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Model Forum / Radio Controlled / Helicopters / September 2004ARG! Concept-60 sr Side-2-side wobble driving me nuts! any suggestions?
Fellow Flyers, I have a concept-60sr which likes to wobble side to side. It is smooth in a hover, then slowly this wobble builds until the heli is near unfly-able. The wobble is about 1 Hz. Changing RPM will extinguish the wobble momentarily, then it comes back. Changing engine mix doesn't seem to affect it. Any constructive suggestions would be MOST welcome... Normally, a side to side wobble indicates the head speed is too low, however if this is OK I would hazard a guess at the damper rubbers in the head. I cant exactly remember, but the concept 60 was allways known for having soft damping, so if the o rings have perished a bit it will be worse than ever. Just a thought > Fellow Flyers, > [quoted text clipped - 6 lines] > > Any constructive suggestions would be MOST welcome... > Fellow Flyers, > [quoted text clipped - 6 lines] > > Any constructive suggestions would be MOST welcome... Check the damper rubbers and change the blades. those are the two most common cures for the C-60SR wobble. The original (non SR) didn't suffer as badly, but the different head on the SR was a BITCH for it. The dampers need to be relatively stiff, so if the head teeters easily it's the rubbers. If the head is in good condition wrt the rubbers, the blades are at fault. If they're the original SR blades, the chances are the CG is too far back.  SignatureBeav Please note my E-mail address is "beavis dot original at ntlworld dot com" (with the obvious changes) Beavisland now lives at www.beavisoriginal.co.uk Thanks for the info ! What seems to cause the problem with the blades? Chordwise or spanwise CG? When you say the CG is too far back, do you mean toward the tip, or the trailing edge? Can a set of blades be "fixed" with weight, or is it not practical? Is the "alternate" concept 60 head (that looks like a big 30-srx head) better? Thanks again! >> Fellow Flyers, >> [quoted text clipped - 15 lines] >are at fault. If they're the original SR blades, the chances are the CG is >too far back. > Thanks for the info ! > > What seems to cause the problem with the blades? Chordwise or > spanwise CG? Chordwise. they're usually a tad too tail heavy. > When you say the CG is too far back, do you mean toward the tip, or > the trailing edge? Towrds the trailing. Some added weight to the leading edge (near the tip can work if they're REALY bad. > Can a set of blades be "fixed" with weight, or is it not practical? It's "doable" but it's not as easy as just sticking a bit of weight on. the usual method is to trench out a slot (a router does that spectacularly well) and inserting and GLUEING lead rod in the slots. This needs to be done VERY close to the leading edge too, so although is IS doable, it's a "bit of a job" and probably not worth the time/cost. A pair or decent blades will be a quick and easy fix. > Is the "alternate" concept 60 head (that looks like a big 30-srx head) > better? Not better, just better at not wobbling:-) The SR head is stronger and more "tnable" than the grown up 30 head, but I liked the feel of the first head beter than the SR head. Some say the original head was more prone to boom strikes too, but I never found that to be a problem. SignatureBeav Please note my E-mail address is "beavis dot original at ntlworld dot com" (with the obvious changes) Beavisland now lives at www.beavisoriginal.co.uk >> Thanks for the info ! >> [quoted text clipped - 22 lines] > a > quick and easy fix. Just a comment on this. If you understand why we balance out a fixed wing airplane to be a little nose heavy, then you should understand why a helicopter rotor blade that's a little tail heavy (C of G too far back from the leading edge) will be unstable in flight. The flybar and control systems on our helicopters can compensate for a slightly tail heavy set of rotor blades but only to a point. If the cord wise C of G is at or slightly ahead of the rotor blades CL (center of lift), the rotor blade will be more stable, aerodynamically, and the helicopter will be a "lot" more pleasant to fly. FWIW! Fly Safe, Steve R. Fellow flyers, Thanks for all the comments. I'm going to try again this weekend. How important is it that the CG is the same between blades across the short axis of the blade (I can't remember if this is chordwise or spanwise)? >>> Thanks for the info ! >>> [quoted text clipped - 37 lines] >Fly Safe, >Steve R. > Fellow flyers, > > Thanks for all the comments. I'm going to try again this weekend. > How important is it that the CG is the same between blades across the > short axis of the blade (I can't remember if this is chordwise or > spanwise)? It's not VITALLY important that they're both the same, which is good, because adjusting the chordwise CG is a PITA. Spanwise balance is good enough if the blades hang level when attached to the head and the head is OFF the heli and supported across two drinking glasses. I'm not getting involved in a "Dynamic vs. Static" balance argument. Suffice to say that if the blades sit level when they're supported by the flybar, they're balanced enough that your heli will be turbine smooth if everything is straight. SignatureBeav Please note my E-mail address is "beavis dot original at ntlworld dot com" (with the obvious changes) Beavisland now lives at www.beavisoriginal.co.uk |
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