RE: help on balancing low wing planes
"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"
I think what is described here is the "Center of Balance". I'd have to ask my aeronautical engineer friend if that is correct.
As far as Bozarth's deduction that my understanding of physics is wrong, again, why would Great Planes provide a bubble level with their balancer? I know this; when you move the supporting string fore or aft to obtain a level aircraft the point of the plumb bob moves away from its location when the model is hanging nose up or down, This tells me that the CG is moving. And the force present is called moment arm. Nose up or down, the moment arm is unequal.
The following is from their manual:
HOW TO USE THE LEVEL
To assist you in accurately balancing your airplanes, we have included a small, lightweight level vial.You can use this in various ways to help determine when your airplane is truly level, rather than relying on estimation. Although the level vial may be used alone, you may attach it to the 1/2" x 3" plastic strip, with a small piece of double-sided tape (cut from the included 1" square), carefully aligning the vial with one edge of the strip. Attaching the vial to the plastic strip will allow it to be taped to the side of the fuselage along a reference line.You can also place the assembled level on the stabilizer.
Bob