[balloon-makers] Seams and stitches
rescher at rescher.com
Fri Jan 25 18:47:29 CST 2002
Seams and stitches is a great topic to discuss.
Obviously, all the major manufacturers use French felled seams in all
of their balloons. From what I understand, the only exception is
FireFly/Balloon Works, which uses a regular locking stitch (or do
they use the stitch that unravels more easily, can't remember what
it's called) to attach fabric to a sleeve for the "load cord", with
no folding involved. (See http://www.fireflyballoons.net/envelope.htm
for a diagram.) Beyond what the major manufacturers do, I have heard
of people experimenting with a zig-zag stitch applied to two pieces
of fabric which are folded together like in a French fell seam.
Finally, I've heard that zig-zag without folding works great for
small radio-controlled balloons.
But on a mailing list for experimental balloon makers, I feel
compelled to discuss alternatives to stitching our seams with sewing
machines. Several kinds of gluing and heat-sealing have been
experimented with in the past. I clearly remember reading in Balloon
Builders' Journal about an experiment Bruce Comstock made with
silicone glue, resulting in tear strength that was superior to a
French fell seam.
I know that gas weather balloons are heat sealed in a process similar
to the one used to seal potato chip bags. I also have a friend in
Switzerland who used a butcher's vacuum-packing and sealing machine
(while the butcher's store was closed) for an unmanned solar balloon.
From what I remember, both the Lindstrand and Cameron round-the-world
envelopes were heat-sealed.
Personally, I am very interested in testing the cold gluing method.
It seems (pun intended) that a cold glued seam would be the simplest
to assemble and would require minimum tooling. In addition to easier
assembly, a glued seam would distribute the load across the threads
of a woven fabric more evenly than any stitch ever could. At least on
a theoretical level, all those little holes your sewing machine pokes
into your balloon are a structural hazard. (On a side-note, this is
why many constructors say it is dangerous to sew your load tapes onto
the center of the gore, because all the little holes create a
pre-perforated strip that can easily rip. Just think how little
effort it takes to rip a check out of your checkbook!)
Finally, Murray mentioned tear-strength. For obvious reasons, high
tear strength and resistance to heat are two essential features of
any seam employed in a hot air balloon. Even if you employ the good
old French felled seam, I highly recommend that anyone building a
balloon test their seams for educational purposes. If we are to
experiment with new seam variations, no path should skip the
tear-strength testing rig!
>I am looking at alternatives to the french felled seam and would
>like input. Does anyone one know of a web site where standards for
>stitches and seams might be found.
>What would the difference in strength between a felled seam and just
>a flat seam be?
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