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.

Yup - that's a nice opening (and soft). For those folks that have large enough canopies (like a 150sqf canopy loaded at 200lbs), the jumper actually decelerates during the slider-up phase of the opening. So, when the slider heads down and the canopy starts expanding, the jumper's fall rate is slower and the resulting opening force is lowered (compared to that of a very fast opening - remember, canopy drag is proportional to the square of the fall speed). So, a long snivel is beneficial in most cases.

Good point.

Compared to what you went through my training had been "streamlined" already, along the lines described by winsor. My training did not include the stuff you described b/c my equipment was "more modern". But then we spent a lot of time on physiology, figuring out how to calculate from tables the time for decompression stops etc.
(They have a computer for this now).

So like in skydiving the equipment evolved, in a way to reduce the stuff to be covered in training - so the sport became more accessible. Not a bad thing really, but that makes the sport less interesting to those personality types previously described by tdog.

Ill be interested to see how the current generation of kids being brought up on computer/TV games will choose their entertainment in adulthood.

This is a very good discussion. I learned to scuba in the early 70's, attending 14 saturdays of pool and classroom training, followed by open-water testing in February in Quebec (after chainsawing our way to the water through thick ice). I quit scuba in the 1980s when I had to move to a place that had no lakes or oceans nearby (I took on mountaineering then).

I learned to skydive before the Piras fatality in the early 1990s.

Am I to understand that the bulk of scubadiving business today is being drawn from people going to fancy resorts near warm/clear ocans rather than going to their small local lakes and scuba clubs?
Has this led to the demise of local clubs and to the rise of the "occasional scubadiver"?

To me the evolution of scuba, skiiing, skydiving, etc. described in this thread have all to deal fundamentally with the competition with many other indoors/outdoors activities that have made their appearance since the 1980's; and also with the fact that some of them are cheaper and/or more convenient. Its like TV-watching: In the old days there were 3 channels only. Now we can choose from a few hundred channels! this mind-numbing choice can only lead to a decreasing (percentage)number of viewers per channel.

The way I see it (and others, in other threads...) the slow-down in skydiving is a result of many things, all happening at the same time:

1) the emergence, in the past 10 years, of many other, affordable extreme-type sports to the high-adrenaline crowd

2) the competition with other sport/activites like golf, scuba, motorcycling,etc. that are becoming more attractive to the older segment of skydivers

3) the competition with actitivities that are cheaper and more convenient (not necessarily those items
quoted in 2) above)

4) burn-out/boredom - Yes - skydiving may become
less exciting, after x000 jumps, to those who need high excitment on a regular basis

5) being less attractive to the current generation of young adults that have been raised by their TV and computer games
(I remember being rationed to 1 hr/day by my parents some 40 yrs ago - Im sure glad they did!).

etc. etc.

Finding the causes for the apparent death of skydiving is like finding those for hard openings: there are lots of factors involved, and they all contribute in small but equal manner.

Im glad you're bringing this up - in terms of the force generated, I have seen only a small number of cases where the snatch force IS the peak load. However, I agree with you that a brisk snatch, even when lower that max load, can hurt a lot since it is snatch that makes the body rotate from belly-to-Earth to toe-first. In that transition a wrong movement of the head and neck can bring pain and the feeling of hard opening.

Moreover, I have read elsewhere that a very brisk snatch could also precipitate the unfolding of the canopy nose/inlets and encourage fast inflation and a harder-than-normal opening.

So, yes, snatch might be as important of a factor.

J

D-bag inspection:
I was thinking about ways a mis-sized or neglected D-bag might contribute to very hard openings - for example by allowing the relative wind to start unfolding the canopy,
and perhaps opening the canopy before the suspension lines are completely stretched. So I would:

1) make sure the rubber bands are always tight on the line bights - so to avoid line dumps (a concern especially with big canopies), or to avoid the canopy pushing the bag flap 1/2-opened when being extracted out of the container by the pilot chute.

2) make sure that the canopy is not "sloshing" about in an oversized bag - here I would want the folds to to unfurl only AFTER the canopy has been pulled out of the bag BY the suspension lines.

In other words, I want a canopy that stays titghtly folded inside a bag that is sized just right.
I would hate to have one of those off-staged openings, especially "sans" suit! ouch!

J

Yes indeed, while jumping your canopy repeatedly (at the same suspended weight and freefall speed), you will find that those slow openings will always yield softer openings than the faster openings. The reason for this is that during a slow opening, the drag generated by the partially-opened canopy
is high enough to slow you down some (even during the slider-up/snivel)- so when the canopy is finally reaching its maximum surface area (during slider-descent), you are actually falling at a somewhat slower rate than during a swift opening. So your canopy will generate less drag at that moment and the opening shock will feel softer.

