There is no relationship between the location of counterweight used for mass balancing flight control surfaces and the ground. Does the CG of your airplane change during vertical maneuvers? Why would the CG of a control surface change?

In a perfect world, the hinge line would be recessed in a rounded leading edge and the counterweight could be placed in the leading edge, forward of the hinge line. Since we can't do that here, we attach it externally. This is sometimes done in full scale too with the addition of spades. In addition to adding mass forward of the hinge line, spades provide an aerodynamic balance to the control surface as well. This results in less force required to move the surface.

Scroll down this page and read "Aileron spades".

http://www.airandspacemagazine.com/a...2/AM/fusd.html

-Ben