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  • Help With Wing Rib Evaluation (a model)

    Looking for a little advise/feedback.

    While inspecting the wing parts I picked up recently and trying to figure out where to dive in I’ve come across a couple things that I don’t feel qualified to make a determination on so I thought it might be good to ask here. I won’t be surprised if the answer is to ask Bob…

    Also I'd like to say upfront that I am still quite happy with my purchase and the value it represents. Even if I wind up remaking a bunch of these parts I still feel like I’m way ahead from a cost and time perspective.

    Ok questions of the day.

    1) Looking at my tip ribs and center ribs, when I line up the cord line and jig holes the bottom camber is right on but the top camber a strong 1/8 inch short of the line when compared to the full-size plans template. The nose ribs appear to be a better match and I haven’t taken a close look at the back, flap, or aileron ribs yet. Concern here is that it’s no longer the intended airfoil I'm i'm not sure what implications it will have.
    2) The inboard center .032 rib’s aft lightning hole should be cut to match the dashed circular hole on the plans. On my parts they were cut as the elongated hole intended for the 0.025 outboard ribs. Then an additional hole is cut to allow for the aileron cable to pass through. This represents quite a bit more material removal than per plans.
    3) In the Eric Newton's build manual it notes that the lightning holes for the .032 ribs do not need to be flanged, mine are.

    4) In the plans all the nose ribs are spec at .025 on mine they are matched with the material thickness of the closest center rib, so the inboards are .032. I don’t expect this would be an issue it’s just some additional weight.

    Finally, the challenge with a lot of this is that none of the form blocks used to construct these parts were available so making replacements if needed is going to wind up being an exercise similar in effort to just making form blocks per my plans.

    Trying to decide if it’s time to order some aluminum sheets and have a rib party.

    Thoughts?
    Joe
    Gaithersburg, MD
    EAA Chapter 524
    Cherokee Driver
    Bearhawk 4-Place Builder #1582

  • #2
    #1
    -Is there variation in the ribs or are they all exactly the same?
    -Is the rib off by a 1/8 inch on the top? Or is it off by 1/16" on the top and 1/16" on the bottom?

    I'd want to see uniformity of all ribs. Thats important.

    It seems to me like the rib gets installed onto the spar will result in centering things so that its .062 off on each side. Realize also that the line on the mylar airfoil can be viewed a couple of different ways. It may represent the size of the rib. Or it may represent the dimension of the finished wing with skin....025" skin on the top and bottom? So now are you off by .125" or .063" or something less? I have no heart burn accepting what you've shown me so far.

    #2 It will be easy to fabricate and install a small patch onto the effected ribs to restore the strength of that elongated hole. Don't make new ones.

    #3 Flanges of Rib 1.....Factory ribs at the inboard station are flanged.
    Last edited by Bcone1381; 02-19-2020, 03:28 PM. Reason: clarified myself
    Brooks Cone
    Southeast Michigan
    Patrol #303, Kit build

    Comment


    • #3
      Thanks Brooks,

      - All that i've checked exhibit the same error. I have some more checking to do though.
      - Right now the error seems to all be along the top camber. When comparing i'm lining up the jib pin holes in the parts with those on the plans. the bottom matches up with the line on the drawing perfectly, the top is shy. The one I took a measurement came in at .162" shy of the top line at the largest gap. Others were eyeballed to be similar.

      #2 hadn't thought about that but I like it! AC 43-13 here I come.

      #3 good to know.
      Joe
      Gaithersburg, MD
      EAA Chapter 524
      Cherokee Driver
      Bearhawk 4-Place Builder #1582

      Comment


      • #4
        Joe,
        You received spar webs too, correct? Do the ribs fit the spars?
        Mark
        Scratch building Patrol #275
        Hood River, OR

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        • jsuhre
          jsuhre commented
          Editing a comment
          I did, but haven't checked that fitment yet. Hoping to do so this weekend.
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