[TowerTalk] AN tower
Roger (K8RI) on TT
K8RI-on-TowerTalk at tm.net
Sun Jun 21 12:08:15 EDT 2015
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
>>> _______________________________________________
>>>
>>>
>>>
>>> _______________________________________________
>>> TowerTalk mailing list
>>> TowerTalk at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>>
>>
>> _______________________________________________
>>
>>
>>
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--
73
Roger (K8RI)
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