John, that 71 ft. vertical with the dimensions that you gave will NOT
WORK for long. With a 75 mph wind the following sections will be
overloaded by 600 to 800 % of the maximum yield strength of 6061-T6 AL
pipe and tubing. The section with .25 in diameter, .375 inch, .50 inch,
.625 inch, .75 inch, .875 inch, and 1.0 inch are overloaded.
You need to lengthen the bigger sections and also start with a bigger
section at the bottom. . 0.25 in diameter tubing is too small to use.
If you use it at the top you could only go 4 feet with it. If 0.375 in
diameter tubing is used as your top section you can only go 5 feet max
with it before it gets overstressed.
You also have to check your taper schedule to see if you have a .25
wavelength electrical in the end after you have all the tapered
mechnical sections put together.
There was a spread sheet in December 1998 QST by K5IU for calculating
element strengths.
Denis Ve6AQ
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