Stiffness (not strength) is proportional to the quantity:
OD^4 - ID^4.
In your current case, this is 2.5^4 - 1.5^4 = 39 - 5 = 34
The best you could possibly do with an aluminum insert is to emulate
a solid rod, in which case the stiffness would be higher by
a factor of 39/34 which is a 15% increase in stiffness. I
believe steel is about 3 times stiffer than aluminum, so
a solid steel rod would get you a factor of 49/34 or 44%.
Rick N6RK
Barkey, Patrick M. said:
> I've been using 24 foot, half inch wall, 2.5 inch OD aluminum masts
> on all of my towers for quite a few years, with no failures or real
> problems. During the recent ice storm, however, a couple of them
> flexed a little more than I'd like to see (they've since sprung back).
>
> Now that I have the opportunity to think this over, I am wondering
> if it would be of any value to try to add a little more stiffness to
> the existing mast by driving something into the hollow center.
> I've got a 1.5 inch ID hole to work with - perhaps some pipe or
> solid rod could be driven into it?
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