On 9/3/19 5:16 PM, Steve Maki wrote:
K6MR was kind enough to send me an article by K5IU that sheds some light
on this issue. It's not intuitive (at least for me), but when you look
at his drawings of the vectors and accept the formulas, you can see that
the boom does NOT go in-line with the wind even in the case of a one
element yagi with the element at one end of the boom.
K5IU shows, in the course of debunking commonly accepted methods of
determining wind area of a yagi, that when you have crossed tubes, the
minimum wind force occurs when NONE of the tubes are either in-line with
or perpendicular with the wind. It doesn't matter how the elements are
distributed. Only the relative areas of the boom vs the elements. If the
areas are the same, than minimum wind force occurs at 45° offset. If one
or the other has more area, than it's some other angle, but always
oblique from the wind direction.
By extension (my take from the article) is that if allowed to, the
assembly WILL rotate to the minimum wind force position. It may be that
the torque for a given wind speed is not all that great, but the torque
must be there.
So it still seems to me that the assertion that yagis are automatically
torque balanced just by mounting them at the boom center is not true.
I hope Dick Weber won't mind if I post a url to his article.
https://app.box.com/s/40l9icahrtlpqoyd0zppp9vdxn5ck1xc
an excellent article..
Although, the reference to drag coefficients from that Eiffel guy...
Yeah he designed built freestanding towers and kit churches, but his
aerodynamic work was done *after* he built the tower. In fact, he used
the tower to drop stuff from to measure the drag properties.
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