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what is everyone's tolerances for a PC to be considered non-symmetrical?
I understand that sewing mesh to ZP and to tape in a circle is difficult and there may be a couple of mm difference in load tape lengths, but we have just received a PC that has a load tape length of 470mm (18.504 inches) and the opposing tape is 460mm (18.110) in length.
All the PC's I have ever jumped have been near perfect so this one would seem to me to be too far out. I'm interested to hear what others think?
Thanks for your input, I will email the manufacturer to see what their manufacturing tolerances are as well.

My rule of thumb is 1 cm.

If it's within 1 cm, I don't worry about it. If it's more than that, I get another PC.

Personally, my first thought would be: WTF?!?!?! Because, for this 1cm to make it in your hands, at least two unspeakable acts of sloppiness would have had happened: person cutting and/or sewing the tape was sloppy, and Quality Control was either sloppy or nonexistent. 1cm is way larger than reasonable accuracy of measurement, cutting, and sewing.

BASE and such sloppiness are not compatible.

I agree that in general, BASE is not the place for sloppiness, but some jumps are more forgiving of others.

I think 1 cm is an acceptable tolerance for most jumps, if for no other reason, I think it would be silly to apply extremely tight tolerances to a system component that is not rigid.

Bridles are typically attached using a larkshead knot. Do you make sure the knot is perfectly symmetrical and tack it in place? Do you do the same at the bridle attachment point of the canopy? Do you somehow make sure that pull force exerted by the bridle on the pins will be perfectly symmetrical?

The point I am trying to make here is that the main benefit of a perfectly symmetrical pilot chute *may* be more psychological than performance-oriented. Since tunnel time is very expensive I don't know that anyone has really studied what the tolerances should be on BASE pilot chutes but I strongly suspect that there is no real benefit to super-tight tolerances.

Walt

True. I'm sure 1cm won't affect PC performance much. That's not my point, however.

If 1cm diff was produced when cutting pieces of tape, any normal person would at a very least do a sanity check when assembling something symmetrical from pieces: lay all pieces on top of each other and verify they're all the same length (and ensure the length is per spec). If that was the case and the check was not done, that's some serious negligence right there.

If 1cm diff was produced when sewing the pieces together, again, you would think that the proper positions of stitches would be marked first and followed at least with some reasonable precision (I don't think 1/8" or 3mm precision is that hard - I have little sewing experience, yet I can do 3mm. You need to be blind not to see the deviation of the stitch from your marks by 3mm. Or intoxicated.)

And then, QC missed it, too. Or they don't even know what QC is at all.

So when you encounter such examples of sloppiness and negligence, you ought to start thinking, "hmmm... what else they slopped away or neglected?!"

Partied in the same room where the spools of thread are stored, and sparks from those little sparky fireworks damaged the thread used to make life saving equipment?! Cut the tapes drunk, made a small erroneous cut too short, said "ooops", and then cut longer and used this defective piece in production?! Stored fabric or harness webbing close to some chemicals that weaken nylon?!

I wouldn't tolerate negligence like this on principle, regardless of whether it actually affects visible performance or not. But everyone has their preferences.

Even worse is when a hot knife is used on the center line near the crown, perhaps resulting in a small hook, which can grab the mesh and result in a total mal on the pilot chute. careful inspection is key.

I've seen a PC go out of trim by almost a centimeter over time. It needn't have been that way from the manufacturer.

He did say "we have just received a PC that has a load tape length of 470mm (18.504 inches) and the opposing tape is 460mm (18.110) in length".

Even if (?) PCs lose their symmetry in several months while waiting for the sale, I think it's healthy to ask manufacturer for nothing but excellence when it comes to BASE equipment. Otherwise, sloppiness will proliferate. ("don't worry, it's OK... left risers 2 inches shorter? don't worry, we made left lines 2 inches longer... it's alright... it'll work... it makes no difference...")