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skydiverek

Vigil service bulletin from Nov 9

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dorbie

For those skydivers who jump a repack cycle without an AAD when the 4-year service rolls around that represents a 12.5% lack of AAD coverage, if all other things were equal that would be the statistical equivalent of poor reliability rate, but because it's couched as an informed choice and part of the service plan the risk that represents is never mentioned.



Most Cypres users manage to figure out which 3 weeks in the 13-month service window works best for them. For example, it's winter now in Minnesota and all the bears are white, which makes a good time for the 4-year service.

Even f you jump year-round, the 3 weeks it takes for service are about 1.5% of the 4-year cycle.

Reliability is not the same as availability, and putting the words "statistical equivalent" in front does not make it a good analogy.

I jump an M2.

Mark

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mark


Most Cypres users manage to figure out which 3 weeks in the 13-month service window works best for them.....
Even f you jump year-round, the 3 weeks it takes for service are about 1.5% of the 4-year cycle.

Reliability is not the same as availability, and putting the words "statistical equivalent" in front does not make it a good analogy.



This is not merely an analogy. It is the statistical equivalent "all other things being equal", primarily that you jump the same, that's the caveat. I chose my words carefully, they are accurate.

Yes, some ground themselves for the window, I was talking about the others, that much at least was clear, and even within that group behavior varies, 180 days vs. 3 weeks. As I said it depends on jumper conduct in the field.

You not accepting that it can be the statistical equivalent from a safety point of view because it is a visible imposition of an inconvenient choice only reinforces my second point. For you it remains a hidden risk associated with particular AADs because those jumpers could have chosen not to jump, well they could also have chosen another AAD. You are in fact doing what I described, dismissing a risk factor because of the way it is presented.

Again my point is not to favor one AAD over another or to influence anyone's conduct, it's to point out that something like a service cycle is not merely a no-brainer, it is a complex proposition with associated risk in a different form, so shaming with analogies to internal combustion engine maintenance is a bit misguided.

Debating the details about 3 weeks vs. 180 days vs. what fraction of jumpers don't ground themselves and can't rent an AAD only affect the degree of exposure you attribute to this, they don't alter the underlying point that it is not some simplistic straightforward choice.

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My memory was that short term rental units, at a reasonable price, are available for those that would not want to have any down time. Of course this would require a little extra coordination with a rigger to be willing to do the swap when the original AAD comes back from service. SSK did the 4 year service on my unit in slightly less than the 2 week quoted time.
People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

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cjdskydiver

Do you trust that a 20 year-old cutter will fire...?



Well seeing that cypres requires the cutters to be inspected every 4 years I do not trust that a cypres cutter will fire.

Again, the sample size might be to small to determin that vigil cutters age badly and are inherently unreliable because of that. But I dont think that is the case. Since 2003 vigil has entered the market, that means that there are cutters in the field over 12 years old. I nor you have any statistics to prove or disprove that these vigil cutters are more or less reliable accept a talk a PIA that I guess was held by someone representing cypres or representing a party selling cypres (assumption on my part but you state it like he had some pretty good inside info on cypres, so I assume it was not a guy selling vigils or argus or fxcs :P)

And yes, I've paid the Belgiums a lot of money (yeah not really an argument, you can pay a lot of money to a nigerian prince and get away broke), they have been making safety equipment since 86, so Im happy to trust their 20 year old cutters if they say they are reliable. (didnt cypres shorten its lifespan at some point?)

Edited to add: Do you replace or let the mfr test the airbags in your car every 4 years? its also a electronic life saving devide
Parachute gear garage sale at :http://www.usedparachutes.eu

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rastapara

Well seeing that cypres requires the cutters to be inspected every 4 years I do not trust that a cypres cutter will fire.



Do you trust your reserve to open?
Heck, someone is always wanting to inspect it every 180 days (or maybe some other number where you live).
Must be something dangerous with it??

You may argue engineering quality if you want, but I think the 4 year Cypres cutter requirement is clearly based on their inspection philosophy rather than engineering issues. Cypres cutters have clearly been the most trouble free. (Although one can, say, crack the hard plastic where the wires lead in to Cypres 2 cutters) Also, the design philosophy of their one blade cutter seems superior when explained, compared to the two blade (circular blade) that others have had to go with due to the patents Airtec uses.

