I have recently been the culprit of ackerman. When setting up my rudder pull/pull I could not get my control horns right on center of the hinge line due to some interference on the end of my fuse. I overcame this setback by compensating at the servo wheel. Measure how far your control horn hookup is set back from the center of the hinge. Then measure back that same distance fromt the center of your servo wheel and drill holes for the hookups at the servo negating the Ackerman effect. Saved me a big headache in hooking up my rudder.