[TowerTalk] Antenna & Tower Wind Load Ratings

[Kurt Andress]

Jim Varney,
I think you are describing the basic problem correctly!
But, I think it is important to notice some possible caveats that do 
occur and are relevant to the discussion.
Having only one maximum "projected area" for each antenna, is not always 
useful for every tower/antenna installation!
I have found that for almost all HF yagis, the area of the elements will 
be higher than the area of the boom. But, that doesn't always apply to 
long boom VHF/UHF antennas. Sometimes, their booms will have a higher 
"projected area", and in some cases like the Innov Antennas, UK 
configurations, which utilize square booms, the higher Cf(Cd) also needs 
to be applied to the projected area to produce the actual loads on the 
tower structure in that wind exposure direction.
Additionally, I have encountered installations where antennas were not 
all pointed in the same direction on a Mast/Tower..... Example: a 40m 
yagi above a tribander is installed 90 degrees off of where the 
tribander is pointed to minimize deleterious RF interaction! We need to 
know both antenna areas, for each of the antennas, and where they are 
positioned on the support structure to figure out which wind impingement 
direction provides the worst case loads on the antenna support structure 
(tower)!

I did not intend my initial post go much further than simply reminding 
this reflector of the problem I cited around the early days when it 
first came on line, nothing has changed and it really needs to be 
changed.....antenna manufacturers and tower designers need to all be on 
the same page, and they are not! I would love nothing more than to sit 
down with all these entities and straighten out this eternal disconnect, 
that is not correct, and is not supporting those that purchase, and 
those that try to design their products!

Thank you again for contributing to the discussion!
73, Kurt, K7NV