RE: GSP Sukhoi very tail heavy. HELP!!!
My GSP 80" Sukhoi ARF is still in its box, so these comments are conceptual rather than based on actual experience. First off, a 25% MAC balance point is the forward limit. I would be looking to test-fly at about 33% MAC, which would be 5.94" by calculation, so 5-15/16" would be my first set-up. Second, it sounds like the tail servos need to come up under the canopy. That would get 6-8 oz out of the tail. That would mean covering over the servo sockets in the stabs and running dual elevator pushrods from under the canopy, and putting pull/pull cables on the rudder. Also look around for the lightest tailwheel you can find. With servos under the canopy, light tailwheel you could find yourself pretty close to 5-3/4" balance point. If you can get it balanced anywhere in the 5-1/2" to 6" range, I'd give it a test flight and see what changes you might want to make after that. No way do you want to be flying a 20 lb aerobat on 40 cc gasser. It would fly, but nothing like a Sukhoi.