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JohnSherman

Re: [masterrigger1] Hard Opening Incident-DeLand 5/25/2013

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They also offer more grip to the line stows and grommets, thus providing less chances of line dump and slower slider travel.



"Grip on the line stows"?
There is no "gripping line stows" at 120 MPH. Any coefficient of friction was long lost with the speed.

Lines strip or dump because of mass imbalance between the span of lines between the bights and the bights themselves.

See:http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=NEWSTOW&SortBy=DATE_D
for the full definition of the phenomeon.

The SPEED Bag, designed for thoes who prefer safety over work load, was a later development.

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"Grip on the line stows"?
There is no "gripping line stows" at 120 MPH. Any coefficient of friction was long lost with the speed.



John,
Really!
How did you come up with that equation?

Do this for me:
With a fish scale measure the difference between the stows (of the same size, exact same rubber band, and the same number of lines) of Spectra, Technora, Dacron, and Vectran.

Then report your findings to us.

I guess we should not be double stowing (more grip) the rubber bands by your theory![:/]


MEL
Skyworks Parachute Service, LLC
www.Skyworksparachuteservice.com

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JohnSherman

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They also offer more grip to the line stows and grommets, thus providing less chances of line dump and slower slider travel.



"Grip on the line stows"?
There is no "gripping line stows" at 120 MPH. Any coefficient of friction was long lost with the speed.

Lines strip or dump because of mass imbalance between the span of lines between the bights and the bights themselves.

See:http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=NEWSTOW&SortBy=DATE_D
for the full definition of the phenomeon.

The SPEED Bag, designed for thoes who prefer safety over work load, was a later development.



John, I'm calling BS here.

The force that it takes to extract lines from their stows is an important factor in the deployment sequence.
I'll refer you to the several articles published by Purvis and Meyer (yeah that would be me) that address this issue.
You are smart enough to go look them up. Let me know if you have trouble finding the articles.
I have them sitting on my bookshelf.

Unlike you, I have no vested interest to promote a particular mfg's product.
My work was done as a scientific research project.

.
.
Make It Happen
Parachute History
DiveMaker

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I guess we should not be double stowing (more grip) the rubber bands by your theory!




That is correct! Double stowing is a waist of time on bags with balanced line stows. To demonstrate how this is used in everyday jumping we use standard rubber band on our tandems.
Sure if you have bights about an inch long you had better double stow them. However if the bag has balanced stows it is unnecessary.

JS

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Let me see if I understand your ( MEL & Jan) positions correctly. You are saying that the friction or gripping of the lines to the rubber band is the most important aspect of preventing line dump.
I am saying that by having balanced mass within the line stows, the friction becomes academic as the downward forces are equal and it would require some sort of lateral force to pull the stows out of the bights which doesn’t exist until the lead line begins the deployment sequence.
At his point I would agree that as each stow releases , accelerating the mass, that the more that release can drag the more it can accelerate. But this sequence is long past the line dump phase.

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JohnSherman

Let me see if I understand your ( MEL & Jan) positions correctly. You are saying that the friction or gripping of the lines to the rubber band is the most important aspect of preventing line dump.
I am saying that by having balanced mass within the line stows, the friction becomes academic as the downward forces are equal and it would require some sort of lateral force to pull the stows out of the bights which doesn’t exist until the lead line begins the deployment sequence.
At his point I would agree that as each stow releases , accelerating the mass, that the more that release can drag the more it can accelerate. But this sequence is long past the line dump phase.



No John.
We are saying that line tie strength is an important factor in deployment and cannot be ignored.
Other factors include and are not limited to:
- the location of the line ties
- the length of the loops on each s-fold
- the roll relationship between payload and bag
- the width of each s-fold
- the number of s-folds


BTW, since we are talking about packing.
IIRC, Mike was an extremely fast packer and packed for himself.
He used a standard flat pack to fold the canopy.
He stowed the locking loops on the bag.
What I can't remember is if he stowed the rest of the lines on the bag or not.
Can anyone from DeLand or watched him pack recently, confirm that he stowed the rest of the lines on the bag?

.
.
Make It Happen
Parachute History
DiveMaker

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The force that it takes to extract lines from their stows is an important factor in the deployment sequence.



The data has been scientifically acquired in the form of a data acquisition on actual jumps. The elastic band attenuation was hard to observe as the peaks were minuscule and almost lost in the "noise"

If it's your claim that the elastics are forming mini snatch forces to minimize actual snatch, the data I see refutes that. If it is you claim that better retention allows for proper sequence, now we're getting somewhere. However, it still doesn't prove the efficacy of double stoes on a balanced bag. I would agree, however, on double stoes on the older end of the bag type were a small bight is done. The elastic acts like a noose and resists the lateral forces better.

I would be very interested in your articles :)
I would rather be a superb meteor, every atom of me in magnificent glow, than a sleepy and permanent planet.

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JohnSherman

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I guess we should not be double stowing (more grip) the rubber bands by your theory!




