[TowerTalk] Aluminum mast
uglyatc at msn.com
Wed Mar 15 16:31:17 EST 2006
Thanks for your email.
The mast is 1 1/4" OD. Solid, round. Side writing on the states it is ASTM
6061-T6511 grade aluminum. It was $66. Weighs about the same as the seet
6' mast that came with the tower. I just don't like mounting a rotor right
in the open section of Rohn25g,... it's gotta be lower inside the tower.
The beam is a Mosely TA-33M Tri-bander. Longest element is 26ft---13ft each
side of boom. Boom is 14ft long.
The beam and stacked vertical 2m/440 will probably weigh under <40lbs at the
Also,... your formula,....
1 1/4" OD *4 (to the 4th power) minus 0 ID (zero) (my mast is solid),... is
this correct? The mast is solid,...there is no ID,...please recalculate the
formula with the details I have provided.
>From: Jim Lux <jimlux at earthlink.net>
>To: "Bruce Ferratt" <uglyatc at msn.com>, <towertalk at contesting.com>
>Subject: Re: [TowerTalk] Aluminum mast
>Date: Wed, 15 Mar 2006 06:14:13 -0800
>At 07:56 PM 3/14/2006, Bruce Ferratt wrote:
>>Hello and thanks for letting me post a question.
>>How strong is a solid aluminum mast compared with a walled/hollow mast?
>almost all the strength for a round member comes from the outside.
>Consider bending.. the maximum stress is at the edges
>For torsion, the derivation is a bit trickier, but it's the same
>So, to answer, for the same weight of tubing (which is how you buy it, by
>the pound), the tube is stronger than the rod.
>it goes as od^4-id^4
>>I secured a solid, round 12' aluminum mast 6061-T6511 grade. What is the
>>likelihood of bending when loaded with a TM-33A and VHF 2m/440 vertical at
>>a rated 70mph wind load in Northern Virginia? 8ft of mast will be exposed
>>above the point of the tower peak (Rohn 25G), with about 4 ft inside the
>>tower to rotor plate.
>That must weigh a bit!... You forgot an essential dimension: the diameter
>of the mast, and the cross sectional area of the antennas. Ballparking, a
>load of about 300-350 lbs at the end will bend a 2" solid bar 8ft long.
>There is an old QST/QEX article around that goes through the calculations,
>and I think there is a spreadsheet that accompanies it, either on the ARRL
>site, or maybe K7LXC's site?
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