On 10/27/11 10:54 AM, henry.lonberg wrote:
> Jim/Steve etal:
> You forget that this is just the air mass density force at a velocity.
> There are modifiers beyond Cd (drag/shape) that need to be taken into
> account which modify the force due to height and exposure. This other
> modifiers are not insignificant. To provide a more accurate
> determination of the area these will need to be taken into account.
Oh yeah.. there's a whole lot more than just tower face loading, Cd
variations with Reynolds number, etc.
Any "real" design needs to take all that stuff into account.
(I was real surprised when I started calculating wind loads on a 40 foot
mast intended to be supported by parking a car on the base and tying it
to the roof rack. If it's anything more than flimsy, it'll rip the rack
right off the car.)
I've always assumed that the "square foot rating" of a tower was sort of
to get people in the ballpark. A "3 square foot" tower wasn't even
close for your 40-10meter log periodic, but would probably work for the
Ringo Ranger or the TV antenna.
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