RE: Aeroworks 35cc Extra 300
I had ot set up a 50cc Aeroworks using similar specs. the 50 called for 4" back from the tips. I used two carboard boxes high enough to clear the landing gear, marked the CG on the wingtips. I used a piece of 1/4" sqaure balsa under the marks. balance was perfect.
I tried to use my CG machine by running a string across the plane from mark to mark, then measure back from the leading edge. It made the plane slightly morenose heavy for some reason.
Certainly not the usual way of balancing an airplane, but it appears to work fine on these bigger sizes. FWIWflytreetimes