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Thread: PA18 Horizontal Stabilizer Travel

  1. #1

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    PA18 Horizontal Stabilizer Travel

    Ive mounted my horizontal stabilizer. I was checking the up travel and down travel, I don't have enough down travel. The prints state the up travel is 2.5 deg +- 1/2 deg and down travel 4 deg +- 1/2 deg. I have 3 deg up and 3 deg down.
    The way I checked was leveling the fuselage buy using a digital level placed on the bottom of the door frame and leveled. Then I placed the level on the rear seat crossover tube to level lateral axis. I checked the tubes the firewall mounts to and it's plumb.
    I moved my level to the horizontal stab and adjusted the stab to level condition. Adjusted full down and recorded 3 degrees with the cross over link tube on the yoke bottomed out on top longeron. Adjust full up and recorded 3 degrees. The drawings state the degrees is in reference to horizontal centerline. What am I missing?
    Last edited by Bucrepus; 09-15-2020 at 08:21 AM.

  2. #2
    www.SkupTech.com mike mcs repair's Avatar
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    Sounds like you leveled it well

    Old fuselage? Homemade??




    Sent from my iPhone using SuperCub.Org

  3. #3

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    Mike, The fuselage is an VR3 tube kit I have built, I've checked all the fuselage dimension and they are on spec.


    Steve

  4. #4

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    Click image for larger version. 

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    Mike, here is some pictures. I'm just trying to make sure I have the required travel in the stab before I finish welding the jack screw tower in place and welding the rear support.
    Steve
    Last edited by Bucrepus; 09-15-2020 at 09:20 AM.

  5. #5

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    It looks like you didn’t use the VR3 rear pivot that came with the kit. Have to checked to make sure what you used is the same height.
    when I get home I’ll check my travel and see what mine is. Also a VR3.

  6. #6

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    Mike, I choose to use the piper style rear support, VR3's support is different. I liked the piper style support. more beefy! lol

    Steve

  7. #7

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    But is it the same height. If it’s shorter it would change your down angle.

    gonna send you pm with my number. Would be nice to talk. I’m only slightly ahead of where your at.
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  8. #8
    Gordon Misch's Avatar
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    Turn the yoke over???
    Gordon

    N4328M KTDO
    My SPOT: tinyurl.com/N4328M (case sensitive)

  9. #9
    www.SkupTech.com mike mcs repair's Avatar
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    PA18 Horizontal Stabilizer Travel

    Quote Originally Posted by Gordon Misch View Post
    Turn the yoke over???
    Yoke is installed correctly in his picture


    Sent from my iPhone using SuperCub.Org mobile app

  10. #10
    Clyde Barker's Avatar
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    When I built my cub I found that the stabilizer trim had too much nose up trim (front of stab too much down travel) and not enough nose down travel. It had the correct total travel.

    I had purchased my finish welded frame from Wag Aero. The top longerons on this frame didn't have the correct down angle between the jack screw mount and the tail post, causing this problem.

    I drew a rough sketch of a change to the yoke with dimensions that would correct the problem and sent it to Jay at Javron. He fabricated a beautiful yoke for me. With this yoke the up and down travel is perfect. That was a long time ago, not sure if he still has time to do custom work.

    Maybe something like that would work for you.

    Here is the yoke and jack screw...

    Click image for larger version. 

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  11. #11

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    G280Driver,
    I checked the rear stabilizer horizontal support bracket VR3 sends with the tube kit ( consit of the tube and four legs you jig) not the standard cub part. From the center line of top longeron at the bracket area to the center of the bracket is 1/2 inch taller. I simulated the height with a temporary jig, and the down travel works out to 4 degrees down. Why they changed this area, I'm not sure. Now jigging this bracket up is next challenge, like trying to get all the legs of an octopus straight at the same time.
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  12. #12

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    Thanks for the discussion and input gentleman.

  13. #13

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    Clyde,
    That's nice.

  14. #14

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    Steve,

    It just doesn't "look" to me that the upper longerons aft of the screw jack slope down enough. i.e. there is not enough of a bend. But it's hard to tell from the photos you've posted.

    If it was bent "down" more at the back, you would get the travel figures you need since your overall travel is sufficient.

    I've not long ago built this area on a Super Cub frame and it's a Chinese puzzle working off the Piper drawings. The young lad they must've had doing the drawings didn't really seem to understand he necessity of using a practical and consistent datum....

    Cheers,
    Andrew.
    Last edited by MainlandCub; 09-16-2020 at 02:12 AM. Reason: Clarify
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