I just did the initial test flights on my GS540. It flew well enough, but seems to be set up a bit on the tail heavy side. I installed the motor and radio equipment to get the recommended CG location, which is about 7.5" aft of the LE. This seemed to be like it was quite a bit behind the spar at the time (it's about 35% MAC), but I figured the designer would have it set pretty conservatively.

When I roll the airplane inverted, it starts an immediate, pronounced climb and requires up elevator to keep it level.

I've seen quite a few of these models going together here on RCU, where's your sweet spot for the CG?

//Karl