[Balloon-makers] [cloudhoppers] Problem with homebuilt parachute

Thu May 7 11:02:36 CDT 2009

May I suggest that "Shrink sewing" would be best done by using a tape or
webbing rather than just thread to supply the new structure.  Then use a
walking foot  (Singer 111 or 211 or old reliable West German Pfaff 145 - my
favorite rock crusher, as an example) to work the excess fabric in.

An experienced technician can do that by "feel" but more reliable and
consistent results will come from match marking or indexing the webbing and
the fabric.  Let the machine do the work, but control it to the indexing as
you go.

Don Piccard
www.N6US.com - new revision up now...
612 333 6912

-----Original Message-----
From: balloon-makers-bounces at taleos.com
[mailto:balloon-makers-bounces at taleos.com] On Behalf Of Jon Radowski
Sent: Thursday, May 07, 2009 10:31 AM
To: cloudhoppers at yahoogroups.com; balloon-makers at taleos.com
Subject: Re: [Balloon-makers] [cloudhoppers] Problem with homebuilt
parachute

(Cross-posting this to Balloon-Makers as it has pertinent information
for both lists)

Re: Jim Pratt --- That's essentially the same process I use to tie in
a brand new parachute. Good suggestions, but he's got more underlying
problems than just short line lengths. They are a few inches short,
but no amount of re-tying will fix this problem.

-----

Ian: Kasey and Don hit the nail on the head - there is no
circumferential stress on the top opening (girdle). The top edges of
each of the gores are allowed to billow up between the vertical
overlying load tapes when they should be straight across, under
tension (the "cutting edge"). There are two ways so attempt fixing
this, as Kasey suggested - shrink-sew the circumferential girdle tape
and hope for the best, or let out the overlying vertical load tapes a
little.

Before you start, you should take current measurements of the diameter
of each overlying load tape (all the way from one side, across the
crown ring, to the other) and also measure the width of each gore at
the circumferential load tape (add these up to find the
circumference). Doing simple geometry will probably show that the
circumference of the top opening is actually larger than it should be
for the measured diameter, and that's why your gores are billowing up.
The parachute valve tries valiantly to do it's job, but it can never
quite puff up enough to make the seal.

This factory-built Colt 31 also exhibits the same traits, so
apparently Jacobs did an excellent job copying the design!
http://www.njhotair.com/images/local/20021103/Dscn2544.jpg
In this balloon's case, the parachute has sufficient extra diameter so
that it is let out enough to be able to billow up and make the proper
seal against the circumferential girdle. I've never observed any
leakage problems when flying it or crewing for it.

I also noticed that you've got an 8-sided parachute (Viva-style) in a
16-gore balloon. Cameron Balloons has a habit of doing this (putting a
12-gore parachute in a 24-gore N-series, Z-series, etc.), and it's
perfectly fine as long as there's sufficient overlap to account for
the difference in parachute overlap (radius) at each even or odd
vertical load tape on the envelope. However, in your balloon's case,
the parachute overlap is minimal in areas, and may also play a minor
part in the leakage problem. I prefer an overlap of about 16"/40cm,
which is certainly not there. You'll want at least an 8"/20cm overlap
minimum.

An almost insignificant extra issue is that the parachute valve is not
quite centered in the hole due to "slightly off" line lengths.
However, the small-ish diameter of the parachute is a much higher
priority issue that will need to be addressed when the envelope's top
geometry is fixed (if using option 2).

Option 1 (shrink-sewing) should be undertaken first, as it's easiest
to accomplish and with it comes the fewest other "required fixes."
However, there's a lot of extra circumferential length to suck up in
each gore, and it may very well not be possible to shrink it all up
enough by sewing. It's worth a shot, though.

To shrink-sew, set up a double-needle sewing machine to have as close
to the maximum top and bottom thread tension possible (of course
without snapping threads). This means screwing down the bobbin tension
springs to get maximum resistance, and turning the top tension
thumbwheels clockwise to match the bottom tension.

