[amsat-bb] Wind load of a mesh dish

["Wayne Estes W9AE" <w9ae@xxxxxxxxxxxxx>]

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.

The rotor and support structure for a 6 foot mesh dish should be designed to
withstand the wind load of a 6-foot solid dish, because that's what the mesh
dish will effectively be in a 60 mph wind.  A mesh dish may be cheap, light
weight, and easy to form.  But it does NOT have significantly less wind load
than a solid.  If you have a good memory, you could always park your 6 foot
mesh dish pointing straight up when you're not using it, to minimize the
wind loading.  But a Yaesu rotor is almost certain to be damaged in a storm
if the dish isn't pointing straight up.

Wayne Estes W9AE
Mundelein, IL, USA




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