Knots was: Rubber Lubes ?

From: Tapio Linkosalo <tapio.linkosalo_at_helsinki.fi>
Date: Thu, 3 May 2007 10:56:16 +0300 (EEST)

On Thu, 3 May 2007, Don DeLoach wrote:

> Tapio,
> My mistake. I meant 8,000 to 9,000 cts.

Ok, now we are on the same scale. I think 8k to 9k is about as good as 14k
that I use. It all depends on what you can get your hands on.

> I have not had a problem with dry knots, then lubing afterward with this
> thick silicone.

Well, I have had. My break-in method is to stretch the motor to about 80%
of breaking load, and keep there for 4 minutes. With dry knots it was too
common that the lube seeped into the knot, and then after a minute or two
the knot slipped. When a 28 strand motor is fully strethed, and the know
slips, the rubber will cut itself when slipping loose, and that motor is
waste. Well, the pieces are usable for indoor flying, but no good for
wakefield any more.

Another thing with dry knots is that they are hard to pull tight enough
that they hold, without the rubber cutting itself while tightening. Saliva
works some, but not good enough So I had to discard dry knots and move
over to lubed ones. To make a long story short, it also took a while to
find out that here the lube must not be too good. Thinner silicone works,
it seems to let the knot slip while tightening, but eventually the rubber
will cut through the silicone and hold. Now majority of my motors survive
break-in and testing. Yet the knot is the weak point, in most of my F1B
motors the rubber is broken at the knot after the first flight, while
often a couple of other strands are broken too. Still would need some
development in the knot department... Indoor does not seem to be so
critical, probably because I get plenty of broken-in rubber from outdoors
to fly indoors, and thus do not need to stress the motors and knots as
heavily as while breaking-in.




-tapio-
Received on Thu May 03 2007 - 00:57:14 CEST