On 7/12/2013 12:31 AM, Grant Saviers wrote:
"with guys of course", the only limit is the spring rate of the trailer
and the load rating of the tires. The guy down force can be
substantial, so you might need to block the trailer so the load is not
on the tires/springs. Finding something to tie the guys to will be a
huge problem.
I have a Will-Burt 42' pneumatic mast guyed into a trailer or the bed of
my 3/4T truck. The mast is rated for 10 sq ft antenna, 140lb weight, at
60mph fully extended. My calcs show this load will tip over my 3/4T 8'
bed extended cab 4WD truck (5000#). For the hydraulic dump 10K# GVW
dual axle trailer, which weighs 2300#, I have 40" long outriggers at
each corner of the 6'x10' bed and 3500lb trailer jacks at the end of
each outrigger. The outrigger beams are not sized for the max tower
load/wind speed and enable the trailer to be leveled so the tower is
vertical. My plan is to not have the mast up in more than 35mph winds
which is the max load for the beam section/cantilever length I used for
the outriggers. Otherwise, the outriggers need to be long and heavy and
probably need to be made as a truss.
This mast on the trailer played well at Field Day with a CC A4S at the
top. btw the air pressure was only 12psi for full mast extension with
the A4S and Yaesu rotator.
There are pickup pulled boat trailers from 500# to 20,000# capacity, so
you need to do some calcs to size the max tower loads. Generally, since
the legal max width without oversize permits is 8'6", outriggers will be
needed and that is another structural design problem.
Trailer mounted crank ups and pneumatic masts that go to 100' are
mounted on trailers, but at that height they are guyed. I can only
guess at how one would install the "temporary" guy anchors. Of course
these are purpose built heavy duty trailers with truss outriggers, plus
the guys. I checked out a trailer mounted 100 footer at a surplus
auction last fall. A beautiful piece of engineering was reduced to
scrap aluminum when a hoist cable failed.
I agree with Grant, but would use a simple base with rods driven in at
each corner. The plate would support it and the rods would supply
lateral stability. If put up in the conventional manner and liberal use
of strong temporary guys. I use Phillystran.
The guy anchors are a serious problem. If they are going to hold much,
I'd use at least 3/4" steel rod with at least 4" wide plates welded on
the sides. I'd use an air hammer to drive the rods in at a 90 degree
angle to the guys. Getting them out is another problem.
Better yet a crane would be handy for setting it, but I'm assuming one
is not available. With good guys and anchors plus good nerves, it's as
strong as a permanent tower.
Just make sure the guys are tensioned before putting up the next section
and those anchors are well seated in solis soil. Sand won't do it!
73
Roger (K8RI)
Grant KZ1W
On 7/11/2013 6:44 PM, Eric Cary wrote:
I have been talking with some friends about setting up a temporary
tower on a trailer something like a boat trailer.
Something like this:
http://home.comcast.net/~k8cc/images/100_0137.JPG
http://home.comcast.net/~k8cc/images/100_0816.JPG
What is the highest you would go with a Rohn 25 or 45 tower with guys
of course?
73, Eric N3TD "Touch Down!!!"
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