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3-blade prop question - 9/13/2007 2:26:49 PM   
ForkedTailDevil


 

Posts: 156
Joined: 2/3/2003
From: Lexington, KY, USA
Status: offline 		Hey yall..i'm runnin a US 41cc on a jap zero weighing the lighter half of 20lbs. Turnin a xoar 20x6 prop...i was curious if I could run a 3 blade prop without loosing alot of performance, what size would be acceptable, and at what rpm should i run if I choose to go to a 3blade. All comments are welcome thanks!

-Bubs
       Post #: 1

RE: 3-blade prop question - 9/13/2007 2:37:44 PM   
Walt Thyng


 

Posts: 809
Joined: 7/27/2002
From: St. Charles, IL, USA
Status: offline 		The party line is that a single blade prop is the most efficient and efficiency drops as you add blades. Like most theories the effect in the real world is small. Probably because we tend to overpower our planes anyway.

Again, common advice when moving from two to three blades is keep the pitch, but drop the diameter one inch. I'm not sure how well this applies to large props, but it works for me up to 16 inches.
Walt

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RE: 3-blade prop question - 9/13/2007 4:39:25 PM   
da Rock



Posts: 7007
Joined: 10/11/2005
From: western, NC, USA
Status: offline
quote:

ORIGINAL: ForkedTailDevil

Hey yall..i'm runnin a US 41cc on a jap zero weighing the lighter half of 20lbs. Turnin a xoar 20x6 prop...i was curious if I could run a 3 blade prop without loosing alot of performance, what size would be acceptable, and at what rpm should i run if I choose to go to a 3blade. All comments are welcome thanks!

-Bubs



Master Airscrew sells the most 3 bladers around here. On their packaging, they suggest that you choose a 3 that is one inch less in diameter and one inch more in pitch.

I've been doing prop tests recently, looking at 3bladers for the first time. And I've found that 3bladers work far better than conventional wisdom suggests. And that it's definitely worth trying any one of them that even seems like it might work. One of the best so far is a 3 blader that is the same diameter and pitch as the engine's favorite 2blader. That's not possible, right. Nobody told the engine.

A lot of our conventional wisdom needs to be re-tested.

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RE: 3-blade prop question - 9/13/2007 5:48:44 PM   
ForkedTailDevil


 

Posts: 156
Joined: 2/3/2003
From: Lexington, KY, USA
Status: offline 		hmm interesting comments and thanks!!! so therefore your tellin me that for a threeblade i should go for a 18x8?

(in reply to da Rock)
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RE: 3-blade prop question - 9/13/2007 6:20:25 PM   
JohnMcGowan


 

Posts: 828
Joined: 12/14/2001
From: Birmingham, AL, USA
Status: offline 		Hi Bubs, if you are interested in 3 blades, check out the Graupner props sold by Hobby Lobby in Tennessee. The blades are much wider than the Master Airscrew brand, altho Im not sure how big the props go. I have a 14x7 graupner, and compairing it to a master airscrew, the graupner looks much better. I hope this helps some. Good luck,
John

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RE: 3-blade prop question - 9/13/2007 9:55:28 PM   
da Rock



Posts: 7007
Joined: 10/11/2005
From: western, NC, USA
Status: offline
quote:

ORIGINAL: ForkedTailDevil

hmm interesting comments and thanks!!! so therefore your tellin me that for a threeblade i should go for a 18x8?


I guess what I tried to say was to try anything that seems within reason. Why? Because the rules of thumb are not gospel and don't take near enough into consideration.

As John just mentioned, there is more to it than just the numbers. The reason I think my MA worked when it was the same numbers as a 2blade was just what he mentioned. And to spell it out seemed a bit much. Glad he mentioned it. Props are basically wings. And wing area matters for them too. But trying to explain all that about props is a bit tough.


I take it you're using an 18x8 two-blader now?
Look around at all the 3bladers available. There aren't going to be but a couple available at all for any engine size. If there is an 18x8(3) available, I would try it. But I'd first look for a 3blader that was one inch less diameter and was ANY pitch ANYWHERE close to what seems right. If you find more than one available at all, THEN choose a pitch that's at least your 2blade favorite.