That is correct! Double stowing is a waist of time on bags with balanced line stows. To demonstrate how this is used in everyday jumping we use standard rubber band on our tandems.
Sure if you have bights about an inch long you had better double stow them. However if the bag has balanced stows it is unnecessary.

JS



John,

if you wouldn't mind clarifying a point for this discussion, could you do a little Line Stow 101 on what is the difference between "balanced" and "unbalanced" line stows and how this difference affects deployment? You've touched on most of this, but unless I missed it, there are some fundamental definitions and so forth that have been assumed rather than spelled out.

thanks

:(
44
SCR-6933 / SCS-3463 / D-5533 / BASE 44 / CCS-37 / 82d Airborne (Ret.)

"The beginning of wisdom is to first call things by their right names."

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could you do a little Line Stow 101 on what is the difference between "balanced" and "unbalanced" line stows and how this difference affects deployment?



Sure; The best way is to refer you to previous writings. These are sequential as they track the development of line stows to where we are today.

The first one tells of the new balanced line stows and how they work. However, it doesn't speak to un-balanced stows. Unbalanced stows are where the distance between the stow bands is greater than twice the length of the bight.
http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=NEWSTOW&SortBy=DATE_D

http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=Speedbag&SortBy=DATE_D

http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=Reserve_Speedbag&SortBy=DATE_D

As to how this all affect deployment. When the bag is jerked out of the pack tray only the bag is loaded to the bridle. The canopy wants to stay in the container and the lines also want to stay. The lines are locking the bag giving the caniopy no choice but to go for the ride. The only thing keeping the lines to the bag are the rubber bands and they (the lines)are trying to stay in the pack tray. If the mass of the lines between the rubber bands is greater than the twice the mass of the bights (there are 2 bights) then the lines will pull out of the rubber bands and stay in the pack tray allowing the bag to open and release the canopy before you reach line streatch.
This is what that looks like:
[inline line_dump.jpg]

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If the mass of the lines between the rubber bands is greater than the twice the mass of the bights (there are 2 bights) then the lines will pull out of the rubber bands and stay in the pack tray



No, that is when we need the rubber bands to do their job - provide some resistance.
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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sundevil777

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If the mass of the lines between the rubber bands is greater than the twice the mass of the bights (there are 2 bights) then the lines will pull out of the rubber bands and stay in the pack tray



No, that is when we need the rubber bands to do their job - provide some resistance.



That was my thought exactly. I have a icon d-bag that has outboard tape for stow bands. I use micro-line tube stows, and my bites are not especially large.

I should be having line dump on every opening, because I am certainly unbalanced, with a ratio of more like 40 bites to 60 between the stow bands.

But it seems to work pretty well with the HMA lines, and my openings thus far, knock on wood, have never been hard.
"The restraining order says you're only allowed to touch me in freefall"
=P

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I believe what John is talking about is using balances stoes to reduce the need for elastics to provide all the resistance. Balancing makes the stoe work better.

Rubber bands don't always "do their job" and that's the point. The balanced stoe helps them "do their job" because "their job" is orderly metering out the lines. Loose stoes on a balanced bag aren't as big an issue as loose stoes on an unbalanced bag.

If you're making sure line retention is good, it's not an issue. Balanced stoes make sure that looser stoes aren't an issue either, hence there is no need to double stoe.

Hope that clears it up :)
I would rather be a superb meteor, every atom of me in magnificent glow, than a sleepy and permanent planet.

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JohnSherman

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could you do a little Line Stow 101 on what is the difference between "balanced" and "unbalanced" line stows and how this difference affects deployment?



Sure; The best way is to refer you to previous writings. These are sequential as they track the development of line stows to where we are today.

The first one tells of the new balanced line stows and how they work. However, it doesn't speak to un-balanced stows. Unbalanced stows are where the distance between the stow bands is greater than twice the length of the bight.
http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=NEWSTOW&SortBy=DATE_D

http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=Speedbag&SortBy=DATE_D

http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=Reserve_Speedbag&SortBy=DATE_D

As to how this all affect deployment. When the bag is jerked out of the pack tray only the bag is loaded to the bridle. The canopy wants to stay in the container and the lines also want to stay. The lines are locking the bag giving the caniopy no choice but to go for the ride. The only thing keeping the lines to the bag are the rubber bands and they (the lines)are trying to stay in the pack tray. If the mass of the lines between the rubber bands is greater than the twice the mass of the bights (there are 2 bights) then the lines will pull out of the rubber bands and stay in the pack tray allowing the bag to open and release the canopy before you reach line streatch.
This is what that looks like:



Thanks, John... that's exactly what I had in mind. Now the discussion can continue based on clear definitions of the issues in question.

:(
44
SCR-6933 / SCS-3463 / D-5533 / BASE 44 / CCS-37 / 82d Airborne (Ret.)

"The beginning of wisdom is to first call things by their right names."

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