If you're going to look for a good starting CG (to control the pitch in flight) it's real easy to find that CG based on the things that control pitch. The answer you get matches the measurement usually printed in the model's assembly manual (inches back from LE at the wing root) but is usually more accurate. Which is a lot easier to find than a MAC that has to be plotted on paper and doesn't consider the actual areas of the plane that control pitch. Also, very few model planes today come with any mention of the MAC or how far back on it the CG should be.

http://adamone.rchomepage.com/cg_calc.htm Nine measurements and no plotting on paper. It uses the measurements of YOUR plane and it's pitch stability control, the tail. It also gives you an easy place to find: some inches back from the LE on the root chord.

Run the formula twice, once with 5% and once with 15%, and you will have the safe range for the CG, not just one point. Our models usually perform better and more efficiently aerodynamically with the CG at or behind 10%, and with the info from those two runs, you'll at least have an idea how to do that. or not.... it's up to you.