Young Eagle-induced autopilot servo issue?

[Sportsman7064]

Today our EAA chapter held a Young Eagle event, flying 75 kids. Since my Sportsman is still in Phase 1, I chose to use it as a preflight asset to let the kids see what all the airplane "parts" are all about. All went smoothly until the last kid. She was moving the control stick around and the parents were chatting me up, and the next thing I know, the aileron controls are frozen full left. Moving the stick in pitch did nothing to release the controls. So, since we were finished for the day, I taxied back to my hanger and began investigations. After finding nothing obvious with the control cables and bellcranks, I decided to remove the servo pulley nut (a capstan SV42 servo) and remove the pulley. The controls became fully operational again! So, the servo is "locked-up" somehow.

So, my question. Before I just power it up and have it try to move and get jammed, I wanted to see if there was something in particular I should do, such as run the Calibration or Test modes? I want to avoid removing the servo if I can, since it is a bit of a pain to get it out/in...

Any thoughts would be greatly appreciated!

Russ

(next time, no kids sitting in the plane...)

 

[Garrett]

Is it possible for it to go mechanically over center and lockup. There is a bracket to prevent this. I believe shipped with the servo.

 

[dynonsupport]

The original poster has a Sportsman, which uses a capstan connection to a cable, not an arm. It cannot go over center.

Russ,
The servo should never lock up when unpowered or powered. The only way for there to be an issue is if the motor or geartrain locks up internally.

If the capstan on the output of the servo doesn't spin freely when there is no power, there is something wrong inside and we would like to see that servo ASAP. Please look it over the best you can and make sure it really is the output shaft of the servo.

I have a Sportsman too, so I know what it takes to get it in and out, but you don't want to be flying with that servo in the plane.

Please give us a call or email to get an RMA. We take all servo failures very seriously.

 

[Sportsman7064]

I stopped by the hanger after work and confirmed that the servo (without the pulley attached) freely moves by hand. I think I determined what happened. The cable was routed to the pulley at the six-o'clock position, then one loop and then away to the control system. The anti-slip-peg swaged to the cable was near the three o'clock position, such that at the extreme left-stick condition, the peg was at risk of coming out of the hole in the pulley. I will adjust the servo cable attachments to allow the peg to engage the pulley at the 12 o'clock position, making it impossible for the peg to come up out of the hole. I thought this was how I had it when I installed it, but it must have rotated while pulling the cables tight during installation. I'll mark the pulley somehow to ensure that the peg is in the right position this time.

 

[ACE01]

Would you mind sharing a photo of this installation and the issue you had so that others will not run into the same situation?

 

[Sportsman7064]

Sorry for the slow response.  I didn't snap a photo, but here is a diagram of how the cable was routed through my capstan pulley.  I now have the cable actually going two full circles around the pulley before exiting, so there is no way for the anti-rotation peg to come out.

Hope this helps.

Russ