Lots of good discussions here. I want to bring up a few points.
- Regarding crank up tower one should run two sets of stress calculations, one
for the fully extended position and one for the fully retracted position. Both
numbers are very important. Due to the high winds I get at my QTH the only way
my tower could survive a 122mph wind speed (mandated by the county) is when the
tower is fully retracted. The same applies to those folks living in FL. So if
one is concerned about the ultimate strength/wind loading of a retractable
tower I would look at the numbers for the retracted position. Most retractable
tower failure stories I've heard are with the towers fully extended. I'd be
interested to hear stories where a retracted tower had failed. For those
people living in areas of mild wind they don't have to be concerned about the
tower position as long as they are not overloading the tower at the extended
position.
- The failure points/modes could be different for each tower position.
- When calculating tower stresses should one take the altitude of the tower
into account? When I did my calculation for the mast I had used an air density
factor of 0.8 since I live at 6.000 ASL. I cannot tell if UST did an altitude
correction for my tower calculations.
Best Regards,
Jonathan Woo, W6GX
(970) 646-1711
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