one day i'm just gonna answer, " on the damn plane "
after all, it must be, where it's ballancing right now, thats the CofG, how you find it?, balance it, no calculation can help you find it.
HOWEVER!!! it might be in the wrong place i sold a kid a 15 fun fly, he fitted a 40 and UC, i laughed and sent him away. the CofG wasn't even on the wing.
i rarely use a calculator, the high point or rear is good enough, plans are good too, for own design sweeps, i just draw a few lines and i've not been wrong yet.