Trimming for a good glide.
 

This question is about an RC electric glider. I realize this a FF forum, but I figure you people know way more about trimming than the RC guys. Last winter I built a Dynaflite Butterfly motor /Glider. Some how the wing wound up being 127" instead of the 99" it was supposed to be. That's because I decided to make the wing more like the Bird of Time wing. This bogged everything down so I chucked the fancy wing tips and went back to the original plans. In the end I had a couple extra bays on each side not on the plans. Anyway, the balance point is right on, just as the plans call for.
First test glide showed that it did well,(from 6 feet). I fired up the motor and launched it and it went nutso! It stalled right away. It was up and down, almost uncontrollable. After getting some altitude I chopped throttle and it straightened up right away. Glided beautifully.
Not wanting to destroy my hard work I took it home and gave the motor several degrees of downthrust. Took it back out and launched it. It flew perfectly up to altitude. As soon as I chopped throttle it went nutso again. Swooping up and down, stalling violently, did a couple of loops that I didn't want. The wing was really stressed as I could see at times it showed more dihedral than I had built into it. By giving it a lot of down, I was able to bring it in for a landing on the grass.
Does anyone have any suggestions?
My other favorite plane is a Sig Riser and I've flown it for years. I've replaced the fuselage once and repaired the wing several times but never had any problems with it.

Any advice would be appreciated,

Bernie Gerth
Mount Vernon, Indiana