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Thread: Leading edge screws

  1. #1

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    Leading edge screws

    I have searched, but still have a question:

    leading edge attachment screw #4 diameter, but what length? 1/4” or 3/8” in length?

  2. #2

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    #4x1/4
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  3. #3

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    Is this for both leading edge to rib and leading edge to spar cap?

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  5. #5

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    So, I am making a guess:

    #4 x 1/4 for skin to rib
    #4 x 3/8 for skin to spar cap

  6. #6

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    I think they are all 4x1/4, but the ones that go in the spar are "B". Think of that B as "blunt end."

    Piper, way back when, had really shallow slotted head PK screws. If you can find them, your fabric bumps will be less obvious.

    If you are starting with a new spar, I recommend pre-tapping the holes. I used a 1/4x3/8, gripped in small Visegrips. Tap ten holes, then get a new screw. They are hardened, and if they break off in the spar you get to re-locate the hole.

  7. #7
    Steve Pierce's Avatar
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    I use the #4x1/4 from Spruce on skin to ribs and get the screws from Dakota Cub for ribs to spar and skin the spar. That is how Piper did it and it works.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  8. #8

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    I rather suspect Piper got their screws from Parker-Kalon. Spruce really didn't get started until rag wing production had stopped.

    I would order THA4-4 for leading edge to rib, and THB4X4 for spar attach, from Spruce or Genuine. The 4-4 is a slotted head, and looks like the Piper originals from the picture.

  9. #9
    Lisa Martin LMartin's Avatar
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    How about the little #4 machine screws with split washers and hex nuts that attach brace channel to ribs?
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  10. #10

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    4-40. I hate to say it, but Piper probably got them in bulk at the local hardware store. You can get better steel from Micro Fasteners, but I have never seen one break. Lots stronger than the cap strip.

  11. #11
    Steve Pierce's Avatar
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    I use MS35206-215 and -216 if memory serves me correctly. Started getting split lock washers at the hardware store when I could find the AN version anymore, several years ago.
    https://www.aircraftspruce.com/catal...ickkey=6563645
    Steve Pierce

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  12. #12
    Lisa Martin LMartin's Avatar
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    Thank you!


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  13. #13
    Lisa Martin LMartin's Avatar
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    Now…installing false spar and skin behind the tank bay. There’s a backplate inside at the flap bell crank. I left my parts book at home. Do I need the backplate with new false spar material? Click image for larger version. 

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  14. #14
    KJC's Avatar
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    If it’s certified, then yes you do. It’s easy to rivet in, and provides the proper location for the cutouts for the hinge and pushrod. Additionally, it strengthens the false spar where most of the load is imposed during flap extension. If you having trouble riveting it in, then machines screws, washers and locknuts would be an acceptable alternative. Make sure the nuts are on the inside.

    Its hard to tell but it looks like your splicing in a new section of false spar on the inboard side of the wing? If that’s the case, then you should just use an entire new section. If I’m wrong on that then disregard.
    Last edited by KJC; 01-23-2023 at 09:34 AM.
    PA-12 N418BS
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  15. #15
    Lisa Martin LMartin's Avatar
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    Thank you. This was the old tank bay piece. I thought about reinforcing it, the sheet metal the backplate attaches to is pretty worn out, but decided to install a new section instead.


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