[TowerTalk] Alum Masts

[n4kg@juno.com]

WHOA !   Let's not go overboard here.

Did you perform a stress analysis for the proposed system?

He wants to put a TH3 and a 17M dipole on a 7 ft mast.
Put the TH3 a few inches above and the 17M dipole on top.
NO PROBLEM.

Even if it bends, with that small top load, all he would need
to do is put up a gin pole, tie the rope to the bent mast
and hacksaw it off.  But I seriously doubt that will ever 
happen with such a small load.  One of my 3L20's has
a 24 ft  2 inch OD 1/8 inch wall thickness 6061-T6 
ALUMINUM Boom supporting the 20M parasistic elements 
12 ft out with NO truss support.  It has NEVER bent.

Against K7LXC's sage advice, I have a 5L10 and 4L15
stacked 7 ft apart on a galvanized waterpipe.  It survived
the tornado that took out dozens of trees in my woods.

(I pretested the waterpipe by placing it on a couple of
supports with 7 ft sticking out and stood on the end
without it bending so I knew it could handle a 200 lb load.)

Tom  N4KG

On Fri, 11 Jan 2002  Jerry Kincade <w5kp@swbell.net> writes:
> 
> Tom, I wish you the best of luck, but be sure to plan for access 
> around the
> tower for the $300 boom truck you'll need to safely lift that rig 
> out the
> top after it's bent. At that point, the galvanized steel mast you'll 
> buy as
> a replacement should have a cumulative cost of about $500 to $700, 
> depending
> on how much damage the antenna suffered.  :-)
> 73, Jerry W5KP
> 
> ----- Original Message -----
> From: "Thomas Beltran" <tbeltran@earthlink.net>
> To: "Bill Coleman" <aa4lr@arrl.net>; <towertalk@contesting.com>
> Sent: Friday, January 11, 2002 12:00 AM
> Subject: Re: [TowerTalk] Alum Masts
> 
> >
> > Bill:
> >
> > I plan on using a 10" mast, three with the rotator mounted about 
> three feet
> > below the top of the tower, so 7 feet would stick out above the 
> top of the
> > tower.  The guy at the industrial metal supply told me that that 
> pipe-wall
> > thickness would be 0.120", OD is 2".  So I guess according to your
> > statement, that should be fine.  Tom W6EIJ.
> >
> > ----- Original Message -----
> > From: "Bill Coleman" <aa4lr@arrl.net>
> > To: "Thomas Beltran" <tbeltran@earthlink.net>; 
> <towertalk@contesting.com>
> > Sent: Thursday, January 10, 2002 1:02 PM
> > Subject: Re: [TowerTalk] Alum Masts
> >
> >
> > >
> > > On 1/10/02 1:03 PM, Thomas Beltran at tbeltran@earthlink.net 
> wrote:
> > >
> > > >This discussion of Masts is quite timely for me.  I was 
> planning on using
> > > >schedule 80 Aluminum pipe for a TH-3MKIII and perhaps a 
> rotatable dipole for 17.  Should I consider one of HRO's steel masts?
> > >
> > > Tom,
> > >
> > > What you left out is how high above the tower top you planned to 
> have the antenna(s). That makes all the difference.
> > >
> > > In general, I'd avoid the use of "pipe" of any kind for a 
> structural component, but if the antenna is right at the top 
> of the tower,  the
> > > bending moments are small enough that even "pipe" would work.
> > >
> > > I've got an A3S mounted 6 feet above the top of the tower on a 
> 2" Al tube with a 3/32" wall. Plenty strong enough.
> > >
> > > Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@arrl.net
>
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