The SFA thread that discussed knots for pull testing:
http://www.smallflyingartsforum.com/cgi-bin/yabb2/YaBB.pl?num=1220717685
Tony
To: indoor_construction_at_yahoogroups.com
From: tmathews1_at_sympatico.ca
Date: Sun, 8 Mar 2009 20:54:50 +0000
Subject: RE: [Indoor_Construction] Re: Rubber test figure
Yep,
Got most of my ideas for pull testing single loops of rubber from Alex Andriukov (multiple F1B World Champ). Alex has pull tested a single 1/8" loop of TanII to over 9 kg!! While he currently uses a clever clamp system (ie: no knot) the maximum pull forces were developed from earlier testing with a knot. There was a thread in SFA that covered some of this. I'll find it and post it here. Basically, what I found was that the actual knot used was not very important (somewhat heretical to many perhaps?). Rather the execution of the knot was critical. I use 3 knots to tie a loop. Each end gets a small "Stopper" knot (a simple overhand is o.k.) lubed with Saliva. Then both ends are tied with a single knot (overhand or your favorite "sheet" knot) taking care to gently pull the two stopper knots up tight to the main knot. Lube helps here and I agree with Tapio, a bit less viscosity is probably better (capillary action will wick the lube into the knot). I found that with the 3 knot system, I could use almost any basic knot for the main knot, and get similar performance.
Tony
To: Indoor_Construction_at_yahoogroups.com
From: b.gowen_at_comcast.net
Date: Sun, 8 Mar 2009 15:30:04 -0400
Subject: Re: [Indoor_Construction] Re: Rubber test figure
Tony Mathews tests catapult rubber to loads
that make me shudder. He has a knot that works for this.
----- Original Message -----
From:
Tapio
Linkosalo
To: Indoor_Construction_at_yahoogroups.com
Sent: Sunday, March 08, 2009 3:26
PM
Subject: Re: [Indoor_Construction] Re:
Rubber test figure
RLBailey_at_care4free.net
wrote:
>
> I tried stretch testing motors of F1D size to assess
quality but found
> that the knots, which work OK when winding,
repeatedly fail on stretch
> testing. I found it easier to test via
winding since I could get much
> nearer to maximum and therefore
abandoned the stetch method.
>
Yup, the knot is a problem. Also
when testing and breaking in F1B
motors. For several years every one or
two motors out of 10 failed
during the process, many of these from the
knot, that cut trought the
ruber and then broke away. When one strand of a
fully stretched motor
fails, the motor starts to unwind, and the strands
cut trough each
other, making the whole motor unrepairable. Eventually I
found a knot
used by Bror Eimar, "norsk strykknute", that can stand the
pull of the
test. This knot needs to be tied into lubed motor, in unlubed
rubber the
knot will cut and damage the strand. However, I have found that
when
using proper thick silicone for lubing is too slippery and the knot
will
slip, instead I need to use thinner (1000 cts) silicone for lubing
the
know, this stuff lets the knot slip when tightened, but then lets the
knot "stick" when tight enough.
-Tapio-
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Received on Sun Mar 08 2009 - 14:01:14 CET