ORIGINAL: mmattockx
A lot of pitch issues can be trimmed out between CofG location and wing incidence adjustments, but roll couple does not respond to much that I know of (short of dihedral changes, that is).
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When the CG is pushed far enough forward on a UCD 60 to minimize the pitch coupling during normal knife edge flight, the plane becomes way too nose heavy for hard core 3D. At that point it's only good for hovering and normal knife edge, but high alpha knife edge will still have pitch coupling problems.
Not sure about the UCD 46, but the wing on the UCD 60 is flat.......as in zero dihedral. Since the UCD 60 is a low wing plane, this creates adverse roll coupling issues that causes the plane to roll the opposite of the rudder input. (left rudder = right roll.....right rudder = left roll) Adding the correct amount of dihedral could cure it. Upswept wingtips might fix it too. Mixing out the roll coupling with a computer transmitter can be done fairly well at normal flying speeds, but those mix settings aren't correct at higher rudder deflections.