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Thread: Are my spars compromised?

  1. #1

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    Are my spars compromised?

    The other day, while fastening ribs to spars something caught my eye. At the factory, they Pre-drilled holes through the spar cap for the ribs to attached to. In each case, the drill bit went through the spar cap and then very slightly into the web.

    I have contacted the manufacture. They assured me that this is not a problem. I have heard that this is a very critical area; therefore, I thought I’d reach out to you all for a second opinion.
    The wing in question is for an experimental PA 18


    Thank you

    Ryan

  2. #2

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    I can’t say whether they’re actually compromised or not, maybe one of the engineer types can answer that. But drilling into the web is a well-known, generally accepted no-no, so it raises some questions about the vendor/kit manufacturer in my mind. Who knows, maybe they actually had an engineer look at it and it really is totally fine...
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  3. #3
    Steve Pierce's Avatar
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    I always take great care not to drill into the spar web when drilling the spar cap. The web is in compression and shear, not a place for a hole or a stress risere. There is a reason the spars with lightening holes only have them outboard of the struts.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
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  4. #4

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    I would think the critical area is the U section on top and bottom. The rib holes do go through that, but they are not near an edge. Nicking the web might not be all that critical - surely a good structural engineer could answer that. These things are studied in "beams 101."
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  5. #5

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    I wouldn't lose a minutes sleep! I'd worry more about the holes drilled in the capstrip. Oh ya wouldn't lose any sleep over those either.
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  6. #6
    mountainflier's Avatar
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    To help you out with a good answer, send us a couple good pictures of your drilled spar caps. A question for you? What are you putting in the holes for fasteners?
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  7. #7

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    Thank you all for the input!<br>The fasteners are type B screws.<br><br>A couple of pics...
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  8. #8
    skywagon8a's Avatar
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    Quote Originally Posted by Ryan Murphy View Post
    IMO, I would be more concerned with the threads being made by the screws than that little dimple. Granted the person drilling the holes ought to have placed a piece of metal in there while drilling to stop the drill. You will be drilling bigger holes all the way through when you install the compression ribs and wing attach fittings.
    N1PA
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  9. #9
    Steve Pierce's Avatar
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    Quote Originally Posted by skywagon8a View Post
    IMO, I would be more concerned with the threads being made by the screws than that little dimple. Granted the person drilling the holes ought to have placed a piece of metal in there while drilling to stop the drill. You will be drilling bigger holes all the way through when you install the compression ribs and wing attach fittings.
    Every rag and tube Piper has the threads made by those screws.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
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  10. #10
    Hardtailjohn's Avatar
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    I was just going to say....both of those examples would ground a BUNCH of airplanes if it was a problem. I've seen more with a sloppy drill job than I have without, I think!
    John
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  11. #11

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    Again, thank you all very much for the input. I am not going to loose any more sleep over it. Going to run these spars And continue moving forward with the project.

    Ryan
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