When sewing for maximum shrinkage, do not pull on the back side of the
load tape/fabric as it advances through the machine. You want the
material to pucker as much as possible (opposite how you'd normally
sew), so let the machine take it through on its own accord. You can
even increase the amount of stitching (and therefore shrinkage) by
holding back the front of the material going under the presser foot -
making the sewing machine try to forcefully pull it out of your hands
by the stitching advance.

Shrink-sewing is best accomplished gradually - i.e. set your machine
up for high tension, and make one double-needle stitching run around
the circumference of the top girdle. Re-measure the average width of
the gore at the girdle to see how much of a change there was during
the first lap, and if it's not sufficient (it probably won't be on the
first go-around), do it again. If after three or four laps the
circumference has not shrunk up enough to match the diameter, it might
be time to go with Option 2 - but if you're getting very close, it's
worth another lap or two.

Option 2 - increasing the diameter of the overlying tapes - may be
more appropriate for the amount of excess circumference shown. If this
technique is used to make the fix, be prepared to build a new
parachute valve to fit the larger diameter opening, or you might
instead choose to add a perimeter to the parachute rather than start
from scratch. Either way you do it will probably wind up involving
about the same amount of labor, so I'd personally choose to make a new
parachute rather than improving the existing one. There's not much
material and cost involved, so it's usually best to start from
scratch. Since yours is an 8-gore parachute in a 16-gore balloon, it
should compel you even more to start over with a brand new one. You
probably won't need new centering lines, and you can certainly re-use
the shroud lines (from the perimeter to the pulley).

To find the increase in diameter necessary for the overlying tapes,
you must first find the total circumference of the top girdle by
measuring and recording each gore's width from the center of each
vertical load tape to the next at the girdle. This circumference
amount is your fixed baseline to work from. From that point, do your
simple geometry to find the ideal diameter of this circle. You'll
likely find that the overlying tapes are shorter than the theoretical
diameter you need to fit your measured circumference.

The easiest but not quite most elegant solution is to cut the
overlying tapes at least 12"/30cm above the top girdle to leave
sufficient room for a spliced extension without involving fabric. You
will want to use an overlap of at least 12"/30cm for each load tape
splice. There will be two overlapped splices in close proximity to
each other along each free tape, with only a short distance between
the two (the distance of the extension) - hence the less-than-elegant
solution.

You might choose instead to replace all the overlying tapes and
construct an entirely new spiderweb from the girdle to the crown ring.
This still involves splicing it in, but there will be only one splice.
Again, cut the overlying tapes at least 12"/30cm above the top girdle
to leave sufficient room for an overlap splice without involving
fabric.

A third and much more elegant solution is to leave the overlying tapes
alone near the girdle and instead concentrate on adding the extension
near the crown ring. There's more labor involved in this case, since
there is a circumferential tape near the crown ring to remove before
you can extend the vertical overlying tapes in this area. Once this
circumferential "keeper" tape is removed, unstitch the overlying load
tapes' turnbacks. There's a high probability that there will not be
enough existing load tape to re-sew the turnbacks with enough overlap
once they are let out the appropriate amount to make the proper
diameter. Instead, you'll likely need to add a load tape loop around
the crown ring which will sandwich both sides of the original
overlying tape, again with a sewn length of at least 12"/30cm. Trim
and melt the end of the original tape so that the end of the tape is
even with the crown ring, to make it easy to do the sandwich without
having extra load tape in the way, and to have a guide for easy
installation.

I might suggest using a longer "sandwich piece" than necessary (longer
overlap distance - not longer diameter), sewn with a single needle
stitch for temporary fitment. After the top tapes are extended and a
new parachute is installed to fit, do a test inflation to make sure
all works well. Then go back and reinforce the overlaps with the
proper stitching to seal the deal (and if wanted, add a new
circumferential keeper tape at the crown ring - but it's not
necessary).

New parachute sizing is another simple matter of geometry once the top
girdle circumference is measured and recorded, so I won't go there
unless you need assistance.

I hope one of these two options works (preferably #1, shrink-sewing)!

