Re: [amsat-bb] Wind load of a mesh dish

[Doug Faunt N6TQS +1-510-655-8604 <faunt@xxxxxxxxx>]

   From: "Wayne Estes W9AE" <w9ae@earthlink.net>
   Date: Mon, 19 May 2003 01:10:47 -0500

   On May 12, Rick KG6IAL wrote:

   I'll soon be migrating to a 6 ft.
   dish which will include a triband patch feed that adds U-band support.  It's
   beamwidth is still within the accuracy of a Yaesu 5400/5500 and because it
   consists of a lightweight aluminum dish frame, covered with 1/4" hardware
   cloth, it is very lightweight and offers almost no windload.

   Wayne W9AE replies:

   I just returned from a 2-week vacation, and I'm surprised to see that nobody
   responded to the last statement in Rick's message.  In high winds, mesh has
   almost the same wind load as a solid.  That's because the mesh creates so
   much turbulence that the turbulent air layer surrounding the mesh is
   effectively a solid.

I'd like to see a citation for this statement.  Last time I looked, I
found references to formulas for wind loading that took into account
the percentage of space to structure, and the hole size.  For lower
percentages of structure (such as mesh), wind loading seemed to be
significantly decreased, even at high speeds.  I'm traveling this
afternoon, so can't relocate those references this week.

Or, someone could actually experiment- take a 1' square of sheet, and a
1' square of mesh, and hold them out a car window at 60MPH.

   Wayne Estes W9AE
   Mundelein, IL, USA


73, doug
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