I have this space station structural component I'm trying to launch. It's a ton of girders, girder-to-small adapters, and clamp-o-trons. Eventually it will hold the fuel tanks and any large craft that dock at Minmus for fuel.
But first I need to get it into the sky. The vessel is very stable at launch and at low speeds. As it exceeds 300m/sec, however, I run into problems. It begins to gravity turn too steeply and any deviation from prograde results in a loss of control and tumble. The payload is only 6 tons, IIRC. I suspect the fuel needed to lift it to orbit is simply too far back but I can't figure out how to generate anything like enough drag in the back. I'm already running 8 AV-R8 winglets. When I ran with full-on wings as stabilizers, the elevons didn't have any control authority.
Image included, happy to clarify.