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KFC200 Autopilot or trim issues


milotron

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2 hours ago, Emmet said:


It looks exactly like the issue I had with mine. Long story short - the cause was the bearing on the trim torque tube below the trim servo. It seldom sees some lube during annuals, gets stuck and produces what you are experiencing.

Is this is bearing on the servo itself? How would a tight trim tube bearing impact the operation of the pitch servo which pull on different parts?

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On 1/18/2021 at 1:01 PM, milotron said:

Is this is bearing on the servo itself? How would a tight trim tube bearing impact the operation of the pitch servo which pull on different parts?

If you look in the tail, you will see the trim torque tube running down the center. Above it will be the trim servo. The servo has a sprocket and there is a sprocket on the tube and a chain connects the two sprockets. Directly behind the tube sprocket is the carrier bearing that supports the trim torque tube. This picture (courtesy of Don Maxwell) shows the assembly removed from the airplane and turned upside down. You can see the trim servo below (in the airplane it would be above) the carrier bearing. The sprockets and chain are on the other side of the bracket and can't be seen in the picture.

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IMG_1335.jpeg.953ba714a422387c7c146191c5cb7398.jpeg

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From comments here and elsewhere, what seems to happen is that some always use the electric trim or autopilot and never manually operate the trim wheel. The trim system gets tight from lack of lubrication over time if not maintained properly. The trim servo has a lot of torque but eventually things get to the point where the clutch slips at which point attempt is made to adjust the trim with the wheel and it becomes obvious that the trim is very difficult to move. During annual inspection, the trim wheel should be moved from stop to stop to note it's action. I also make it a practice to manually reset the trim to the takeoff position after landing so I can feel that everything is operating smoothly.

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Good info. Funny, I find I use the manual wheel more than the electric trim. Holdback from my C172 days I think.

Couple of hours of flying today and it seems my plane heard me talking about and now is functioning just fine...I spoke with my shop and they figure it might be the torque setting on the pitch servo clutch. I guess it is supposed to be checking regularly?  Mine was last done in 2012.

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  • 2 weeks later...
On 1/20/2021 at 5:37 PM, PT20J said:

If you look in the tail, you will see the trim torque tube running down the center. Above it will be the trim servo. The servo has a sprocket and there is a sprocket on the tube and a chain connects the two sprockets. Directly behind the tube sprocket is the carrier bearing that supports the trim torque tube. This picture (courtesy of Don Maxwell) shows the assembly removed from the airplane and turned upside down. You can see the trim servo below (in the airplane it would be above) the carrier bearing. The sprockets and chain are on the other side of the bracket and can't be seen in the picture.

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IMG_1335.jpeg.953ba714a422387c7c146191c5cb7398.jpeg

How does one grease this part? It looks like the tube goes into an adapter or is that the bearing? Do you just smear grease on it?

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RM,

What you are describing... is the thing that supports the control tube...

That support, is what skip called the carrier bearing...

It keeps the tube from flexing over the long distance....

It still needs to be lubricated... 

Expect there to be a defined grease point... particular grease... and a procedure to apply it...

If slathering were the method... you probably would see remnants of it everywhere... like the Jack screw...

 

PP thoughts only, not a mechanic...

Best regards,

-a-

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8 minutes ago, rotorman said:

How does one grease this part? It looks like the tube goes into an adapter or is that the bearing? Do you just smear grease on it?

You have to take it apart. It’s a bit of a pain which is probably why it gets overlooked. I doubt its necessary every annual, but every few years would be a good idea. 

318812878_Screenshot2021-01-30at12_49_12PM.thumb.png.5f8e5742844da297e785eac6931c3337.png1730832537_Screenshot2021-01-30at12_49_39PM.thumb.png.e48a88631f807ddc29026b4faeabf095.png

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  • 1 month later...
On 1/30/2021 at 12:54 PM, PT20J said:

You have to take it apart. It’s a bit of a pain which is probably why it gets overlooked. I doubt its necessary every annual, but every few years would be a good idea. 

318812878_Screenshot2021-01-30at12_49_12PM.thumb.png.5f8e5742844da297e785eac6931c3337.png1730832537_Screenshot2021-01-30at12_49_39PM.thumb.png.e48a88631f807ddc29026b4faeabf095.png

I looked at my installation but the part of the instruction that I could not figure out was in step 2. "Loosen the electric pitch trim servo drive chain." I could see no obvious way to accomplish this. It did look as though the grease is old. No evidence of recent greasing and no placard. Any tips on how to loosen the chain?

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2 hours ago, rotorman said:

I looked at my installation but the part of the instruction that I could not figure out was in step 2. "Loosen the electric pitch trim servo drive chain." I could see no obvious way to accomplish this. It did look as though the grease is old. No evidence of recent greasing and no placard. Any tips on how to loosen the chain?

The bracket that mounts the servo has two pieces with elongated holes in one part and if you loosen the mounting bolts you can reposition the servo to free up the chain.

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