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Thread: Wing skins

  1. #1

    Wing skins

    Guys,

    have been hard at work on the drawing board. Doing some design work on a wing for a light aircraft with a relatively high aspect ratio wing.
    I'm torn between building a wood wing or using foam and glass.
    Both have their pros and cons.

    one thing that bothers me about plywood wing skins is that the largest thing I've been able to find between 1mm and 1/16" is only in 4' and 8' lengths.
    that means a scarf joint unless I can find someone that makes long sections of plywood.
    I know it's common to splice wood, but I just do no like the idea of building a wing this way. The skins being one piece would seem better.

    have looked at glass over foam core as well.
    And I thought I had found the answer with the 45deg knitted glass cloth. After working with some samples of it though I've found this stuff to be useless unless I could get rid of the threads as the layup was done. All the knitting holds the glass off from the core material and on a wet layup you end up with far too much resin and strands are not laying as they should.
    the only other thing I know to do is go with two layers of BID cut and layed up at opposing 45 deg.
    which was exactly what I was trying to avoid by using the knitted fabric.

    anyone been in this spot and come up with a good alternative.
    i want the construction to be as fast and simple as possible.

  2. #2
    Matt Gonitzke's Avatar
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    Aug 2011
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    Wichita, KS
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    Scarf joints are nothing to be afraid of. If you want a wooden airplane you are going to have to be comfortable with scarf joints. My glider's wooden wings (~50' wingspan) have numerous scarf joints in them, and so does every other wooden airplane. Done properly they will be as strong as the unspliced plywood.

  3. #3
    Yes I'm ok with doing the scarf joints. They just take time when done properly.
    It looks like I may go with wood.
    I feel like I could build a lighter, better wing out of wood

  4. #4

    Join Date
    Sep 2011
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    58
    If you are designing a wing skin of glass, why not make skin 3 plies of 7781, with first ply down a 0/90 for bending strength and next ply +/- 45 for torsional strength and third ply another 0/90 for additional bending? 7781 is 10 mils thick, close to equal warp and fill count and is cheap. It would eliminate any standoff as woven fabric is smooth.
    Bob H

  5. #5

    Join Date
    Oct 2013
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    1

    Wing Skins

    [QUOTE=Bill Mixon;35768]Guys,

    have been hard at work on the drawing board. Doing some design work on a wing for a light aircraft with a relatively high aspect ratio wing.
    I'm torn between building a wood wing or using foam and glass.
    Both have their pros and cons..................

    Go to Mark Langford's Internet page ( http://www.n56ml.com/ ) and look at how he did his wings for his KR2S. Good steps on how to handle the bi fiberglass etc plus integration of carbon ply to the mix for additional strength. This method was used on the new wing designed for the KR, which is an interesting read all of its own and his building site is awesome!

  6. #6
    Quote Originally Posted by Bob H View Post
    If you are designing a wing skin of glass, why not make skin 3 plies of 7781, with first ply down a 0/90 for bending strength and next ply +/- 45 for torsional strength and third ply another 0/90 for additional bending? 7781 is 10 mils thick, close to equal warp and fill count and is cheap. It would eliminate any standoff as woven fabric is smooth.
    Bob H

    because of all the work and handling involved with butt edges and three layers.
    the ideal layup would be a layup of two layers of un-cut glass straight off the roll. One would be a material that doesn't exist (45deg bid woven) and the final would be a layer of uni.
    In my mind this would be fast, simple and require less hands/handling with no butted edges to deal with.
    the problem is that the cloth doesn't exist, or I'm not aware of it.

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