Thanks Matt,
Yeah, I saw the safety factors for the *cables* on page 7.
But I wonder if the cables are really the "weak" point or if the *pulley frame
assembly* is actually weaker.
Any way to know?
Thanks again!
de Doug KR2Q
----- Original Message ----->
Message: 2
> Date: Thu, 11 Jun 2015 23:27:56 -0500
> From: "Matt"
> To:
> Subject: [TowerTalk] FW: engineering help? Antenna weight for US Tower TX472
> Message-ID: <004a01d0a4c8$28998ab0$79cca010$@gmail.com>
> Content-Type: text/plain; charset="us-ascii"
>
> Hi Doug,>
> The lifting cable stress analysis is found on page 7 of the link that>
> accompanied your message. The analysis shows the factors of safety in the
> cable tension as 15.2, 6.1, and 9.74 for sections 5,6, & 7 respectively. In
> response to your question, the "weak link" is the middle cable.
> The payload assumptions stated at the top of page 7 are as follows:
>Antenna: 200#
> Antenna mount: 50#
> Coax: 22#
> Total payload: 272#
> (rotor weight apparently is considered in one of the above)
> Section weights are 188#, 221#, & 334# for sections 4,5,& 6 respectively.
> Tensions for cables are calculated as follows:
> T1 (top cable) = W4+Payload = 188+272=460#
> T2 (middle cable) = (2 x T1) + W5 = (2 x 460) +221 = 1141#
> T3 (each of 3 bottom cables) = ((3 x T1) + (2 x W5) + W6 ) / 3 = ((3 x 460)>
> + (2 x 221) + 334) / 3 = 719#
> All cables are listed as 1/4" 7x19 galvanized which has a rated break
> strength of 7000#. The minimum recommended factor of safety for
> hoisting applications is 5 to 1, so the maximum payload meeting the 5 to 1
> minimum safety factor is about 400#.
> Hope this helps & good luck on your project!
> 73
> Matt
> KM5VI
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