Got me a Gee Bee .25. Can't remember if its from nitro planes or from AK models. Anyways, I assembled this last year. I put on a turnigy 900kv outrunner. According to the manual, the CG is 55 mm from
leading edge. This comes out to roughly, 2 5/32 inches. On the wing, there is a spar (you can feel it) that is just behind where the mains attach and just about measures with the 55 mm suggestion from the manual. So, this is probably where the cg is. However, I read where some have claimed that the cg (55 mm) is a hair too far back.
Generally, I will test cg from the bottom of the wing (yeah, I know your supposed to have the plane upside down to check). This method works for all the other 30 planes I have. But, the gee bee is way too difficult to balance this way. I will have to turn her upside down to check.
I had put in another outrunner (one that I had in a gp reactor bipe) first and tried to hand launch it since the mains were too short (kept catching in the grass). Plane acted tail heavy and the motor wasn't powerful enough to sustain flight and it dorked in the weeds. Which is why I thru in a bigger motor.
My question is....any of you have one of these and where is it balancing for you?

Lucky...

Measure the chord at the fuselage and then balance it about 28 percent back. Keep your surface throws conservative and your airspeed up!