[TowerTalk] Aluminum Mast Again

[kk9a at arrl.net]

You can use a heaver wall or larger diameter for increased strength.  I just
purchased a 56#  - 2 1/2" diameter x 1/2 wall  x 15' aluminum mast for $250
from http://www.metalexpress.net .

John


In a message dated 9/2/03 3:22:40 PM Pacific Daylight Time,
stetrekve at yahoo.com writes:

> Thanks for the reply.  The 16" should read be 16 feet
>  for the approximate mast out of the top of the tower.
>  The 2 meter antenna is: 2.7 sq ft
>  The 6 meter antenna is: 2.5 sq ft
>  The Force 12 C32XR is: 10.7 sq ft, weight. 82 lb
>  Force 12 HF beam 1 foot above top of tower.  6 meter
>  beam 6 feet above HF beam and 2 meter beam 6 feet
>  above the 6 meter beam.

Hi, Steve --

    The bending moment is 18,641 in-lbs. The mast recommended needs a yield
strength of 42,000 psi and 0.188" wall.

    Since the yield strength of the of 6061-T6 is 35,000 psi, you're pretty
close to a potential failure. One thing you can do is to move the antennas
closer together. Or go to a steel alloy mast. Or put a piece of steel inside
the
bottom of the mast to strengthen up the place where it's going to bend -
right
at the thrust bearing.

Cheers,
Steve     K7LXC
TOWER TECH
Champion Radio Products