Gee, reading all this i suddenly feel the urge to get the manual out and see whether there are any magnetos on my ‘unproven’ diesel engines.. 
Sorry, couldn’t resist. Now, please, no gratituous remarks on gear boxes and clutches please 
Would be interesting to have the entire picture of what the various types of engine’s life cycle cost are. Diesels are ridiculously low in terms of fuel costs compared to Avgas engines, especially in Europe, but clearly the scheduled maintenance is a lot higher, and the TBO/TBR is lower, so that brings it back to even, roughly. But what about unscheduled maintenance? I have had virtually none on the Diesels. But what about avgas engines? I mean maintenance and overhauls of engines not making it to TBO..
Aart, Peter’s suggestion is probably correct for the diesels, where there was an early period where bugs were being worked out, but hopefully there is no rise as they approach TBO.
The curve up though, I think applies to older, more complex engines – for example in the ‘bathtub’ AeroCommander ( see how I did that) – which are not receiving the maintenance investment, and expertise (due to loss of engineering skills) to keep them up to scratch. In other cases, eg Lycoming -360 family the trend may be one of continual improvement as materials improve.
Aart, to be fair, your diesels are low power engines. Avgas engines with lower power ratings are more reliable than the ones in the 300+hp region. And if you get contamination in your fuel, your engines will pack up much sooner because the high pressure common rail injectors are very delicate. Compared to that, a Lycoming can deal with quite some dirt in the fuel system. When operating an airplane like the Malibu (which I consider to the be among the most fragile piston airplane installations), it pays off to get deeply involved in maintenance and be able to handle standard problems like dirt in the injections system yourself. That requires time and dedication though and I have heard there are people that enjoy flying more than swinging wrenches although I have a hard time believing that
Would be interesting to have the entire picture of what the various types of engine’s life cycle cost are. Diesels are ridiculously low in terms of fuel costs compared to Avgas engines, especially in Europe, but clearly the scheduled maintenance is a lot higher, and the TBO/TBR is lower, so that brings it back to even, roughly.
I believe the retail fuel cost advantage for diesels in Europe is mainly due to an unplanned artifact of tax policy that is actually intended to support mass transit via the airlines. Accordingly, government gets a bigger payment from people using a gasoline engine than for a Jet-A engine… for idealogical reasons that are their own. Removing that issue (while recognizing that its not theoretical for those victimized by it!) the actual fuel consumption advantage is about 33% on a volumetric basis. As I look at today’s fuel prices on Foreflight, where the artificial tax situation does not apply, Jet-A prices are about the same as 100LL on a volumetric basis. So roughly 33% less hourly cost for fuel with the diesel in a fair market situation. If I take my total monthly fuel bill and reduce it by 33%, that’s about $100 USD per month. That doesn’t pay for much extra maintenance, is less than 1/4 of my hangar cost, and is probably not far off the global GA average.
Another issue favoring some diesels in over regulated markets is the forced overhaul at some time in service, either engine hours or calendar hours, and that the overhaul to be performed by a repair station or local equivalent. When this applies it creates huge, unnecessary costs for 150 HP gasoline engines that are so often operated only 50 or 100 hrs/year, that will actually last 2000 hrs and several decades between overhauls, and are simple enough to allow the option of being overhauled by mechanics in the field and then run another 2000 hrs. Conversely, it seems to me that today’s diesels with their generally more fussy construction probably do need to be overhauled by specialists on a calendar basis, or replaced.
If somebody (or a group) owns an engine that flies a large number horsepower-hours, has their fuel cost warped by taxation, and is forced by regulation towards high overhaul costs, then the diesel may well come out even. Plus the buyer can buy fuel in places where GA infrastructure doesn’t exist – which seems to me the most compelling issue in favor of diesels. But based on the information and data that I can see, I don’t see cost as an intrinsic driver towards diesels for most GA engine owners. For larger engines in high hour European commercial service, maybe.
I think magnetos in the conventional sense will be gone from most operating aircraft engines in 20 years, because self powered drop-in electronic replacements will have a quick return on investment based on fuel savings at altitude, when operating at high RPM and low MP.
I agree that material development can continue to increase engine performance. Any piece of machinery that’s focused on high power density sits at the limits of material fatigue strength.
If I take my total monthly fuel bill and reduce it by 33%, that’s about $100 USD per month. That doesn’t pay for much extra maintenance, is less than 1/4 of my hangar cost, and is probably not far off the global GA average.
Depends if you include Asia in your global average.
Comparing a somewhat equivalent (not really) Seminole (18gph) at equivalent speeds with a DA42-VI (13gph), flying 150 hrs/year, with local avgas USD8.9/gal vs Jet A USD4.5/gal, my fuel savings against the Seminole amounts to > USD15,000/year.
I think magnetos in the conventional sense will be gone from most operating aircraft engines in 20 years, because self powered drop-in electronic replacements will have a quick return on investment based on fuel savings at altitude, when operating at high RPM and low MP.
Better add a safety margin to your statement, say 50 years. Otherwise that would be too radical and too much innovation in too little time
From a flight in a DA42, it was burning exactly the same amount of fuel at 140kt as my TB20 – just over 11 USG/hr.
That is quite an achievement of course because it is carrying a second engine and has bigger wings sticking out.
That suggests the diesel engines are perhaps 1.5x more efficient (SFC) because twins tend to burn very roughly 1.5x more fuel for the same cockpit size.
Re electronic ignition, I would go for it provided that
However I don’t think anybody is going to do anything for the single shaft dual mag engines because today’s offering (you keep one normal mag and use the electronic ignition for the other plugs, firing slightly before the old mag) cannot be implemented on them. Only a fully electronic system could be done there, which would obviously have to be dual otherwise nobody would buy it (rightly so).
From the NTSB Single Engine, Fixed Wing General Aviation Accidents 1972-1976 report (ok, this report is dated quite a bit, but then again our AVGAS engines haven’t really changed much since then), there were 3058 engine failures (table 10) during 103285497 flight hours (table 3), so that works out to an MTBF of about 34k hours. So Peter’s 50k figure is at least at the correct order of magnitude.
Furthermore, I’ve read in another message board there are about 430 engine failures in the USA per year (but I cannot find a reliable source for this number), and the FAA estimates 25.9 million GA flight hours per year, so this would work out at about 60k hours MTBF.
" i believe the retail fuel cost advantage for diesels in Europe is mainly due to an unplanned artifact of tax policy that is actually intended to support mass transit via the airlines. Accordingly, government gets a bigger payment from people using a gasoline engine than for a Jet-A engine… "
Avgas has always been massively more expensive that Jet A1 in Europe – even back in the days where there was no such thing as “mass airline transit”.
Mass airline transit only started about ten years ago in Europe.
With the possibility of the one drive shaft failing on these dual mags and thus making both inoperative, I would think that some form of separate electronic ignition system would make sense. I’m not sure how it could be implemented on a TC aircraft but I have seen it on LAA (Permit) types.
