ORIGINAL: nonstoprc
if length(R1,R2) = length(S1,S2), and the pivotal points are at the center of (R1,R2), and (S1,S2), then amount of travel of both wires should be the same.
I don't think so. I have drawn it up in CAD and I have also calculated it using trigonometry. When the servo is deflected 45 degrees, the rudder goes the opposite way (when the lines are crossed), but does not end up at 45 degrees (if you keep the line from the servo arm to the rudder at the same length. And the other wire must get either tighter or looser than before it was rotated. Not a whole lot, but a few millimeters different.