Century 2B - S turns while tracking

[joepilotmooney]

Flew with my mechanic today as he tried to adjust the AP while in flight. He could not get the 3-5 degree slight S turns from stopping as we tracked heading and NAV modes. The avionics shop on the field told him it;s likely resistance build up behind the connectors of the servo's and control heads. Can anyone else corroborate this?

I am not in position to replace the old AP, plus it would take months from what I hear, and 40 AMUs or more. Is there just the one servo (for aileron control) or two for this set up? And how hard to get to it? It sounds like it might be worth them trying to clean up the connectors on my 78 J. (My alt hold is separate Stec unit).

[N201MKTurbo]

Mine did that. I took the servo apart, cleaned all the gears in the motor, polished the commutator and re-assembled it with new grease. That was about 12 years ago. Still flies straight as an arrow. 

If you undertake this, be aware there are 4 ways to assemble the motor, two of those ways make it turn the wrong way. Only one is correct, so take a bunch of pictures before you take it apart.

The test is the starting voltage of the servo. The lower the better. When I took mine apart it took almost 6 volts to get it going. When I was done it started at 700mv.

[joepilotmooney]

Rich, THANKS for giving me a little hope for this!! i'll let them know.

[OR75]

22 hours ago, joepilotmooney said:

Flew with my mechanic today as he tried to adjust the AP while in flight. He could not get the 3-5 degree slight S turns from stopping as we tracked heading and NAV modes. The avionics shop on the field told him it;s likely resistance build up behind the connectors of the servo's and control heads. Can anyone else corroborate this?

I am not in position to replace the old AP, plus it would take months from what I hear, and 40 AMUs or more. Is there just the one servo (for aileron control) or two for this set up? And how hard to get to it? It sounds like it might be worth them trying to clean up the connectors on my 78 J. (My alt hold is separate Stec unit).

only one servo .... on the left wing. The panel to open would be the one where the aileron starts    

[Jake@BevanAviation]

Servo start-up voltage is super critical on these servos.  Ideally it needs to be under 2VDC (the lower the better).  Typically, after servicing a unit the start-up is around 800mvDC.  If the start-up voltage is too high, the servo is slow to respond causing issues with oscillations or poor tracking.  Checking servo start-up voltage is probably a good idea if the servo has not been looked at for some time.

[joepilotmooney]

Thanks Jake and OR too for the help.