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Re: [TowerTalk] mount pipe for vertical

Subject: Re: [TowerTalk] mount pipe for vertical
From: jimlux <>
Date: Sat, 15 Jan 2011 05:09:20 -0800
List-post: <">>
On 1/14/11 6:27 PM, K2VI wrote:
> Ok so tomorrow is the day i start this project. I have a 5' piece of
> 1 1/2" fence post pipe. It will be almost 4' cemented in gound and
> 14" above ground. I will have a zero five 43' vertical on the pipe.
> All i hear is schedule 40 plumbing pipe however i have on hand this
> fence pipe. I see no reason not to use it since the vertical has very
> little wind load.

A vertical has a surprisingly large wind load. 2" tube has a drag of 
about 1.5 lb/ft in a 60 mi/hr wind

A quick calculation shows that at 40 mi/hr the wind load is 0.7 lb/ft 
for a total wind load on your 43 feet of 29.5 lbs, and a bending moment 
at the base of 640 ft lb.  Go up to 70 mi/hr and you're up to up to 2.1 
lb/ft, 90 lb total load, and almost 2000 ft lb bending moment.

Just as a comparison, 2" schedule 40 iron pipe (2.375"od, 0.154" wall) 
will fail in bending at around 2400 ft lb.

your 1.5" fence post pipe is pretty small, and probably pretty thin.. My 
catalogs actually don't show 1 1/2" for post, just top rail (1 3/8" 
seems to be the standard size)

I did find some other fence post online
There's a 1 5/8" Allied SS15 post, 0.072 wall thickness, which they 
claim is 570 ft lb bending moment as well as SS20 and SS40, which have 
thicker walls and are stronger.

In any case, your 43 foot antenna, even in fairly light winds, might 
bend a thin wall steel pipe.  On the other hand, it's probably fairly 
easy to fix.  If it bends, you yank it out and put a new pipe in.

I attach verticals to standard wire fence "T" posts, and when the wind 
blows too hard, the post bends, I get the jack out, yank the post and 
drive another.

  Also this pipe was used holding up a cushcraft A3S
> 5 feet above the thrust bearing. I just want to make certain before
> cementing. thanks in advance.
> tony _______________________________________________
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