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pchapman

compared to the two blade (circular blade) that others have had to go with due to the patents Airtec uses.



You prompted a quick search:

US3640169 filed in 1970 has the concave conical piston blade and some extra length to distance the charge from the cutter.

US3523477 filed in 1969 has a "hollow annular cutter" to cut reefing lines.

US3246396 filed earlier in 1963 has a straight "cutting blade" an anvil and even a deformable tubular shock absorber on the anvil, in the diagram the blade is clearly a V shape.

US2755550 filed in 1955 is a reefing line cutter with an explosive charge driving a piston driven blade onto an anvil to cut reefing lines and what is clearly a V blade in the diagrams.

So I don't think patent exclusivity can be a sound reason for this cutter blade geometry.

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That's an interesting line of inquiry you've dug up.

The way I've always heard it was that patents somehow locked up the single cutter for Cypres, which is why others are stuck with circular cutters. Anyone hear different?

Seemed odd to me that a straight line (like the cutting edge of a flint tool as used by proto-humans on the plains of Africa) could be patented for cutting something, but patents have their own complexities and exist in their own world...:S

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pchapman

The way I've always heard it was that patents somehow locked up the single cutter for Cypres, which is why others are stuck with circular cutters. Anyone hear different?



Out of curiosity I read up on a few AAD related things recently. One observation in a report/analysis I saw was that when you have a reefing system a double sided cut from a circular blade makes sense because the system works if either side is cut so it adds some redundancy but with a reserve closing loop that is not the case, if one side of the circular blade fails it can be very bad so in a sense it undermines reliability (in the opinion of that author). I find it interesting that a reliability improvement for one application might become a reliability detriment in another quite similar application.

The patent record seems to indicate annular style cutters were designed as an improvement on V blade cutters for their INTENDED application, that application was not cutting closing loops.

All of those early patents would represent prior art but Aritec might still have had a novel product with that broad V wedge punching through a sealed housing, not so innovative if you know the 1963 prior art but OK let's assume they could claim that. It's all still moot, even if they were able to patent it the first sale of a Cypres unit in 1991 would date any patents covering that cutter design. So any original exclusivity has expired by now and only more recent innovation could remain protected.

Vigil use a circular blade but state that their cutter will "eventually melt the loop" due to internal cutter heating, and that ensures loop separation. I'm glad my loop is guaranteed to separate "eventually" ;)

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I believe Vigil could not use a 'V' shaped cutter due to Airtect patent. So they used a circular one to workr around it.

On a 'V' shaped cutter, 100% of cutting force is delivered to one place in the loop, on circular cutter it is 50% delivered to two places on the loop.

Also, 'V' shaped cutter allowes more room for the cut loop to escape, and not be trapped between the blade and the cutter casing.

Cypres's blade is also harder that Vigil's blade.

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pchapman

Do you trust your reserve to open?
Heck, someone is always wanting to inspect it every 180 days (or maybe some other number where you live).
Must be something dangerous with it??



If it's been packed without opening/airing for four years - no I wouldn't; F1-11 or not.

But a canopy is not a cutter, so I concede your point.:)
"That formation-stuff in freefall is just fun and games but with an open parachute it's starting to sound like, you know, an extreme sport."
~mom

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skydiverek

I believe Vigil could not use a 'V' shaped cutter due to Airtect patent. So they used a circular one to workr around it.

On a 'V' shaped cutter, 100% of cutting force is delivered to one place in the loop, on circular cutter it is 50% delivered to two places on the loop.

Also, 'V' shaped cutter allowes more room for the cut loop to escape, and not be trapped between the blade and the cutter casing.

Cypres's blade is also harder that Vigil's blade.



The prior art I shared above shows the patent US2755550 had a broad cutting blade with a V tip and was filed in 1955. I have not seen an Airtec wedge cutter patent. Even if patentable and patented the Airtec design having been offered for sale in 1991 would have lost any patent protection a few years ago.

There is additional prior art, for example US3175289 filed in 1962 is a pyrotechnically driven cable cutter piston with a broad V wedge with a slight curve to the V.

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