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Thread: PA-12 with PA-18 elevator. Travel stop.

  1. #1

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    PA-12 with PA-18 elevator. Travel stop.

    Working on rigging my elevator travel today. I have about 1/2 the down travel that the TCDS call out for.
    The PO added the silver stop you can see in the picture. I don't see it in the parts manual. I 'm guessing it's part of an STC. Anyone recognize it?


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  2. #2
    TurboBeaver's Avatar
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    Gosh it sure looks like, the cover is going to stay well put with 15 screws in it.!!!
    Anyway what STC was used to install the 18 feathers on your 12...??? Was it a stand alone STC, or part of one of the engine conversion STC's ??? That may be a clue to that limiting part that has been added.?
    Half travel certainly sounds suspect for sure. Elevator travel can be a personal thing, like rudder travel, lots of guys in Alaska have both set outside factory specs. We used to set the rudders up to go over till it was within about 3/8" from hitting the elevator! Way past spec.
    Same with aileron etc.
    Good luck
    E
    Last edited by TurboBeaver; 05-30-2022 at 05:41 PM.
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  3. #3

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    The plane has 2 320 engine swap STCs. The Kenmore STC calls out replacing the elevator and horizontal stabilizer with PA-18 parts. Not other instructions associated with that swap.

  4. #4

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    I also looked though the flaps STC and all the other paperwork and could find no mention of control throw changes.

  5. #5
    skywagon8a's Avatar
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    Quote Originally Posted by Marc Davis View Post
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    That, Could be dangerous to your health. Limiting the down elevator travel defines the safe aft CG limit. IF you are in a full stall while at your aft CG limit, it could be possible to have inadequate down elevator to break the stall. Limiting down elevator travel reduces elevator authority in stall recovery. BAD. Limiting up elevator travel reduces the ability to achieve a high enough angle of attack to get into a full stall, Safer.

    STC or not. Take it out of there.

    The Ercoupe was sold as a safe spin proof airplane. They were able to say this because the UP elevator travel was limited enough so that it would not create a fully stalled angle of attack. Yours is just the opposite.

  6. #6
    Steve Pierce's Avatar
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    The down elevator stop is welded between the top two longerons forward of the elevator bellcrank.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  7. #7
    behindpropellers's Avatar
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    Quote Originally Posted by Marc Davis View Post
    Working on rigging my elevator travel today. I have about 1/2 the down travel that the TCDS call out for.
    The PO added the silver stop you can see in the picture. I don't see it in the parts manual. I 'm guessing it's part of an STC. Anyone recognize it?


    Click image for larger version. 

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    The travel stop for a PA-12 is located below the rear stick. This part is often removed at rebuild and forgotten.

  8. #8
    skywagon8a's Avatar
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    Quote Originally Posted by behindpropellers View Post
    The travel stop for a PA-12 is located below the rear stick. This part is often removed at rebuild and forgotten.
    There are supposed to be two sets of stops (in all planes). One at the control end of the system and the other at the surface itself. The one at the surface is supposed to be the limiting stop. With a small amount of clearance at the control end to account for slop in the system. There is an FAR/CAR covering this which I do not recall. Long ago memory from A&P school.
    N1PA
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  9. #9

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    Steve. I found this in another thread. Thanks, that helps understand how the stock controls work.

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  10. #10

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    Quote Originally Posted by skywagon8a View Post
    That, Could be dangerous to your health. Limiting the down elevator travel defines the safe aft CG limit.
    Skywagon. I agree. I was very surprised to find this. But, generally when you find something like this, there was a reason it was done. I want to understand what it was so I don't run into some other issue it is masking. I have to go look now and see if the stock control stop was removed or something. You never know what you will find in these old birds. This one has 34 STC's and field approvals installed. Not much left of the original plane.
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  11. #11
    behindpropellers's Avatar
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    Just looked in my pictures and I was thinking the wrong part, so carry on.

    Now... If your ailerons do not have enough throw, there is a tab located on the torque tube which increases the throw of the aileron.

    Tim

  12. #12
    Gordon Misch's Avatar
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    [QUOTE=Marc Davis;827308]

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    Both question marks would be answered 'yes'.

    It's interesting that the TCDS specified elevator travels are somewhat different between PA-12 and PA-18. -12 is 27 deg up and 32 down. -18 is 25 up and 15 down (double check me).

    I rigged my -12 in accordance with the -12 spec, using -18 surfaces. No adverse characteristics.
    Last edited by Gordon Misch; 05-31-2022 at 12:49 PM.
    Gordon

    N4328M KTDO

  13. #13

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    With all the information I've gotten here and the facebook PA-12 group I went back to the plane and looked things over. I believe I understand why the bump stop was added. The PO installed a poorly conceived booster seat to the plane at some point. It limited the control throw quite a bit. The stop was added to keep the stick from hitting the seat.
    Anyway, I removed the booster seat and the stop and now it is behaving as expected. I will need to adjust the stick position to center the stick in the available space and I should be good.
    Thanks for all the help.
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  14. #14
    cubdriver2's Avatar
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    Quote Originally Posted by Marc Davis View Post
    With all the information I've gotten here and the facebook PA-12 group I went back to the plane and looked things over. I believe I understand why the bump stop was added. The PO installed a poorly conceived booster seat to the plane at some point. It limited the control throw quite a bit. The stop was added to keep the stick from hitting the seat.
    Anyway, I removed the booster seat and the stop and now it is behaving as expected. I will need to adjust the stick position to center the stick in the available space and I should be good.
    Thanks for all the help.
    If you unhook the cables to adjust check continuities before you start it

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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  15. #15
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    With that type of PO you'll want to keep your eyes open. Once I found a bicycle pump melting itself to the exhaust inside a Cherokee cowling. We all scratched our heads trying to figure how it got there. Next time the owner popped in I showed him where I found it. He was miffed, "hey that's where I keep that, put it back."

    Sent from my SM-G965U1 using SuperCub.Org mobile app
    The heavens declare the glory of God; the skies proclaim the work of His hands. Psalms 19:1

  16. #16

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    This thing went over on it's back so I'm going over every inch of it. I've worked on quite a few tube and fabric Pipers but this is by first PA-12. Always lots to learn.

  17. #17
    daedgerton's Avatar
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    Quote Originally Posted by Marc Davis View Post
    With all the information I've gotten here and the facebook PA-12 group I went back to the plane and looked things over. I believe I understand why the bump stop was added. The PO installed a poorly conceived booster seat to the plane at some point. It limited the control throw quite a bit. The stop was added to keep the stick from hitting the seat.
    Anyway, I removed the booster seat and the stop and now it is behaving as expected. I will need to adjust the stick position to center the stick in the available space and I should be good.
    Thanks for all the help.
    Can you PM a link to the PA-12 Facebook group?

  18. #18
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    Last edited by flybynite; 06-02-2022 at 01:44 PM.

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