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sheeks

Wouldn’t it make more sense if all sliders were less flat?

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So you pull stable, the line stows release in proper sequence, the parachute comes out of the bag when it’s supposed to, and luckily because all the stars are aligned, the direction of air is coming directly directly upwards into the slider, keeping it in it’s proper place as the canopy inflates. Congratulations, you’ve just had a succesful and steady canopy opening.

 

Now, let’s just say the stars aren’t aligned. You rushed the pack because you didn’t want to be late for the next load. Your rubber bands are getting a little old, and you get so caught up with your buddies in the air that you end up losing altitude awareness and seperating a little on the late side of things. You still get to pull at 3500, but this time you still haven’t slowed down from the track and between your increased speed and the age of your stows, your bag starts to open a little prematurely. Instead of opening directly over your head, your canopy is angled and not properly tense by the time it comes out of the bag. This increase in chaos allows some air to start slipping in behind your slider, because the canopy is too sideways for the air to catch into the bottom of the slider in the way it’s supposed to. You get a bottom skin inflation, and your canopy is opened harder than you’d like. At the least you get a few bruises, at the most your family is mourning your loss.

 

Now, maybe if the slider had a bit more fabric to it, and was more domed instead of being shaped so flat the way it is, the chaos of the airflow into the canopy might have been a little more controlled, and instead of that air slipping in behind the slider, it would have been more directed into the path of least resistance inside the slider where it should have been going, and kept the slider up long enough for the canopy to open more controlled in the way it was supposed to. 

Take a plastic bag, and rush it through the air 100 times in a row. How many times does it inflate the way you want it to?

Now cut out a rectangular segment from that plastic bag, give it just a few inches of slack, and rush it through the air 100 times in a row. How many times does it inflate the way you want it to?

 

The point i’m getting at, is maybe slider modifications that help a slider catch air better aren’t only for canopies that open too hard. Maybe instead of only domed sliders on Sabre 1’s, that domed sliders on spectre’s, pilot’s, and safire’s wouldn’t be such a bad idea. If they make a canopy open TOO slow, then maybe a smaller domed slider is better than a larger normal/flat slider. 

 

Sliders obviously don’t have to fill up to the size of a basketball, but maybe just having an extra two or three inches of slack in the fabric could make a world of difference when it comes to less than desirable openings, and would probably only increase opening time by 1-3 hundred feet. 

 

How often do you hear of a hard opening with a pocket slider or domed slider? Far less often than with regular canopies.

 

Thoughts? 

Edited by sheeks

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Flat sliders are easier to build. You try to design some thing that you can build. You try to design the canopy so that you don't have to resort to things like domed sliders. There are some tandem canopies with slightly domed sliders. But you try not to have to go their. You'll see most of these things after market where people are trying to deal with a bad canopy that is prone to aberrant hard openings. 

 

Lee

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58 minutes ago, sheeks said:

The point i’m getting at, is maybe slider modifications that help a slider catch air better aren’t only for canopies that open too hard. Maybe instead of only domed sliders on Sabre 1’s, that domed sliders on spectre’s, pilot’s, and safire’s wouldn’t be such a bad idea. If they make a canopy open TOO slow, then maybe a smaller domed slider is better than a larger normal/flat slider. 

 

Problems:

1) I have owned canopies that opened almost _too_ slowly - 500 foot snivels on one.  Making that into a 1000 foot snivel would not be an improvement.

2) Domed sliders are harder to build and wear out faster.  (There is a lot of force on those not-straight seams.)  Thus they'd be more expensive - and more likely to fail.

Domed sliders are one way to "fix" a problem canopy.  (There are many other ways.)  But it's probably not a good overall solution.

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42 minutes ago, RiggerLee said:

Flat sliders are easier to build. You try to design some thing that you can build. You try to design the canopy so that you don't have to resort to things like domed sliders. There are some tandem canopies with slightly domed sliders. But you try not to have to go their. You'll see most of these things after market where people are trying to deal with a bad canopy that is prone to aberrant hard openings. 

 

Lee

No need for their to be offense or tension, i’m not trying to discredit any canopy manufacturers for their designs. I’m simply putting out an idea that I think would be beneficial for people to consider.

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4 minutes ago, billvon said:

Problems:

1) I have owned canopies that opened almost _too_ slowly - 500 foot snivels on one.  Making that into a 1000 foot snivel would not be an improvement.

2) Domed sliders are harder to build and wear out faster.  (There is a lot of force on those not-straight seams.)  Thus they'd be more expensive - and more likely to fail.

Domed sliders are one way to "fix" a problem canopy.  (There are many other ways.)  But it's probably not a good overall solution.

Adding a pocket to a slider would probably do the same thing without adding any additional wear i’d assume

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2 hours ago, billvon said:

Domed sliders are harder to build and wear out faster.  (There is a lot of force on those not-straight seams.)  Thus they'd be more expensive - and more likely to fail.

