Elevator trim reversed?

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Willie Spence
Posts: 22
Joined: Thu Feb 23, 2012 4:42 pm
Location: Waller, Texas 77484

Elevator trim reversed?

Post by Willie Spence » Sat Jun 15, 2019 6:07 pm

Have done an extensive annual in May/June to include among many other things, replacing the left elevator which had damage near the attach point to the elevator actuator in the vertical stab. Was able to find a replacement elevator that had the trim actuator and cable with it. The elevator trim adjust now works opposite the correct direction. When cranking the trim in the nose up direction the result is nose down trim. No work was done to cables, crank etc. Any ideas of what could cause that. Do other models of the108 trim in the different direction? Could the actuator housing where the adjusting threads are be installed backwards. Thought I'd check for answers here before taking that apart.
Thanks,
Will Spence

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Bob Picard
Posts: 32
Joined: Mon Aug 20, 2018 1:27 am

Re: Elevator trim reversed?

Post by Bob Picard » Sun Jun 16, 2019 8:26 pm

I know that this is a silly response. The trim tab works in the opposite direction of the elevator. Nose down trim make the tab go up which pushes the elevator down and conversely nose up trim makes the trim tab go down which pushes the elevator up. I'm sure you already know that, but it never hurts to check. There is a history of accidents where even knowledgeable people have gotten confused and hooked up flight controls backwards. Another thing to consider is that the trim rod assembly looks very similar to the -3 rudder trim rod assembly. They are a different part number and I wonder if they have different rotation threads. If one has LH threads and the other RH threads the assemblies may have been switched. If all else fails, just use the one off your old elevator.
Bob Picard
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Willie Spence
Posts: 22
Joined: Thu Feb 23, 2012 4:42 pm
Location: Waller, Texas 77484

Re: Elevator trim reversed?

Post by Willie Spence » Fri Jun 21, 2019 12:28 pm

Thanks Bob. I’ll take a look at trim travel in the hangar next week. I’ll put the old one back on if I can’t sort it out any other way. Thought about re-labeling the trim gauge (not seriously). I appreciate your input. This doesn’t seem to be s common problem.
Will Spence

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