What I've found is that any 3blade that is close to the same numbers as the engine's favorite 2blade will fly the airplane pretty good. I've yet to feel I wasted the money on any one of them. They all have worked way better than conventional wisdom predicts.

the real sticky part is finding more than one 3blader to try......... and we try handfulls of 2bladers before proclaiming success, don't we. We got handfuls of them available.

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RE: 3-blade prop question - 9/13/2007 10:45:42 PM   
ForkedTailDevil


 

Posts: 156
Joined: 2/3/2003
From: Lexington, KY, USA
Status: offline 		Very good point "da rock" I'm runnin at 20x6 2blade right now from xoar...xoar's got a line of threeblades avilable, just wanted to get some good clues before i put out the cash for a threeblade...like you said i'v got many two blades to choose from, 3blades are sort of hard to come by...not to mention tryin to find a scale jap zero spinner that will accept 3blade as well

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RE: 3-blade prop question - 9/14/2007 4:57:44 AM   
Walt Thyng


 

Posts: 809
Joined: 7/27/2002
From: St. Charles, IL, USA
Status: offline 		Bubs,
I agree with McGowan. The Graupner 3 bladers are hard to beat.
WT

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RE: 3-blade prop question - 9/14/2007 1:07:30 PM   
timothy thompson


 

Posts: 2761
Joined: 6/19/2004
From: saginaw, MI, USA
Status: offline 		solo props are the only way to go . they are pitch adjustabke and blades are easy to replace if broken. Great company. On a zero you hasve a spinner so you may get by with a standard 3 blade. solo props have scale hubs

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RE: 3-blade prop question - 9/14/2007 4:53:02 PM   
Walt Thyng


 

Posts: 809
Joined: 7/27/2002
From: St. Charles, IL, USA
Status: offline 		Don't forget Vario prop. Lots of good reports, but I've never used them (yet). Where do the "solo" props come from?
WT

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RE: 3-blade prop question - 9/14/2007 7:34:03 PM   
jaka


 

Posts: 4727
Joined: 12/11/2001
From: Upplands Vasby, SWEDEN
Status: offline 		Hi!
If you are running a 41cc petrol engine ...just forget any of the small 18x8 3-blade plastic props.
You need a larger prop!

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MVVS, Motul "Micro" all synthetic oil

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RE: 3-blade prop question - 9/14/2007 8:11:00 PM   
tahustvedt



Posts: 426
Joined: 1/28/2004
From: Bardufoss, NORWAY
Status: offline 		You can get Soloprops here: www.soloprops.com

I'm using a three bladed 20" Soloprop on my 1:6 scale P-40 and its working well.

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       Post #: 12

RE: 3-blade prop question - 9/15/2007 12:27:25 AM   
SCALECRAFT



Posts: 1557
Joined: 1/7/2002
From: MONTEBELLO, CA, USA
Status: offline 		I believe it can be done. However, I think I will be looking to large high torque brushless motors with possible gear down for my 80" 109F/G carbon scale blades.

Blades are 20" arc by variable pitch

I have the blades, I just need something to turn them fast enough.

Steve

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RE: 3-blade prop question - 9/15/2007 1:56:45 AM   
paladin


 

Posts: 1696
Joined: 2/13/2002
From: Vestal, NY, USA
Status: offline 		I’ve used three blades props but have banned them from ARF’s. even with the shimming of the LG some ARF’s are tipsy enough to make ground handling in 20mph wind impossible. So, while taxiing out the wind got under the tail and you need a new prop do you have a spar? I did not and my spinner was a three holer. Then I find my self asking the two blade prop is lighter than the three blade, flying without the spinner cup reduces the nose wt even more. How lucky do you feel punk? On ARF’s I normally keep the CG pretty far aft to help ground handling, so drain the fuel and check the CG.

I’ld rather fly than tinker.

If it is one I’ve built then three blade prop.s are great cause the ground handling is good and the CG is in the middle of the range so a two blade prop is just plug and play.

Joe

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If it don't fly it wont ketch my eye.

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RE: 3-blade prop question - 9/16/2007 11:27:02 AM   
fockewulf37


 

Posts: 1286
Joined: 3/19/2002
From: kannapolis, NC, USA
Status: offline 		Here is a converson chart fro Zinger. They have a new style 3 blade prop that pretty good I have heard..


http://www.zingerpropeller.com/_2_blade_.htm

here are pic's of both style blades they now have....



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< Message edited by fockewulf37 -- 9/16/2007 11:29:31 AM >

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