Silly Century II autopilot has been drinking - video included

k9medic

k9medic

Line Up and Wait
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Sep 27, 2018
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N Central FL and GTC Bahamas when off work
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ATP-H, CMEL, CSEL, CFI/CFII Airplanes and Helicopters
We noticed this new "feature" the other day and had our A&P take a look at the rigging. All rigging is good with no binding. Wires are not corroded and the connections to the AH and the DG are tight.

The rocking motion gets worse when the heading hold is turned off.

Anybody ever seen something like this?

 
I think it's just singing to itself and keeping time. :) I could almost hear it "In my merry Oldsmobile..."
 
When my Mooney did that (with that model autopilot), there were two issues. One is that although the aileron rigging was correct, the flap on one side was off a bit on retraction. The other was that one of the servos needed cleaning or replacing, I don't recall which. My oscillation was not as rapid as yours, though.
 
Was your fuel really unbalanced? Hard to tell from the angle but it seemed that when the ailerons were neutral the airplane rolled to the left.
 
Full of fuel so no unbalance there. Trimmed to fly hands off straight and level. We do have aileron trim on the airplane but there was little movement there.

This is something that started just after we took delivery of it.
 
It sure looks out of trim to me in roll. While not usually that drastic it will have a similar behavior if the trim gets really far off assuming it doesn't automatically adjust the trim
 
Help me understand what you mean by out of trim in roll. Hands off the aircraft flies straight and level. Turn coordinator is level and ball is centered.
 
Watching the video it seems when the yoke is straight the airplane is rolling to the left. Like I said, could be the video angle but it looks that way to me.
 
^^^^^This. I had/have the same issue with my IIC. I found out a coupla things. My aeroplane was a wee bit outta trim. If I hold a big toe's worth of right rudder, it was less of an issue. So, some big toe, and some messing around with the pots, it is nuts on - and follows GPSS great for a 40 year old gizmo.

Might want to check on the roll servo's capstan, it might be loose, or needs attention. This one guy I know that had a similar issue.
 
I do a couple of autopilot 360s and that behavior clears up. YMMV.


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It acts like a student that’s trying to correct back over that last 5 degrees.
 
A little follow up here from the initial post. The plane just came out of annual and we think we found the issue. There is a guide rod that is over top of the roll servo cables. This guide rod evidently got pushed down somehow (most likely during the pre buy) and was applying tension on the servo causing it to stick.

My I/A fixed the guide rod and the autopilot stopped with the rocking motion. Now, oddly, the heading bug doesn't work... Ugh.
 
If you need any parts let me know. I removed a fully functioning Century IIB a couple months ago. Heck, I can even send it all to you and pay me for the parts you end up using/needing and send back what you don't use.
 
I very well might take you up on that. I;m headed out on a Bahamas trip in the morning and it will be the first time I can actually check the autopilot ove a long distance since the annual.
 
k9medic said:
I very well might take you up on that. I;m headed out on a Bahamas trip in the morning and it will be the first time I can actually check the autopilot ove a long distance since the annual.
Click to expand...
Okay just PM me and we can arrange something. Keep me in the loop! One struggling new plane owner to another. :)
 
Had similar problem (same autopilot), talked with Century, and they said to clean all the connectors. I had sent the roll servo in for function check, and that was not the problem. My A & P went ahead with cleaning the connectors and all is well.
 
PM sent back. Maybe try to clean the connectors on the back of the DG? Also before my avionics shop found out that mine was illegal, they went through the wiring and found several wires broken at the connector internally, but I guess it was still making good enough contact to work. They repaired all of the contacts... then had to pull it out when it was discovered as being not legal..... just my luck.
 
Had this issue with my old Tiger. AP was connected to an HSI which required a rebuild. Good news - all was well after. Bad news: rebuilding the HSI was expensive.
 
The little blue connectors are notorious for causing problems, fairly simple to trace and correct. I discovered Stabilant 22 years ago with a service bulletin for columbia aircraft. I put it on every connection I see and wager it will not hurt here.
 
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