If you go to this page

http://www.pcprg.com/pifprog.htm

you will find an easy-to-use computer program that tells how much force may hit you - depending on the duration of the opening.

So, to not get hit by swift and hard openings, you always make sure that you dont trash-pack, have your deployment bag regularly inspected by a rigger, and maintain a good body position at deployment time.

J

First, to recap a similar debate on the PIA riggers' forum
(the thread is “canopies/Reserve Fabric Strength Testing”):
1- The 40lb tensile test of TS-108 can be traced back to a US Air Force requirement for the breaking strength of the fabric used to build the C-9 canopies, i.e. 42lbs, for MIL-C 7020, 1.1 oz. Type I nylon
2- The F-111 fabric modern canopies is rated at 45lbs according to PIA standard PIA C-44378 (Type I)
3- Note that zero-P fabric is stronger that F-111 (duh!) – see Performance Textiles’ spec for its zero-P Soar-Coat fabric is rated at 47lbs (http://www.perftex.com/milpara.htm).

I understand the reluctance by many to use the 40lb test on fabric that is rated at 42lbs, being so close the rated failure point. A lower pull test force, say 30lb or whatever, seems more palatable. BUT! A canopy that passes a 30lb tensile test is still un-airworthy if it fails the rated breaking point of its fabric (be it 42 or 45 or 47lb). Were does a 30lbs test leave us riggers????

In a way I like the idea of parachute manufacturers mandating a maximum pull test force in their packing instructions. The issue of pull-testing then becomes an issue of following a manufacturer’s packing instructions. Here the “airworthiness” issue that the FAR mandates us riggers to uphold then hinges on what the manufacturer thinks is airworthy, not on a given rated fabric strength.

Jean

Ah, some data at last! Thank you very much!

The Precision study is indeed informative. I guess my next question is this:
is the increased porosity seen all over the canopy? or is it most likely
at some special locations on the canopy (caused by the way reserves are packed)?

The PD study adds data also - but here too I have questions:

>These two parachutes were then packed and deployed from
>reserve containers after an intentional cutaway in the same manner as is done
>for TSO testing. The result was a noticeable increase in the time and distance
>required for both parachutes to open...

Do you happen to know how much opening time was involved? With TSO C-23d
the maximum opening time is 3 sec (excluding deployment - see paragraph
4.3.6 in SAE AS8015 Rev B)). Were
the opening times "noticably" greater than 3 seconds? how much?
Perhaps someone from PD could chime in.

So indeed increased porosity
"may" invalidate the TSO-status of a particular parachute.
Is the "may" underlining the fact that not all reserves with over 40 repacks
will fail the test? What is the likelyhood of this?
We cant say since it appears that PD has done two tests only (but "thank you PD" for those!).
Will we retire perfectly good reserves by grounding them after a set number of repacks?

To me (as a rigger) the issue of airworthiness is all about individual parachutes
meeting the TSO requirements. If indeed the increase in porosity due to repack
is a problem, then so be it - and I shall certainly ground the parachute.

Concerning:

>In addition, sometimes old gear simply is not up to the standards of newer gear.
and:
>They will certainly degrade to a point that the landing characteristics will not be
>acceptable to their owners or to the standards of the manufacturer, even if
>they do pass the TSO tests for landing performance."

Althoutgh I aggree with the fact that more modern designs land better that older designs
(factory-fresh or many-times repacked) it seems that the decision-making involved
in the grounding of parachutes is going beyond meeting the TSO requirements. I surely dont
agree with that. If indeed landing performance has become
a determining factor in deciding to ground an emergency parachute, then what should we do
(as riggers) with customers who have gained a significant amount of weight since purchasing
their emergency chutes, but not enough to invalidate the TSO? we all know that their "landing
characteristics will not be acceptable to their owners ", even with factory-fresh reserves.
So, should I ground the rig? I think not (but a stern warning shall be issued).

The debate goes on.

This is a topic that has frustrated me for many years.

Yes, I can see that porosity increases with the number of (tight) pack jobs. It is the conclusion that "...with greater porosity the parachute may no longer meet the TSO req's..." that bothers me.

Where's the data for this assertion? I have never
seen any. Here's what I would like to see:

1) By exactly how much is the fabric permeability
increasing? 5%?10%?50%100%?

2) Has anybody tried to do a complete
TSO test program with a
many-times repacked parachute system? and
if so, did the chute take too
long to inflate (thus failing the TSO)?
As far as I know, no such tests have been performed. (Please prove me wrong)

If there is no such data, why is the industry so
quick to retire old gear?

JP