I measured on the top wing at the center conecting rib for proper distance. then i used a sliding square to mark my mesurments at different intervals and used the finger method to see where it ballances. I have heard some folks drill several small holes in the center rib and run string at different measurments and ballance that way but i use the ole finger meathod. i am like Busted I am thinking of putting an evolution 26 gas motor on this plane. I think it will handle it.