Packing to prevent hard opening

[pilatus_p 0]

I have been posting in 'incidents' recently about a hard opening I had that caused two discs in my spine and two ribs to fracture.

Two knowledgable guys on the forum suggested that it may be to do with 'losing control of the slider or the bottom of the canopy' during packing.

Please can you provide detail of how one can pack to avoid such a situation and how easy it is to have a hard opening of this type?

You can watch the opening here

http://www.skydivingmovies.com/ver2/pafiledb.php?action=file&id=4782

and read the threads in 'incidents' which may help to answer the question.

Thanks

Ross

http://www.teamtechnology.co.uk/troll.htm

[rmcvey 0]

Hi Ross, how you doing?

Packing techniques are very difficult to describe let alone teach on an internet forum.

But basically if the slider isnt all the way up against the stops when you open, it doesnt work as it should.

And as its main job is to slow the opening, you get the opposite, bang.

It may have been this, it may have not, who knows. Like a few have said already, it could be a number of things, or none.

Bad openings just happen sometimes mate

Best bet is to get yourself to a dz and find someone to teach you to pack, some dz's even have packing courses you can attend. They should go over all the tips on how to try and prevent this in the future. But if you jump for long enough youll get hard openings from time to time.

Get well soon mate.


Rob

[jerry81 10]

Slider control is easier demonstrated than described, but anyway: when I teach packing, I tell people to keep one hand (normally left, since it's non-dominant for most) around the lines at the top of the canopy and pushing the slider against the stops during the wrapping and laying down part. Then, when coccooning, I prefer to keep a knee on the lines where the hand was before, so now you're using your leg to keep the slider in place while you get the air out. For folding, I put the hand back around the lines and keep the slider against the stops until the moment tha flap goes over and you start the first locking stow.
Hands are of course interchangeable, the key is to never let the slider move away from the stops.

I notice that a lot of people lose it when they put the canopy on the ground, don't control it as they squeeze the air out and then stuff it in the bag like that.
I agree with the guys in the other forum about 85%. A majority of slammers can be attributed to poor slider control. Then of course you have the general chaos and construction factors. My canopy, for instance, will slam me if I leave the nose out, regardless of my slider control. Push it well into the center, and it's happy. On a Katana and a few Sabre2s that I packed and jumped, doing this seemed to result in weirder and often harder deployments, while leaving the nose hanging out (as PD suggests) improved them.

Anyway, the best way to learn would be to get someone to show how they do it, but I hope I at least gave you a general idea of how my method works...

[pilatus_p 0]

Hello Rob!

Doing ok apart from the sore back and ribs. I'm starting to get the impression that hard openings are one of those necessary evils. I think i'll invest in something with a bit less braking power than a 270 though - at least if I get another hard opening, a more zippy little canopy will fall a bit further first what with the lower drag.

Send me a PM as would be good to see how your coaching got on
Ross

http://www.teamtechnology.co.uk/troll.htm

[pilatus_p 0]

Hi Jerry

Thank you for your suggestions. As I will not be jumping for a while I am going to get myself to a local DZ and take a packing course with your tips in mind.

It sounds liek you have had a few whacks in your time from canopies - do you find that a hard opening on a smaller canopy is kinder or worse than a big one?

Thanks again

Ross

http://www.teamtechnology.co.uk/troll.htm

[jheadley 0]

If you're really gunshy about jumping again because of hard openings, once you get your own gear, you can get canopies that are known to open very very soft. A Spectre, for one opens very soft. A Pilot, also. Also getting thick dacron lines will also slow down the opening, and, if you do get a hard opening, the lines will stretch, absorbing much of the shock.

I've had a few openings that were semi-uncomfortable, but honestly the last "hard" opening I had was about 400 jumps ago. Good packing, good body position, correct airspeed at deployment, and a good choice of main canopy almost eliminates the problem completely.

[justinb138 0]

Quote

It sounds liek you have had a few whacks in your time from canopies - do you find that a hard opening on a smaller canopy is kinder or worse than a big one?

I don't think size has much to do with it.

People have been injured from openings on canopies of all sizes.

[jerry81 10]

Quote

It sounds liek you have had a few whacks in your time from canopies - do you find that a hard opening on a smaller canopy is kinder or worse than a big one?

Hehe, not that many, now. Actually, working as a packer, I received more complaints from people who wanted it to open "just slightly faster this time" and the 'harder' openings I was writing about were merely harder, not slammers, with the exception of when I was experimenting with different packing methods on my canopy. It's a 120, but the slammers I got from it were probably close to slider-off base openings...

---

[xlh883 0]

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A Spectre, for one opens very soft. A Pilot, also.

I can speak for the Pilot. It does normally open soft, but I packed myself a good slammer last Saturday. I got the bruises to prove it! But usually it opens fine. This was my mistake as I lost control of the slider I am pretty sure. I had issues packing that pack job.

