Blind Faith

[SkymonkeyONE 4]

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I've been to PD's manufacturing facility. I've seen their cutting tables, and the way it used to be done (hot knife with a template). I've seen how they line canopies, and what kind of QC they go through. I was impressed. the cutting table can hold much tighter tolerances than hot knifing.

Well, my brother, let me tell you a little story:
The "other" team I jump on (the USASOC command demonstration parachute team) has 16 brand-new rigs with Flight Concepts StarTrac 1 and StarTrac 2 mains. We have blown up several of them, snapped A-lines on several more, and blown up sliders on others. All of these mains were cut with a laser plotter and are technically "accurate" in that regard. This, of course, has nothing to do with sewing tollerances, which was the subject of the original post.
What is the problem with our StarTracs then you ask? Well, in the "old" GlidePath days, they were cut by hand off of a stencil. Those parachutes were fine, but eventually the stencils wore out and then the owner of the "old" stencils took them with him when he left the company. The "new" stencils that they made were not perfect copies and the info plotted into the computer is off those "new" stencils, thus the problem. The canopies were just fixed with a fairly straightforward nose-mod on the center cells, but not before the damage was done to our necks and backs; not to mention equipment.
My point is, just because one manufacturer uses a laser cutter does not mean their product is "better" than one produced in the "old" manner. In the end, it is the sum of all things ( airfoil design, accuracy of cut, sewing tollerance and technique) that makes one parachute better than another.
Chuck
My webpage HERE

[GrumpySmurf 0]

And...
if you are doing an analog to digital conversion - make sure the analog copy is the best quality master you can find

• Quote

[Hooknswoop 19]

Dan & Chris-
To expand on Skycat's post;
Instead of ripping out a seam because the bobbin ran out and re-sewing, doubling the number of holes in the fabric, why not just make sure there is enough thread in the bobbin before starting the seam?
It seems to me that a small section, 3-5 inches, of overlap would be preferable to re-stitching the entire seam. I haven't run across a canopy that failed because of an overstitch in a seam.
Also Chris-,
For repairs, you said PA replaces the entire panel, but unless you replace the entire canopy, you will have at least one seam with double holes from a replaced panel. If replacing a panel resulted in less re-stitching and reduced the number of "extra" holes in the fabric, then it makes sense. But if replacing an entire panel results in more re-stiching than a patch, seems to me that a patch would be the way to go. Of course if I had access to a cutting table programmed with every panel on a canopy I was repairing, I would replace the entire panel too, because that would be esaier than a patch and would look nicer and help the re-sale value of the canopy vs. a patch.
Hook

[weid14 0]

in reply to:
My point is, just because one manufacturer uses a laser cutter does not mean their product is "better" than one produced in the "old" manner. In the end, it is the sum of all things ( airfoil design, accuracy of cut, sewing tollerance and technique) that makes one parachute better than another.
I didn't say it was better. I said the laser can hold a much tighter tolerance. tolerances are additive, tight control on as many as possible gives the best chance in the end for a decent final product.

[cobaltdan 0]

in our opinion overlapping stitching is not preferable to removing the seam and re-stitching.
first: when a seam is removed and then replaced our seamstress' incredibly, take care to re-sew the seam through the original needle marks(we use fabric pullers). if you inspect a re-done seam you will not be able to tell the difference.
next: even if a second set of holes were put in the material. the needle spacing is such that both methods re-seam or overlap seam exhibit equal strength, this is not about one vs the other breaking.
the difference is with a re-seam we can maintain much higher tollerances. putting in an overlapping seam creates an area with different tension on the fabric. you can visually see this as the material is pulled in causing wrinkles between the stitches.
if your goal is perfection, you do not overlap sew, as it makes it impossible to have uniform tension across the canopy's seams.
canopies are flexible membrane structures. the inflated shape is directly influenced by construction method in addition to design. random overlaped seams impose change in the tension pattern of the canopy. this changes slightly the inflated shape of the canopy. this is the basis for a series of filed patents by atair. we control the tension pattern on our canopies by design and specific construction.
on some canopy designs you migh not notice the difference caused by minor variances in seam tensions but on modern canopy designs it is increasingly more important, to insure consistent opening characteristics, and high aerodynamic efficiency. my partners, insane attention to construction detail is a major reason why we have been able to push atair canopies designs so far. who would have thought that a 9 cell could be ranked 2nd in distance after a year competeing against all x-braced, or that 9 cell designs could prove efficient enough to be reduced to 65' with loadings approach ing 4-1....
as far as laser cutters vs. hotknife patterns: atair is the proud owner of a brandnew laser cutting table. however we do not use the laser table to cut production work. the machine is used to cut prototypes and production patterns. hot knifed patterns are equally accurate to laser cut material, in fact we can hold higher tollerences as far as cuting exactly on the grain. when cutting one rib at at time a cutter exactly places the pattern on the grain before cutting. when laser cutting material all your parts are nested to plot out on to as large a piece oif fabric as will fit on your table typically 6' * 100'. it is not practical to lay a 100' long swath of fabric on your laser cutting table and be able to ensure that if you cut a straight line down the table it will fall exactly on your fabric grain line.
sincerely,
dan
atair

-one quick indication of construction quality is to inspect your tail tape seam. look if it is uniform and lies flat or if it is strongly wrinkled between the stitching.

[GrumpySmurf 0]

Dan, I think I may be so bold as to speak for alot of us here - thanx! Taking time out of you day to explain you fabrication and repair technique and why you chose this method is greatly appreciated.

[polarbear 1]

Yes, thank you. That is really good information...the kind that is hard to come by.
I hadn't thought about overlapping stitching causing unequal tension, but that makes sense.

[freeflir29 0]

That was a bit of reading but like the others...Thanks....It was worth my time. I wondered how much attention manufacturers were having to pay on High Performance canopies. It seems obvious to me that as canopies become more and more high performance the "slop" allowed in the tolerances decreases exponentially. So...it's good to know you guys are paying attention.
"Here I come to save the BOOBIES!"