallon for avgas. (As noted in this months editorial, the $5 mark has been passed without much fanfare.) Yet even with the reality of a $200 fill-up for a Cessna 172, there’s not much evidence to suggest that North American aircraft owners are agitating for more efficient engines. They may be buying fewer twins, flying less and even considering dumping the airplane altogether, but herd a bunch of owners together and theyll complain about high gas prices without considering more efficient alternatives.

This, more than anything, explains why one of the most promising new technologies-aero diesels-is showing faint signs of dying on the vine in the U.S. market. Three years ago, Diamond shook up general aviation with a proposal to build a diesel-powered twin-the DA-42tdi Twin Star-promising Baron speeds on Archer fuel flows. Although it hasnt quite delivered the hoped-for performance, the Twin Star is no slouch. From our paper review of the airplane, no twin flies as fast as the Twin Star on as little fuel and only the most economical singles approach the Twin Stars efficiency. (And there arent many of them.)

We would like to give you good performance numbers on both Diamonds diesel single, the DA-42tdi, and the Twin Star. Unfortunately, there are no North American versions of these airplanes and there may not be for some time to come. Diamond has concluded that market conditions arent yet right for the diesels in the U.S. and, further complicating the equation, the company believes the Thielert diesels used in these aircraft will require an extensive, specialized service network that doesnt exist. Then there’s the legal climate. Its benign in Europe and, by comparison, frightening in the U.S.

Hot in Europe
While the North American aero diesel market has thus far been a snoozer, diesels are hot in Europe, both for airplanes and cars. Market penetration of diesel cars in Europe is between 40 and 50 percent. In some European countries, diesel sales outstrip gasoline engine sales. In the U.S, market penetration remains at under a paltry 1 percent for cars. While our editorial focus has been on new gas-powered airplanes from Cirrus and Lancair, Diamond has been selling diesel-powered DA-40tdi Stars in Europe-about 130 are flying-and just this spring, it began deliveries of the DA-42tdi diesel Twin Star, again, only in Europe.

Thats not say there’s no interest in the Twin Star in the U.S. Weve heard from more than a handful of readers asking where this thing is. When can we fly it? When can we buy it? Meanwhile, Diamond has been laying low on press demo flights and, if anything, has pushed back on generating more buzz for the diesels in the U.S., something we rarely see from an aircraft company. Whats up? Is the idea about to tank?

Not at all, says Diamonds North American president, Peter Maurer, but the company has certainly delayed its plans to push diesels in the U.S. Maurer told us the earliest conceivable introduction would be in early 2006 but we wouldnt be surprised to see it later than that.

The DA-40tdi single has been selling in Europe since mid-2004 and is fully certified by the European EASA, but not by the FAA nor Transport Canada. Were told that these certifications are largely pro forma based on bilateral agreements with the European agencies so Diamond faces no certification dealbreakers in the U.S. The FAA has issued a type certificate for the engine.

Maurer told us Diamond is going slow on introduction in the U.S. for several reasons. Leading the list is lack of a service network for what is essentially a sophisticated and relatively complex automobile-style FADEC-controlled engine. Thielerts 135-HP Centurion 1.7 is based on a Mercedes Benz product used in the A-class hatchback, popular abroad, but not marketed in the U.S.

In the aero diesel version, this turbocharged in-line four cylinder engine has dual-channel FADEC, intercooling and watercooling, plus a high-pressure direct injection fuel system and a sophisticated engine monitoring system. Its the sort of thing the blue-coated German-trained tech at a Benz dealer can fix in his sleep but definitely not something a Lycoming or Continental wrench will want to confront without training.

Diamond has been down this road before with the original DA-20 Katana, which had an Austrian-built Rotax 912S. That engine was neither turbocharged nor FADEC-equipped, but it was complex enough to have stirred maintenance heartburn in the field. Not every shop could or would offer to service it. For that reason, and because it was shy of power for high-density altitude ops, the Rotax didnt survive in the North American market, having been replaced by a low-tech IO-240 from Continental. Diamond hopes to avoid repeating the misstep.

Although Diamond leads the world in aero diesel experience, the fleet-primarily European airplanes-hasnt accumulated a large sum of hours and none of those hours have been in the kind of extreme conditions found, say, in the desert Southwest or on a February morning in Fargo. Typically, diesels have issues with starting in extreme cold and because the fuel is delivered under high pressure, they tend to pump heat into the injection system. Diamond thinks it would be nice to know how the engine might behave in such extremes before customers find out on their own.

Although Maurer didnt mention it to us, there are a couple of other reasons even well-executed diesel airplanes-and we think the Diamond airplanes are we’ll executed-may not be slam dunk hits in the U.S. What if U.S. airplane buyers think like U.S. car buyers, which is to say their notion of diesels is that theyre noisy, slow and smelly? What if buyers don’t want to give up performance to save a few bucks on fuel costs?

Yet another potential barrier that buyers may be thinking about is durability and longevity. The Diamond production airplanes being delivered in Europe have engines with a stated TBR-time between replacement-of 1000 hours. This is expected to increase to 2400 hours and may go beyond that, but it hasnt yet. In the meantime, to lessen the sting of a replacement cycle thats half that of a typical Lycoming, Thielert is pro-rating the cost of the TBR on a 2400-hour basis. In other words, betting on the come that the TBR will be extended sooner rather than later, Thielert is offering pro-rated pricing support to any buyers who reach TBR before the extensions are available.

Maurer believes that TBR limitations wont be an issue for U.S. or European buyers because the high utilization experience in flight schools and commercial operations will have driven the TBRs beyond 1000 hours.

