[TowerTalk] Building a Tower Trailer
jimlux at earthlink.net
Mon Jun 26 18:35:02 EDT 2006
At 02:41 PM 6/26/2006, Dino Darling wrote:
>I'm certainly not going to start a little banter war here, but let me
>point out a few things...
>First, while some of the following applies to Jim's comments, not
>everything in this post is directed specifically at him. It may appear
>I'm being "a little hard on the Beaver" later in this post, but I only
>mean to point out issues with posting a response to a question that has
>nothing to do with the topic (or any topic on here for that matter) at
>hand. I know you know what I mean!
>Kelly has a Force 12 LPT-1242 weighing in at 145 lbs which is real close
>to a "few hundred pounds". If we were talking about a W-51, then that
>would be different.
>Kelly needs it SMALL and LIGHTWEIGHT so he can "push it along the side
>of my house into the back yard." Hydraulics, generators, etc etc etc
>does not sound like an option in this case. A horse trailer conversion
>would be a nightmare!
You're definitely right there. I suppose the takehome from all my generic
comments all boils down to the "manage the mass".. the LPT1242 is a nice
lightweight aluminum rig, and would probably be nicely compatible with a
small lightweight trailer.
If you set up the pivot points right, that 145 pound load can be almost
perfectly balanced, so with a 20 pound push, you can get it upright. no
winches, rams, etc.
HOWEVER... watch the wind load issue. You may find that the 40 foot mast
with a small beam on it has enough overturning moment in a fairly low wind
(e.g. 60 mi/hr) that outriggers are impractically big.
That 60 mi/hr and 9sq ft is a force of 82 pounds at the top of the mast.
That results in an overturning moment of about 3500 pound ft + about 4000
lb ft for the force on the mast itself (assuming it's 42'x6"). Let's call
that 8000 lbft. If you've got a 10 ft outrigger, it's going to have to
take a 800 pound load (and also implying that the trailer has to weigh 800
pounds to hold it down, although, ballast on the upwind outrigger would help)
There's some similar calculations at
http://home.earthlink.net/~w6rmk/antenna/mastcar.htm when I was trying to
figure out if I could use my car to hold up a 50 foot portable mast.
I suppose the issue is whether you expect the setup to be "totally self
contained" or "a convenient carrying device for the rig"
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