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importance of chordwise balance?

Virtual1

Senior Heliman

Waterloo, Iowa - USA

I decided to try out some maverikk brand woodies for my Raptor, they're like 40% cheaper and so far TT blade quality had not impressed me.

The two sets I received have an interesting issue. The first set of blades are precisely the same weight, and their spanwise CG is within about 1/2mm. BUT the chordwise is significantly off. I balance my blades by epoxying on tiny washers, and in this case it's going to take two on the leading edge of one blade and two on the trailing edge of the other. That's more than I'd like to add, but doesn't seem like too terribly much.

(for anyone that's interested, these are brass washers, 10mm od, 4.5mm id, 1.1mm thick, not sure what they weigh)

"Not so bad" I think, and move on to the other set. This pair is not quite equal weight, off by about one washer. Spanwise CG is identical. (I was impressed by this because every set of TT's I've bought has had serious spanwise issues) But when I get to chordwise, it "pegs out" the bubble on the Koll. When all was said and done, I had a stack of 7 washers on the far leading edge of the light blade and a stack of 6 washers on the far trailing edge of the heavy blade to equalize weight and CG. Sheesh, that's a lot of weight to add!

I realize there's a lead/lag issue that develops when CG is off, but just how big of a problem is it? Will these blades shake my heli apart, or just cause a little vibration, or what? It's nothing fancy, just an R50. (that's been getting beaten up a lot lately anyway) Your advice is appreciated.

05-19-2002 Over year old.
HOMEPAGE  
Conrod

Veteran

Melbourne, Florida

CW

If CW is out...then while flying the SW will be out.
I believe that CW is more important than SW. Had a set of woodies once that would go out of track when given cyclics. Didn't realize it was blades until I tried a friend's set. Perfect. Only difference was his was checked and balanced on Koll ....CW. I bought me one and balanced that same set for CW since SW and Total Weight were perfect and resolved the problem.
conrad

05-19-2002 Over year old.
Dragon2115

Key Veteran

New England

If you have any plank experience look at the blade as a wing. What happens when the cg is too far back from the leading edge? It becomes very sensitive to changes in angle of attack. IOW it becomes pitchy. In a plank this can make it unflyable. In a heli it causes the blades to bite into the air too much and robs the rotorhead of power. You can see where this could really be a problem if the cg's weren't close, one blade would be grabby and the other wouldn't.

Btw, I wouldn't recommend epoxying washer to your blades. Sooner or later your going to fling one. They may be small washers but they're already traveling at close to 300 mph if they're out at the tips. If a blade can't be matched using tape then IMO it's too far mismatched for use.

05-19-2002 Over year old.
Virtual1

Senior Heliman

Waterloo, Iowa - USA

Dragon: So in this case Ray's manual is giving bad advice? He shows balancing blades by flattening lead sinkers and glueing them on. FYI, I'm not merely glueing the bottom of the washer to the blade, I'm planting the washer in a small "pool" of epoxy, completely encasing it. For what I can tell, it should have a better grip than the standard lead weight.

05-19-2002 Over year old.
HOMEPAGE  
Ivan

Veteran

Hutchinson Kansas

I always balanced woodies by drilling a hole. or a slot as it may be and inserting lead sticks. Cover with some model magic and set with CA glue. Never had any problems with loosing weight.

I guess it seems that you are just glueing the washers on the surface of the plastic blade covering. Is this assumption correct? If so, I would suspect that the weights would brake off if the covering ever flexed. But the proof is in the pudding and if you have never had one come off, more power to you.

Ivan

I came, I saw, I hovered

05-19-2002 Over year old.
HOMEPAGE  
ed vega

Key Veteran

nyc, queens

a good practice to follow , also done in conjunction with the other balancing acts.. don't use washers..

balance the lighter against the heavier blade, first weighted on a scale like a triple beam or digital scale for equal weight . lighter to match the heavier in weight .. diagonally check, using a verticle razor blade for the 'X" chordwise balance , determine where the cg is , first place like "/" then like "\" with each blade over the razor/edge. the more leaning forward chordwise the better , not aft , the heavier blade is the target . mark each location too with a pencil. theres no damage to the rotor blade ,the razor will grab the location well, use a small vise to hold the razor verticle . mark it underside with a pencil.. another balance is the root bolt to tip weight like on a schulter blade balancer or similiar. longitudinally .. using tape to shift the balance.. should expect and receive zero vibration after the tracking tape was applied add some more tape balance as needed under 1gm .. then balance the rotor head and flybar / paddles, without the blades with or without weights. then weights if using .. then add the blades ,

in short , lengthwise, chordwise, diagonally..these are not secrets - just common sense maintenace for woodies or repaired glass blades ..


05-19-2002 Over year old.
ed vega

Key Veteran

nyc, queens

for composite blades most can be balanced with just a strip of tape on the tip.. unless they are not matched due to weight or are damaged and repaired the above still applies .. new composite blades are good to go .. cg corrected ..

on the other hand unequal , or slight damage where epoxy resin is added, or woodies are not the same in balance and need more work.

05-19-2002 Over year old.
jetranger

Veteran

PERHAM M.E.

blade

One point you missed is that adding washers to the trailing with epoxy when you cover the blades there will be a bump on the blade this could act as wash out or wash in on the tip just as on a plane wing. Drill a hole and epoxy them flush with the surface.

05-19-2002 Over year old.
oldfart

Elite Veteran

Vancouver, Canada

CCG

Not only is the SCG and CCG match of importance , but their proper relationship with the feathering axis relative to the center of lift of the airfoil used are of equal or greater importance.

It is easy to mill a wooden blade, many have the means and limited skill to do so, but few of them have the appropriate understanding of aerodynamics to relate the many factors involved to develop and manufacture a good set of stable/neutral blades. But they certainly can be low priced because there is no R & D costs to be factored in.

Some relatively inexpensive woodies that are consistantly well made are the Century Aerotech CN2300 series (530mm, 550mm and 600mm covered in white heat shrink) and the longer 60/GS size units (660mm, 690mm, 710mm covered in multi-colored stick-on).

Just glue on the supplied blade roots and go fly.

Phil

05-19-2002 Over year old.
Dragon2115

Key Veteran

New England

Virtual1,

If that is how Ray's book is telling you how to do it then yes, Ray is giving bad advice. Equally as bad as the way he shows how to adjust the needles on the engine. You know the one with the guy in the motorcycle helmet with the heli strapped to the step ladder going full bore. Tell me that isn't an adventure in Darwinism. I had a guy at the field try that, against my advice, and he found the ground resonance I warned him about. It almost cost him his Raptor 50, and his head.

05-19-2002 Over year old.
volare

Veteran

N/A

[]

05-20-2002 Over year old.
Dragon2115

Key Veteran

New England

Actually the easiest way is as Ed pointed out, buy a set of carbon blades and be done with it. Most good carbon blades can be fully balanced with one or two pieces of trim tape. My top three choices would be TG's, SAB's, or V-Blades.

Other than that the Koll Rotorpro balancer is probably the best static balancer on the market.

05-20-2002 Over year old.
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importance of chordwise balance?

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