airbuswhiz

I would like to know if anyone has some pictures or hints on jigs for balancing giant scale planes. I have an 84" w/s biplane, as well as a scratch-built 1/3 scale Pitts. I want to be able to build up a jig that i can get under the top wings with to accuratly set my c of G.

This is just the start of the big planes, so if I can use this jig to set the C of G on monoplanes as well would be of great benefit.

Anyone have any hints or tips..??

Thanks guys...Don H.

majortom

My method works only when you're building, not when you have a finished plane, but it simplifies everything. I build in a vertical dowel at the recommended or intended cg, framed & glued to the main spar in a high or low wing, or into the belly for a mid-wing. Drill a pilot hole in the dowel for the appropriate size screw eye, and hang the plane a few inches off the floor from whatever you have overhead to tie into. Makes lateral and longitudinal balancing a snap for the first balancing act. If repairs or mods change your CG, or you just want to move it up or back at some future time, it's easy to readjust back to level, or let the nose or tail dip a few degrees, whatever you want to do.

For a plane already built, the suggestion I favor is to suspend your plane just off the floor with a rope/twine/strap/folded-rag harness running from fuselage just forward of the tail, through a ring (or could be a pulley) and back down to a convenient point at front of plane. Then hang a plumb bob from the same hanger point, long enough to hang just above the airframe. As you shift weight around, the plane will shift such that the changing CG will always be directly under where the plumb bob is pointing. Keep the weight/bulk of your harness light, since it is part of the hanging mass and gets included in the indicated cg.

joetsunami

airbuswiz,
Easiest, simplest, cheapest, most accurate I've found is a string/rope and plumb-bob.
Cut a string (with a loop on each end, .40 sized would be about 5 feet long) with a loop at each end large enough to go over the rudder/rear of fuse and a loop large enough to go around the prop hub. Make yours larger/tie around fuse instead of under rudder. Now tie another string around this string, so that it will slide, and you can move the center point so that plane will hang level.

Here's where I run this through a hook on the ceiling, and lift the plane off the ground. Tie off string to appropriate non-moving object.
You now have a plane with a string that is tied to its' nose and tail, with another string tied somewhere near the center of this string (really, it's right above the CG), that is holding the plane off the ground (not too far!)

Now tie a plumb bob on a string to the string that passes through the ceiling hook, and adust the plumb bob so that it hovers just over the plane. The Plumb bob now points right THROUGH the CG. IOW, the CG lies directly below the plumb bob.
Hope this helps.....but you've probably seen this thing used before. I'll send a picture if you haven't seen it, there's NO WAY you could build it from my crappy description!

Joe Myers

GalenB

My Feedback: (18)

I bought one of these:

http://www.kollercraft.com/

The Daddy Long Leg model to be exact... Placed the order Friday night and the balancer was on my doorstep Monday when I got home from work. Great service!

Won't do the bipe by the upper wing unless you balance with the model inverted.,,

airbuswhiz

Thanks guys for all the ideas and replies. You now have given me something to think about for balancing.

Galen, those balancers that you posted look interesting...you will have to tell us how they work for you.

Thanks again gents...Don

Geistware

My Feedback: (16)

I guees I get the plane slightly nose heavy (balance using a helper with my hands) then fly the plane and adjust it until it flies like I like it. If you make small changes it is easy to see when you are going too far.