David

[pilatus_p 0]

Hi jheadley

No im not put off by the canopies - just the fact that I can't currently jump because my spine is fractured!

Once I'm back in the air I want to know I'm doing everything in all safety spheres, including minimising hard openings. I like your suggestions - is it bouncy when you have springy lines? That sounds like fun. Arch, reach, throw, boiiiing ....

Ross

http://www.teamtechnology.co.uk/troll.htm

[kelpdiver 2]

It's not that bouncy (dacron). It's just that spectra lines can honestly be compared to steel cables in their elasticity. No give at all.

[littlejohn 0]

packin paracutes is easy just keep the tail tight round the lines dat will make life easier

death before dishonor

[riggerrob 558]

Quote

packing parachutes is easy just keep the tail tight round the lines that will make life easier

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Yes!
And keeping the tail wrapped tightly around the lines usually keeps the SLIDER HARD UP AGAINST THE BOTTOM OF THE CANOPY.

[mjosparky 3]

Quote

SLIDER HARD UP AGAINST THE BOTTOM OF THE CANOPY.

For those not listening: Not doing this will hurt. Not doing this is the cause, IMO, of almost all slammers.

My idea of a fair fight is clubbing baby seals

[Ronaldo 0]

Hi Ross,
IMO the opening process is a chaotic event thus you should expect an eventual slammer even if it’s a good opening correctly packed canopy. I also agree that slider placement is the key to good openings. One trick that I find very useful to control slider position during packing is to start wrapping the tail area close to the lines, then placing a finger on this first roll, roll the rest of the tail. Also, when narrowing the canopy, try to place your knee right bellow the slider (over the lines), not at the slider grommets. If you put pressure right over the slider you may end up spreading it and unrolling the tail.
IMHO a good canopy should open soft with just a good flaking and the slider against the stops. If you have to do a lot of tricks to make it open properly then it's a canopy problem (design, construction or line trim). Just my opinion though.
Blue skies!

Engineering Law #5: The most vital dimension on any plan drawing stands the most chance of being omitted

[pilatus_p 0]

Thanks Ronaldo

Yes that is the view expressed by many. I would rather have had my first slammer further down the line though, when I'm jumping smaller rigs.

Hopefully not teaching you to suck eggs - If you look at the engineering of parachutes / wings etc you will see that pressure drag (the dominant braking force caused by the downward movement of the canopy) is directly proportional to surface area presented to the air flow. For those as geeky as me, its given by

braking force due to pressure drag = 1/2 x air density x air speed squared x surface area x coefficient of drag.

At the moment of opening, the important surface area is the full lower surface of the canopy (due to the premature full inflation) - which at this stage is barrelling directly downwards at 120 mph.

The last term, coefficient of drag, is unique to the canopy but varies only very slightly from one canopy to the next. As all the other elements are essentially constant, the surface area is the defining factor in the braking power, and hence opening shock, transmitted to the body in the event of rapid opening.

Most people progress rapidly to around a 190 from big sizes such as the 270 I was jumping. If you do the engineering equations you see that a 270 has 40% more area and hence 40% more pressure drag (braking power) than a 190. This may explain why there is a seeming greater history (at least as far as this board is concerned) of student jumpers sustaining large injuries from hard openings than experienced jumpers. Its also part of the reason why BASE rigs dont give such a big whack despite rarely having a slider - the speeds invloved are often slower (eg if the jumer does not reach terminal) and the canopies smaller.

For this reason it would seem that some sort of fool-proofing for sliders on student canopies would provide a distinct benefit, though I am unsure as to what form this would take - perhaps pilot chute controlled sliders?

Purists may also point out the skin friction and induced drag present in the above calculations, which will be very small compared with the pressure drag and so are not as important. Lift induced by the aerofoil section of the canopy cannot be considered until the motion of the canopy changes to forwards.

I'm STILL learning to pack like a pro though.

RossL

PS link to discussion on hard opening prevention on these boards http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=2418093;sb=post_latest_reply;so=ASC;forum_view=forum_view_collapsed;;page=unread#unread

http://www.teamtechnology.co.uk/troll.htm

[chutem 0]

I think there may be more to it than that. I may not be as "booksmart" as you, or geeky if you want to call it that. My 210 sillouhette opens much slower than my stilleto 170. The student canopys I jumped 280-220 navigators opened much slower than my 170 stilleto. I have heard stories of original sabre's slamming people in all sizes. It would appear to me that canopy design, slider design, and pilot chute size all play a major role here. If I'm wrong I'm sure someone will correct me.
James

[pilatus_p 0]

Hi Chutem

I agree with you completely - student canopies SHOULD open slower and when this happens it is a good thing, and I am sure they are excellently designed just like most canopies. All the parts of the rig affect this I am sure.

From a book perspective the time it becomes a problem for me is when you have an instant opening. In this situation the design has essentially failed and all the factors - slider, pilot chute design and size etc - become irrelevant. The canopy has functioned incorrectly and opened straight away at full freefall speed, as in my incident which you can see on video. That is a given in my argument.