Hi Bill,

Hopefully, you or anyone else will never hear me say that I know it all about parachute equipment.

I have built a fair number of flat sliders ( ~ 15 - 20 ) & a few domed sliders ( ~ 4 - 5 ).

a.  Depending upon the domed slider design ( they are not all the same design which means that the material costs & labor costs will vary ), I question whether they 'are harder to build.'  As to 'wear out faster,' once I see some data supporting this, then I will believe it.  At this time, I have doubts regarding this comment.

b.  As to 'there is a lot of force on those not-straight seams,' once there is some tension on those seams, they straighten out immediately.  I think that any differentiation in forces would be neglible.  And there is at least one domed slider design in which the seams are straight.

c.  As to 'Thus they'd be more expensive - and more likely to fail.'  Having built both types, I doubt that they would be more expensive; again, it comes back to the design of the domed slider.  The OP did say build it slightly smaller but domed.  Smaller would be less fabric = less cost in materials which could offset any additional labor costs during mfr.  As to 'more likely to fail,' I have never read or heard of anything that supports this comment.  I am open to input from anyone on this.

Just my $0.20 on these issues; others may disagree & that is OK with me.

Jerry Baumchen

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15 minutes ago, JerryBaumchen said:

Hi Bill,

Hopefully, you or anyone else will never hear me say that I know it all about parachute equipment.

I have built a fair number of flat sliders ( ~ 15 - 20 ) & a few domed sliders ( ~ 4 - 5 ).

a.  Depending upon the domed slider design ( they are not all the same design which means that the material costs & labor costs will vary ), I question whether they 'are harder to build.'  As to 'wear out faster,' once I see some data supporting this, then I will believe it.  At this time, I have doubts regarding this comment.

b.  As to 'there is a lot of force on those not-straight seams,' once there is some tension on those seams, they straighten out immediately.  I think that any differentiation in forces would be neglible.  And there is at least one domed slider design in which the seams are straight.

c.  As to 'Thus they'd be more expensive - and more likely to fail.'  Having built both types, I doubt that they would be more expensive; again, it comes back to the design of the domed slider.  The OP did say build it slightly smaller but domed.  Smaller would be less fabric = less cost in materials which could offset any additional labor costs during mfr.  As to 'more likely to fail,' I have never read or heard of anything that supports this comment.  I am open to input from anyone on this.

Just my $0.20 on these issues; others may disagree & that is OK with me.

Jerry Baumchen

Hey Jerry thanks for the input, as someone who’s built both regular and domed sliders before, do you see any particular advantages to flat sliders that can’t be had with domed sliders assuming they both wear at the same rate, aside from the philosophy of “if it’s not broken don’t fix it”?

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5 hours ago, sheeks said:

. . . you still haven’t slowed down from the track and between your increased speed and the age of your stows, your bag starts to open a little prematurely. Instead of opening directly over your head, your canopy is angled and not properly tense by the time it comes out of the bag. This increase in chaos allows some air to start slipping in behind your slider, because the canopy is too sideways for the air to catch into the bottom of the slider in the way it’s supposed to. 

I don't understand this.  Can you use different words to explain it?

--Mark

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3 hours ago, sheeks said:

any particular advantages to flat sliders that can’t be had with domed sliders assuming they both wear at the same rate

Hi Sheeks,

Unless I am wrong, your OP was to address a domed slider, for a main canopy only, that had fairly acceptable opening shocks when everything went right.  You ( I think ) are concerned with that out-of-nowhere slammer opening that could result in permanent damage and/or death to the jumper.  Given that, you have gotten my mind working, as all of my efforts in the past, and what I have read, are for the use of a domed slider where the 'normal opening' was too much for the jumper.

You do present an interesting take on this idea of reducing the probability and reducing the possibility of a slammer opening.  Especially, where you talk about using a slightly smaller domed slider, that would result in the same opening forces that a 'factory' flat slider would provide when everything went normally.  As you mentioned, the domed slider might have the potential to reduce the occurrence of the slammer opening.

It would be very interesting to take two exact canopies, have one with a standard flat slider & one with a slightly smaller, domed slider & get some input from the users.  If I were running such a study, I would have the two jumpers exchange canopies after each jump to increase probability of the consistency of the jumps & the jumper's input/response.

Given what I have written above, I ( right now, as I sit at my computer ) do not see any particular advantages to a flat slider vs a smaller, domed slider.  However, until some side-by-side jumps could be made, I'll reserve making any statement that would be more definitive.

It is a damned interesting concept.  If only I were 20 yrs younger; hmmm.

I won't speak for Sheeks, but what about you other folks on here; what say you?

Jerry Baumchen

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2 hours ago, mark said:

I don't understand this.  Can you use different words to explain it?

