Almost as common as the question: What Size Prop? Is the question: where is the CG? Here is an address for a CG calculator that every RC pilot should have in his favorite file. Mater's not weather you are a builder or will never know anything more then the ARF, this question will boggle your mind at some point in time, trust me on that, I have been given some real odd ball planes in my time and had to locate a CG for them. This calculator works so well I have used it on two meter pattern planes that didn't even have a name but after using this to locate the CG I never moved the balance point again, it works that well.
http://adamone.rchomepage.com/cg_calc.htm
Add it to your favorites right now before it gets lost again in the void we call the RCU back pages!!