go 25 % back from the leading edge of top wing and the same for the bottomwing.....put your balance spot in the middle of that and you will be in the neighbor hood...then fine tune it[cg] as you fly[you know if ya run out of elevator on landing move the cg back,etc,etc]...but,if ya have plans ,you will always go off of the recommended cg. this method has always worked for me on those swap meet bipes we all pick up from time to time