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Re: [TowerTalk] Wind loading

To: "Towertalk" <>
Subject: Re: [TowerTalk] Wind loading
From: "Don W7WLL" <>
Date: Tue, 30 Aug 2016 19:04:45 -0700
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As Roger has pointed out, wind gradient is an important aspect in the design of any structure - tower or skyscraper.

I host a wx station here which feeds into the NOAA system. Until recently I had an anemometer at ground (now not in place) and one at 30 feet (the NOAA anemometer height recommendation). I am planning on one at the 70 foot level on my larger crankup.

Wind typically increases in speed with height, but obviously the terrain within a defined area will have a bearing on what wind speeds are. As Roger noted, terrain plays an important role. I often experienced a significant difference between the ground and 30 foot levels, sometimes as much as 25 MPH or more. The ground anemometer was located on flat grassy ground with little obstruction for some 2-300 feet. The anemometer at the 30 foot level is 8 feet about the house roof at the front peak. Our second level deck is between the two as far as height. We would often see no wind at the ground level, be experiencing a moderate wind on the deck and see only a light breeze or a significant wind speed at the roof anemometer (not the best location by the way!).

Roger has touched on a situation that many hams should consider doing, getting a fix on how the winds at their location are affected by terrain and by obstructions. The latter two factors will have a significant bearing on what happens with wind speeds. Knowing how ones physical obstructions on the property affects the wind currents can help lead to better tower siting.

A little hand anemometer is a cheap investment and can be successfully used if you really want to know what is happening on your property and are willing to walk around a bit. Plotting this on a property map showing buildings, trees and other obstructions is easily done if you want a GENERAL idea. Your results may differ with certain storms of course (also a good time to do a walk around).

If really interested in wx at your location there is a NOAA-NWS manual dealing with wx instrument siting standards. I don't have it at hand but if anyone is interested contact me and I'll go chase it down.

MesoWest AS-531
Cranky Old Guy with Crankups

-----Original Message----- From: Roger (K8RI) on TT
Sent: Tuesday, August 30, 2016 5:24 PM
Subject: Re: [TowerTalk] Wind loading

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

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.


Roger (K8RI)

On 8/30/2016 Tuesday 2:33 PM, Dick Blumenstein wrote:
Hi Gary-

I found this link from K7NV <>. 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

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,


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