I suspect I might be genetically unable to trim model gliders.
I tried and tried with the little homebrew FF glider (see previous post). I moved the CG forward then experimented with all possible variations of wing and tail incidences. I was not able to get two consecutive consistent flights: with what seemed like the exact same settings, one flight would be lovely, floating down to a nice pretty flare, and the next twenty would either climb and stall, or dive.
Perhaps it's my launching method. I mean, I can't really say I was consistent in my (hand) launches, and the six feet from my hand to the ground does not give the glider lots of room to settle into a nice trimmed attitude and speed. But still.
I suspect I should just buy some RTF (better than a Guillows toy, but not necessarily the fanciest) and follow the instructions (especially about CG settings) religiously, hoping to build experience in how a properly constructed glider should feel. Or maybe I should join the AMA and get someone to teach me. Or something.