Cables have been used in light aircraft controls for many years because (amongst other reason) they have the wonderful attribute, when properly routed, of being minimally effected by motions of the structure due to aircraft loads. This is not true of pushrods, which have to be very carefully designed, routed and installed to achieve the same response. I might venture a guess (and only a guess) that when the wings are loaded, they deflect enough so that the mechanism is not working as designed?
Considering that the 601XL has notoriously heavy ailerons in the stock configuration, the idea of making them even heavier is a bit scary. And usually the dual-stick airplanes, which have a higher mechanical advantage than the center stick, feel lighter. My cable-actuated, dual-stick airplane has large spades (aerodynamic counterbalance) specifically to make the ailerons lighter and more in line with the elevator forces (which I made heavier by adjusting the linkages and adding a damper).
Custom instrument panels are now available directly from Zenith Aircraft Company exclusively for Zenith builders and owners. Pre-cut panel, power distribution panel, Approach Fast Stack harnesses, Dynon and Garmin avionics, and more.
Developed specifically for Zenith builders (by a builder) these videos on DVD are a great help in building your own kit plane by providing practical hands-on construction information. Visit HomebuiltHelp.com for the latest DVD titles.