In a message dated 98-03-26 18:58:23 EST, Robert.Turner@ibx.com writes:
> I needed 19 feet of 2'od 4130 mast for my design. However, a 24' length
> was delivered. To cut or not to cut, that is the question.
>
> Are their any guidelines as to what the minimum percentage of the mast
> that should be in the tower? I'm concerned that if I use the whole 24',
> with 4.5 feet inside and 19.5 feet outside, that I will over stress the
> tower and rotor. The tower is the 9' Create Roof tower. Rotor is Yaesu
> G-800SDX.
>
Congratulations on getting an investment-quality mast. While you'll be
able to use it for your entire ham career, it is somewhat overkill on your
roof tower. Don't let me, though, discourage you from over-engineering your
installation.
I think the overturning moment on the tower base will be the limiting
factor. While Burlington County is an 80 MPH windspeed zone, it's within 100
miles of hurricane oceanline. I'd recommend over-engineering everything else
as well.
If you get a BIG wind through there, I think the tower will break off at
the base or some other place. It'll hit the ground somewhere and be a pile of
bent aluminum. Your chromoly mast OTOH will survive unscathed.
While the additional 5 feet of mast is less than one additional square
foot of wind loading, my biggest concern is the bending moment/lever arm
acting on the tower and base.
Don't cut it - you can always use it in a real tower in the future. A
5-foot chunk of chromoly doesn't get you much.
> If I stick to my original plan I will have 4.5 feet of mast inside the
> tower with 14.5 outside the tower.
Like others, I'm a little skeptical. You didn't mention what you're going
to put on that mast. Please elaborate before we go too ape on this thing.
73 and GL, Steve K7LXC
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