There is a lot of half truth floating about when it comes to the diesel engines avalble for the DA42.
Both the engines are based on Merc car engines with Thielert favoring the alloy crackcase and Austro going for the steel, the Thielert is lighter but the Austro produces more power, in realistic terms the performance delivered to the aircraft is much the same. Austro have been very conservative with the rated power and I am told that in the test cell the Austro has run as for a long time at power settings of up to 200bhp.

The Austro has the advantage of using the experience of Thielert in the development, the biggest problem that was encountered with the Thielert was corrosion in the cylinder heads, Thielert had no problems with this in the aircraft that they retrofitted or with the Robin instalation that they had total control over. The corrosion was found to be an electrolytic reaction between the cylinder head and the heat exchangers with the coolant forming the electrolyte. Who wrote the spec for the heat exchangers is unclear but following the problem Astro have been very carefull to mandate the approved coolant.

Thielert now have a lot of running time on the engines in UAV's and the engine is starting to mature, I am not sure what other products the Austro is used in but I would think that Austro will have a long way to go to match Thielerts flight time.

The Austro was an engine born out of the difficultys between the two company's and it is interesting to see how two engines based on a very similar car engine have evolved, I do however feel that Austro have taken advantage of a lot of hard won development at Thielert.

With constant power, IAS declines with increasing density altitude. TAS does increase since drag decreases, but to keep IAS constant would take more power, since IAS is proportional to the drag and power = force x distance / time, ie. at a given IAS it takes a certain energy to cover 1nm through the air. At higher level and higher TAS, that happens in less time, so energy expended per unit time (power) must be higher. IIRC, prop efficiency is a minor effect. As a very rough example, in the 421 at 60% power, IAS is 165 at SL and 140 at 20k' but TAS is 200kts.
Many turbo piston engines maintain SL boost well above 15k, to >20k

In that case, how come my TB20 does exactly the same IAS of 138kt at constant engine power, say 23" / 2400rpm / 11.3GPH (peak EGT, maybe slightly LOP) at all altitudes below which 23" can be obtained.

I don't know. The effect of declining IAS is small at lower levels and there may be other effects outweighing that, of prop efficiency etc and power not being exactly constant with constant MP/RPM/FF at increasing altitude. The TB20 may do many things, but defying the laws of physics isn't one of them!

How sure are you about that, 421C?

I totally agree that the future is diesel, either in the form of turbo prop or diesel engine.

It would be interesting to see how the DA42TDI (2.0L engines) compare in terms of economy against, lets say a TB20? For arguments sake lets say at FL100 at 60% and 80% power.

Perhaps someone could do a direct price comparison based on AVGAS price v JET A1 using UK prices per litre? For ease of calculation lets say a direct flight of 500nm, the interesting figures would be estimated time of flight, cruise speed, total fuel cost for the flight and total fuel burnt in litres.

Peter - your thoughts on this?

A and C - your correct about the respect the UAV industry has for Thielart engines, the use of Thielart engines in the Grey Eagle and earlier Warrior UAV's has shown extreme performance, good reliabilty and most importantly the ability to withstand harsh operating regimes. It also operates on a fuel with a much wider spec tolerance than Jet A1 without adverse affect on power and reliability

I don't think a DA42 diesel v. TB20 comparison is very useful because the diesel has a huge advantage in fuel availability in Europe and even more so in the 3rd world.

But, FWIW, I have flown in the original DA42 TDi and it was doing 140kt at a combined fuel flow of ~ 11 USG/hr which is almost exactly what my TB20 does. This makes sense since the two have similar volume cockpits, the DA42 has the extra drag of the 2nd engine, but is more streamlined, has a higher engine compression ratio, and there is no free lunch :)

At FL100, the TB20 does 140kt TAS on about 9.5 USG/hr, at peak EGT, 2200rpm.

The UK diesel v avgas price comparison is difficult too because they have just stuck a tax on diesel for "leisure" use, which you are supposed to self declare. However "training" is exempted, AIUI, so I guess everybody is doing a lot of training flights now. I really have no idea how this is supposed to work, and I don't know avtur pricing around Europe. Certainly the avtur tax in private use kills the diesel engine market for private-aircraft retrofits, totally.

Interesting comparisons Peter, The DA42 TDI does a little under 9 galls per hour (total) at about 150kts at FL100. Even with the UK tax rules it still works out at approximatly 65% of the fuel cost of Avgas, so a saving per mile of around 35%. Even more saving if its a training flight.

There is of course the added safety advantadge of a proper deice system, two engines and a significant improvement in instrumentation / autopilot system.

The other advantadge is a composite construction with modern aerodynamics and wing section, less parasitic drag, higher aerodynamic efficency etc..

Whilst the TB20 is a great aeroplane, natural evolution has seen its design superseded.

Will they do a diesel version equivalent of the IO540?

Yes. They (SMA) have built and approved the SR305-230E diesel, which is very promising. I have one ordered for a client's C 182 amphibian. It's the way of the future. The power is 230 HP, more powerful versions will come in the future.

If natural evolution means having an aircraft with engines that don't work, a finished product which delivers 20% less speed than I was told when I placed a deposit and a residual value that makes a brand new Vauxhall seem a good buy you can honestly keep it. As for training, ask around and you'll find very few schools sing their praises due to unservicabilities.

Not sure I'd call TKS a proper de ice system to be honest. Certainly better than nothing though.

