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New turboprop (etc) engines

Thread split off from the Mooney thread.

What options are there that actually exist?

Just the RR (formerly Allison) helicopter engines, as e.g. used in the now-dead Grob 140.

Administrator
Shoreham EGKA, United Kingdom

This will be a short thread ;-)

A while ago I was very peripherally involved with this

I think the SFC of such a small axial compressor is a lot worse than the 1950s helicopter engines, which use centrifugal compressors. In fact Bladon moved to a centrifugal compressor eventually, too.

However I think marketing factors dominate i.e. to get a useful MPG you need to fly high, so you need pressurisation, which results in a big expensive plane, which needs to be loaded with stuff to look like it is worth the money, which makes it bigger and heavier – which is why we don’t have small turboprops.

The Grob 140 was priced at €1.4M, according to a 2004 email I have from their former marketing man. The engine was a few hundred k, OEM cost, max. The rest of the price was worked out on the basis of what people will pay. And all the time people do pay that sort of money, nobody is going to develop cheaper engines. Why should they? Nobody is going to bomb the market. Garmin can make the GTN650 for something like $300. Do you think they will suddenly drop the price to something reasonable, like $1500 (that includes a 25% dealer margin) which would be appropriate for B2B manufactured goods?

Administrator
Shoreham EGKA, United Kingdom

Peter, thanks for accepting my suggestion – but I wasn’t really after discussing turboprops, about which I know next to nothing. Rather, I wanted to continue on

Piston diesels are so much more efficient than turbines and there are technical solutions to their problems. We were technically more advanced during WW II with the 2-stroke aviation diesels, Jumo, Napier, etc. If that comes back it could very well power King Air and much bigger. Nothing beats a 2-stroke diesel when it comes to fossil fuel efficiency.

to state that basically a 2-stroke is inherently less efficient than a 4-stroke, but makes up for that in small engines with less weight and less complexity. Hence their success in scooters and lawn mowers. The Jumo’s were indeed marvels of engineering and efficiency, but that took a good deal of complexity too. I’d love to see the principle taking shape again, but just like for small turbines, the market is too small, or the development cost too heavy, for the possible sales volume. Remember the DAIR diesel? That was a 2-cylinder 2-stroke on the Jumo principle, looked VERY nice – fifteen years or so have passed, where is it now?

EBZH Kiewit, Belgium

Bizzarely, weight is not a major MPG factor in light GA, because we fly so far beyond the Vbg speed.

So saving e.g. 50kg on an engine which weighs 200kg (an IO540 with all the accessories) but losing say 20% on the SFC is a complete non-starter. You will lose very close to 20% of your range, which is a massive hit on a touring aircraft.

Especially as anybody can save 50kg on a 1000kg+ aircraft, by throwing some money at more exotic materials here and there (titanium landing gear, etc).

50kg is probably equivalent to not eating burgers or drinking coke for a few months, across 4 occupants

Obviously if you are trying to get under 450kg / 650kg / 750kg then that’s different, but Rotax (and maybe others – not my speciality) are established players.

I’ve edited the thread title.

Last Edited by Peter at 25 Jan 22:20
Administrator
Shoreham EGKA, United Kingdom

In terms of acquisition and ownership cost, one of the best options for low-end turboprop engines currently around is probably 600-something-horsepower Walter M601B or M601Z, as opposed to later M601 submodels. Walter (now GE Aviation) abandoned them several years ago, and a used M601B can be bought for next to nothing – I heard of prices as low as 2000 euro for an inoperative but repairable one. A small maintenance company at LKBU picked up the type certificate and is doing turbine overhauls at a price of 30-40k euro, depending on the condition; mid-life hot section work is priced at 12k flat. Propeller overhauls are available from the original manufacturer, Avia Propeller.

Garmin can make the GTN650 for something like $300. Do you think they will suddenly drop the price to something reasonable, like $1500 (that includes a 25% dealer margin) which would be appropriate for B2B manufactured goods?

One way to overcome that would be to follow the initiative of makerplane.org (and possibly other similar organisations designing open-source airframes) and design open-source avionics. Judging by the progress of open-source software industry, the idea may actually be profitable but does certainly need some critical mass to start.

Last Edited by Ultranomad at 25 Jan 22:35
LKBU (near Prague), Czech Republic

… is probably 600-something-horsepower …

600 horsepower will tear most airframes to pieces (a Cessna 414 has about that much in both engines together and is a pressurised 8-seater…). And six hundred hungry horses need to be fed a lot of petroleum! If the engine gets derated to 300 or 350 hp in order to fit a typical four-seater single, it will be to heavy and still too thirsty for the power.

EDDS - Stuttgart

Thanks again, Peter, and yes, we seem to be on the same idea.

saving e.g. 50kg on an engine which weighs 200kg (an IO540 with all the accessories) but losing say 20% on the SFC is a complete non-starter.

and that is precisely what a conventional two-stroke engine would do, whether running on petrol or avgas or CNG.

And indeed it is not difficult to save weight in the airframe, it is only expensive – witness the Colomban MC30 Luciole with its carbon-fibre wing spar.

But we can all dream of all the airframes and all the engines that today’s technology can offer – very few, if any, will work in today’s market.

EBZH Kiewit, Belgium
?How about this one http://www.pbsvb.com/turboprop-engine-tp-100-and-turboshaft-engine-ts-100
EDxx, Germany

Pratt & Whitney have the aircraft turboprop market sown up pretty well. For smaller applications it seems that helicopter engines are used eg the Allison 250 in the Silver Eagle. I don’t know that space – are helicopter turbines seeing much development?

EGTK Oxford
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