Hanging over the entire diesel initiative is the legal climate in the U.S. Both serious contenders in the diesel realm-Thielert and Frances SMA-are accustomed to doing business in Europe, where tort law exposes manufacturers to a fraction of the risk of litigation they face in the U.S. As we reported in the April issue, Lycoming was successfully sued for some $96 million in damages as a result of the massive crankshaft recall in 2002. As part of the Textron group, Lycoming has the backing of a deep-pockets conglomerate but Thielert does not. U.S. buyers cant be blamed for wondering how Thielert or SMA will fare in the face of a major lawsuit. Although the U.S. still represents the richest market for general aviation aircraft, its not outlandish to think that foreign diesel manufacturers would decide not to sell their engines here merely to avoid the risk of litigation.

World View
Diamonds Maurer told us hes confident that demand exists for diesels in North America, especially for the DA-42 Twin Star, which, in our estimation, has generated more interest than any airplane introduced within the past decade and represents the first clean-sheet twin weve seen in a lot longer than that. Maurer is refreshingly honest about the airplanes performance shortfalls. Based on its early flights with a prototype twin, Diamond had predicted maximum speeds of 203 knots at high cruising altitudes. But because of unanticipated cooling limitations and power lapse at higher altitudes, top speeds fall short of that mark. Were told that cruising speeds in the mid- to high 170-knot range are realistic, on fuel flows totaling 12 GPH or less.

On a ferry flight last summer, Diamond test pilot Gerard Guillaumaud flew a 1900-mile non-stop leg from St. Johns, Newfoundland to Portugal in 12.5 hours, at an average total fuel burn of 5.7 GPH. He landed with five hours of fuel in reserve. (The airplane carries 78 gallons in its optional long-range tanks and had an additional 26-gallon ferry tank aboard.) Average groundspeed on that flight was 158 knots. Whether U.S. pilots would choose to fly an airplane at such miserly power settings is questionable, but 1500- to 2000-mile range in a twin burning under 12 GPH is remarkable capability at any speed and will find some buyers in North America. It could find many buyers if avgas reaches $4 a gallon, which seems inevitable.

If the diesel charge ever gathers momentum in the U.S., flight schools flying twins for training will probably represent the leading edge of demand.

The economics, if borne out, are attractive. A diesel twin flown 100 hours a month in training burns two-thirds as much fuel as an equivalent gasoline airplane, so fuel savings alone could amount to-conservatively-$2000 to $3000 a month. Thats a big number for a school flying a handful of twins and pinching pennies to eke out a profit.

If a diesel-powered trainer can match the dispatch reliability of a gasoline-fueled version, the diesel looks like a hands-down winner. For a private owner flying 100 hours a year, the savings are less compelling, amounting to perhaps $2000 a year in fuel savings but requiring an investment of $400,000-plus in a new airplane just to join the economy club. The interest alone on that sum will buy a lot of avgas and Diamond knows it. For that reason and because it knows North American buyers value performance over economy, Diamond is likely to offer two versions of the DA-42 Twin Star in the U.S., the Thielert diesel model and a version powered by off-the-shelf 180-HP Lycoming IO-360s, a model thats currently undergoing certification trials in Europe.

The Lycoming variant will carry slightly more fuel-95 gallons-but have similar full fuel and useful loads because the Lycoming engines are lighter. But the Lycoming model clearly wont have the long legs of the diesel model. Nor will it have the simple, single-lever push-button operating logic of the diesel airplane.

If U.S. owners follow their car-buying habits, the Lycoming version will outsell the diesel version by a 20 to 1 margin. But were not convinced that will happen. During our annual visit to the Sun n Fun fly-in, the subject of fuel prices came up repeatedly, suggesting to us that buyer psychology may be approaching a tipping point in the performance-versus-economy equation. If thats true, Diamonds delayed diesel introduction may, in fact, be perfect timing.

We arent taking the position of being diesel fundamentalists, Peter Maurer told us, We are airframers. We build airplanes. That means integrating other technologies, including diesel. We are going to hedge our bets so we can react to economic conditions. If buyers want diesels, we have them. Were building them.

Of all the engine initiatives weve examined, the Diamond/Thielert diesel project has been the most successful. Its delivering diesel twins and European buyers are pottering around in some 130-plus diesel-powered Stars. In the U.S.-thanks to cheap gas prices and the tenaciousness of leaded fuel-diesels havent made such inroads. FADECs for existing gasoline engines have fared even more poorly, eliciting a giant yawn from buyers. Rising fuel prices might not help the FADEC initiative much if the pricier gas still contains lead. Thus far, the quest for economy hasnt been a player in FADEC sales and the quest for octane remains a non-starter.

At this juncture, we cant tell if the diesel revolution has a firm foothold or is merely a flash-in-the-pan fad. Our guess is the former, however. Diamond has sold more of these airplanes than we thought they would and despite the lack of a U.S. market entry, theyre further along than we imagined they would be.

Two things could squash the diesel initiative: The discovery of a giant, heretofore unknown ocean of oil, or some other reason for a sharp decline in oil prices, or the emergence of some dreadful design fault in the Thielert diesels that make them incapable of reaching a 2000-hour TBO.

Were pretty sure the oil ocean thing is not going to happen, so its up to Thielert and Diamond to prove that the 200,000-mile reputation diesels have earned in cars can be carried over to airplanes.

Also With This Article
“Attitudes on Diesels: U.S. vs. Europe”
“Flight Impressions: Smooth, Quiet, Leisurely Cruise Speed”