[TowerTalk] Aluminum mast

[Jim Lux]

At 12:49 PM 3/15/2006, Bruce Ferratt wrote:
>Doc-
>Hello.
>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>.