I saw Scott's Schmidt's question about autopilot settings (twitchy stick) and decided to post some experience I have had. First, to answer the question of twitchy stick on autopilot; the Installation Manual says that that is an indication that the Roll Servo Sensitivity needs to be decreased. Here is a link to New Blues autopilot settings: http://www.vansairforce.com/community/showpost.php?p=653797&postcount=7
Note that on a scale of 1 to 25 his roll servo sensitivity setting is 5. Default is 10. Mine is set on 10 with hardy no stick twitching.
But before making changes to the default settings, is the aircraft in roll trim? If the servo has to work hard to maintain roll trim this seems to me would contribute to a twitchy stick condition.
My plane has had a heavy left wing. I partially solved this by the recommended method of pinching the opposite trailing edge. This never completely solved the heavy wing and when the stick was released the aircraft would begin a gently left turn. With iron mike flying the plane, the stick had a moderate amount of jiggle.
Now just recently I removed the flaperon rod end bearings to Loctite them according to the plan sheet 18-06 which was revised to include the Loctite after my flaperons were built. I noticed that one of the rod ends was screwed in a bit further than the others. I may have made a measurement error when originally installing this rod end bearing or it might have been moved when the flaperons were off for painting. Without the Loctite they screw in and out very easily. Putting them back in with the Loctite, I was very careful measuring the 11/32" distance on the plans using the depth gauge end on my dial caliper. When I next flew the plane, I noticed something was noticeably different. The heavy wing was gone. I now believe that the misadjusted rod end bearing was putting a twist in flaperon spar. It would not take much to put the aircraft out of roll trim.
Now in addition, the stick movement when the autopilot was working is noticeably less. It barely jiggles now.
The autopilot alerts you on the EFIS if you are out of trim in pitch, so you can correct that with the trim switch. But in roll you have no roll trim. First, I would correct any wing heaviness. Check the flaperon rod end bearing distances, squeeze/bump trailing edges, whatever it takes. Then if there is a twitchy stick on autopilot, I would first turn off ALT by pushing the ALT button. Then if the stick is twitchy it is the roll servo working. Then I would adjust roll servo sensitivity if necessary.
Tony
Note that on a scale of 1 to 25 his roll servo sensitivity setting is 5. Default is 10. Mine is set on 10 with hardy no stick twitching.
But before making changes to the default settings, is the aircraft in roll trim? If the servo has to work hard to maintain roll trim this seems to me would contribute to a twitchy stick condition.
My plane has had a heavy left wing. I partially solved this by the recommended method of pinching the opposite trailing edge. This never completely solved the heavy wing and when the stick was released the aircraft would begin a gently left turn. With iron mike flying the plane, the stick had a moderate amount of jiggle.
Now just recently I removed the flaperon rod end bearings to Loctite them according to the plan sheet 18-06 which was revised to include the Loctite after my flaperons were built. I noticed that one of the rod ends was screwed in a bit further than the others. I may have made a measurement error when originally installing this rod end bearing or it might have been moved when the flaperons were off for painting. Without the Loctite they screw in and out very easily. Putting them back in with the Loctite, I was very careful measuring the 11/32" distance on the plans using the depth gauge end on my dial caliper. When I next flew the plane, I noticed something was noticeably different. The heavy wing was gone. I now believe that the misadjusted rod end bearing was putting a twist in flaperon spar. It would not take much to put the aircraft out of roll trim.
Now in addition, the stick movement when the autopilot was working is noticeably less. It barely jiggles now.
The autopilot alerts you on the EFIS if you are out of trim in pitch, so you can correct that with the trim switch. But in roll you have no roll trim. First, I would correct any wing heaviness. Check the flaperon rod end bearing distances, squeeze/bump trailing edges, whatever it takes. Then if there is a twitchy stick on autopilot, I would first turn off ALT by pushing the ALT button. Then if the stick is twitchy it is the roll servo working. Then I would adjust roll servo sensitivity if necessary.
Tony
