> Stan's article was the first to address mast forces. But according to
>Dick Weber, K5IU, PE, Stan's article has some errors in it. Unfortunately he
>didn't elaborate on them or provide the proper equations.
> The better and more accurate mast forces info is in Dave Leeson's, W6NL,
>ex-W6QHS, book "Practical Design of Yagi Antennas" which I think is out of
>From: Dino Darling <firstname.lastname@example.org>
>You can buy this book at HRO (http://www.hamradio.com),
>as well as other places I'm sure!
The W6NL(ex-W6QHS) book does not contain the current methodology either,
it was published prior to Dick Weber's paper. But, it is still a great
source for all kinds if valuable information, like wind load formulas
for zone wind speeds from different specifications. The URL below
contains a page about that also, which should help everyone think twice
before they cite a wind speed relating to something.
The "crosswind principle", presented by Dick Weber (K5IU), for
determining loads developed on antennas by the wind is explained in the
ARRL Antenna Handbook, 19th Edition (circa Y2k), Chapter 22 "Antenna
Supports". Along with, how to determine mast stress, and a new allowable
antenna area limit for a freestanding tower when the load (or loads,
antenna, mast, rotator) is not placed in just one location right at the
top of the tower like the guy who designed the tower expected.
20 sqft at the top of the tower is different from 20 sqft in several
places on a mast above the tower top. This chapter also contains a
diagram and explanation of a technique for "tramming' an antenna up into
place on a tower, and another technique for cleverly snaking it up past
guys. All useful stuff for those contemplating getting antennas off the
As discussed many times in the past on this reflector, all of these
things require antenna "projected areas" to be used with the wind load
formulas, not the so called "effective areas" that are reduced by some
amount (usually 2/3 of projected). BE SURE TO ASK your antenna
manufacturer what his area figure means, unless he has already explained
it in his literature. You need the right area for evaluating everything
that holds the antenna up there.