[TowerTalk] Wind Load Question

Jon M. Knodel jknodel at msn.com
Thu Apr 27 01:19:43 EDT 2006

First, I would like to thank all those who responded to my last post regarding guy leads for my tower project this spring/summer.  I really want to install the tower properly and heed the recommendations of Rohn.  This is where my second question comes up though.

I am planning a 60' tower at the 110 mph wind rating (the city in which I live has adopted 105 mph)...it's not always fun living on the coast...high winds are a fact of life here.  

According to Rohn, I will be limited to 8.2 sq. ft. of antenna load (at the top of the tower).  My question is this:  Do I need to take into account wind loading for the rotor and mast that I am planning on using, or do these Rohn wind load limits already account for this?  I am planning on installing a minimum 12' long mast and therefore have the rotor set at least 10' down from the top of the tower.  So, do I need to add wind loading for the mast and rotor and if so, do I need to account for the entire area of the rotor and mast, or just that portion of the mast that is extending above the top of the tower (as seems to be the specified loading in the Rohn drawings), due to the fact that the rotor will be well "within" the tower itself?

Also, I plan on hanging dipoles for 160, 80 and 40 off the tower along with a small weather station and a surveillance camera.  Do I need to account for the wind loading for these items also, or are they of no significance due to the small "wind loading size" they present?

The reason that I am so interested in pinning down my exact total allowable wind load is that I am looking at the 3 element SteppIR antenna with the possibility of adding the newly introduced 30/40 meter element.  The 3 element beam alone is rated at 6.1 sq. ft. of wind load and the additional element adds another 2 sq. ft.  So, at a total of 8.1, I should be just within the 8.2 sq ft. of wind load the tower is rated at.  But with the addition of rotor, mast, dipoles, etc., I may not be able to add the 30/40 meter addition to the antenna if I need to account for wind load for these items.  However, if they are negligible, I could add the additional SteppIR element.  

Any insights would be greatly appreciated.  I will take any and all opinions I can get.  Thanks again for the previous help and for whatever guidance you all can give me on this.

Jon, N7XW

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