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Thread: Wing Inter-Rib Bracing...What to do???

  1. #41
    Buzzcola777's Avatar
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    [QUOTE=cubpilot2;794356]
    Quote Originally Posted by mike mcs repair View Post
    I would tie top of spar to leading edge with a L angle. That gives allot of strength to wing.

    Compare a uncovered PA-12 wing with partial wrap leading edge to a full wrap -18.


    I think that this is a very important point.

    IMHO
    With the extended leading edge installed without any other anchoring other then with screws to the ribs; damage to the ribs will eventually occur.

    A PA-12 wing is very easily twisted due to the design of the leading edge. This allows it to flex more in response to turbulence then a PA18. Pick up one end of a bare PA12 wing and you will quickly see how easy it can twist and you will also see buckling of the leading edge skins as you do. You will learn to handle it with care.

    A PA-18 wing with the majority of the leading edge locked to the spar, is much more rigid. Enough so that the “wash out” needs to be preset when building. This almost creates a type of “box spar” which is highly resistant to torsional or twisting forces.

    Extending the leading edge without this support will leave the wing with same ability to flex or twist when in turbulence or heavy loading. This twisting action with the extended metal will cause similar and more pronounced buckling of the skins and over time, could cause the screws or rivets at the cap strip to loosen or tear out completely. I think that this will be even more accelerated if the stitching to the fabric is not present.

    My opinion is that locking the leading edge to the spar is vital at a minimum, especially with the heavy gross weights which we often experience.
    I also feel that the stitching is well worth the time. The only problem is that the skin for this particular project needs to be loosened from the ribs to drill the holes, which need to overlap the cap strip.

    I like the extended leading edge and have it on my 180 cub.
    It is installed as an addition to the standard piper skins; which lock to the spar along with stitching.
    I have just completed recovering them after 20 plus years in service. There was no looseness or damage observed.


    Very interesting points and thanks for sharing!
    I wonder just by curiosity if we have any owners here that have the same extended LE as I do and noticed over time problems with buckling of the skin ` loose rivets/screws etc...?? If yes, I would pass it on to Nick Smith in order to rectify / modify the wing construction for the next buyers...
    Likes Hardtailjohn liked this post

  2. #42
    skywagon8a's Avatar
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    Quote Originally Posted by Buzzcola777 View Post
    Very interesting points and thanks for sharing!
    I wonder just by curiosity if we have any owners here that have the same extended LE as I do and noticed over time problems with buckling of the skin ` loose rivets/screws etc...?? If yes, I would pass it on to Nick Smith in order to rectify / modify the wing construction for the next buyers...
    Dan, My wings are identical to yours except they only have one fuel tank. They were built by Turbine Cubs just after the Smiths sold to them. S/N 39
    The extended leading edge skins have an L angle screwed to the back of the top spar cap and riveted to the extended leading edge skin. There are three screws in the spar and three driven rivets in the leading edge skin. The Ls fit between each rib with one piece per rib bay and are not otherwise connected to each other. The skin is very solid when you push down on it.
    If you do this, I recommend you use driven AN470-3 or AN426-3 rivets rather than "pop" rivets as they stand up better in flexible, vibration locations. "Pops" tend to work loose. If you use AN426 in a dimpled skin, the joint will be tighter than with the AN470 as the sides of each dimple have more bearing area. Besides they leave a smoother appearing surface on the fabric.
    N1PA

  3. #43
    Buzzcola777's Avatar
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    Quote Originally Posted by skywagon8a View Post
    Dan, My wings are identical to yours except they only have one fuel tank. They were built by Turbine Cubs just after the Smiths sold to them. S/N 39
    The extended leading edge skins have an L angle screwed to the back of the top spar cap and riveted to the extended leading edge skin. There are three screws in the spar and three driven rivets in the leading edge skin. The Ls fit between each rib with one piece per rib bay and are not otherwise connected to each other. The skin is very solid when you push down on it.
    If you do this, I recommend you use driven AN470-3 or AN426-3 rivets rather than "pop" rivets as they stand up better in flexible, vibration locations. "Pops" tend to work loose. If you use AN426 in a dimpled skin, the joint will be tighter than with the AN470 as the sides of each dimple have more bearing area. Besides they leave a smoother appearing surface on the fabric.
    Very good info Skywagon8a!! Thanks!
    This ''L''angle bracket made with .032'' AL 2024 / 6061 ??
    Dan

  4. #44
    www.SkupTech.com mike mcs repair's Avatar
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    Wing Inter-Rib Bracing...What to do???

    .020” 2024T3 is what Univair uses for leading edge skins.


    Sent from my iPhone using SuperCub.Org

  5. #45
    skywagon8a's Avatar
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    Quote Originally Posted by Buzzcola777 View Post
    Very good info Skywagon8a!! Thanks!
    This ''L''angle bracket made with .032'' AL 2024 / 6061 ??
    Dan
    I can try to measure it. I would make it the same as the leading edge skin. My wing uses a lot of 5052-H32. As mike mentions Univar uses .020" 2024-T3. This would be better as it's not as soft as the 5052. I would prefer the 2024 as it's stiffer. It's likely a cost issue why 5052 is used.
    N1PA

  6. #46
    Buzzcola777's Avatar
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    Quote Originally Posted by skywagon8a View Post
    I can try to measure it. I would make it the same as the leading edge skin. My wing uses a lot of 5052-H32. As mike mentions Univar uses .020" 2024-T3. This would be better as it's not as soft as the 5052. I would prefer the 2024 as it's stiffer. It's likely a cost issue why 5052 is used.
    So I would imagine that with three screws in the spar and three driven rivets in the leading edge skin this ''L'' angle is about 2'' wide

  7. #47
    skywagon8a's Avatar
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    Quote Originally Posted by Buzzcola777 View Post
    So I would imagine that with three screws in the spar and three driven rivets in the leading edge skin this ''L'' angle is about 2'' wide
    Yes, 1" x 1" And it appears to be .020"
    N1PA
    Thanks Buzzcola777 thanked for this post

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