Porosity on a reserve

[cvfd1399 0]

I just bought a new rig and was just had a question about porosity. The rig is a mt1-xx it has a 4 jump camouflage main with bright white lines. The owner did not know how many jumps the reserve (Paraflite 370 sqft F-111 DOM 1990) had, but he said he tested the porisity of it to see and it came out a "5". Is this good? He said it was good, but I have no clue about porosity. what say ye?

disregard spelling

[mjosparky 3]

Did he say where he tested it? There are not that many permeability testing machines around. New the fabric should be 0-3 cfm so the 5 is not out of line.
Sparky

My idea of a fair fight is clubbing baby seals

[darkwing 4]

I'm with sparky. I'd add that if I tested the porosity and it came out unaccaptable I would have made a big note on the canopy saying "Not Airworthy for Reserve Use". Ordinarily I wouldn't expect a canopy from 1990 to have porosity problems, unless it had quite a few deployments and/or pack jobs on it.

The last time I told a reserve owner that his reserve wasn't airworthy he packed it himself anyway. After he got out of the hospital his lawyer called me. No problem. He wanted to sue the manufacturer of a canopy that two riggers said was worn out, then packed by a non-rigger. Ha Ha.

-- Jeff
My Skydiving History

[cvfd1399 0]

pm sent.

[scottjaco 0]

Why wasn't his reserve "air worthy"?

What happened when he used it?

[darkwing 4]

I forget the details, as it was a long time ago. I do remember that it was a surplus 26-foot Navy conical, which was a very popular reserve. I think that it convincingly failed a standard thumb test (i.e. you can push your thumb through the fabric). Anyway, it blew up when he used it.

-- Jeff
My Skydiving History

[mjosparky 3]

Quote

I forget the details, as it was a long time ago. I do remember that it was a surplus 26-foot Navy conical, which was a very popular reserve. I think that it convincingly failed a standard thumb test (i.e. you can push your thumb through the fabric). Anyway, it blew up when he used it.

Jeff,
My first reserve was a 26' navy and if he blew it up it had to be obvious it was trash. They were build hell for stout. Some people just have to learn the hard way.
Sparky

My idea of a fair fight is clubbing baby seals

[pchapman 262]

Quote

The owner did not know how many jumps the reserve (Paraflite 370 sqft F-111 DOM 1990) had, but he said he tested the porisity of it to see and it came out a "5". Is this good?]

I can't give a definitive answer but can add a little bit of related info:

Although it is above the "0-3" brand-new value for F-111-style fabric, 5 sounds acceptable. Worn from packing or whatever, but not ragged out. The very limited evidence I have for this:

I saw some test results by the Canadian military on a about a dozen used civilian student MAINS like Mantas. These were canopies in current use at a large Cessna drop zone, with ages likely in the 5 to 10 year range. (But with many sets of gear, no one canopy had an excessive number of jumps on it.)

The desired limit was no more than 13.0 cubic feet per minute. That's what it showed on the printouts, but it didn't say how "hard" a limit it was, especially given that a canopy with one cell outside the range would not be nearly as poor as one with most of its cells outside the range.

Most of the used canopies had porisities across different cells in the range 6-10 cfm, with an average of perhaps 7-9 cfm. The worse canopies would have much wider variation, such as measurements ranging from 6 to 22.

Tests were done typically on the upper surface nose of all cells, or also the upper surface tail for the center cell.

There were no really clear trends across the span of a canopy, but sometimes one could see higher porisities on the end and center cells. This matches the cells PD says to test when doing reserve pull tests.

Interestingly, a saw a couple canopies where exactly the reverse occurred, with lower porosities at the center and ends -- but those were canopies where the center and end cells were a different color. So different colors may wear slightly differently.

That's a topic I've never heard much discussed in skydiving, other than for particular bad batches of fabric, or about faster deterioration of some fluorescent colors in UV light. I think in paragliding and BASE jumping there's been some talk about the subject.

For the record, the porosity testing used a test area of 38 square cm, and 125 Pascals air pressure, using a "Textest FX 330-III" machine.

(I've used the term "porisity" as that's what skydivers say. In the aerodynamic decelerator design world, porosity has a slightly different meaning, and the term permeability is used instead.)