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Permalink Reply by Brad Hughey on October 2, 2012 at 5:49pm

I have found a spot, thank you.  Fortunately, it's not too far from here.

You are not to be faulted for lack of discovery here.  This forum is not too user-friendly for just browsing about.

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Wiki NinjaPermalink Reply by Gary McCray on January 12, 2013 at 11:46am

Hi Brad, I put a comment at the end of your Large Multicopter forum, then found this with the picture.

Absolutely amazing!

I know it's the middle of the winter there now and lots of snow, so I presume outdoor testing is unlikely to resume till spring, but have you gotten it to fly remote yet?

The picture shows what seem to be the aluminum center foam covered rotors you described.

Are those working out?

I would really like to see a Info BLOG on DIYDrones about the best commercially available propellers / rotors available for multicopters of various sizes and you definitely seem like one of the best qualified people who contribute to this site to provide valuable input.

I am definitely not. I am a retired microcomputer engineer and although I am a pilot and was briefly involved in the construction of an RV4 I am much more qualified on the electronics side of things.

As I became more and more involved in multicopters it did become clear to me is that perhaps the most important single aspect of them was very poorly understood, the propellers / rotors.

Most of what we have are simply slow flight fixed wing electric propellers, some of which have been strengthened to take the higher stresses of static thrust.

Bottom up design completely. - Sucks!

What we need is top down design specific to multicopters of various sizes and capabilities of this singularly most important component.

I read the PDF you linked to about the "flapping" rotor and the blades on those were certainly radical though I doubt that the flapping mechanism is a requirement or of primary importance for use.

In any case I will probably start a BLOG about "Best propellers for Multicopters" and I would greatly appreciate it if you would consider contributing to it.

Basically I would like it to provide a basis for discussion of the best currently available propellers and to provide a forum for future proper propeller design for multicopters.

Our needs are clearly not the same as planes or variable pitch helicopters and the designs we eventually see in use are likely to be very different from what is in use now.

Thank you in advance for considering this request to participate.

PS. I do tend to be a little wordy, - - but thorough.

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Permalink Reply by Brad Hughey on January 12, 2013 at 3:10pm

@Gary: Thank you.  Yes, as much as I admire Paul Pounds' work, his "flapping" concerns are a bit of a tempest in a rather small teapot.  I've not talked to him in years, but it might be likely that he's mixing up flapping and coning.

Coning is a natural byproduct of blade flex and the fact that the highest thrust is generated closest to the tip.  Flapping, on the other hand, is a method of mitigating nonsymmetrical lifting plane torque moments due to forward flight (the advancing blade has a higher airspeed and therefore more lift than the retreating one).  Any electric multicopter with an even number of counter-rotating blades has these torque moments effectively cancel each other out anyway.

I'll be happy to share my opinions on propellers, with the caveat that test results trump design philosophies every time.  My default source of information on real-world production hobby-class prop performance is the UofI website:

http://www.ae.illinois.edu/m-selig/ads/coord_database.html

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Wiki NinjaPermalink Reply by Gary McCray on January 12, 2013 at 3:59pm

Excellent reference, thank you.

And I agree that actual comparative test results are the obvious important arbiter of existing propeller design.

I am giving consideration to putting together a simple prop thrust test rig designed solely for static thrust performance determination.

Seems like the requirements are fairly simple Motor, ESC, servo simulator, Variable Voltage and Variable current DC power supply, a tachometer and a tareable digital scale.

I was also thinking of eventually setting it up for 2 or possibly even 3 motor sizes to allow reasonably useful information to be provided on a variety of prop diameters and performance levels.

The main information would be thrust per rpm and power consumed while simulating various LiPo voltages.

This wouldn't directly translate to efficiency with any given motor, but it should serve as a decent basis for extrapolation.

I've got an adequate DC power supply with adjustable voltage and current to start with and will probably initially use a representative small/medium size multicopter type motor capable of dealing with up to 12" props.

If it works out and seems worthwhile I might eventually try and computerize the whole thing so performance could be reasonably graphed rather than just reporting a few manually extracted data points. (Bigger project though).

Thank you for your offer to contribute, I am sure your input will be very valuable for us all.

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