I hope I did not open a can of worms. Don't get I'm wrong I love the stringray and It flys even better. On the speedbrake on top maybe I would use metal hinges and operate the speedbrake with a aircylinder from the rear.I think the twisting is caused by the way the servo drives the speedbrake,with the nylon hinges.I have also used wingtanks to help slow up the plane and it helps.
I am building my second one and may make some changes.
Thanks Paul