Another term you might have heard if you’ve hung around antennas or satellite systems is wind load. This term describes how much wind affects something. It’s a combination of how much wind you have, how much drag the object has, and how big it is. There’s a lot of science here, but here’s the basics of it:
Wind Pressure is a measurement that equates to wind speed. You take wind speed in MPH and multiply it by itself (in other words square it) then multiply that by .00256.
Coefficient of Dragis a measurement that tells you how easily something slips through the air. You’re probably familiar with this measurement in cars, and it’s something you need a wind tunnel to measure. A water droplet has a drag coefficient of .4, while a 2×4 with the flat size facing the wind has a drag coefficient of about 1.6.
Area is just “how big it is.” Drag coefficient is the same for anything that is the same shape, in other words a model car has the same drag coefficient as a real car. But in the real world, wind affects big things more than small things. Area is measured in square feet, just multiple the measurement of one side in feet by the measurement of the other side in feet.
Add that all together and you get
F (wind load) = A (area) x P (pressure) x Cd (drag coefficient.)
Why do you care about all of this? Chances are you’ll never have to worry about it at home unless you live somewhere really really windy, but if you design antennas you really need to know this stuff. It tells you what will stand up and what will blow down. As things get bigger, they’re affected by wind and in the case of skyscrapers, wind load can be a bigger factor than gravity. A dish has a bigger wind load than an antenna, because it has that big reflector. A new-design UHF antenna has a bigger wind load than an old-school VHF one, for the same reason.
We’ll be talking more about wind load in the coming weeks — we’re getting wind load data from all our manufacturers and will share it and tell you what it all means!