A caveat regarding wind generators on towers. A good friend had a 100
ft tower with wind generator on top. Unfortunately it was not properly
engineered for a wind generator although it was sold expressly for that
purpose as a package deal. In just a few years the tower failed and
crashed to the ground destroying the generator and mangling the tower
components.
The tower was constructed of seamless steel tubing with 1/4 walls and 4
inch ID in 20 ft lengths with welded on flanges for bolting together.
The three legs are on 14 ft centers at the ground, a fairly substantial
tower. Each leg sat on an 18 inch diameter 7 ft deep concrete pier. So
why did it fail?
When spun up by the wind the generator makes a considerable gyroscope.
When the wind changes direction without slowing considerably first the
gyroscope translates a change in azimuth to a force trying to tilt the
generator up or down (aim the generator's axis of rotation out of the
horizontal.) This gyroscopic action was not properly allowed for and
eventually led to the towers dramatic catastrophic failure.
Towers well designed for supporting antennas may not be built such that
they will survive the gyroscopic force translations. Sufficient
materials were salvaged from this collapsed tower to reconstitute the
bottom 40 feet. I tilted that 40 ft recreation over (two hinged legs)
and dismantled it for transit to my QTH and have refurbed it. It may be
seen on my QRZ page along with the three foundations for its legs. The
guy on the ladder is my good friend John who is mech eng with 35 years
hands on experience. He sanity checks my wild ideas as well as visiting
me for 10 days each year to help with projects.
Executive summary: Be careful just sticking a wind generator on a tower
designed for antennas. You might be in for an exciting surprise.
Patrick NJ5G
On 6/19/2015 7:30 PM, David Gilbert wrote:
Well, in my case, I had to allow for some ridiculous wind issues here
at my QTH and I wanted to make sure that whatever tower I put up would
handle any large antenna (or wind generator) I might one day decide to
install on it, since I certainly was only going to have one tower ...
ever. I live on an easterly hillside near the south end of a mountain
range where the dominant wind direction is from the southwest. The
winds that get blocked by the south end of the mountain range recover
in the form of swirlers that roar down the hillside and across my lot
like a freight train. Spring thermals bring wind gusts every three to
five minutes that often reach 70 to 80 mph, and I've seen days where
90 mph is not uncommon. The strongest I've recorded was greater than
100 mph, and that on a clear day.
So I bought the strongest tower I could reasonably afford, although
the Trylon might be the better value in terms of cost versus utility.
To each his own.
I do agree that the foundation seems to be overkill, though, and mine
took 20 cubic yards of concrete. That's roughly 40 tons worth planted
six feet in the ground, and if the tower was five times stronger than
it is now I bet it would still fail before the foundation budged.
The rebar cage design looked odd to me as well, but I didn't have any
problem at all building it --- as the pictures on my web site show.
Shipping (from Pennsylvania at the time) was also expensive. I bought
mine in 2008 and the freight cost to southern Arizona was almost
$1200, and it would probably be even more now.
No doubt about it ... my tower and antennas have far and away been the
most expensive aspects of my ham radio addiction.
73,
Dave AB7E
On 6/19/2015 10:29 AM, K7LXC--- via TowerTalk wrote:
Howdy, TowerTalkians --
I've installed dozens of towers at amateur and commercial
sites over
the years and I have found the AN towers to be battleship stout
(which in
many cases is not necessary for a ham installation) but expensive to
buy and
install.
One of my major complaints is that the base design is WAY
overbuilt
compared to all the other towers I've installed. The last one specified
approximately 3 times the amount of concrete than for similar towers
from other
manufacturers. To me it's a pure waste of time and money for the
unneeded
additional concrete.
Also the rebar cage is overly complicated in its design. I've
built
many rebar cages but I had to hire a concrete contractor to be able
to build
it per their spec. Even the concrete contractor was scratching his head
over the design.
To me, this is another instance of an engineer working in an air
conditioned office who designs it but never has to be out in the
field to
install one. (They're not the only manufacturer to do this.)
For a similar tower height and capacity, anyone installing a
Trylon
Titan tower would save up to $3000+ by buying it rather than the AN.
Just
offering a money saving option.
Yes, I sell Trylon towers but that's because I've found them
to be the
best value in a self-supporting tower around and lots of people are
interested in that.
Cheers,
Steve K7LXC
TOWER TECH -
Professional tower services for amateurs
Cell: 206-890-4188
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