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Thread: Spar Taper

  1. #1
    Join Date
    Mar 2010
    Location
    Queenstown New Zealand
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    382

    Default Spar Taper

    Hi Mik, I'm curious as to the mathematics/method of determining a mast or other spar taper. (No I don't want to mess with things, I'm just curious. Have seen this picture on your website and am intrigued.

    Just if you have time.

    Thanks, Ian

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  3. #2
    Join Date
    Jul 2005
    Location
    'Delaide, Australia
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    65
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    Default

    Howdy Ian,

    In some ways the method is arbitrary and there are a few different ones. Their action is mostly to get a reasonably even bend from thick part to the ends and to save quite a bit of weight up high. As the bending moment is less toward the ends the spar can be thinner.

    The method is arbitrary, but I use a very traditional method that uses a semi circle - flat base horizontal. You draw in a radius at 90 degrees to the base of the semicircle and then draw some other vertical lines to (say) the right of the line to touch the outside of the circle. These equally divide the right side of the horizontal diameter. Each vertical line will be shorter than the last with the last point being the end of the diameter - you can't use the last one as you don't want the end of spar to have zero diameter. So you discard that one.

    There are other methods too, using slanted lines inside the half circle. But they make little practical difference to the diameters as you go up with the small spars I design so I use this simple method.

    To some extent it is arbitrary like I said but any scheme that gives you too much weight at the end or allows the spar to bend too much as some point won't match the criteriia.

    The reality is providing the spar is stiff enough to carry the load without excessive deflection and is not too heavy and stiff at the ends then you can make a sail to match the actual curve.

    Best wishes
    Michael

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