potvinj

This NASA mission is the coolest! This site appears to have them all: http://phoenix.lpl.arizona.edu/imageCategories_lander.php These overhead photos taken by the MRO satellite shows the Phoenix lander, its jettisoned heatshield AND cut-away parachute: http://phoenix.lpl.arizona.edu/images.php?gID=647&cID=13 http://phoenix.lpl.arizona.edu/images.php?gID=650&cID=13 http://phoenix.lpl.arizona.edu/images.php?gID=651&cID=13 Man, I wish we could use Earth-orbiting sats to locate canopies lost in the corn...... :(

Very nice video. Thanks for sharing it with the rest of us. Notice that by the time you looked up, 1) the slider was already all the way down. 2) although the canopy had totally expanded to its full span length, the center cells were not inflated & the canopy appeared flattened. This suggests a case of bottom skin opening, which occured because the slider had lost its ability to generate drag and remain at the top of the suspension lines. So the slider did not slowdown the canopy expansion the way it was supposed to. This explanation is part of a pet theory of mine about hard openings http://www.pcprg.com/sliderdragcancel.pdf Finally you mention the opening lasting about 1.2 sec...Im thinking that the canopy opening itself lasted probably 0.5sec or less. J

I would like to echo what pilotdave has said, and with a simple calculation. See the estimates in: http://www.pcprg.com/fallspeedunderbaglock.pdf Given the numbers in current PC size and drag coefficients, and the dimensions of the human body, the fall rate could be either slower or faster than the belly-to-Earth fall rate - but not that much faster or slower. I have learned something today, since I always thought that the jumper would fall fatser, way faster. Jean

My understanding of "slider rebound" is that, right after the canopy is out of the bag, the slider is somehow not resting against the stops. As a result, the relative wind throws the slider against the stops. This is then followed by the slider "rebounding" off the stops, aided in part by the contacts forces between the stops and slider grommets, and also by the cancelled slider drag as you pointed out. Our main point though is that slider drag can be cancelled even when the slider rests squarely against the stops (ie no rebound necessary) - all is needed are the "right" initial flows during canopy unfolding, affecting slider aerodynamics in the "wrong" way. This could happen even with a "perfect" pack job. We mentioned dome sliders as a remedy, but no doubt other solutions that we are not aware of probably exist

Yup! I have seen those bottom-skin openings before. Note that the canopy appears fully extended prior to the cells being inflated. Ouch! Anyway Peek and I just posted a possible explanation for this kind of openings. Its a hypothesis, mind you, but one that makes sense at least to us. http://www.pcprg.com/sliderdragcancel.pdf

Hello, peek and I have been thinking long and hard on the possible causes of hard openings. There are many as you know. But we came up with one that we think is new: namely, that the slider comes down the suspension lines prematuraly because of its drag being cancelled by an anomalous pressure buildup on its top surface. To learn the details please go to http://www.pcprg.com/sliderdragcancel.pdf Comments are welcome. Jean

I would ask 2 questions to your rigger: 1) Can the rig be legally jumped wihtout the RSL? remember, at least one rig manufacturer has recently mandated RSLs on all its rig 2) Supposing that the rig can be jumped w/o the RSL, what do the packing instructions say about the routing of the ripchord cable?

Correction: the technical standard for TSO C23c is defined by SAE AS8015A. The standard NAS 804 is for TSO C23b.

Like you Im using older mains that have hundreds of jumps and a "few" hours of UV exposure. I dont fear this gear. But although I havent realized it, Im sure the descent rate and the opening time have increased slightly since I began jumping it 16 yrs ago. No big deal for openings at 3000', but that could be an issue for openings much closer to the ground. In the case of the TSO that affects the old gear discussed here (i.e. C23c/NAS-804), the reserve canopy must be "fully opened" within 3 seconds from pack opening, in a cut-away scenario. Also, after opening it must descend no faster than 21ft/sec when loaded at 170lb. A canopy that deploys and opens in 3.5 sec, and or descend at 22ft/sec as a result of higher porosity would still be an acceptable main. But it would no longer qualify as a reserve. So Im thinking that's what manufacturers are looking at when evaluating old gear. Now I see your point that if it opened in 3.5sec and descended at 22fps at year-20, it must have done that too at year-19. Im not sure that we have the technology today to nail a canopy opening time and ROD within 10% or less, without performing a quazillion test jumps. I guess the next best thing is to establish a time marker (or "re-certification time"; not necessarily a "limit") for which performance reduction can be assessed in a meaningful manner, and lead to an objective decision on whether a canopy can be put back into the field. I think that PD, Strong and others use such times that way.

