Autopilot limiting bracket

[docron.ski]

I recently noticed that the aileron deflection was not equal on lt/rt ailerons. On further investigation, this was due to the AP limiting bracket not being placed symmetrically and therefor limiting the stick travel to the LT more than the RT. The bracket is attached in the fourth hole on the Lt and the third on the RT. it must have been installed that way as there is nothing in the logs relating to AP repair. I am the second owner, SN 170, 2011. The bracket has not been changed to the new design yet. I have not been able to remove the old bracket and have been flying with the AP circuit breaker off. My question is whether this was on purpose or a mistake and if it was a mistake, which hole is the proper one? Also, any suggestions on how to get the bracket off. A 2 mm Allen wrench seems to be too small and slips and nothing larger than this will fit.

[turbopilot]

I recently noticed that the aileron deflection was not equal on lt/rt ailerons. On further investigation, this was due to the AP limiting bracket not being placed symmetrically and therefor limiting the stick travel to the LT more than the RT. The bracket is attached in the fourth hole on the Lt and the third on the RT. it must have been installed that way as there is nothing in the logs relating to AP repair. I am the second owner, SN 170, 2011. The bracket has not been changed to the new design yet. I have not been able to remove the old bracket and have been flying with the AP circuit breaker off. My question is whether this was on purpose or a mistake and if it was a mistake, which hole is the proper one? Also, any suggestions on how to get the bracket off. A 2 mm Allen wrench seems to be too small and slips and nothing larger than this will fit.

Not knowing what type of installation you have, I have a couple of general thoughts. First, the bracket stop should never be used to limit servo travel. It is a safety backup. In most installations servo arm travel should not come close to the stop to avoid an over center control lock. Pulling the autopilot CB will have no effect in preventing an over center control lock situation. You must disconnect the linkage before attempting flight to be on the safe side until you get the problem fixed.

[Springloaded]

Be careful with that. If the the auto pilot doesn't hit the stop it's possible depending on installation that it will go to far cam over and lock the stick up. I had to either lengthen or shorten the control link between auto pilot and control arm I can't remember off the top of my head. If it's not right it (WILL LOCK UP) mine did! There is a new stop from Tru Trac.but you will need to make sure it won't cam over center with the auto pilot in use. The stop bracket on mine wasn't centered it is now. Long story short the stop bracket wasn't the issue the control link length was. It can only cam over center when auto pilot is in use. So pulling breaker will eliminate a bad situation.
Chuck

[Pete D]

The arm on the servo should not touch the stop bracket on the servo. The control stop, auto pilot or no is at the back of the torque tube, right below the rear stick. The stop on the servo is there as a safety backup to prevent over center situations. If the arm on the servo contacts the stop on the servo then the length of the rod between the servo arm and the bellcrank on the torque tube needs to be adjusted.

[Springloaded]

Yes your right I wrote that wrong. But if the rod length is wrong which I know of three that were it can cam over when in use and just changing the the stop won't fix the problem is what I was getting at. When I got the new bracket i was told that would take care of it I spent some time with Tru Trac on the phone and taking pictures to fix the problem. I'm the one it locked up on and when mine locked up I mangled the stop brackets to over come the servo and my stop bracket was put on not centered on the servo for some unknown reason.
Chuck

[turbopilot]

Be careful with that. If the the auto pilot doesn't hit the stop it's possible depending on installation that it will go to far cam over and lock the stick up. I had to either lengthen or shorten the control link between auto pilot and control arm I can't remember off the top of my head. If it's not right it (WILL LOCK UP) mine did! There is a new stop from Tru Trac.but you will need to make sure it won't cam over center with the auto pilot in use. The stop bracket on mine wasn't centered it is now. Long story short the stop bracket wasn't the issue the control link length was. It can only cam over center when auto pilot is in use. So pulling breaker will eliminate a bad situation.
Chuck

I learned it is a little more complicated than it would seem. My servo arm (this is the roll servo) moved properly with the stick hitting the stops leaving 1/8 to 1/4 inch between servo arm and servo bracket stops. Geometry was such that it would be impossible to go over center at the servo by using the stick and hitting the stick stops. However, I found out by manually pushing on the servo arm, I could over center the servo arm and lock the stick with the stick all ready against the stops. This means the only thing preventing the servo from pushing the stick over center is the electrical calibration that is done on the servo during autopilot installation which limits servo travel. Not good.

In my installation this occurred using the center hole on the servo arm which does give more torque but changes the geometry a little. I had to move the actuator rod up to the top hole in order to secure the installation from over centering either with the stick or in the event of a hard over of the servo motor itself.

Everyone should double check their installation to make sure you cannot over center with the stick at the extremes of travel, then make sure that you cannot over center the system by manually pushing on the servo arm with the stick all ready against the stops. It would appear that the servo arm stop bracket does not protect entirely from an over center event depending on the geometry of the installation.

[Springloaded]

Turbo pilot I agree.
It scared the crap out of me when mine locked up. I don't remember all the particulars but I just had to change the rod length Im pretty sure I had to lengthen it. It can't go over center over now
Chuck

[richphil]

Turbo pilot I agree.
It scared the crap out of me when mine locked up. I don't remember all the particulars but I just had to change the rod length Im pretty sure I had to lengthen it. It can't go over center over now
Chuck

I'm not sure if you are using Tru-Trak or Dynon servos, but you need to know that the safety bracket (at least on Dynon servos) is there to keep you from going over center and will do so if properly installed. While I agree with all that it should not be used as a stop, it must be installed so that it will stop an over center regardless of stick movement. I would suggest taking your linkage loose and rotating the servo arm in both directions until it hits the stop and does not go over center. If you are not sure please find someone who is. Also, it is possible to install the safety bracket upside down and it will not stop the over center position.

Richard

[Springloaded]

Thanks Richard
I fixed mine.
Chuck