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Jeff5050

PD's permeability test

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Hi Jeff,

Quote

Can someone shed some light . . .



Back in the early 90's I visited their mfg facility in Miami Beach.

John Leblanc took a swatch of new F-111 and put it over this air mover machine and got a value reading. He then wrinkled this same piece of fabric in his hands a few times & then again put it over the machine. He got a substantially different reading.

Re: ' . . .how they come up with a certain CFM number . . . '

They hold the TSO-aurthorization. They get to establish whatever number that they want. It is the nature of the beast.

Jerry Baumchen

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Thanks Jerry,

Makes sense to me. Would it be pretty common that F-11 thats 20 years old that visually looks great just from time alone degrades enough to fail there CFM rating? Understanding theres a lot of other factors involved the would also cause it to fail. What are you thoughts on 1990's reserves being in service today?

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Have you read the PD reserve owners manual? It talks quite a bit about these things. They currently authorize a yearly repack cycle where the local laws allow for it. And they specify a permeability test after 40 repacks. That would be 40 years later. As far as service life goes, they say it is undetermined, and is based on condition.

Link to the manual:

http://www.performancedesigns.com/docs/Reserve_manual.pdf
Always remember the brave children who died defending your right to bear arms. Freedom is not free.

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Your statement of the annual repack per PD is correct, but it also says "Currently, up to one-year repack cycles are authorized for Performance Designs reserve canopies when cared for properly. But it also says in the next sentence, You must use the shortest repack cycle of the your country’s applicable legal requirements, harness/ container manufacturer’s requirements, and AAD manufacturer’s requirements.


With that, in the USA as per the FAA 180 day repack cycle, if 40 blocks were marked on the data panel, with no reserve activations, assuming it got packed every "180" days would be just shy of 20 years, not 40...

Not saying you're statement is incorrect, but a new inexperienced rigger may read your statement and assume without further review that the FAA now requires an annual repack and not every 180 days...

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One big thing I have noticed is canopies that have been packed their whole life from a messy rigger, even after a few neat pack cycles "looks" a lot worse than ones that have been packed their whole life by a neat packer.

I have been considering making my own permability tester out of automotive parts since I already have a flow bench that can give calibrated airflows and I can control the speed to achieve a specific amount of pressure. I think it would simply require a 1 sq foot fixture.

-Michael

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If a customer brought you early 90's PDR that only had a few repacks checked in the box and zero rides checked without knowing any of the history on it, how would you proceed. Would a visual and a rip test on it be enough to satisfy its serviceability to you? Just curious, and I'm not a rigger.

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To answer your question :

One put the fabric sample well spread between two rigid plates made of metal or plastic. Those two plates have a hole of a known area, square or circular. One place the mounting (plates/fabric) into an air column (which is fed with an airflow generated by a compressor or a fan). The mounting is perpendicular to the air flow. The air can only goes thru the fabric since the junction between plates and air column is sealed.
Depending of the type of fabric, type of test, the standards required... the air flow is adjusted to make a specific pressure on the fabric (verified with a manometer). The volume of air flowing thru the fabric is measured with respect to the time like how many cubic feet per minute ie. 3 cubic feet per minute or 3 CFM.
Such a device is called a permeometer.
Learn from others mistakes, you will never live long enough to make them all.

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The PD reserve manual linked earlier in the thread specifically addresses this question: if there are any unknowns in the canopy's history or reasons to suspect it has incomplete history, you must do complete permeability testing (ie. send it to PD for factory inspection). This is because visual testing is not sufficient to establish the critical parameters of the fabric, without which the reserve is unsafe.
"Skydivers are highly emotional people. They get all excited about their magical black box full of mysterious life saving forces."

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