OK Keith, excellent I would be pleased to divulge the simple method. Just got back from the field and had some pleasent flights with my Wee Waco and lot of good BS around the burn barrel
OK first for that type of airplane and in reality the majority of airplanes I test. I always start out at 25% MAC not one third. That Mac stands for mean aerodynamic cord, actually just the average cord from the leading edge of the wing to the trailing edge of the wing.
Now how do we find that average cord? well thats easy with a board wing with equal cord its just the measurement from front to back anywhere along the wing. The confusion starts though when you have a single taper wing (just leading edge) as yours or a double taper wing, heck even an eliptical wing.
Its easy with these wing type too, simply measure out half way from the fuselage to the wingtip. At this point measure the cord. Divide this measurement by four and measure this back from the leading edge out there at this half way point. This point is going to be your target CG and you only need to use a straight line from this 25% point or quarter cord out there inward to the fuselage side and thats all you need to do. This is your target CG and what you want to balance to.
This will give you an absolutely safe starting point every time with the majority of model types you will ever fly and you can apply this method in just a few minutes. I use this method with all of my aircraft every time particularly so when as often happens many manuals are wrong and this happens far to often.
John