On 9/25/2012 8:25 PM, Ralston, William wrote:
Tonno ES5TV posted:
<email link to pictures of a monstrous 15m array of 8 x 15 ele yagis in a 2-D
stack on a 70meter tower> - an impressive engineering feat!
Roger K8RI asked:
I wonder how well that'd scale to 40 meters and what tower height would be
required.
Don ND8E replied:
Considering that 40m is 3 times 15m in wavelength +/- a smidge, looks like 210m
tower to me.
Gotta win the lottery two or three times to do that one!
I say:
While wavelength and linear dimensions scale linearly, area (e.g., wind
loading) scales as the square, and volume/weight scales as the cube. Thus, a
scaled up tower/antennas would have about 9 times the windload and the whole
mess would weigh about 27 times as much.
Unfortunately, material strengths don't scale up as fast as the weight (I think most
stuff scales with the square) ... thus leaving the scaled structure too weak (Google
search "Why Giant's Don't Exist"). So, it might be quite the engineering
challenge to do a 40m version even if you have the lottery winnings to bankroll it.
I'd be happy with even half of that 15m monster scaled to 10m in my yard. :-)
Remember the full size, IIRC 5L 75 meter beam that had a boom you could
walk though "inside"?
I don't remember just how many tons it weighed, but it was a monster!
The elements, let alone the boom were larger than most towers.
73
Roger (K8RI)
--Bill N7VM
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