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Re: [TowerTalk] Aluminum mast

To: "Bruce Ferratt" <>,
Subject: Re: [TowerTalk] Aluminum mast
From: Jim Lux <>
Date: Wed, 15 Mar 2006 13:56:13 -0800
List-post: <>
At 12:49 PM 3/15/2006, Bruce Ferratt wrote:
>My mast is 1 1/4" OD.   It is solid, round.

So, you can apply a bit of simple mechanics..
bending stress is =Moment/section modulus

Section modulus for a solid rod is pi/32 * D^3 or 0.19 inch^3 for your rod.

Yield for 6061 aluminum is probably around 40,000 psi, so rearranging a bit:

40,000 lb/in^2* 0.19in^3 = 7700 in lb.

You've got 8 ft (96 inches) sticking out, so 7700/96 = 80 pounds.

One generally likes to leave a reasonable safety factor to allow for 
imperfections in the material, etc.  Maybe, a factor of 2 would be 
reasonable here?  So, your at 40 pounds load at the end of the mast.

I believe you said 70 mi/hr.  For air drag, load (lb/ft^2) = V(mph)^2/391.. 
12 pounds/square foot.

So, you get a total windload area of 40/12 or about 3.3 square 
feet.  (don't forget to allow for the half square foot or so for the 
mast).  Doesn't look like you're going to be putting up a full size 80m 
yagi on this<grin>. 


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