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- Aug 21, 2010
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Just had my attitude indicator overhauled, and am noticing a change in my autopilot behavior (Piper Autocontrol III (Century II)).
Before the AI was overhauled, the a/p had a very small roll hunt that moved the yokes back and forth in a step function: jerk left...jerk right...jerk left...etc. with a few seconds between yoke movements. The motion was very subtle...I noticed the very small yoke movements because I'm holding the yoke, but pax only noticed it from seeing shadows move around the cabin, or seeing wingtips move against the horizon. Not really noticeable in seat-of-the-pants or from looking out the front windscreen. Definitely acceptable performance.
After the AI overhaul, the a/p tracks rock-solid in perfectly smooth air, but with the slightest disturbance, it will get "twitchy" in roll--the yokes swing rapidly back and forth chasing the level position and the motions damps out very slowly (maybe ~10 sec). The motion is much more extreme than the little jerks it used to do in smooth air---very noticeable out the front view and in seat-of-the-pants. George is very obviously shaking the plane, and it's not pleasant!
My flight conditions yesterday were about as smooth as I could want, but still the a/p was sensitive enough that these roll disturbances were happening nearly constantly. I had to fly with a pretty firm grip on the yoke to damp out the autopilot's twitchiness.
I'll talk to my mechanic, but I'm wondering if the AI overhaul might have changed anything about the signals being sent to the a/p. Is there an amplifier board that could have been replaced, or a gain setting that could have gotten changed? Or should I expect that all the changes I'm seeing are simply because my AI gimbal bearings have a new lease on life, and it's just more responsive than the old AI was?
Either way, I'm thinking it might be time for a visit to Mineral Wells or Tulsa for an autopilot grooming session....
Before the AI was overhauled, the a/p had a very small roll hunt that moved the yokes back and forth in a step function: jerk left...jerk right...jerk left...etc. with a few seconds between yoke movements. The motion was very subtle...I noticed the very small yoke movements because I'm holding the yoke, but pax only noticed it from seeing shadows move around the cabin, or seeing wingtips move against the horizon. Not really noticeable in seat-of-the-pants or from looking out the front windscreen. Definitely acceptable performance.
After the AI overhaul, the a/p tracks rock-solid in perfectly smooth air, but with the slightest disturbance, it will get "twitchy" in roll--the yokes swing rapidly back and forth chasing the level position and the motions damps out very slowly (maybe ~10 sec). The motion is much more extreme than the little jerks it used to do in smooth air---very noticeable out the front view and in seat-of-the-pants. George is very obviously shaking the plane, and it's not pleasant!
My flight conditions yesterday were about as smooth as I could want, but still the a/p was sensitive enough that these roll disturbances were happening nearly constantly. I had to fly with a pretty firm grip on the yoke to damp out the autopilot's twitchiness.
I'll talk to my mechanic, but I'm wondering if the AI overhaul might have changed anything about the signals being sent to the a/p. Is there an amplifier board that could have been replaced, or a gain setting that could have gotten changed? Or should I expect that all the changes I'm seeing are simply because my AI gimbal bearings have a new lease on life, and it's just more responsive than the old AI was?
Either way, I'm thinking it might be time for a visit to Mineral Wells or Tulsa for an autopilot grooming session....
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