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Balance question

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Balance question

Old 06-21-2002, 02:08 AM
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ctatham
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Default Balance question

finnishing up my GP skybolt and have all equipment installed. When I pick it up at the balance points under the top wing with the tips of my fingers it comes up pretty evenly. The tail does sit a bit low though. Am I going for just the ability to balance it or does it have to be level at the horizontal stab?
Old 06-21-2002, 02:56 AM
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majortom-RCU
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Default Balance question

Getting the cg right is fundamental to every other trimming procedure you may want to take to get any model trimmed to fly by itself straight, level & stable. For me, flying only gets to be fun after all this trimming is done, which usually takes several flights, sometimes many flights. I find it worthwhile investing a little trouble in being able to adjust or re-adjust cg readily. I do this by installing a hardpoint skyhook at cg, which fortunately with most models is at the center of the main wing spar, usually already containing some plywood for a screweye or hook to bite into. If there is just balsa with no plywood, I drill (on a drill press) through the spar top to bottom and run a 6-32 threaded rod through it so I can hang everything from a fender washer. Drop a piece of nylon cord or whatever from the ceiling and hang your model by the hook at whatever cg you are looking for. I eyeball for level, but I want the nose to either be flat level or just a little bit down. If I see the tail is low by any amount, I shift ballast to the nose. I also look for wings to be level in lateral balance, and sometimes can minimize lateral imbalance by installing a flat battery pack against the side of the fuselage interior. Put a little lead on the high wingtip until wings are level.

High wing models hook goes on top, low wing models hang upside down with hook on the bottom. Models I am not going to be flying for awhile I hang from the ceiling to store them away from the abuse of things knocking against them and leave my floor space free to move around in. Plus they're more inspiring to look at when they're "in the air" with wing & fuse assembled.

Fingertip balance is better than nothing, but not much. Tail-heavy by any amount on fingertips spells trouble to me. CG to me is too important to deal with in approximations.
Old 06-21-2002, 03:45 AM
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djlyon
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Default Balance question

If the tail sets a bit low it's tail heavy. A little drop in the tail may not seem like much, but on a bipe it's alot. See where your fingers are to get it level. That'll give you the answer.

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