[TowerTalk] Fiberglass Guy Rods- correction

[Mark, N1LO]

Oops, let me make a clarification on the elasticity comparison:

 I failed to include that the relative elasticities among the materials 
is for the same cross-sectional area! Sorry for the confusion.

It is possible to have equivalent stretch between steel and fiberglass 
guy materials if the fiberglass rod is oversized.

Compared to a solid, 0.25" diameter steel rod, a fiberglass rod of the 
properties previously mentioned would have to be about 0.25 x 2.2 = 0.55 
in diameter to have the same deflection rate (spring rate)along its 
length.

 The cross sectional area of the fiberglass rod in this case would then 
be about 2.2 squared = 4.8 times that of the equivalent steel rod.

The breaking strength of this fiberglass rod would then be about 28,500 
lb, based on the strength of 120,000 lb/sq in given before.

 Based on the densities of 0.282 lb/cu in for steel and 0.073 lb/cu in 
as previously reported for the fiberglass, the weight per unit foot of 
the fiberglass works out to be about 1.25 times that of the steel.

Since the fiberglass is a little stiffer, yet heavier per unit length, I 
would guess that the sag would be close to or only slightly less than 
the steel.

The point is, you *do* have to look at the 'stretchiness' of the guy 
materials. The more 'stretchy' they are (low modulus), the more 
oversized they must be for the equivalent stabilizing effect on your 
tower.

FWIW,

--...MARK_N1LO...--



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