On 3/5/2013 10:45 AM, Patrick Greenlee wrote:
My apology for using the term "pipe" loosely. Of course it is structural
tubing with circular flanges welded to each end of each of the 12 ends.
Multiple through bolts attach the 20 ft sections together at the flanges
to make 40 ft.
Here's a tower with a similar stance although the base was not "tip up"
it did use 3 separate concrete piers.
http://www.rogerhalstead.com/ham_files/skyhook.htm
Over all it was just shy of 200 feet with IIRC the top 120' rotating.
I took two men, (WD8RXP & WD8RZE) several years to complete. It even
made the January 87 cover of QST
That's Ken (WD8RZE) working 120 feet above me in the cover shot.
They used square flanges with 4 bolts at the leg junction. The base was
5" structural steel tubes. I don't remember for sure, but IIRC the base
alone weighed 4 tons. There were several truck loads of concrete in
those piers.
I'm sure if the tower had been used to support an antenna
it would still be in fine shape but the gyroscopic forces eventually
work hardened the bolts and caused the failure.
It depends on the length, speed, and mass of the blades as well as the
speed of direction change, but the force from precession could have
been tremendous. Every time it changed direction the top of the tower
would have tried to tip up or down.
Like has already been mentioned this is one very large base compared to
the size of the antennas and for only 49 feet
73 es good luck,
Roger (K8RI)
I will be replacing the
bolts. I intend to cut off the tops of the tubing embedded in the piers
to be able to reuse the flanges. I will weld on telescoping tubing to
replace that left behind in the piers.
As regards "The Base", the installation didn't have one large "lump" of
concrete for a base, just the 3 piers 18 inches in diameter and 7 ft
into the ground with tubing embedded to provide flanges to mount the
tower. I think the width of the tower's "stance" at over 14 feet
contributed greatly to its stability and lack of a requirement for a
massive lump of concrete. Given its aspect ratio with the top 60 ft
removed (over 14 ft wide at the bottom and only 40 ft high) erecting it
on the ground and tilting it up should be relatively straight forward
considering I have a tractor with a front end loader to let hydraulics
assist muscle, a 12,000 pound pull winch on the front of a one ton
dually diesel Dodge truck, and two of the tower base connections are
very stout tilt over hinges.
This may not be the first time something like this has been done but it
is a first for me and I have never heard of nor seen anything like it. I
haven't worked out the details of how to mount a crank-up free standing
tower inside this 40 foot tower but it will not include concrete. Even
with a crank-up tower fully extended from inside it with a couple
antennas on that the load on the tower base will still be significantly
less than it had when the original full 100 ft were intact, and more so
if you consider the load and drag of the wind generator which is
considerable.
I suppose I could take a few more progress snaps and post them as there
might be some interest in seeing how this project goes. Next Monday is
the date of a brush clearing expedition to clear brush and trees that
have grown up and are intertwined with the legs and braces of the first
20 ft section.
The picture labeled Big Tower is a shot of one of the tilt over hinges.
The misspelled Flangte and pier is a picture of one of the piers and
flanges.
Tower is a shot of the whole thing as it sits in the brush.
The rust is light, superficial, and not flaky. It will clean up easily.
I will paint it with Rustoleum brand hamertone paint intended to be put
on rusty metal with no primer. I have used it on rusty metal before on
outdoor steel and after 10 years it still looks new. This paint comes
in spray cans or quarts at the big box stores. I have found it in colors
in spray cans but only black and silver in quarts. Silver can be tinted
and gives a slightly pastel metallic look when I had it tinted as dark
green as they could.
73,
Patrick AF5CK
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