RE: help on balancing low wing planes
A couple of quick pictures.
The actual CG of a plane is going to be somewhere inside the plane. Almost never will it be somewhere along the top skin of the wing. Very seldom will it even be somewhere between the top and bottom of the wing. When the plane is tilted, not a one of our methods of finding the CG is going to work accurately. We'll have to guess or judge from what we see where it might actually be.
We're actually trying to find out where the vertical plane of the CG passes through the wing. When the wing doesn't pass through the CG, things go bad for every one of our methods.
The way to make every method work accurately is to have the plane horizontal at the time we mark the CG. Then we will accurately mark 'where the CG is on the wing'.
Here's a picture of where the CG really is on a model. It's the red spot. And the yellow arrow points to where a plumb bob would be pointing at the wing when that model had quit swinging in the rig or quit tottering on a CG tool. There would be nothing that pointed out where the CG was along the wing for balancing purposes. There wouldn't be a blue arrow. It's your best guess if your CG is located where the mfg suggested it be.
If the mfg had suggested the CG should be where the yellow points on the wing, you'd really have it forward of that. How much forward? How would you know.