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When will a diesel be available for my aircraft? |
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News, facts, and comments on the coming revolution for piston-engine aircraft.News of July 29, 2002Aviation Consumer's special report on aerodiesels: where they are right, what they don't know, what they forgot, what they can't say
By Dr. Andre Teissier-duCros
The August 02 issue of the excellent general aviation publication, Aviation Consumer, runs a report of six pages on diesels for general aviation. Aviation Consumer's information is quite accurate. That diesel gets so much of AC's attention is in itself an event. AC's position varies from skeptical to cautiously supportive. AC is right to note that, if it's all true, then by 2003 Diamond's Star with Thielert engine will be the best buy as new plane, and Cessna 172s and Cherokees will be re-engined with a Thielert at a competitive cost while gaining in performance, fuel economy, and TBO. AC is right is reminding that aero-diesels have been the next best things for general aviation for decades and yet nothing ever took off. Yet it agrees that this time might - just might - be the right one. Regarding fuel economy and cost, AC forgets to say that Jetfuel is denser than Avgas by around 10%: Your tanks will contain 10% more Lbs. of diesel fuel. Advantage: that's an extra 10% gained. Drawback: it also means that with full tanks your plane will lose some payload. On my Cessna 182, the extra fuel weight will be around 50 Lbs. If you add up 30% of engine efficiency, 10% extra density and 15% economy on fuel price, we are looking at some 50-55% economy. If on top of that you burn autofuel instead of Jetfuel - and a diesel is far more tolerant than a gasoline engine to difference in fuel - the savings could reach as high as 70%. Think about that if you operate a flight academy with 10 C-172's flying 1,000 hours/year each, or a fleet of Piper Navajos flying 2,000 hours/year. AC is right in assuming that Avgas will always be around, but forgets to say that the price trend will see Avgas increasing in expense relative to Jetfuel as Avgas usage diminishes and as regulations and taxes get more stringent. Already, this trend in Avgas price is occurring. AC is right: diesels still have to prove their better TBO, or rather TRO since most of them will be replaced rather than reman'd. However, all diesels and aerodiesels of the past always demonstrated a far superior longevity and reliability than ignition engines. AC forgets to say that ignition alone is the most important factor in engine incident, and that diesel fuel induces far less engine corrosion than gasoline. We will tell the story in our first print issue. AC is right: a challenge will be weight. The SMA engine illustrates perfectly the extra weight induced by diesel's higher compression if RPMs are the same and if both engines are four-stroke. Weight goes down if the engine runs faster than the prop, which means a geared engine such as the Thielert. Weight goes down if cycle is two-stroke because you have twice more explosions per RPMs. The Zoche, DeltaHawk, and Continental GAP diesels are two-stroke. SMA's problem therefore will be to explain to a Cessna 182 owner (such as myself) that he must pay $80,000 instead of $20,000 for a reman'd O-540, and find himself with 70 Lbs. less payload caused by the engine and 50 Lbs. less payload caused by fuel density. All right, I was born French, got educated as a French engineer and kept a soft spot for French technology, but I am 275 Lbs, my wife carries a lot of luggage, and my pocketbook knows only dollars saved and payback. AC is an excellent consumer report magazine. It is right to discuss only what they tested themselves, or what can be surveyed through a large number of US consumers. But they forget to mention all the piston-engined planes which suffer of regular engine trouble --Piper Mirages are famous for that. So are some Mooneys. All ignition engines require of pilots that they become Michel-Angelo's in the art of leaning, and check what good artists they are when TBO comes earlier than expected… or when their engines quit on them. Here diesels will be as reliable as turboprops. Also, AC cannot take into account the first reports coming out of Europe on diesel performance. We will write more on them. For instance, the Diamond Star/Thielert does demonstrate 4.5 Lbs./hour of fuel at 100 Knots. If you want to dream, that's 1500NM range with reserves… Goose Bay to Italy in 3 legs only, round trip for $600 of fuel, plus the stuff to relieve your bladder. It also demonstrates a better performance with a 135HP diesel than with a 180HP Lycoming. Finally, AC forgets a factor: I just got my Cessna's O-540 reman'd. I had to wait for ten weeks. These Lycoming and Continental refitting shops have plenty of work ahead of them, are short on trained personnel, and are not in a hurry. If we are going to simply replace the engine each time, I can hope it will take a few days only, perhaps less. We are waiting for your input and your subscriptions! Andre Teissier-duCros
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posted at 4:34 AM |
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