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HelicopterScale Model RC Helicopters › Multi Blade head - Blade weights and balance question...
11-23-2006 03:19 AM  11 years agoPost 1
racer944

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Greely, Ontario - Canada

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For you guys that have experience with multiblade setups I have a question...

On a 4 blade head, how critical is it that all 4 blades are equal in weight? I can match up two blades in weight fairly easily, but getting 4 blades to all match at equal weights is become a bit of a challenge...

So in a nutshell, if the blades are balanced properly in pairs and set opposite each other on the head, can one pair be out a bit in weight (say 5 grams) over the other pair and not cause issues?

Cheers;
Eric

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11-23-2006 03:49 AM  11 years agoPost 2
AGRAV8

rrProfessor

Mosquito Coast......Houston Texas

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yes

as you stated, pairs together.

GOOD guy list-39, BAD guy list-0

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11-23-2006 08:10 AM  11 years agoPost 3
PETER ROB

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Devon UK

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Blade balance

Sorry I have to disagree with AGRAV8 post,with any blade setup they have to be balanced correctly
With the 2 blade, you find the heavy blade and add weight to the lighter blade to get the balance correct
With the multi blade head, do exactly the same, find the heavy blade and balance the remaining blades to it
peter r

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11-23-2006 04:12 PM  11 years agoPost 4
Peter Wales

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Orlando Fl

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My vote is half way between the others.

I bought a set of blades from OF. They come in 2 pairs. The pairs are exactly equal in weight but each pair differs from the other by about 3 gms.

So, my vote is with James, no, they dont all have to be exactly the same, and with Peter, they have to be pretty close. These are within 1%

Peter Wales
http://scalehelicopters.org

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11-23-2006 04:35 PM  11 years agoPost 5
AGRAV8

rrProfessor

Mosquito Coast......Houston Texas

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Experiences WE have had

When Payton was messing with his FIVE bladed head, the weights and balance were CRITICAL to the smoothness of operation. I would transfer that experience to the THREE blade head sets as well.

On the 4 blades (and 6 in theory) the opposing blades are balancing themselves against each other. I have a couple 4 blade heads, and the Vario 2 bolt unit has blades that were matched up, weighted, and span balanced by none other than Mr. Len Mount himself. He related to me that I should get them "spot on" when painting. Note these are 1680's. I take it from that comment that it is BEST to have them equal all over.

My other head is a Century (latest version, all metal) and the blades I use are 600mm SAB's, and they have a 3-4 gr difference in weight between the two pairs. (these are 145's, BTW). So far, no problems with that during testing. I DO, however, keep the heavy ones opposite each other.

In agreement with Mr Wales, I don't think a few g is a big deal between the pairs....but I would NOT, even to see what happens, run a difference larger than 5-7 g myself.

Our friend Eric might want to employ some tracking tape to equal them out if in doubt.

One a related note, I would NOT mix diferent lengths OR airfoils in a multi setup. (ie TT 600's with SAB 600's) The dissymmetry of lift would be a MAJOR problem.

GOOD guy list-39, BAD guy list-0

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11-23-2006 09:42 PM  11 years agoPost 6
racer944

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Greely, Ontario - Canada

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Thanks very mcuh for all the info guys... good discussion that is very helpful for a multiblade newbie like me.

I am going to buy the best blades that I can, and I do hope to have them as close as possible, but its good to know that there is a bit of tolerance in blade weight on a 4 blade setup. I will of course be very precise with my balancing and if I can equalize them with tape will do so.

By the way for those that have been following my thread about my hover tests, I will be reducing the size of my blades down to 570mm (from 600mm) and the new blades wiill have a CG at about 23% of the blade and a weight of about 115grams each. Hope this will give me a bit more authority on the collective... Its tough finding good blades for a multi setup in the 550mm/600mm range.

Cheers;
Eric

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