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Thread: Inter-rib sag reduction

  1. #21
    pylon500's Avatar
    Join Date
    Oct 2011
    Location
    Taree Airport (really) North NSW, Austrlia
    Posts
    18
    I think we're going to need a lot more info on your structural concepts to give any real advice.
    I don't think anyone would try to build a wing of that shape and have it externally braced, so I'm assuming you're going the Bede route and having a large alloy tube main spar.
    Although this seemed like a good idea from Bede at the time, using a large diameter alloy tube with fibreglass skins (BD-4 etc) worked until they decided to skin the wing with aluminium.
    The problem now was that the tube spar was capable of flexing more than the skin sheeting, and caused buckling of the skins.
    Putting thicker skins tended to negate the reason for the tube spar, as the skins now did most of the work, and concentrate the loads at the root of the spar.
    Watch the wing in this vid;
    <https://www.youtube.com/watch?v=bu9jpREQ56A>
    Better to design a propper 'D' cell wing.

  2. #22

    Join Date
    Aug 2011
    Location
    Alabama
    Posts
    2,051
    You said the magic word - ultralight - so I'll jump in.

    Want to reduce the "sag" between ribs? Don't shrink the fabric to full tightening. You probably don't want to do it anyway, as light structures are easy to warp when shrinking fabric!

    Next up, my advice is not to worry about it too much. Your ultralight should have a pretty fat airfoil, so a little "sag" isn't going to hurt a thing.

    That is if you're using ceconite in the first place. Look at the powered hang glider craft - they use sail cloth sewed as an envelope instead.
    The opinions and statements of this poster are largely based on facts and portray a possible version of the actual events.

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