The RC Airplane center of gravity or cg of
the aircraft is to be located at 25% or 0.25c
(of the mean aerodynamic aerodynamic chord).
For the rc airplane, mark a vertical line on the mean aerodynamic chord. At 25% or 0.25c of the mean aerodynamic chord. Mark a horizontal line on the wing. At the center point of the joint of two wings mark a straight vertical line. The two lines will intersect each other at a point. That point is your reference cg point.
An RC Airplane can be either nose heavy or tail heavy. If you have chosen your airplane to be statically stable you will most probably chosen 25% of the Mean Aerodynamic Chord as the reference Now you have got your reference cg point. Now, you need to check if your airplane cg is at the reference cg point or is it nose heavy or tail heavy.
To do this, you need two people. One person on either side of the wing. Lift the wing with a single finger (don't lift up/touch any other part of the aircraft during this check) along the reference vertical line which passes through the reference cg point. If your airplane is nose heavy or tail heavy it will automatically move in either direction. If airplane not at the cg point add ballast either to the nose or tail until you have reach the cg point.