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These days, most jet engines feature axial compressors and turbines. However, there are some older aircraft engines with centrifugal compressors, like the Rolls Royce Nene. But I've never heard of any engine with a centrifugal turbine (radial flow turbine).

Does such a thing exist? Has one ever been built, tested, and flown? I'm interested in turboprops, turbojets, turbofans, even very tiny ones for RC aircraft.

Edit: Okay a radial flow turbine will not produce much of a jet of thrust, so I guess the only possible engine for this would be a turboprop. Edit 2: Not necessarily, a centrifugal compressor can redirect air outwards to another path, then downwards into a centrifugal turbine, which redirects it back to axial direction after all.

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    $\begingroup$ I've only ever seen them in turbo chargers, and air cycle machines in air conditioning packs. Even the itty bitty Jet Cat RC turbojets use an axial turbine. I think they are just too inefficient for turbojet purposes, the compressor torque demands for a TC or ACM being much lower than a turbojet, but it'll be interesting to see if someone dredges something up. $\endgroup$ – John K Jan 13 at 5:29
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    $\begingroup$ I think you're misunderstanding how radial turbines work. Centrifugal force works against gas flow in a radial turbine; gas is inducted at the periphery and moves toward the center. This is more like the operation of a Peltier water turbine than that of a centifugal compressor. $\endgroup$ – Zeiss Ikon Jan 13 at 18:34
  • $\begingroup$ @JohnK An impeller is the compressor portion -- though I usually see that used in pumps for liquids, it occasionally applies to gases, too (a fan is an impeller, whether airscrew type or squirrel cage, for instance). You may be conflating with an "impulse turbine" which is the Peltier type I referenced above, also used in steam turbines where a de Laval nozzle blows on the moving blades. $\endgroup$ – Zeiss Ikon Jan 13 at 19:47
  • $\begingroup$ Oops brain fart... $\endgroup$ – John K Jan 13 at 20:42
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    $\begingroup$ @DrZ214 The geometry of a radial turbine is mirror image of a radial compressor -- see a common turbocharger for the easily found example. However, in the compressor, air enters at the axis, is compressed by centrifugal motion, and exits at the periphery, where in the radial turbine, the hot gas enters at the periphery, does work on the rotor and against centrifugal force and exits at the axis. Doing part of its work against centrifugal force automatically extracts a penalty that's not present in an axial flow turbine, which is why almost no jet engines were built with radial turbines. $\endgroup$ – Zeiss Ikon Jan 14 at 12:10
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The Heinkel Hes 3b, which powered the Heinkel He 178, had a radial turbine. This was the first operational jet engine to power an airplane.

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  • $\begingroup$ Thanks, but now I'm looking for a good diagram of the engine and can't find one. Do you know where one is? I want to see how many times the exhaust is redirected to make a jet of thrust. With the turbine redirecting things radially, it should require at least 1 more change in direction. $\endgroup$ – DrZ214 Jan 13 at 21:28
  • $\begingroup$ I don't really have much more than what I linked. There's another image here: airandspace.si.edu/collection-objects/… $\endgroup$ – Fred Larson Jan 13 at 21:29
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    $\begingroup$ @DrZ214, the cut-out on the (linked) Wikipedia page is not that good, but good enough to show that the flow is inward. Basically reverse of that in the compressor. $\endgroup$ – Jan Hudec Jan 13 at 21:31
  • $\begingroup$ @JanHudec Oh i think i get it now. The compressor redirects air upwards along some other path, then it goes downwards to the centrifugal turbine, which redirects it back to axial exit flow. So it is a jet of thrust after all. It's still strange tho because the compressor looks axial, not centrifugal. $\endgroup$ – DrZ214 Jan 13 at 21:34
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    $\begingroup$ @DrZ214, also google image search gives me link to <valka.cz/…>, which is in Czech, but it has a cross-section diagram with the flow marked around mid-page. It confirms the turbine flow is inward. $\endgroup$ – Jan Hudec Jan 13 at 21:40
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I'm interested in turboprops, turbojets, turbofans, even very tiny ones for RC aircraft.

I don't know about any practical designs for aircraft that use a centrifugal turbine. That seems unlikely to me, given the history of development of turbine aircraft engines as compared to other turbine designs (especially the automotive turbocharger, which predates aircraft engines).

But there is a significant community of people dedicated to converting automotive turbochargers (with centrifugal turbines) into jet engines. My own perception of the results is that this constitutes mainly people who manage to get a turbocharger-based engine to run self-sustaining on a bench as a proof of concept and go no further, but there are claims of success in installing such engines on small vehicles, such as go-karts and model aircraft.

Are those claims justified? I can't say. There are a lot of people on the Internet claiming all kinds of outlandish things that have no basis in reality. Feel free to judge for yourself. :) Here are some examples:

Will a JET ENGINE made from a LOO roll holder WORK?
FIRING UP THE TURBOJET!
GR-1 Experimental Jet Engine
Jet Engine full power run Afterburner HX Monster Homemade jet engine
Jet and Turbine Owners (Proboards discussion web site)

Note that in none of these examples is the turbine engine purpose-built. These all involve taking the automotive design and attempting to adapt it for direct propulsion purposes.

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