I have a 1/10 scale Ag-Cat that I scratch built from highly modified free flight plans. When I finished it it needed a little down thrust to keep from going vertical when I applied full power. It has sat dormant for 6 months or so until I flew it this afternoon. The wings are very lightly built and the flying wires are very functional. I believe that over the dormant period the wires warped the wings. When I flew it today, it acted as if it had a large amount of down thrust. After liftoff it almost ran itself into the ground. In flight, if I trimmed for level flight with full power, when I reduced the power to idle it would do a loop. The engine thrust angle doesn't seem to be any different than it used to be, leading me to believe that the problem is in the wing or tail incidence. Has anybody encountered this kind of problem? Any suggestions? I am considering uncovering the wings, jigging them straight and them making it into a D tube construction.

Sounds like you need to use an incidence meter to determine where the problem is before you start butchering. I'm sure there's people out there who could tell you what kind of incidences will work well for the Ag-Cat. Sorry, I'm not one of them. Biplanes aren't my thing (yet). Good luck!