Basically, when an avgas engine runs out and needs to be overhauled, the conversion must be in a price range to make sense, so the engine alone similar or maybe 10% on top of what a new IOxxx would cost plus maybe a one time 20k to convert the airframe. Anything else nobody will go for it.
That just about sums up the whole diesel retrofit story, because nobody has ever got anywhere hear that 
My guess is that the STC (for an engine which is already certified for the right sort of operation, say to FL280 for a pressurised twin) would cost of the order of $1M.
How did you compute these numbers?
I didn’t “compute” them. It is based on some previous numbers, reported from other projects. Stuff like the Jetprop conversion. I also said “of the order of”
Are you aware of more specific data, mh?
There is a lot of flight testing involved. A lot of data collection, and report submission to the certification authority. That’s assuming the developer actually knows how to do it… most newcomers don’t and have to go up the learning curve. I was somewhat involved on one project some years ago and after they spent a few M they still didn’t have a clue. To be fair they ran parallel developments for other markets and those sort-of succeeded.
What helps is if you don’t modify the performance (as in e.g. TB20 to TB20GT, being called “Mod 151”) so the POH perf data remains the same, but then you reduce your market because the whole case will hang on the cheaper fuel. Also I doubt anybody could get away with that charade if you are replacing a simple petrol engine with a complex computer-controlled diesel.
The case for a direct “plug in” diesel replacement for say an IO540 has been “obvious” for many years and that was the original SMA objective, but it was never achieved. Also the low hanging fruit in GA is not retrofits sold to private owners, but the FTO business, and it is no coincidence that that is what Diamond went after. A well utilised DA42 makes a lot of money for an FTO. But Diamond succeeded only because they sold the whole plane. There is no evidence that any retrofit package (e.g. for the old piston twins) would have succeeded even for FTO sales.
Are you aware of more specific data, mh?
I do work in GA certification as an aircraft engineer. I haven’t calculated a sole engine swap though.
That’s assuming the developer actually knows how to do it… most newcomers don’t and have to go up the learning curve. I was somewhat involved on one project some years ago and after they spent a few M they still didn’t have a clue.
There is a nice company (Aircraft Design & Certification; www.aircraftdc.de) that has specialised in certification as a service. We have a booth at the Aero, if you want to talk about a Diesel for your TB20 ;-)
They’ve hinted at $100K for the engines, but I know that won’t be possible to do. A bog standard IO-540 from Lycoming is over $120K when all the items are added – and that’s for an engine that’s been manufactured for 50 years and where the R&D costs are long paid off!
STC was just a minimum I could think of. Unless you have a lot of airframes you can amortize the STC cost over, it’s going to be a non starter.
Interesting site Adam. I see my engine is $72k (TB20, IO540C4D5D) and the TB21, TIO540AB1AD, is $101k. Exhaust system, mounting frame, etc are on top, but you don’t normally change these on an overhaul (turbo engines are more likely to need a new exhaust, unless made in inconel). With the bulk of IO540 engines out there being even cheaper, especially given the overhaul option (perhaps 50% off) this means the market for IO-540 diesel retrofits is even tighter. You would have to sell the engine for say $50k to make it a clear case, or perhaps $80k for a TIO-540.
We have a booth at the Aero, if you want to talk about a Diesel for your TB20 ;-)
I don’t think I can swallow any more projects after the TKS installation but I will pop over and say Hello
AdamFrisch wrote:
They’ve hinted at $100K for the engines, but I know that won’t be possible to do. A bog standard IO-540 from Lycoming is over $120K when all the items are added
I’d say that in that case it would have potential, even though most people will not buy a new engine but rather exchange or overhaul. If the engines to be replaced are in the same ballparc and the total price of the exchange does not go over say double the price of a comparable conventional engine, people who have a good reason to go Jet A1 rather than Avgas will be interested.
I am not quite sure how it was with the Thielert STC’s pricewise but they did have a considerable number of planes converted so it must have been attractive to some extent. There still are quite a few PA28, Robins and Cessna 172’s flying with the Continental/Thielert engine. So I would not say that nobody ever got to the stage of having a valid and attractive Saurus to Diesel upgrade offered, only that it appears that after the bancruptcy and under the new ownership it was not continued. Had Thielert survived, I think we would see a very different diesel scene today.
AdamFrisch wrote:
STC was just a minimum I could think of. Unless you have a lot of airframes you can amortize the STC cost over, it’s going to be a non starter.
So in other words you have no information at all how much an STC for something like that could cost. Cleary, an STC for single airframes is out of the question for cost. They would have to do STC’s for most if not all of the airplane types in question and then try to retrieve the outlay via selling engines in bulk, counting on a break even after several thousand shipped. Otherwise, it is a non-starter.
There still are quite a few PA28, Robins and Cessna 172
…and there will probably be many more. It is possible to convert Piper Warrior and Cessna 172 to diesel today.
http://w3.vliegwerkholland.nl/convert-to-diesel
Also Austro has 180hp diesel engine. I think it used in Diamond DA62.
Another thing that works against all these things is that a new/used turbine plane you can finance. A nebulous STC upgrade of an engine, from an unknown and unproven entity, no financial institution is going to touch. So, lets say you have a twin you want to upgrade. Now you need $300-450K in cash. I would venture that anyone who has that amount of cash sitting in a drawer, would rather use most of that and finance a newer turboprop.
AirV wrote:
Also Austro has 180hp diesel engine. I think it used in Diamond DA62.
180 hp? Wow. Need to look into that. However, I don’t think Austroengine is supporting any STC to retrofit other planes? Otherwise, with 180 hp this would be the O360 replacement a lot of people have been waiting for….