Good luck,
Jon

Soft Landings,
Jon Radowski
--
http://www.apexballoons.com
http://www.hotair.tv
http://www.hotairships.com
Elverson, PA - 908-208-1869

On Wed, May 6, 2009 at 10:01 PM, j p <av8tor17b at yahoo.com> wrote:
>
> Alright- I see the problem.
>
> Your lines are very close to being correct- but still a bit long.  Also-
it
> is possible they are not all the same distance from the center of the
crown
> ring to the tie off loop.  I see a few spots where the length is not
exactly
> even on the load tapes over that distance.
>
> I am left handed, and you may have to reverse these directions for it to
> work- but here is how I would rig from here:
>
> Here is my first suggestion:
> 1.  Using two people, expose the inside of the balloon along one gore, so
> that you have the tie off loop exposed. Tighten the line along the load
> tape up to the edge. Now look at how much overlap there is of the
parachute
> edge.  The cord should be about 4 to 5 inches shorter when tied than the
> edge of the balloon. I would wager than right now you've got about three
> inches.  Take one to two inches out of the line, and stretch it again. You
> should have proper overlap now.
>
> 2. Record on a sheet of paper the gore number, and the length of that
> distance, from the loop, to the edge of the balloon.  It SHOULD be
identical
> on all 16 gores. It is possible that it is NOT the same.  IF it's off by
> more than an inch or so on any particular gore, that is part of the
> problem.   The solution then is to repeat tying each cord until you have
> proper identical overlap. Then reinflate and try again, and see how it
fits.
>
> 3.  Based on the visual, I would say that your current length of 211
should
> probably be 208 or 209.  That should fix it.  The only problem may be if
> there is a different anywhere of the distance from the center of the crown
> ring to the tie off loop.  If one load tape is longer above the edge of
the
> balloon, or if the panels were not identical, and there is a difference of
> length from the tie off to the edge of the balloon, then you would have to
> do each line individually to get a good fit.
>
> Does that make sense?
>
> Jim

On Wed, May 6, 2009 at 10:46 PM, Kasey Schwemmer <kaseyict at yahoo.com> wrote:
>
> Hey Ian,
>
> How much overlap is there on the parachute?
>
> I had a couple thoughts about it...
>
> 1.) It looks like maybe the top opening could be a bit larger than the
> amount of webbing allowed. i.e. Say the top is 12 ft across. Perhaps the
> webbing is only 11' 9" making the fabric inbetween the vertical webbing
for
> each gore bunch up a bit. So maybe letting out a few inches per gore would
> give it a better fit?? (hope that makes sense)
>
> 2.) Another builder on the list once recommended to me to sew back over
the
> edge of the opening a few times, which is supposed to cause the opening to
> shrink a little, creating a better, tighter fit. This was for the turning
> vents in my 32k though, not the top vent.
>
> Hope that helps! And that my thoughts arent too far from correct... ;]
>
> Happy Hopping!
> Kasey Schwemmer
>
> ________________________________
> From: Aerovision Balloons <aerovision.balloons at virgin.net>
> To: cloudhoppers at yahoogroups.com
> Sent: Wednesday, May 6, 2009 4:52:15 PM
> Subject: [cloudhoppers] XLTA - Problem with homebuilt parachute
>
> I really wish that I was joining you guys - maybe another year..
>
>
>
> Back here in the UK, we have a Russian DKBA built 77 envelope that is
> classified as homebuilt..  Flies beautifully and made out of polyester.
> Heavy, but nice envelope.
>
>
>
> Also, we have a South African (Jacob's) homebuilt 16 gore 35 envelope (RSA
> ripstop - the type that Kavanaugh use).  We have spent some time getting
the
> turning vents sorted and working, but cannot get the parachute to stop
> leaking at the edges, no matter whether we lengthen or shorten the lines.
>
>
>
> Wonder if any of you XLTAers could offer us some advice.  We have in
flight
> photos of the chute from above and ones from the ground looking up in to
the
> envelope which I can private e-mail.
>
>
>
> Any help very much appreciated.
>
>
>
>
>
> Best regards,
>
>
>
> Ian
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