I have a tower hobbies 40 trainer. I put a super tiger gs-40 engine on it. The engine is heavy at 19.08 oz, but is listed as a recommended engine for this plane. The CG is supposed to be 3.5 inches aft leading edge. At 3.5 inches, I have to add 4.5 oz of weight on the tail fin to balance it ( fingertip method). My other engine thats in a spad is a GMS47 and is 16.75oz. The OS 40LA is even lighter than this and would probably be just the right weight on it. The battery is as far back as possible without moving it to the rear of the servo tray. So , What would be the best way to balance this thing? I hate to change to a lighter engine as this was ordered for this plane, and I hate to have to add 4.5oz to the tail either!