Wind varies with height. Even with 20 feet there can be a substantial
difference. Much depends on the size of the rocks. As the page the
previous link, said: close to the ground the wind is irregular. The
rocks will make it even more so. You also have the rising air currents.
Will the bases be well above high tide? I've flown along much of that
coastline and IIRC there was an abrupt drop off at, or just beyond the
shore.
You have increasing wind velocity as you go from the base to the top
while the antennas taper. Going from 3/4" to 3/8ths will make for a
pretty flexible vertical.
I think the safest would to calculate the flat plate area for ea
section, and use the average. Then use the top wind speed. This will
give you some safety factor on the higher portions of the verticals.
73,
Roger (K8RI)
On 8/30/2016 Tuesday 2:33 PM, Dick Blumenstein wrote:
Hi Gary-
I found this link from K7NV
<http://k7nv.com/notebook/topics/windload.html>. Hopefully, this will
help. I would assume you would do a force calculation for each
diameter piece and add the forces up of all the different pieces.
Dick, K0CAT
=============================
Gary Smith wrote on 8/30/2016 2:20 PM:
I'm having to play games with setting up eight, short, active
vertical elements on an incredibly rocky area. I am not able to drive
in ground rods, much less the base of the antennas. I'm coming up
with a plan to make wooden bases for them and hold them down with
rocks.
Since I live on the ocean's edge and have to contend with hurricane
force winds every so often, I'm trying to figure out the wind loading
of the verticals I'm considering. I'll buy the aluminum sections from
DXE and prefer to use larger sections just because of branches
falling at the marsh edge, as they always do. But thicker pieces will
have more wind loading and that is a problem.
If I use the thinnest configuration I'll have about 22 feet tall made
of .375, .5, .625 & .750 sections.
I asked what the wind loading would be and nobody I talked to was
able to give me a clue. Does anyone know a formula to figure the wind
loading of tapered elements?
Thanks & 73,
Gary
KA1J
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73
Roger (K8RI)
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