[TowerTalk] Wind loading comment misdirected? W7VP
jimlux at earthlink.net
Sun Mar 26 18:40:49 EST 2006
At 02:44 PM 3/26/2006, NPAlex at aol.com wrote:
>I don't think I said a thing that contridicted your comments and Rohn's
>requirements. I believe it is IO (intuitively Obvious) that a Flat surface
>drag/profile factor would be larger then a round surface.
While intuitively obvious, it's also wrong.
Oddly, there are lots of situations where the Cd of a round member is >1.0
(i.e. the drag area is larger than the projected flat plate area)..By the
way, a flat plate usually has a higher Cd than a long body with a flat
front of the same cross sectional area; think about the flow behind the
plate. It all depends on the Reynolds number and all those things about
laminar and turbulent flow.
You can play with the numbers at:
Try putting in different diameters of the cylinder like 0.1, 0.01, and
with airflows of 10, 50, 100 ft/sec (88 ft/sec = 60 mi/hr)
0.1 ft = 1.2 inches..
The classic area where this comes up is in biplanes, where the bracing
wires, although small in cross section, have a drag area that's larger than
that of a substantially larger streamlined strut.
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