From the info that has been submitted in this discussion I can see that fabric aging and wear are pretty much dependent on the history and type of each individual rig: - A skydiver's reserve repacked 3 times/year over twenty years (with the rig jumped 10 months/year) will age a lot faster than a pilot's rig that is repacked twice a year, used in the cockpit 4 months/year and stored in ideal conditions over the same two decades. - For reasons that have to do with descent and flying performance, I can see the aging issue for rounds being different from that of squares. - And the material used to make each rig also has an effect. I think that we should NOT have a blanket age limit for all equipment (even though some contries have done it), less we want to throw away perfectly good equipment. I say: leave it to the individual manufacturer to set their own retirement policy .

Thanks for the data. Here's a link to an old thread that discussed other experiments that manufacturers have done. See entry by billvon, dated Sep 28, 2006. http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=2456291;search_string=potvinj;#2456291 Edited by slotperfect to make the link clicky!

Hummm...I see your point. But then, if the sweat was really a factor, should'nt we see drastic fabric aging in most old parachute equipment? As far as I know, not all equipment shows that. But obviously, that should be a factor to consider. As for "stressing the fabric" - I guess that could come from using strong packing clips, or putting a canopy in an undersized deploy bag, thumb-testing, or any other general "canopy handling" strategies that would cause thread displacement - and hence porosity changes. It seems to me that just handling the fabric should'nt really cause such thread displacement but thats my understanding of what I have read elsewhere (mostly statements of fact, but no numbers from actual measurements I might add).

Another thing about the chemical change of fabric over the years. Someone from the industry should chime in on this but I have read somewhere that different batches of nylon fabric come with different actual breaking strengths (but same rated breaking strength), so thread degradation would be different with each batch. That would mean that individual canopies would perform differently, say over a 20- 50yrs stretch, with regards to meeting TSO-mandated strength requirements. Yes?

Thanks for recalling those passages from Poynter's manuals. They sure do point to something that is rarely mentioned. The way I understand this age/wear debate is that fabric on reserves can be damaged in two ways mainly: - application of stress on the fabric during packing - continuous changes over time, of nylon chemistry even in ideal storage conditions. Concerning the latter there are reports out there that show how nylon degrades over the years, under all sorts of storage humidty and temperature considtions (PM me if you want copies). They seem to point to a reduction of about 10 -30% of actual breaking strength over a period of about 20yrs. Now, as actual breaking strength (of a given batch of fabric) is typically higher than the rated (or required) breaking strength, such degradation can still yield strong enough cloth as examplified in P2. Unfortunately, the results of these studies are hard to compare since the experimental conditions (and fabric and nylon types) are different - so their use to riggers and manufacturers is rather limited. But as you said, at least old canopies were built like tanks so that a "little" aging should not affect the rated/required strength. Heck, I have several 40yr-old USAF C-9 canopies in my basement that have survived repeated 40lbs tests! It seems that the stresses applied during packing is what concerns PD and others the most. I can see this at least with tight rigs, where some areas of the canopy get really stretched - to levels high enough to affect the permeability of the fabric. As related by billvon in a previous thread, PD and Precision (?) have performed experiments showing this. That said, one would conclude that canopies packed in "looser" rigs would not be as susceptible, which would jive with the findings of other manufacturers that show little permeability changes. So I would agree that the issue of retirement age should be left to each manufacturer to determine. After all, - different type of parachutes are used differently - the manufacturer should have a good idea of the ways the equipement is used.

I think you just said it: "....With the boom in "x-games" and adventure type of sports I expected the number of jumpers to be growing by large amounts...." Today skydiving has to compete with many more "adventure"-type activities than in the past. Also, Im wondoring whether, as a whole, the new generation is that interested in "real" adventure - given that it has been overexposed to it on TV, and "experienced" it since young age with computer games. When I started skydiving, you seldom saw anything like that on TV - so I was really intrigued when, after watching the movie Point Break, I was given the opportunity to give skydiving a try. My point here is that there seem to be a fine line between exposing the sport at the right level to get lots of new recruits, and over-exposing it to the point of making it look "old hat". Or, it could be simply an "old vs new" generation thing, where junior is not really interested to do stuff that mom and dad have done, or are doing.