stretching lines

• Subject: stretching lines
• From: Darrin.Skinner@ebay.sun.com (Darrin Skinner)
• Date: Fri, 13 Aug 1993 09:38:45 -1000

Patrick Prosser write:
-] Date: 13 Aug 1993 12:06:34 +0100
-] From: pat@cs.strath.ac.uk (Patrick Prosser)
-] Subject: stretching lines (was Rev II stack problem solved and another question)
-] 
-] Everything creeps :-) Long long ago, I used to work in
-] the Creep Lab at the NEL (one of the most boring times 
-] in my career). If you put a load on something it will 
-] deform through an elastic stage, then through a plastic stage, 
-] finally to catastrophic failure. To pre-stretch I assume you
-] have to eliminate the elasticity. The plastic deformation will always
-] be there. Put a small load onto something, and leave it for some time,
-] and it creeps.
-] 

As Patrick indicates there are two kinds of 'stretching' that a line
does.  It creeps and it stretches (see the article in American Kite 
Magazine ~about 2 years ago~ that tells all the technical details about 
line).  Stretching is defined as the amount the lines stretch and then 
retract (i.e. the elasticity).  Creep is the amount the lines stretch 
and DON'T retract.  When the lines are getting LONGER over time, they
are (technically) creeping.  A predominatly right-handed flyer will
get more creep out of their right line.  This makes for uneven lines
over time.

Ok, lecture over :) ... now back to the issue...

When we (Air Art) pre-stretch lines we are really trying to remove
the creep.  We fly 95% of the time on 300# line (really 320#) Speed
Line [(dis)claimer, we ARE sponsored by Speed Line] and really notice
any creep in the lines.  We pre-stretch the lines by staking out both
ends of the line (with ground stakes or whatever) as taunt as possible.
We then leave the lines this way during the day (while practicing), 
retensioning them ever 30 minutes or so.  When we are all done we re-balance
them and hope that we have taken most of the creep out.  This has worked
ok in the past.  Over the course of the first week or two of actual use, 
we usually have to rebalance the lines.  After that they don't creep any more.

I was hoping that the weight hanging idea would yeild good enough results
to eliminate the rebalancing we go thru after actual use.  From what I've
read, it does not sound like this is possible.

Darrin
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