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1. 07:19 AM - Re: Re: wing strut flutter (Jack B. Hart)
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| Subject: | Re: wing strut flutter |
At 02:27 AM 10/11/12 -0700, you wrote:
>
>
>> is there an inexpensive fix for this
>
>
>My curiosity gets the better of me ;-) I am just wondering if a length of
chord wrapped in a helical manner around the strut might stop the
vibrations. It would definitely be the most inexpensive fix I would
think.
>Similar effect to the strakes on chimney stacks. See the nylon chord on the
pole of the weather station about half way down this page;
http://www.tigranetworks.co.uk/blogs/tigranetworks/preventing-vortex-sheddin
g-with-a-helical-strake/
>
David,
A cord spiral wound around a round strut will reduce the drag and lessen the
tendency to produce von Karmann vortices that cause the strut to strum.
What you are doing is tripping the boundary layer, which moves the flow
separation further back behind the strut and this reduces the drag.
Spiral cord wrapping with a high pitch angle is much like the smoke stack which
has to withstand wind loads from all directions. But with
a wing strut one has to worry about only one direction, and so the tripping
can be accomplished by placing or gluing a wire to the top and bottom sides
of the strut. If you would like to see some better explanation of this
check out page 20 on of:
http://www.bakker.org/dartmouth06/engs150/11-bl.pdf
The struts on my FireFly strummed, and I streamlined my struts and the noise
disappeared. How it was done can be seen at:
http://jackbhart.com/firefly/firefly91.html
Jack B. Hart FF004
Winchester, IN
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