New explanation for hard openings?

[potvinj 0]

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

[diablopilot 2]

There was a guy calling that "Slider Rebound" a couple years back.


Hard openings IMO come n two flavors.

What you get before you stand up, and what you get after.

The before is commonly a function of body position. A head low condition will worsen the "sling" to upright.

The after upright conditions can be a function of canopy and slider choices, and I think the effect you're talking about can be mitigated most of the time through good control of the slider during packing and ensuring it remains against the stops till the canopy is completely out of the bag and beginning to inflate.

If you want to test your theory, try some direct control slider techniques as seen in slider up BASE packing.

----------------------------------------------
You're not as good as you think you are. Seriously.

[pilotdave 0]

Check out this video and pause it during the slow motion deployment. Watch the slider...

http://www.skydivingmovies.com/ver2/pafiledb.php?action=file&id=6386

His slider comes down before the canopy even begins to slow him down. You can see it's fully inflated at the beginning. Hard to tell from the compressed video, but it looks like maybe the back of the slider started coming down first, kind of dumping the slider drag. It actually looks like the slider collapses itself on the way down.

So what's the technical explanation for this one?

Dave

[darkwing 5]

Quote

His slider comes down before the canopy even begins to slow him down. You can see it's fully inflated at the beginning. Hard to tell from the compressed video, but it looks like maybe the back of the slider started coming down first, kind of dumping the slider drag. It actually looks like the slider collapses itself on the way down.

The back side dumping drag and descending is pretty consistent with their theory, which would attribute it to a strong airflow over the back, top of the slider.

-- Jeff
My Skydiving History

[potvinj 0]

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

[davelepka 4]

Quote

We mentioned dome sliders as a remedy, but no doubt other solutions that we are not aware of probably exist

One of the best preventative measures is to tend to the whole slider, not just at the stops. Reaching into the center of the slider and making sure that it's pushed down (in a pro-pack) into the canopy. This will help to prevent any build up of pressure above the slider.

I see many people pack, and they push the slider to the stops, and maybe concern themselves with the front edge and its placement relative to the nose, while ignoring the rest of the slider. It's stupid.

[diablopilot 2]

Center, front, back, left, and right.

Or that's what I teach anyway.

----------------------------------------------
You're not as good as you think you are. Seriously.

[tombuch 0]

Quote

Quote

We mentioned dome sliders as a remedy, but no doubt other solutions that we are not aware of probably exist

One of the best preventative measures is to tend to the whole slider, not just at the stops. Reaching into the center of the slider and making sure that it's pushed down (in a pro-pack) into the canopy. This will help to prevent any build up of pressure above the slider.

Remember rubber banding the slider to the canopy from back in the day? I had an old square that was set-up with a rubber band on one of the stabilizers to hold the slider, and another with a rubber band on the tail. The idea was to keep the slider at the top of the lines until the canopy started inflating and pushed it off the rubber band.

I had another canopy with a packing strap that closed everything off with a single line stow until all the lines had extended. The slider was packed above the packing strap, so it couldn't move until full line extension.

Tom Buchanan
Instructor Emeritus
Comm Pilot MSEL,G
Author: JUMP! Skydiving Made Fun and Easy

[diablopilot 2]

Nothing under the sun is new.


http://www.basejumper.com/Articles/Packing/Direct_Control_685.html

----------------------------------------------
You're not as good as you think you are. Seriously.

[badlock 0]

The more I read about hard openings the more I have doubts when I read the explanations.

The point is: There do exist many "theories" (or better: speculations) but where are the scientifical datas?
Where are the statistics that show (including control groups) *significant* effects from any of the described "reasons"? I guess that there isn't any statistic out there that shows even correlations - and much less studies that can show causal determinations.
Further reasons for my doubts are two:

1st, some explanation are hard to believe because the even phenomena that should be the cause for hard openings aren't documented by even one single video/photo (i.e. "line dump").

2nd, if I look around people packing chutes I can see ALOT packjobs with smaller or bigger packing errors resulting in perfect fine openigs and also perfect pack jobs resulting in slammers.
AND: I bet, if you wold open some sloppy packjobs and some of the good pack jobs with the neatly quartered sliders (and so on) on the ground you couldn't tell the difference in many case.
This is because of the bagging destroying most of the tiny tricks.

Don't be a Lutz!

[packertom 0]

Guys, slide rebound exists.... basically the slider is caught perfectly in your burble and slides down the lines without catching wind, with only the resistance of the lines on the grommets slowinging it down.... the slider works only because in the opening sequence it must remain dominant over the main for the longest period possible... if the main becomes dominant over the slider too early in the process, bang, you have a hard opening.... it happens, it is rare, but it happens... I've seen hard openings on normally docile canopies like spectres and safires have violent openings for no reason... this is what I believe is the reason.. it's a phenomenon kind of like the loch ness monster... we can't really catch it on video.. but I believe it's there... slider rebound.. not the loch ness monster...

tom@velocitysportswear.com
www.velocitysportswear.com
What's YOUR Zombie Plan?

[peek 21]

Quote

.... even the phenomena that should be the cause for hard openings aren't documented by even one single video/photo

I agree, that is a huge problem, and we may never get video of some of these things if it is related to a quick (hard) opening, because the jumper/videographer would not have time to look up!

(The Tandem manufacturers however, may have some video or stills of some line slump or such from the days before they knew how to control it, because Tandems often had "outside" video.)

[peek 21]

Quote

Remember rubber banding the slider to the canopy from back in the day?

Yes! My Pioneer Titan had that. And "Red" at Flight Concepts mentioned this technique to me a while back when we were talking about hard openings, so he is thinking of it too.

I think that if people started doing that again that we would see the number of "rogue" hard openings go down, (rogue meaning an occasional hard opening of an otherwise nice opening canopy).

But I don't think that is going to happen, for a number of reasons.

[davelepka 4]

Quote

Remember rubber banding the slider to the canopy from back in the day?

--------------------------------------------------------------------------------


Yes! My Pioneer Titan had that. And "Red" at Flight Concepts mentioned this technique to me a while back when we were talking about hard openings, so he is thinking of it too.

I know a guy who still does this. He's got a rubber band hanging from the attachment point of an inboard C line.

This is on a Spectre, no less. The catch is that this guy is old, jumps a loaded FTP, and isn't shy about cranking out the jumps, so the extra insurance from the rubber band makes sense.