We have a lot of wind generators in the area (County) where my farm is
located. Of course those are the monster, commercial generators with
the entire farm generating many megawatts. (Look up Gratiot county wind
farm)
It covers a large area and another two wind farms to the S and SW have
been added. Studies have shown the wind speed is ideal most of the time
with power that is price competitive with conventionally generated power.
Those are mounted on a single pole that is massive.
A windmill tower on steroids, which this appears to have been, does not
scale well from the 8 to 10 or 12' windmills of old to the large 3 blade
props large enough to generate useful power in average winds. Most are
variable pitch so they keep the RPM to a level limiting that gyroscopic
action, or even shut them down in high winds. A "windmilling" prop has
far more wind resistance than one that has stopped. An airplane will
glide much farther with a stopped prop than one that is windmilling. I
wonder what the wind resistance, or equivalent area of one of those big
props would be.
I've seen quite a few home systems that appeared to be on 45G or even
25G, guyed towers. It "appeared" to take quite a breeze to get the
smaller blades turning. They "appeared" to be turning the equivalent of
2 or 3 car alternators. What they were really turning? I don't know.
They told over at the farm that some of the prop tips can reach as high
as 400 feet
I wonder if this generator had a variable speed prop with speed control.
A prop large enough to give useful power in average winds must be quite
massive with the associated gyroscopic action.
73
Roger (K8RI)
On 6/21/2015 9:43 AM, Patrick Greenlee wrote:
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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73
Roger (K8RI)
---
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