I have one, and have been flying it for the past 2 years. I don't think inverted or upright matters much as far as CG measurements. The 5 1/8" location is pretty safe; if desired, the cg could be moved back a little more. I have a CRRC Pro 26cc gas engine on it, with about 2 3/4" of spacer between it and the firewall. (A little more engine wouldn't hurt it.) The main thing is that you have to land with some throttle on - otherwise it will drop suddenly and bounce. It isn't a trainer, and it isn't a slow floater!