1974 M20F STEC 30 Autopilot "Drag"

[AlbertF]

I recently noticed a recurring issue after switching my STEC 30 autopilot off, I'll feel a slight catch or drag on the ailerons.  I can turn through the light drag and feel a "release" of this drag off the ailerons.  My impression is when the AP is turned off, a component is still slightly engaged on the aileron system.  Again, only slightly with a very small amount of pressure I can feel a hardly perceptible release.   Is this potentially a lubrication issue or adjustment of the AP system?  Does anyone know what mechanism the AP uses to operate the ailerons and would this be considered a safety of flight issue?  Annual is in 3 months and I'd like to have this resolved at that time as it feels like a very minor issue.  But, I'd like to have an idea of what the issue might be.   Thank you.

[mike_elliott]

It sounds like your aileron servo clutch might be "hanging" up. Wheel that guy over to JD or up to Paul Maxwell and they can deal with it. Brian Kendrick should also be able to properly diagnose and fix..All close to you.

[PT20J]

You can pull the autopilot circuit breaker to see if the problem is mechanical or electrical. I’ve always found the S-TEC tech support folks helpful. But I’d expect that the servo would likely have to come out and be sent out for repair.

[mike_elliott]

  On 11/2/2020 at 3:33 PM, PT20J said:

You can pull the autopilot circuit breaker to see if the problem is mechanical or electrical. I’ve always found the S-TEC tech support folks helpful. But I’d expect that the servo would likely have to come out and be sent out for repair.

Expand  

Oh yea....thanks for reminding me about that "b!tch bolt" skip....

 

[Rwsavory]

It's worth a try "exercising" the clutch by engaging the a/p and then turning the yoke manually in both directions several times.

[AlbertF]

Now that I know the names of the parts and researched this, it looks like the servo clutch is the culprit.  Nothing I can lubricate.  Ill talk to my mechanic about inspecting and removing it for repair.  In the meantime, I'll test the circuit breaker and see if the feeling is the same as disconnecting the AP.  I've read people have had problems with the STEC AP servo still engaging even with AP off, until the CB is pulled.  Don't need that kind of nonsense happening!  Thanks for the input.

Just read the last post about exercising the clutch.  You mean during the ground test, as the yoke goes left or right, use a little opposite force?  There should be a limit which it wont fight anymore...I read somewhere about 30-35 pounds of resistance should get the AP to release.  Can I ruin anything with this kind of test?

Edited November 2, 2020 by AlbertF

[Rwsavory]

  On 11/2/2020 at 3:45 PM, AlbertF said:

Now that I know the names of the parts and researched this, it looks like the servo clutch is the culprit.  Nothing I can lubricate.  Ill talk to my mechanic about inspecting and removing it for repair.  In the meantime, I'll test the circuit breaker and see if the feeling is the same as disconnecting the AP.  I've read people have had problems with the STEC AP servo still engaging even with AP off, until the CB is pulled.  Don't need that kind of nonsense happening!  Thanks for the input.

Just read the last post about exercising the clutch.  You mean during the ground test, as the yoke goes left or right, use a little opposite force?  There should be a limit which it wont fight anymore...I read somewhere about 30-35 pounds of resistance should get the AP to release.  Can I ruin anything with this kind of test?

Expand  

Yes, that's it.  And no, it won't hurt it.  It's designed to be overridden.

[Ragsf15e]

  On 11/2/2020 at 3:45 PM, AlbertF said:

Now that I know the names of the parts and researched this, it looks like the servo clutch is the culprit.  Nothing I can lubricate.  Ill talk to my mechanic about inspecting and removing it for repair.  In the meantime, I'll test the circuit breaker and see if the feeling is the same as disconnecting the AP.  I've read people have had problems with the STEC AP servo still engaging even with AP off, until the CB is pulled.  Don't need that kind of nonsense happening!  Thanks for the input.

Just read the last post about exercising the clutch.  You mean during the ground test, as the yoke goes left or right, use a little opposite force?  There should be a limit which it wont fight anymore...I read somewhere about 30-35 pounds of resistance should get the AP to release.  Can I ruin anything with this kind of test?

Expand  

As @Rwsavorysaid, you should be overriding it each time you do the ground test (so every flight... no, I don’t do it every time either) to make sure you can.  That’s part of the test.  But no, it won’t hurt it.  In fact, I’ve heard people say they had problems if they aren’t exercised regularly.

[Stanton R]

The clutch has nothing to do with the drag when the autopilot is off. It sounds like the solenoid, that causes the output gear and motor to engage, is not releasing. I have had several Stec servos with this problem. Some time it just needs the to  be cleaned and lubed. A couple of times I had to send it in to be overhauled. 

Edited November 2, 2020 by Stanton R