I have no doubt diesel is the future, it's a certainty. But if I were gambling my hard earned right now I wouldn't touch it. And that's exactly what it is. A gamble. Diamond didn't look after their customers last time round. Why would they if the Austro went wrong.

In my experience a 2.0L DA42 will give a 165Kt TAS cruise at 12 USG (6 per side) per hour at 10,000' at 75% power. When the original DA42 did a flight from Newfoundland to Porto in Portugal it used $200 of Jet A and took 12 hrs non stop. No need for ferry tanks either if you get the extended range tanks.

I have heard various things about Diamond quality and customer service, but I presume this is a European thing as it seems quite different in the USA?

However...if you want to take your light aeroplane on a long distance trip, then burning Jet is undoubtedly better. I know of someone who took their DA42 from the USA to South America and did a tour down there before flying home....something next to impossible with Avgas. For us in Euroland, the same applies....

I am sure the same was said about Diesel cars in the past, and if you look at the USA ,in California you can't even buy a Diesel VW which does 60 MPG , yet you can buy a crappy new petrol Mustang which does 20 at a push (and has a 3 speed gearbox). Every second car in Europe is a diesel, it is efficient, and is the norm (and arguably better), and the technical advances are light years ahead of the old skool US cars with diesel engines running half a million miles without batting an eyelid.

But I agree, if you fly where Avgas is available and priced correctly then there is not much incentive at the moment. I do think it is time for these gas powered Lycomings to be controlled by FADEC though which would improve efficiency and also engine life and make them easier to fly.

Trouble is someone has to be first to buy this new tech....I would if I could afford to, but I can't.

AIUI, Diamond were able to walk away from a % of the Thielert engine liability because the original aircraft were sold with separate warranties for the airframe and the engine. Under EU law this is unenforceable (it is IMHO obviously illegal to do such a stunt) on a private user, but many were sold to schools and they had no recourse against Diamond for engine issues. This is what one FTO owner told me.

This time round, if they get any trouble, Diamond won't be able to do that. What that means, one cannot tell. If there is a small amount of trouble they will have to deal with it. If there is a lot of trouble, they won't be able to afford to deal with it and will do all they can to wash their hands of it.

I don't know any Diamond owner who would trust the company (in Europe) as far as he can throw them, so the issue is really a bet on the reliability of the product.

OTOH, I bet Diamond looked after their American customers a lot better. They have to.... trash your reputation in the USA and it is game over, for ever.

I recall SMA (now owned by Continental) were doing an IO540- engine mounting compatible diesel. Oddly enough Socata do have a TB20 flying with it, and have had it for about 10 years, but the project was abandoned, reportedly due to severe vibration issues.

Silvaire - I do think the way forward is diesel or turbine. The high cost of Avgas is enough motivation to see that happen.

With regards your statement about Thielart powered UAV's being dogs, please explain why and on what basis you pass that opinion. Grey Warrior was a development of Warrior and later deployments of similar type were regarded as good. The main issue was finding an engine that could cope with a very wide specification fuel in theatre operations

I think that SNCEMA would vigorously disagree with this.....

I think Peter made one of his famous typo's and intended to say "Continental are rumoured to have bought a licence to use SMA technology"

SMA

AOPA Online: Continental to offer Jet A engine

http://www.smaengines.com/IMG/pdf/fiche_SMA_ang.pdf

I also see that SMA are currently flying a TB20 with one of their latest engines in it, as are two other companies with their own engines, all of this is news published in the last 18 months. No hint of giving up with a diesel TB20 due to vibration has said by Peter

It was Socata who gave up on it a while ago.

However there is nobody left in Tarbes who has any interest in anything other than TBM sales.

If somebody else has since picked it up, that's good news :ok:

Any one know what has happened to the deltahawk engine ? the advantages listed on the website would even have Slivaire1 chopping in his avgas burners for a diesel !

I agree but the problem is the aviation market isn't big enough to spread the development costs of new engines and make a product that everyone can afford. Lycoming and Continental had the luxury of living through the hey days of GA aircraft production in order to develop and refine their Avgas engines. Those days have gone, there were more aircraft sold in a few weeks then than there is in a whole year now.

I agree the diesel is where we should be heading however unless there is development that can be plucked plucked from a mass market (probably automobile) without any or much further development I don't see much new in the future for GA aircraft engines. Remember also where the biggest market is for GA aircraft, and that market right now or in the foreseeable future doesn't have much of a demand for diesel aircraft engines.

Another example, the flash new EFIS screens with their AHRS that we are now seeing in GA aircraft, like the Garmin, Avidyne, Aspen etc owe their heritage to the stability systems used in the modern car. If is wasn't for the mass production in the automobile industry to spread the development costs over we wouldn't seeing these nice glass GA cockpits.

There are two things driving diesels in Europe:

1) Tax concessions (and these can do do disappear, and don't exist in the USA)

2) Reliance on avgas (which is not an issue for those suitably based who don't fly far, and is not an issue in the USA)

So, in Europe, take out the reliance on avgas and what have you got? A bet on future tax policy...

Diesels do have a bit better SFC, due to their higher compression ratio, but this brings technological problems with the severe torque pulses going into the prop. I am sure this will be solved eventually, but the jury is going to be out on long term diesel reliability for a long time.

I think that is very well put, but I also think that the current diesel retrofit options are priced right at the very top of what is perceived anybody anywhere might possibly pay, with the "anybody anywhere" being the busy flying school business model. This doesn't exactly help wide adoption.