“I would have two questions on this.
How did Thielerts ever get certified, when a total electrical failure shuts down both engines on a DA42? I know it’s unlikely to happen, but it’s been (very famously) done.
What is complicated about a little alternator which powers just the ECU+ignition? The mfg cost of such a device is of the order of $100."
It wasn’t a total electrical failure, it was the ECU being intolerant of voltage drops. The alternators did work fine. Having a separate alternator could help, just as a higher output amp could have helped as well. Or sticking to Otto Lilienthal’s pure design.
Going from 155-160kts @17gph running Avgas
To 180-200kts @10-12gph jet a(x) @FL100
Is that really so? That would imply a massive free lunch; much more than is accounted for my the gain from the higher compression ratio, which is approx 0.4th power of the CR i.e. 10% more CR gives you 4% more power (for same fuel flow).
My carefully measured figures:
TB20: 11.5 USG/hr for 140kt IAS (low level) – mine, 2002 GT
DA42: 11.5 USG/hr for 140kt IAS (low level) – one rented from Shoreham from the FTO there
SR22: 11.5 USG/hr for 140kt IAS (low level) – N147KA; the one which went for a swim with an RBS banker inside
C400: 11.5 USG/hr for 140kt IAS (low level) – N400UK
The avgas ones were at peak or LOP, obviously. The IAS figures were all the same within 1-2kt.
The DA42 is the total for both engines so, yes, this is more economical than one engine, but there is no directly comparable (250HP+) diesel SEP. If there was, it would do ~30% more MPG.
Obviously, in Europe, we have the big tax advantage on avtur, but the UK has killed this, albeit on a self declaration basis and with a “training” exemption 
The main market – the USA – has none of this, so all we will see over there on diesels is a lot of hedging of bets, and maybe some movement on sales to China, but those won’t happen until that country changes from its utterly corrupt and opaque “Stalinist-capitalist” model and actually allows GA formally rather than via bribing half the officials with US$ and under-age callgirls.
Peter, i can only say what we see in our club.
the old DR40 with 180HP Lyco used to burn 35l/h with about 120kt
the new DR401 with 155HP CD155 burns 23l/h with about 125-130kt.75% power 5000ft, you have 100% power up to 8700ft (testet myself)
I’m really suprised how the crusing speed is increased compare to the old aircraft.
What i do no know, is how much a CD155 is costing against a O360 180HP
A sticking point has always been that the engine must be able to continue to run with no outside source of electrical power. That has always been a show stopper for electronic ignition development for certified aircraft.
No. The sticking point is certification regulations living in the past and manufacturers of electronic ignition modules have no clue about failure modes, redundancy and reliability. There are lots of electronic ignition modules available for the experimental market. Some of them are even drop in replacements for magnetos (E-mag/P-mag) requiring no external electrical power. E-mags have been around for 20 years or something, and other systems much longer.
The main failure mode for a magneto is it stops working. This is excellent, because a dual independent system will greatly increase overall reliability due to the nature of the failure mode. The failure modes of those electronic systems can be anything from catching fire to way too advanced ignition, or retarded ignition or whatever. Too advanced ignition (in one module) is a very dangerous situation, and very confusing, and at least one aircraft in Norway has crashed due to this, probably 100s? world wide. Installing a dual system will not increase the reliability against that failure mode, it will only make if worse, double the chance of failure in fact.
the old DR40 with 180HP Lyco used to burn 35l/h with about 120kt
the new DR401 with 155HP CD155 burns 23l/h with about 125-130kt.75% power 5000ft, you have 100% power up to 8700ft (testet myself)Quote
This might be a comparison of apples to oranges. A turbo diesel is not really comparable to a normally aspirated (perhaps carburetted) gasoline engine. And, the propeller is likely a factor.
“Old” engines are good, they’re just not great. We have that legacy, because of US development, mostly military paying development and certification costs. that’s not happening any more.