In a comparison between an instant opening big rig, and an instant opening small one, you will naturally have more opening shock on the larger than the small one. So my concern is accidentally fast opening big rigs, the added braking force and their apparent greater capacity for spinal damage, rather than the speed with which they are MEANT to open.

If all goes well, which in 99% of situations it does, then you are right - the bigger rig will open slower.

Thank you for bringing your experience to the thread. I agree that the solution to the problem lies in the construction of the parachute.

RossL

http://www.teamtechnology.co.uk/troll.htm

[chutem 0]

I was not saying that big rigs open slower than small when things work as designed, but that design plays a larger part in the quickness of the opening. I'm curious if you jumped the same canopy design in a 230 and a 150 (sq ft) with no slider which one would slam you harder. I understand that no one would want to do this and that it would most likely result in injury. Simple logic says the larger canopy would open harder as you describe. Do any of you more experienced jumpers/test dropers have an answer based on experience rather than calculations?
James

[pilatus_p 0]

Agreed - I would like to see this too, as experience is important. Jumper physiology plays a large part too. A very fit person with lots of muscle and good bone density is less likely to be hurt than someone not so well endowed under the same canopy -so my interest as an engineer and in safety applied to all body types would be in measurements of actual opening shock force - as you say - test droppers out there anywhere?

Ross

http://www.teamtechnology.co.uk/troll.htm

[Ronaldo 0]

I totally agree with you that the drag coefficient varies slightly from one canopy to another as it depends basically on the form. I think the drag coefficient varies also with the stage of inflation (from center cells to a fully inflated canopy). Obviously I don’t have any data to support but I would assume it has a higher Cd once it is fully opened due to the concave shape of the canopy. I also agree that the surface area plays the most important role in the opening shock. The key to a soft opening is not allowing this surface area to increase too fast (make the canopy snivel a little bit), that’s what the slider is there for. I think the snivel is the most important stage of the opening, that’s when you lose most of the airspeed. That’s where the canopy should stay longer (IMO).
If you consider that a larger canopy has larger cells then it is very reasonable to expect higher drag forces from the beginning (when only the center cells are inflated). It is important to note that large canopies are usually low performance, high drag airfoils. They usually have large nose openings which contribute to fast inflation. Possible ways to slow the openings include, covering part of the nose (such as with the h-mod), controlling slider and crossport sizes.
Regarding student canopies, I guess you don’t want to slow openings too much as you increase the chances of line twists due to poor body position. One positive aspect about students and BASE canopies is dacron lines which absorb part of the shock.
BTW, I think engineers should be banned from these forums, they’re just too geeky

Safe skies!

Ronaldo

Engineering Law #5: The most vital dimension on any plan drawing stands the most chance of being omitted

[pilatus_p 0]

Aha right found some more geekiness - a bit of research on opening shocks for those with a penchant for nerdiness, snipped from the Parks College Parachute Research Group:

http://www.pcprg.com/s01out.htm

Key quote being "Interestingly ... instant openings should give higher opening shocks on large parachutes than small ones (at the same jumper weight and fall rate). The reason is that bigger parachutes have a bigger surface area and thereby produce more drag than smaller parachutes at the same rate of descent. A parachute that is twice as big (i.e. span, chord, suspension line etc. twice as long) would open twice as hard during line dumps. On the other hand the opening time would be about twice as short... The figure shows that for most [differences in size], smaller parachutes actually open harder [under normal conditions] than the larger ones, a trend which is opposite to that of instant openings."

So the research suggests that small canopes open harder under normal operation than big canopies, but under instant opening conditions, big canopies give far higher opening shock than small ones.

I think what I would want to see is a mechanism for ENSURING correct opening speed, as opposed to slowing it any further.

And hey! You need engineers - they're the guys designing your canopies

http://www.teamtechnology.co.uk/troll.htm

[inextremis 0]

My first square, a five cell Stratostar purchased new in 1978 for $475, had the relatively "new" slider system, and had a rubber band on the tail attached to a loop similar to those on a D bag. The slider was to be "stowed" in the rubber band after being pulled all the way up the lines to the slider stops, prior to bagging the canopy. I now prefer to quarter my slider in the usual pro pack, but it's interesting that at one time, manufacturers used a more "positive" method of keeping the slider up.

[pilatus_p 0]

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It's not that bouncy (dacron). It's just that spectra lines can honestly be compared to steel cables in their elasticity. No give at all.

Hi Kelpdiver. Turns out my lines were Dacron - so back to the drawingboard ...

Ross

http://www.teamtechnology.co.uk/troll.htm

[jheadley 0]

Quote

Quote

It's not that bouncy (dacron). It's just that spectra lines can honestly be compared to steel cables in their elasticity. No give at all.

Hi Kelpdiver. Turns out my lines were Dacron - so back to the drawingboard ...

Ross

Well you should be glad they were. The opening would have been even worse if they weren't!