Tower Ratings - Stupid Question

[Bill Coleman AA4LR]

>The tower is heavy duty model, rated @ 30 sf / 50 mph  (I know, I know,
>the wind blows harder than that!!!)

This raises an interesting question. If the lowest wind in the TIA 
standards is 70 mph, why do tower manufacturers specify tower capacity in 
terms of 50 mph wind? 

Since wind pressure increases with the square of the velocity, and 50 mph 
is roughly 1/sqrt(2) * 70 mph, this has the effect of presenting DOUBLE 
the capacity at 70 mph. (Other things being equal -- which they rarely 
are, since the tower face itself contributes considerable drag)

Also, for crank-up units, shouldn't there be different ratings for the 
extended and nested positions?

Sign me, Confused.



Bill Coleman, AA4LR           Mail: aa4lr@radio.org
Quote: "Not in a thousand years will man ever fly!"
            -- Wilbur Wright, 1901


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