What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Autopilot

P

Pat Stewart

Well Known Member
Tru Trac Digiflight IIVS

My RV10 has been out of Phase 1 for awhile however I have never used the autopilot. When I installed the autopilot I had full range of motion for both Pitch and roll. I had not yet done any calibration. This morning while working in the hangar I pushed the elevator down and heard a clicking noise which led me to take the aft baggage panel out and find the source. The source was the pitch servo. I continued to move the elevator up and down trying to isolate the noise in the servo. After moving it several times I encountered another problem. The servo locked up in one direction (forward pitch) however continued to work in climb pitch.

I decided to go through the setup procedure and see if that fixed the problem. The problem remains as well as the pitch is backwards. I found the jumper instructions in the manual to fix the pitch direction issue however the locking issue remains. During the calibration the roll axis continued to try to turn left regardless of left or right input. The autopilot was professionally wired all the way to the servo’s so I don’t think its wiring.

What are the symptoms of a sheared pin and any other advice/experience would be appreciated.
 
I have a Trio so I can't help directly, but:
1. "professionally wired" doesn't mean there can't be errors. After all, they got the pitch jumper wrong, right?
2. If the shear pin shears, then the controls should move freely completely independent of the internal gears, motors, etc of the servo.
3. Do I understand the elevator is hanging up with the autopilot off? If so do not fly until this is resolved. Are you sure it's the servo, and not the near-by bell crank? If the control system is mis-adjusted it's possible for the lower thru bolt on the bell crank to limit elevator motion.
 
Thanks Bob,

I disconnected the pitch servo at the bellcrank and the elevator now moves freely. The 10 pitch servo has a wheel driving a metal slider with a cable inside. When I move the slider i also feel the binding so its in the servo. I have decided to take the safe option and send it back to Trutrac.
 
I found another thread with this same problem caused by screws backing out. The 10 pitch servo has a different setup and actually uses one of the screws locations to clock the wheel. The only screw installed is the one that clocks the phenolic looking wheel, the other three are not installed. I consider this a serious concern for the 10 pitch servo. It will be in the mail to Trutrac tomorrow and I will post the findings.

Pat
 
I don't get it.

Pat,
Are you saying the servo locked up?
The pics show the installation before TruTrak issued a fix to keep the capstan pulley from coming loose. There is no clocking of the phenolic wheel, just a brass shear screw that could be installed in any of 3 threaded holes in the pulley.
I am curious to hear more about this.


Photo%2520%2520%25202.JPG


IMG_1702.JPG
 
Make sure the bolt head isn't getting caught on the servo arm. Like Ernst's pics I left out the an960-10 washer on the one bolt so there would be more clearance for the arm. I'm curious too.
 
The brass shear screw was the screw I as referring to and as still in place and yes it did lock up in one direction. Interesting pictures however. You show a screw with nut holding on the wheel and I only have a pan head screw which was still tight.

Pat
 
At some point over the past few years TruTrak changed the design of the output shaft. I know this because I sheared the shear the screw trying to get my torque wheel off (long story). I had the old design with the pan head screw which I had loctited (is that a word?) in place. I had to ship the servo back for repair (awesome service btw) and they replaced the shaft with a new one that is threaded for a nut instead of tapped for a screw.
 
Last edited:
Correction

Correction
My pics do show the servo with the new threaded nut to keep the capstan pulley from coming loose. The old version only had a #10 pan head screw
holding the pulley in place. The servo had to be shipped back to TT for the fix.
 
OK,
I got the results back today on my servo. It seems that the pin that was pressed into the pulley was not properly swaged which allowed the cable to slide through the pin which then allowed the pulley to turn to a point that it pulled the pin out of the pulley. The pin then traveled up to near the center of the slider where it was impacted by the pulley. That is why I had full pitch up but once the pulley hit the pin it locked in pitch down.

Trutrak said a few years back they had a problem with the swaged tool but did correct it. They also said that they tested my issue and that with enough force this would have been overcome. That may be true however if this had happened in a high pitch climb I would worry that it may have stalled before this could have been corrected by force.

The folks at Trutrak were very professional and did not charge me for the repair or the AD upgrade which was appreciated however I also believe this is something that everyone should be aware of.
 
RV10 Servo issue

N427EF said:
Pat,
Are you saying the servo locked up?
The pics show the installation before TruTrak issued a fix to keep the capstan pulley from coming loose. There is no clocking of the phenolic wheel, just a brass shear screw that could be installed in any of 3 threaded holes in the pulley.
I am curious to hear more about this.


Photo%2520%2520%25202.JPG


IMG_1702.JPG
Click to expand...

The pitch servo linkage may be unique to the RV10, not sure, however if more than two years old I would be asking TruTrak about the pin issue in my previous email.
 
You must log in or register to reply here.
Back
Top