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I've got a '73 PA-28-180 that came from the factory with the Autocontrol III system. It's got a radio coupler and after a recent panel re-do, also has GPSS.
All aspects of the autopilot seem to perform well, with one exception: During what should be straight-and-level cruise, the a/p "hunts" in roll, such that heading slowly oscillates within about a 5-deg range, making a complete cycle every 15-20 seconds or so.
Watching the yoke while this happens, it looks like there is "sticktion" in the system: Starting at a 000/360 heading, the yoke will jerk a bit to the right, and the plane slowly rolls that direction; when the HI gets to about 005, the yoke jerks a tiny bit back to the left, and the plane slowly rolls that direction. When the HI gets to 000/360, the yoke jerks a bit to the right and the cycle repeats.
When manually controlling the plane, I don't feel any sticktion in roll control, so I'm guessing it's in the servo motor.
For others with the same autopilot: Do you see similar oscillations? Should I consider that "normal"?
It's certainly not a problem in flight, but I wonder if it's something that could be improved by a visit to Century Systems in Mineral Wells or Autopilot Central in Tulsa....
All aspects of the autopilot seem to perform well, with one exception: During what should be straight-and-level cruise, the a/p "hunts" in roll, such that heading slowly oscillates within about a 5-deg range, making a complete cycle every 15-20 seconds or so.
Watching the yoke while this happens, it looks like there is "sticktion" in the system: Starting at a 000/360 heading, the yoke will jerk a bit to the right, and the plane slowly rolls that direction; when the HI gets to about 005, the yoke jerks a tiny bit back to the left, and the plane slowly rolls that direction. When the HI gets to 000/360, the yoke jerks a bit to the right and the cycle repeats.
When manually controlling the plane, I don't feel any sticktion in roll control, so I'm guessing it's in the servo motor.
For others with the same autopilot: Do you see similar oscillations? Should I consider that "normal"?
It's certainly not a problem in flight, but I wonder if it's something that could be improved by a visit to Century Systems in Mineral Wells or Autopilot Central in Tulsa....
