random idea. micro turboprop engine. - RC Groups
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Mar 12, 2012, 01:05 AM
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nemoskull's Avatar

random idea. micro turboprop engine.

been tossing an idea around in my head for a while. a jet engine with a prop on it, a turbo prop engine. but very small. like a 4 oz plane small. cox .020 scale.
been thinking of a simple paddle wheel turbine with a shaft attached to a simple paddle wheel compressor. a chamber linking the two. output shaft turning brass gears on a 50:1 ratio or so. attach that to a prop.
carb on the intake, run 1/2a fuel for the oil. Ball bearing or perhaps use castor oil like modern turbochargers on cars.
basically a engine that can be made on a lathe, drill press and minimal routing.
i can figure out how to start the thing, tho (in my head).

fuel delivery is a problem as well. the main question is can you make a combustion jet from non pressureize fuel. like use a velocity vs pressure effect and a shaped nozzle to create a jet. i dont know, yet.
well, what u think?
i'll dootle some idea later.
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Mar 12, 2012, 03:11 AM
You made that out of trees?
Boomerang1's Avatar
Before tossing the idea too far take a look at what very knowledgeable people have made to run or even better developed to the point where they can offer them for sale.


Is the smallest succesful turbine.


Is the smallest succesful turboprop.

The Lambert turbine runs at over 240,000 rpm, these are not things you 'make on a lathe & drill press with minimal routing'.

Jet engines have constant pressure in the combustion chamber known as case pressure, that's why they use a fuel pumps to deliver fuel & control speed.

Mar 12, 2012, 09:07 AM
Registered User
I was approached by a university student to help fabricate parts for an axial flow jet engine 20mm in diameter.
I politely declined explaining that I didn't think it would work.
Interesting idea, but not practical IMO.
Last edited by 706jim; Mar 12, 2012 at 06:08 PM.
Mar 12, 2012, 10:09 AM
the great Gassif´er
Never say never, 35 years ago a turbine that could fit in a model airplane was considered impossible until some English guys made one.
Later Kurt Schreckling constructed a turbine that could be made with under 100$worth of materials by anybody who could use a lathe and had some sheet metal working skills.

So far, turbines are not yet REALLY small, and for now we do not have the materials to handle RPM and temperatures, and efficiency cannot yet be boosted to a level where such a small turbine would actually be self-sustaining.

Carbs will never work on a turbine, due the incredible temperature rise in the compressor stage (you have to compress an explosive fuel/air mixture in a way that generates probably sufficient heat to make the mixture ignite while still in the compresion stage) so the real problem, even if you could really build a super small turbine, would be the fuel supply and turbine monitoring and control system.

Most likely nothing that cannot be solved in the (maybe near??) future, but for now such solutions would most probably terribly expensive.
And for what? An engine that has by nature of things a horrible fuel efficiciency (needs a tremendous amount of fuel for a very small amount of useable output)....

Brgds, Bert
Mar 12, 2012, 11:24 AM
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gkamysz's Avatar
The problem is compressor and turbine efficiency. All of the ideas suggest that there is no knowledge of turbine design behind the concept.

Could a 50 shaft watt turbine be built today and run? Yes, I think so. With paddle wheels and a drill press, no.

Right, Jim. Axial flow presents it's own set of problems. Axial flow is impractical in model sizes, let alone 20mm.

Mar 12, 2012, 02:07 PM
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coriolan's Avatar

Small Japanese turbine

Bigger than 20mm but not by much!
I think there is video of it running somewhere on Youtube
Mar 12, 2012, 02:33 PM
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gkamysz's Avatar
20mm axial flow is not the same as 31mm radial flow. Turbines based on the Borg Warner KP-31 compressor wheel are common (Lambert Kolibri). It was the smallest available turbocharger compressor available a few years back. I'm not sure if it still is.

Mar 12, 2012, 07:49 PM
Gas Only
Fokker DII's Avatar
Only $4,995 for a Wren Turboprop from a dealer right here in Cal. And it only burns 6Oz of fuel per minute. I don't want one that bad ....
Mar 15, 2012, 09:18 PM
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nemoskull's Avatar
Well for now it's a moot point. But fuel delivery is the thing I can't wrap my head around. I could edit the thing with a very small computer but an injector that small is not here yet. And the idea is not to be the best but just usabe
Mar 15, 2012, 10:57 PM
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gkamysz's Avatar
Yes of course, the turbines in production today are far better than the first one made by Kurt Schreckling. A fundamental understanding of how a turbine works is needed, however. There is no "injector" in model turbines!


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