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Author Topic: Single bladed props?  (Read 521 times)
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Tapio Linkosalo
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« on: February 06, 2017, 04:11:55 AM »


I recall reading in Aeromodeller many years ago an article on how to make single-bladed props (how to make the counterbalance and most of all how to dynamically balance the prop). Unfortunately I cannot locate that article now. Would someone have pointers to the issue, or some other reading on the subject? Thanks!

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dputt7
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« Reply #1 on: February 06, 2017, 04:23:58 AM »

  Tapio,
                There's a comprehensive article in the plan gallery here, good luck, I found it was mostly trial an error.
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USch
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« Reply #2 on: February 06, 2017, 09:37:45 AM »

As Dputt says there is a comprehensive article on the plans gallery, look for "Single Blade Propellers (julio) ".
If you dont like to work through all the math's go to the conclusions and find easy to follow details for the counter weight and his location. At least for me it worked out first time.

Urs
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Tapio Linkosalo
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« Reply #3 on: February 06, 2017, 11:35:59 AM »


Found it - quite interesting. However, I put this question to CL forum, as the Aeromodeller paper was about F2A props (maybe written by Eisner), and I'm looking for an article on IC motor props.

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faif2d
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« Reply #4 on: February 06, 2017, 02:33:04 PM »

Back when I was semi serious about F2D I purchased a single blade fiberglass prop.  The counterweight was a piece that was made from a single piece of I think brass.  The thought was if it worked I could run a bigger diameter prop, easier to cut the streamer, and perhaps increase the speed.  I can not remember the Dia. nor pitch but think they were both larger numbers than normal.  I only got 2 flights, one that allowed me to determine that the speed was faster and the tip was still subsonic although very close (if you whipped the plane it would go supersonic which was very noticeable.  On the next flight I did a bunch of full control maneuvers to see how that would work.  It worked just fine and then my to small lead outs broke and it pile drived into the dirt.  I think that this was an area ripe for experiments but never tried to do it again.
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Tapio Linkosalo
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« Reply #5 on: February 07, 2017, 01:27:38 AM »


Did you get instructions on how to balance the prop? In the Eisner (?) article I read in Aeromodeller decades ago, I think it said that the counterweight needs to be a tad lighter than the blade, to reduce vibration in dynamic balance. This was achieved by filing the counter weight until the prop did not balance vertical, but was canted at ~45 degrees. Without having the article at hand, I cannot understand how this was achieved, unless the prop was balanced with a rod through the shaft hole, in which case the "vertical" position would have been with the prop CG on the outer edge of the shaft hole, and thus counterweight actually a bit heavier than the blade. Puzzling! Also some F5D pages suggest that the counterweight should be installed in the spinner, closer to the motor than the blade. I suppose this aims in having a momentum of the counter weight opposing the lift from the single blade, in the same way as described in the Presnell paper linked aboce.  I just wonder is such a light weight and short moment could suffice to counter the high lift force (and moment) from the F2A/F5D prop. Should work on a slow-rotating rubber prop where the counter weight is supported by a long wire arm, but does it also work on a high-revving IC or electric motor?
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gossie
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« Reply #6 on: February 07, 2017, 03:12:49 AM »

I have a couple of carbon fibre Mario Rocca single blade folders that I have used on Rossi 15s.   They are just perfectly balanced using a weight just out from the center.
No vibration and work very well.

Have several single blade props. for rubber models.   I have the wire arm with a weight to balance them as perfectly as I can.
Work very well, and have been told long ago a single blade on a prop. is always in clean air so is efficient.
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Tapio Linkosalo
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« Reply #7 on: February 07, 2017, 03:38:08 AM »


Sorry, I'm not sure I got that right. The Rocca props balance (have their CG) on the center of the shaft hole?

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