New airframes will be developed with old engines because certification requires that the engine chosen for the airframe is type certified. Type certification of innovative designs seems easier for airframes than engines. I have many hours flying the DA-42 diesel, and Lycoming powered. They are two very different planes. Both very pleasing in their own right, but apples to oranges.
The “market” will certify and build for sale, whatever design has the market inertia to make it through. The number of DA-40’s and 42’s and Cirrus out there shows that there is a market. But, it’s not a market many pilot will afford to support. Aviation is a tiny market, for big cost, so selling to only a small part of that is a poor business model.
I opine that we will see a shift toward electric planes for local use, at a rate which will surpass development of engines in the less than 200 HP range. But, that will require a whole new set of certification rules….
The main reason one cannot compare diesel SEPs with avgas ones is that the diesel ones are smaller and fly slower e.g. 120kt v 140kt and the airframe is different.
If we had 250+ hp diesel 4-seater SEPs it would be different. The diesel advantage is mainly due to the CR.
A DA40-TDi for example will deliver great MPG because it is a much smaller cockpit than e.g. a TB20/SR22 and it flies about 20kt slower which means much less parasitic drag.
We just don’t have a diesel and 250-300HP TB20 or SR22 to look at.
the old DR40 with 180HP Lyco used to burn 35l/h with about 120kt
the new DR401 with 155HP CD155 burns 23l/h with about 125-130kt
I don’t doubt your figures but can’t see how that can be accounted for by the different type of engine and fuel.
Re apples and oranges, I tend to be with Peter.
One should compare the Thielert with a 160hp IO-320, operated LOP, since that is the way it should be done. The latter comsumes about 28 litres in a 75% LOP cruise, so that’s merely about 15-20% less than the aforementioned CD 155. That’s a fair comparison of technologies I think.
On the other hand, there are no SEPs out there with an IO-320. The reality is that in the 150-180hp class, most aircraft use O-320s or O-360s, which cannot really be run LOP…
there are no SEPs out there with an IO-320
Before somebody points this out… there is the Lancair 320
But that is a tiny 2-seater homebuilt-category aircraft, with uncertifiable handling characteristics. It probably doesn’t have enough aileron authority to counter the prop torque at Vs. It probably doesn’t have enough rudder authority to counter the prop torque at Vs. In fact I don’t know if anybody would agree on what the actual Vs really is, and whatever it is, it will be way above the 60kt Part 23 limit for a SEP, if defined as a speed at which the control surfaces actually work at MTOW and all around the loading envelope. So it is very fast for the fuel flow, and probably great fun to fly
So, yes, apples and oranges.
IMHO there cannot be more than a 30% difference in MPG between avgas and diesel. The physics of burning the stuff doesn’t support it.
A diesel runs “leaner than LOP” all the time. This has large impact for training flying touch and go. I think the DR401 really shows what is going on because it is an efficient airframe, more so than old Pipers and Cessnas. I’m really not all that excited about these turbo-diesels, way too expensive and complicated for experimental use, but they seem to gradually and slowly increase in numbers for certified aircraft. Still, I do not understand it, the only effect they have is to make the certified marked more expensive to enter, unless you fly 500+ hours each year. They make sense in a factory setting where “producing” lots of hours is important, but they do not make sense for private ownership flying 50-100 hours each year.
I see it as customer, better cabin (DR401) less fuelburn, lower operating cost, higher speed, single power lever, why should i want a AVGAS engine?. I do not need to know more… und do not care if apple or orange ( like it more ) in my view there is no reason today to build a new designed aircraft with Avgas (or UL91) engine. Cirrus is testing the CD300 as mutch i know, for the TB20 the CD230 would fit powerwise. Imagine, you could fly to greece nonstop and half return with your TB20 powerd like this, or at least no hassle in greece about getting Avgas
Is a CD155 really double of price then a Lyco ? ok, its newer and has maybe more potential then a 60 year old model? and has brought in his money!?
