I find it amusing that the behemoth HDX-5106 is now rated at just 1 sq foot @
90 mph. And that’s with the ant no more than 1 foot above top of tower.
I have the slightly shorter HDX-689. This is the older style with Z
bracing...and a combo of Z and X bracing on the overlaps. Mine also has
re-enforced, via 7 foot long tubes stuffed into the bottoms of each section.
EG: my very bottom section is 2.875” OD, sched 80, ( .276” thick)..
but with the extra re-enforcing, it’s at least .5 “ thick. That’s the way it
was built. Tower weighs a hair below 5000 lbs.
They rate it at 75 sq feet in a 50 mph wind.....and 50 sq feet in a 70 mph
wind.... based on ant load no more than 1’ above top of tower.
When UST sez a 20’ mast can be used, they mean total length of mast is 20’....
and NOT a 24’ mast, with 20’ above top of tower.
As soon as any mast is added, like in my case, a 20’ mast, with 14’ above top
of tower, you have effectively added another section of tower.
Depending on ant area, and location up the mast, and how many additional
yagi’s, etc, the wind rating will drop like a rock, so beware.
UST used UBC-97 for their calcs on my older tower, and used exposure B. Now
exposure B assumes with a 70 mph at top of tower, you will eventually end up
with
a 56 mph wind at 8 foot above ground level. It’s kind of a BS rating imo.
In an open field, wind speed could easily be 70 mph from top to bottom of a
tower.
With a uniform wind speed from top to bottom, that’s called exposure D..which
is what really should have been used. If you have looked at UST’s site these
days,
they also now warn about ice loading, their towers are not rated for ice.
I ended up using 105 ksi anchor rods, 12 of em...and each is 5 foot long, with
a 6 inch thread on each end. Galvanized and came from portland bolt. A 9 inch
square
x .375” thick steel plate, with 4 x holes punched, is placed at the bottom of
each of the groups of 4 x anchor rods. That alone will increase the pull put
capacity a huge
amount..and cost very little to implement. I used 5075 psi strength
concrete. 24 x vert rebars, each is 1”, and 60 ksi. 14 x horizontal hoops,
made from one piece of
5/8” rebar. A grid of rebars at the very top....and a 2nd grid of rebars half
way down the 9 foot deep hole. 17 yards of concrete used.
Bottom line is... you gotta be glued to the WX forecasts at all times. If
they predict high winds wed night, then crank it down. If they predict snow,
ice or both,crank it
down. If you go outa town for the weekend, crank it down. UST now sells
this handy dandy device, that fits over top of the 14 inch diam pulley....so
you can hand
crank the tower down, IF you lose commercial AC power. It takes aprx 2-4
times as long to get the tower fully retracted using this method.
If you want to test out the .6 laminar flow experiment, try sticking a 3” diam
tube out the car’s sun roof..then again with a piece of 3” wide flat bar. Try
the experiment
again, but with 1” and also 2”, and 4” tubes and flat bars. You will get an
eye opener.
I would do the yagi/ant surface area calcs by hand....as most ant makers have
it screwed up in a lot of cases.
Later........ Jim VE7RF
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