Actually, when the wing are pulled back on that model the center of lift in relation to the center of gravity changes. The difference in flight is evident in the difference of the flight paths, the aircraft does not gain the altitude as it does with the wings extended (the wings folded was for high speed pursuit, and they opened and closed in dog fights to suit what ever was needed). It is not only the center of gravity, but the center of lift that changes in that craft. Also, without seeing how hem made the mechanism to fold the wings, it could be that he worked it out to get manageable flight in both configurations. There's no argument, just the physics of flight. They all come into play when building a glider, and since there is no one in there to correct the flight path, glider inherently demand closer attention to detail, whether by instinct, or gained knowledge, the physics involved are always there.
When I was making a F-20 Tiger Shark looking planes, I made a wing I really liked. I coated the outside with Steel Epoxy Putty, leaving the leading and trailing edge as the separation points. This became a mold. I would tape it closed, then fill with "Great Stuff", (I used a thing layer of Vaseline as a release agent, and coated the inside with shiny tape.. That would be the core of my wings. It made mounting a main spar very easy. The wings were able to take much abuse, I did the same thing with the nose tip, and had actually designed the first 1/4" inch as a replaceable peace. There are tons of things that can be done with this. I think a Gliding model section would be a blast!
Please, I apologize if I came off wrong. I was very excited to see someone making models that flew well, as opposed to another "designers" who's models barely fly. That is why I am so enthused with your work.
