[TowerTalk] AN tower

[Patrick Greenlee]

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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