Re 550 parachute cord:
I used to load that stuff with my bod, back in the good old days...28 foot "
doube L" cheapo back in the early 70s.
Also packed and serviced parachute systems as a rigger...long time ago.
Modern parachute cord is rarely the stuff they called 550 cord. The
rectangular wing parachutes of the last 25-30 years demand precision length,
non stretchable suspension lines, that are usually woven dacron, or
sometimes kevlar, or kevlar-like fibers.
The 550 cord, if the real stuff, is pure nylon, very stretchy, has an outer
woven nylon shell covering about 6-8 thin nylon strings, one of which is
distinctively colored, identifying the manufacturer, and date of
manufacture.
The nylon shell carries something like 60 percent of the load, and the inner
lines the rest... The nylon shell takes the UV hit over time and, as all
nylon, weakens, sometimes severely, more if the shell or nylon is thin, and
the UV reaches through it. It to a great degree shields the UV from the
inside lines. If your stuff has no inside lines, but frizzy nylon fill it
is not real 550 cord. Parachute cloth in the old days of round parachutes,
was often 1.1 ounce per sq yard, and then the skydivers, who got tired of
pounding the ground with their body on landing made thicker (1.6 oz) LO-Po
low porosity ripstop. The 28 footers with lo po landed considerably softer
than the mil surplus "cheap-os". Anyway, we had to be careful to get the
nylon out of the sun, or it would weaken over time, and in the application,
that was not good. 1.1 cheapo fabric would turn to dust in weeks if left
out in the California sun. Telltale signs of weakness are loss of the nylon
shiny look, and it becomes dull, and pasty over time.
It is non-trivial to maintain the rated 550 tensile strength of the line.
most knots in it severely (~40 percent) decrease the load capacity of the
line. Parachutes use carefully terminated and sewn, ends, and polished
metal link hardware to attach to the nylon webbing of the harness.
I have use it for decades for suspending dipoles, etc, and found it lasts
quite a long time but eventually the UV gets to it and first the outer
hollow shell separates, and then the UV works on the strands, eventually
breaking the line, under load. Chafing or movement through pulleys will
also weaken it, (quickly) but it actually lasts a good long time, at least
for me in California.
Good stuff for antennas, esp temporary supports.
73, DX, de Pat Barthelow AA6EG aa6eg@hotmail.com
>From: Greenacres113@aol.com
>To: towertalk@contesting.com
>Subject: [TowerTalk] 550 -parachute cord
>Date: Fri, 7 Oct 2005 08:17:15 EDT
>MIME-Version: 1.0
>Received: from dayton.akorn.net ([216.1.128.73]) by MC8-F24.hotmail.com
>with Microsoft SMTPSVC(6.0.3790.211); Fri, 7 Oct 2005 05:17:47 -0700
>Received: from localhost (localhost [127.0.0.1])by dayton.akorn.net
>(Postfix) with ESMTP id 10C5D31944D;Fri, 7 Oct 2005 08:17:35 -0400 (EDT)
>Received: from dayton.akorn.net ([127.0.0.1]) by localhost
>(dayton.akorn.net [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id
>27176-05-3; Fri, 7 Oct 2005 08:17:33 -0400 (EDT)
>Received: from dayton.akorn.net (localhost [127.0.0.1])by dayton.akorn.net
>(Postfix) with ESMTP id 20C6731941F;Fri, 7 Oct 2005 08:17:27 -0400 (EDT)
>Received: from localhost (localhost [127.0.0.1])by dayton.akorn.net
>(Postfix) with ESMTP id 39DAB319418for <towertalk@contesting.com>; Fri, 7
>Oct 2005 08:17:23 -0400 (EDT)
>Received: from dayton.akorn.net ([127.0.0.1])by localhost (dayton.akorn.net
>[127.0.0.1]) (amavisd-new, port 10024)with ESMTP id 26946-06 for
><towertalk@contesting.com>;Fri, 7 Oct 2005 08:17:23 -0400 (EDT)
>Received: from imo-m15.mx.aol.com (imo-m15.mx.aol.com [64.12.138.205])by
>dayton.akorn.net (Postfix) with ESMTP id 036FF319410for
><towertalk@contesting.com>; Fri, 7 Oct 2005 08:17:21 -0400 (EDT)
>Received: from Greenacres113@aol.comby imo-m15.mx.aol.com
>(mail_out_v38_r5.5.) id g.19d.3de80109 (4340)for
><towertalk@contesting.com>; Fri, 7 Oct 2005 08:17:15 -0400 (EDT)
>X-Message-Info: TiNwL5K19MGNYpef8fbEfgp0EwLwXw4NTo6qhVyJ9kY=
>X-Original-To: towertalk@contesting.com
>Delivered-To: towertalk@contesting.com
>X-Greylist: whitelisted by SQLgrey-1.4.2
>X-Mailer: 9.0 SE for Windows sub 5017
>X-Spam-Flag: NO
>X-Virus-Scanned: by amavisd-new at contesting.com
>X-Content-Filtered-By: Mailman/MimeDel 2.1.6b3
>X-BeenThere: towertalk@contesting.com
>X-Mailman-Version: 2.1.6b3
>Precedence: list
>List-Id: "Tower and HF antenna construction topics."
><towertalk.contesting.com>
>List-Unsubscribe:
><http://lists.contesting.com/mailman/listinfo/towertalk>,<mailto:towertalk-request@contesting.com?subject=unsubscribe>
>List-Archive: <http://lists.contesting.com/pipermail/towertalk>
>List-Post: <mailto:towertalk@contesting.com>
>List-Help: <mailto:towertalk-request@contesting.com?subject=help>
>List-Subscribe:
><http://lists.contesting.com/mailman/listinfo/towertalk>,<mailto:towertalk-request@contesting.com?subject=subscribe>
>Errors-To: towertalk-bounces@contesting.com
>X-Virus-Scanned: by amavisd-new at contesting.com
>Return-Path: towertalk-bounces@contesting.com
>X-OriginalArrivalTime: 07 Oct 2005 12:17:48.0231 (UTC)
>FILETIME=[214EBD70:01C5CB39]
>
>any users of this cord? i recently got a few hundred feet of the '550'.
>before i change out the rope supports on my wire antennas i'd like to
>know
>more. is it UV resistant. better or worse that other ropes? seems to be
>very
>strong so wx/sun survival is my main concern.
>
>k9il
>_______________________________________________
>
>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
>Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
>questions and ask for Sherman, W2FLA.
>
>_______________________________________________
>TowerTalk mailing list
>TowerTalk@contesting.com
>http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|