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Thread: Trim indicator

  1. #11

    Join Date
    May 2011
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    Weatherford, TX
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    Default Re: Trim indicator

    There is nothing in the indicator mechanism system that could stop the trim from working (in either direction). If you are trimming for 'nose up', a 10 foot long piece of safety wire is pulling the indicator "rivet" towards the rear of the indicator slot (against a spring that pulls the "rivet" towards the front of the slot). If the "rivet" binds in the slot, you will either break the wire, or (I suppose) distort and ultimately pull the "rivet" out of the slot. But nothing in the indicator 'system' is strong enough to prevent the trim from working - that jack screw gives you a LOT of 'leverage'. The fact that it works on the ground kind of proves that it is not the indicator. While having someone turning the handle, try holding the stabilizer against the movement and see if you don't see the cable slipping on the pulley (or the cable stop moving, because it is slipping on the front pulley).

    It is a very common problem for the grease to become hardened and bind the jack screw, and not uncommon for mechanics to simply add more grease on top of the old.

  2. #12

    Join Date
    Apr 2014
    Location
    Cary, NC
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    10
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    Default Re: Trim indicator

    Thanks everyone. The jack screw looks clean and well greased, but I will take the advice and do the experiment with someone holding the stabilizer.

    I am attaching a pair of before and after photos of the trim indicator, so you can see why I wanted to get that fixed up first. Before, the rivet was only partway through the slot, and someone had wrapped a bit of copper wire around the rivet above the slot for some reason. The after photo shows that I removed the wire and put in a nylon washer, a la Steve Pierce, to hold the rivet in the slot and make for smooth sliding.

    Regarding my earlier question of what would happen if the rivet jammed, the answer that the indicator wire would break makes sense. As the tension in the wire increases toward breakage, I imagine there must be some small resistance felt at the crank, but probably insignificant, based on your responses.

    Again, thanks all! two photos attached.
    Before.JPG
    After.jpg

  3. #13
    andya's Avatar
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    Dec 2007
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    UT47
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    Default Re: Trim indicator

    If you are turning the trim handle and the trim indicator is not moving, can you feel the change in pitch trim when flying the airplane..
    "Progress is our most important problem"

  4. #14

    Join Date
    Apr 2014
    Location
    Cary, NC
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    Default Re: Trim indicator

    Quote Originally Posted by andya View Post
    If you are turning the trim handle and the trim indicator is not moving, can you feel the change in pitch trim when flying the airplane..
    It just seemed intermittently unresponsive. Now that the indicator is improved, I plan to do the ground test where someone tries to hold the stabilizer still while I turn the crank. Then I will do a flight test and pay attention to get the answer to your question.

  5. #15

    Join Date
    Jun 2020
    Location
    Virginia
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    Default Re: Trim indicator

    Let us know how the ground test turns out.

  6. #16
    Stephen's Avatar
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    Nov 2007
    Location
    Lopez Island, WA
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    3,519
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    Default Re: Trim indicator

    Cleaning off the old grease is important. Looking clean may not be good enough. I put newspaper down inside the fuselage first. Then wash the jackscrew with a solvent degreaser. I run the jackscrew up and down then degrease one more time. Then I wipe it down. I spray Boeshield on the screw. Don't forget to also lube the pulleys and crank. It's usually good to go until next annual. I immediately notice how much easier the screw works. Another, possible issue is lack of spring tension on the cable. It may be time to replace the spring.

    Nice tip on using a nylon washer to hold the indicator button in place.
    Last edited by Stephen; 07-04-2020 at 09:19 AM.
    "You can only tie the record for flying low."

  7. #17
    andya's Avatar
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    Dec 2007
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    Default Re: Trim indicator

    Another technique for cleaning the jack screw I have used (need two people),
    remove the covers on the fuselage where the stab comes thru,
    get some shade/blinds cord (is usually about 1/8" thick or a little less) and
    feed it thru one of the openings and get it wrapped around the jack
    screw at least one full turn and bring the end back out the same side as you went in.

    Hold both ends and have some one run the trim up and down full travel
    While it is turning put some tension on the cord and feed the cord so
    the jack screw is getting fresh cord as it progresses up or down the threads
    of the jack screw. The cord will come out black and greasy and after
    a couple iterations, the jack screw will be clean. Have also soaked the cord
    in solvent or mineral spirits if the grease is really caked.

    To lube the clean jack screw, some mechs I know use a spray solvent like LPS 2
    or TriFlow. When I have used grease, it has always been that white lithium
    grease that comes in a small tube.
    "Progress is our most important problem"

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