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How practical a test of a "Jetoptera" Fluidic Propulsion RC scaled

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How practical a test of a "Jetoptera" Fluidic Propulsion RC scaled

Old 05-30-2021, 10:12 AM
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critx
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Default How practical a test of a "Jetoptera" Fluidic Propulsion RC scaled

Hello,
I'm not active on the forums, but I do follow new posts . I'm building balsa planes my own.

I've been reading about "Jetoptera" design and seem interesting. Coanda effect, augmented thrust and other interesting stuff...
I'm no expert in fluid flow science but willing to test some ideas.
There's a first simple question for more experienced once - will this make sense trying?

A main concern to me is the air comming from a fan loosing a lot of energy/speed in the ducts to the output slits.
I've thinking of using a centrifugal fan - this also need expert confirmation. To me a big diameter centrifuge would be better than an EDF. The power plant would be an electric outrunner 3S/4S 40A.
As a start idea I'm thinking of bench-testing it first see the output power then integrate a big diameter centrifugal fan inside a fuselage then direct the airflow to one augmented exhaust.
There would be other question - what size for the slits?

Hope for some answers/ideas...
Old 05-31-2021, 06:52 AM
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allanflowers
 
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The so called Coanda effect is greatly overrated. It might work for a quiet cooling fan in your house but not much else. I remember reading the "aero" report (often quoted for performance claims), done at Illinois Institute of Technology (where I graduated) and the test setup violated the most basic wind tunnel requirements. The Jetoptera website looks like classic vaporware designed to lure gullible investors.
In short - this won't work.
Old 05-31-2021, 08:29 AM
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critx
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allanflowers, That is a fair feedback.
Interesting ... I'm wandering how (?) the investors are not able to figure out their money are already lost - as you suggest. Although I'm not really looking to go into a political discussion.

Thanks

Last edited by critx; 05-31-2021 at 10:54 AM.
Old 06-08-2021, 12:44 PM
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Critx, consider that most, if not all, of today's model size turbojets use centrifugal compressors. But then consider the RPM needed to make them work. Keep that in mind when looking at motors to drive them.

For this to work the air needs to be ducted in a way that it won't "pile up" against any internal resistance caused by air forming turbulent bubbles in the ducting. Consider the plight of airflow in intake manifolds in cars as an example. It won't be quite that bad due to the pressurized nature of your setup rather than being less than atmospheric. But the internal ducting to turn the airflow will need careful attention.

The other issue is that you're trying to turn pressure into velocity. And more to the point that velocity needs to all go straight back. So by the time the air leaves the nozzle at the end of the model you don't want a lot of left over pressure. Otherwise it spread out to the sides as well as back. And any that goes to the sides will do so equally and in a way that cancels out. And that's lost energy that could have been pushing forward.

Not that I'm a fancy jet engine engineer. But a guy on YT that goes by the account name of AgentJayZ has a good series of how pressure and velocity play out in a jet engine. And a lot of this is pertinent to how EDF's or EDC's, in your case, would want to operate.

As for augmenting the flow of the air this came up in some other reading and videos I saw a bunch of years ago. When you mix in augmenting air you add to the mass. But by that time there is only so much kinetic energy to go around. So as mass is added velocity drops. Adding in augmentation air might be something that helps at takeoff and for the initial climb..... provided you run a variable opening tail nozzle to avoid a higher than atmospheric pressure at the tail nozzle. But for high speed you'd want to shut out any extra mixed air and just go with the highest possible speed out flow.

At least that's how I've come to understand this EDF and jet stuff.

This is also the reason why when big jets cut in the afterburner that they open up the tail nozzles. It's so the extra gas volume of the jet exhaust does not cause the internal pressure in the tail pipe to go up. They want to allow the extra volume to contribute to the SPEED of the outflow, not pressure.


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