I got the CG range from flight testing...the flyable range is actually much broader than the best "glide home deadstick" range...but those landings can't be avoided. For the first flights there are wraps of lead solder around the engine that get progressively peeled off as the flight testing progresses, with the ultimate goal of being totally lead free... but a 1/4-1/2 oz of the "metal of shame" placed where nobody can see it or knows it's there but me has been known to happen.