A while ago one engine shop explained to me the requirements. They are staggeringly lax. It is something like 150hrs on a dyno, of which only a bit is at max power.
That information contradicts what I have seen. I visited the Austro engine plant several times and have seen engines being run on dynamometers at max continuous power (92%). The manager told me they do that for hundreds of hours.
I fly Thielerts by the way, and I have no information how they have been tested during development. I also have heard stories of flight schools suffering from Thielert reliability. The problem is indeed what you say Peter, where is is the complete set of data?
Thielert actually claims superior reliability but I don't know what to make of that. For one, they are comparing apples to oranges, because it is not fair to compare engines that are 1-10 years old to those that are 1-40 years old..
Check their news release of jan 11, 2012. http://www.thielert.com/
We do discuss engine issues on the Diamond Aviators Network forum (DAN). The pattern seems to be that the first iteration, the 1.7 liter engines, had more than their fair share of issues and resulting SB's. To add insult to injury, Thielert effectively orphaned the engine by not allowing increased life-time interval on components to apply to that engine. So far, the 2.0 engine seems to do OK. Many have changed from 1.7 to 2.0 (or to Austro).
My gut feel is that the 'milder' usage profile of a private operator as compared to a flight school also plays a role. I did not have any real issues, only a couple of annoyances, but I am just one data point, at 550 hrs on the clock.
At this stage, for the Thielert 2.0 engine, one could say that here in Europe, when comparing to AVGAS engines, the saving on fuel more or less off-sets the extra costs (maintenance, engine reserve). Thielert claims that we can expect the cost to decrease through longer life-times of components and TBR of the engine in the future. Let's see.. On paper, the Austro proposition is cheaper than running an AVGAS engine. Less component change-out, TBO instead of TBR.
That information contradicts what I have seen. I visited the Austro engine plant several times and have seen engines being run on dynamometers at max continuous power (92%). The manager told me they do that for hundreds of hours.
It's very possible that those engines get tested for longer, for data collection etc, but certification testing doesn't appear to need testing anywhere near TBO.
Also there is a tendency to spec diesel aircraft performance at higher continuous powers than Lyco/Conti aircraft which "should" cruise at something like 65% for best engine life, and I don't think anybody would say 85% is a good idea, never mind 92%.
I fly Thielerts by the way, and I have no information how they have been tested during development. I also have heard stories of flight schools suffering from Thielert reliability. The problem is indeed what you say Peter, where is is the complete set of data?
You won't find anybody in the FTO business (which from what I see accounts for most DA42 sales) going public... I can think of two FTOs who had a number of DA40s and DA42s which were mostly grounded, for long periods. At the same time both were publicly saying they were delighted with the aircraft and the excellent relationship they had with Diamond and Thielert.
Private owners also got shafted but were able to make it work better because (from memory) the 300hr clutch life limit was probably 3-5 years' flying for the ones I know.
Anyway let's hope this is now sorted.
Also there is a tendency to spec diesel aircraft performance at higher continuous powers than Lyco/Conti aircraft which "should" cruise at something like 65% for best engine life, and I don't think anybody would say 85% is a good idea, never mind 92%.
Agree. Although indeed Austro claims 92% MCP, I would not fly it that way. Reducing power to -say- 75% would take the speed down by just 10-15 knots, specific fuel burn down, oil burn down, range up, noise down and a higher probability of engine longevity. Nobody is going to convince me that it is fine for a Mercedes Diesel to blast full speed all of the time.
Flight schools are not going to do this 92% thing, not in cruise anyway.
I don't know if anybody has researched this, but there is probably a "best operating point" in terms of power.
I am not sure how to explain it, but take an extreme example: fly at 40% power. You will be only a little above Vbg, which is great for MPG, but it will take for ever to get anywhere, and you will be clocking up loads of airborne time (great for building hours towards a CPL 
), so your engine fund is going to be higher, and the "50hr check fund" is going to be a lot higher.
It's not clear, without plotting some figures, whether the optimal cost-per-mile point does lie above say 40%. It might lie below that, but I doubt it because below Vbg you are on the back of the curve and no way can that be worth doing because you are going slower for more juice.
Flying really slowly is great for MPG until you have a headwind. The slower you go the worse effect a headwind has (imagine a Cub flying at Vbg into a headwind strong enough it makes no forward progress at all, then you have 0 mpg. In that case flying at 100% power will have better MPG).
Agree. Although indeed Austro claims 92% MCP, I would not fly it that way.
The SMA people openly recommend flying at full throttle all the time. MPG apparently doesn't change much and the engine is designed to go at full throttle without limit. I think that is great.
This also works because the SMA engine cannot keep 100% BHP for long, it is more similar to a NA AVGAS engine than to a turbocharged AVGAS engine. This is rather unfortunate because that makes it unsuitable for the higher altitude aircraft. For example my TR182 comes iwth an Lyco 540 with 235hp which is very comparable to the SMA engine with 230hp. However, my Lyco can keep its full power until FL200 and therefore I can fly at 175KTAS there and keep a very good climb rate while the SMA engine would quickly lose its power.
This is because the diesels need a lot of turbocharging to make good power considering their weight and one cannot install enough turbochargers to compensate for the loss in airmass at altitude. The new generation SMA is already much better with a custom designed turbocharger but not good enough to compete with AVGAS engines at altitude.
I think that is great.
It will be with 5-10 years of maintenance history behind it 
My IO540-C4D5D is also rated at 100% power, continuously. If you think that's not smart, why?
The new generation SMA is already much better with a custom designed turbocharger but not good enough to compete with AVGAS engines at altitude.
I am sure you are right but FL200 is not a practical cruise level, due to the oxygen situation. It nice to have it (my TB20 will go to FL200, on a cool day) but it is a purely convective wx avoidance strategy.
My IO540-C4D5D is also rated at 100% power, continuously. If you think that's not smart, why?
Yeah but you have to be very stupid to operate your engine at greater than 75% BHP and thus full rich. The SMA engine always operates at the stoichiometric fuel rate.
It will be with 5-10 years of maintenance history behind it
The SMA engine has more than 5 years of history and it is looking good. Very sturdy design. Diesel generators operate at 100% and some ship engines, too.
Achicm, can you compare AE300 and SMA in terms of turbocharging efficiency?
Achim, can you compare AE300 and SMA in terms of turbocharging efficiency?
According to the SMA web site, it can only keep its 230bhp to 10,000ft. After that it will will bleed off at the usual rate. Given that air mass and thus bhp fade more quickly than drag, 10,000ft will be the fastest cruise altitude for SMA equipped aircraft. This is still a bit better than NA AVGAS engines which have their sweet spot at around 8,000ft.
The Austro Engine AE300 has the same critical altitude, ca. 10,000ft. In their data sheet, they compare it to a Lycoming IO360, i.e. a NA AVGAS engine which illustrates my point that turbo diesels are turbocharged to get the MSL power and are not capable of keeping that power for very long.
We need better turbocharging therefore. One solution could be variable geometry turbochargers like they have in cars nowadays. Aircraft turbochargers are rather primitive compared to what we have in cars today.
