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alexey

Technical question about packing volume

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Can somebody describe how manufacturers calculate necessary container measurements for preset volume of canopies?

For example, if I calculate “deliberate” size of Javelin J 2, I found:
Packing volume – 1\2 * length * width * height of the reserve packing tray.
1\2*12*10,5*4=252 c.in.

But, as you know – in that size I can pack 170-210 reserve, 400-500 c.in.

Is there any coefficient (for multiplying “calculated” volume) for designing and manufacturing of a reserve pack tray?

Sorry for bad English…
Lexa

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I haven't taken geometry for a long time, but I believe that you are using something like the formula for the volume of a pyramid (1/2 base x height) not a cube, which is roughly what a main pack tray is. The correct formula is L x W x H = V. (12 x 10 x 5.4 = 648 cu.in.) Add the volume of the bag, and risers, and links to the volume of the canopy, and it comes out about right, doesn't it. No magic here.

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I think he may be referring to a reserve container? I've found main container volumes pretty straight forward, but reserve volumes get pretty whacky. In particular, the width of the pack tray plays a pretty large role in how accurate the calculated volume for a given "target canopy" is.

I've had this come up a couple of times since I have the measured container volumes in the Infinity owners manual. Those numbers are based on straight lines and perfect angles- things that don't exist when packing a parachute. We will change that to a list of compatible canopies the next time we revise the manual:)

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Juggling numbers is an amusing way to ... amuse yourself.
The only accurate numbers come from packing a bunch of different canopies into a given container, then asking the rigger which was easy, moderate or difficult to close.
Ergo, you can ignore most numbers published by canopy manufacturers and only trust recommendations made by container manufacturers like ... say Bill Booth or Kelly Farrington.

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Quote


Can somebody describe how manufacturers calculate necessary container measurements for preset volume of canopies?

For example, if I calculate “deliberate” size of Javelin J 2, I found:
Packing volume – 1\2 * length * width * height of the reserve packing tray.
1\2*12*10,5*4=252 c.in.


Canopy volume estimation for reserves is truly one of the dark arts.

Mick.
But, as you know – in that size I can pack 170-210 reserve, 400-500 c.in.

Is there any coefficient (for multiplying “calculated” volume) for designing and manufacturing of a reserve pack tray?

Sorry for bad English…

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Just to add to our problems... Two "identical" reserves (same model from the same manufacturer) might vary up to 10% in pack volume, due to the actual thickness of the bolt of fabric they're made of, as well as several other reasons. Then humidity and temperature can also affect pack volume, as can the skill of the packer. All we can do as rig manufacturers is to give a range of model numbers of reserves that MIGHT fit in any particular rig. The closer you are to the bottom of that range you are when you order, the greater your chance of a reasonable fit. And as we all know, a too tight reserve container makes for a very uncomfortable rig.

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