--Mark

I just mean that I think a lot of the reason why slammers happen is because the wind force isn’t coming at the slider from the right direction to keep it in place, assuming that it’s properly quartered in the first place. It was just a mostly irrelevant hypothetical scenario to basically get around to the point that I think domed sliders might act as a bit of a safety feature by helping the wind penetrate the slider more efficiently in unusual circumstances

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Sheeks, your idea and concept may have body to it or may have draw backs. It is people like you, with those kind of thoughts, that will push the equipment forward. Keep thinking not only of the line eating sliders, but anything you may question that could be better. If you can figure how to get rid of the slider, you hit the jackpot. I respect your thoughts.

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7 hours ago, sheeks said:

I just mean that I think a lot of the reason why slammers happen is because the wind force isn’t coming at the slider from the right direction to keep it in place, assuming that it’s properly quartered in the first place. It was just a mostly irrelevant hypothetical scenario to basically get around to the point that I think domed sliders might act as a bit of a safety feature by helping the wind penetrate the slider more efficiently in unusual circumstances

Ok.  It's not an irrelevant hypothetical scenario, though.  It's just wrong.  The relative wind experienced by the slider is exactly opposite the direction of fall or flight regardless of orientation to the earth or horizon.

--Mark

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18 minutes ago, mark said:

Ok.  It's not an irrelevant hypothetical scenario, though.  It's just wrong.  The relative wind experienced by the slider is exactly opposite the direction of fall or flight regardless of orientation to the earth or horizon.

--Mark

Although what you said is unarguably true, it is also true that the relative wind is not always effective at keeping the slider in place till line stretch. That can and has had fatal consequences. Some openings allow the slider to travel down the lines far enough and early enough to make it ineffective. The slider needs to inflate like a mini parachute immediately as it becomes exposed to the relative wind or it will not function correctly. We do not fully understand why this fails to happen sometimes. Deflection of the airflow off of the much larger bottom skin of the canopy may be a factor. The heavy wide tape around the edges of the slider folding inward making the effective size of the slider may also contribute. But in any case the slider failing to do it's job is the primary cause of brutal rouge openings. It is possible but unproven that a domed slider is more likely to reliably function as the mini parachute needed to catch the relative wind and stay in place until line stretch. However the only reason I feel it may do so is that it is shaped more like a parachute than a flat slider is. In other words it is strictly intuitional thinking with no data to back it up.

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2 hours ago, gowlerk said:

[...]

Deflection of the airflow off of the much larger bottom skin of the canopy may be a factor.

[...]

It is possible but unproven that a domed slider is more likely to reliably function as the mini parachute needed to catch the relative wind and stay in place until line stretch. However the only reason I feel it may do so is that it is shaped more like a parachute than a flat slider is. In other words it is strictly intuitional thinking with no data to back it up.

If deflection of the airflow off the bottom skin is the cause, then a domed slider would inflate in the opposite direction, and the deflection would push it down the lines harder, no?

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34 minutes ago, Deimian said:

If deflection of the airflow off the bottom skin is the cause, then a domed slider would inflate in the opposite direction, and the deflection would push it down the lines harder, no?

Maybe, I don't know and neither does anyone else as far as I can tell. In my mind the picture I have is the slider filling up faster therefore not allowing a space for the deflected air to fill and begin the process. But it's all just a theory.

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20 hours ago, sheeks said:

So you pull stable, the line stows release in proper sequence, the parachute comes out of the bag when it’s supposed to, and luckily because all the stars are aligned, the direction of air is coming directly directly upwards into the slider, keeping it in it’s proper place as the canopy inflates. Congratulations, you’ve just had a succesful and steady canopy opening.

 

Now, let’s just say the stars aren’t aligned. You rushed the pack because you didn’t want to be late for the next load. Your rubber bands are getting a little old, and you get so caught up with your buddies in the air that you end up losing altitude awareness and seperating a little on the late side of things. You still get to pull at 3500, but this time you still haven’t slowed down from the track and between your increased speed and the age of your stows, your bag starts to open a little prematurely. Instead of opening directly over your head, your canopy is angled and not properly tense by the time it comes out of the bag. This increase in chaos allows some air to start slipping in behind your slider, because the canopy is too sideways for the air to catch into the bottom of the slider in the way it’s supposed to. You get a bottom skin inflation, and your canopy is opened harder than you’d like. At the least you get a few bruises, at the most your family is mourning your loss.

 

Now, maybe if the slider had a bit more fabric to it, and was more domed instead of being shaped so flat the way it is, the chaos of the airflow into the canopy might have been a little more controlled, and instead of that air slipping in behind the slider, it would have been more directed into the path of least resistance inside the slider where it should have been going, and kept the slider up long enough for the canopy to open more controlled in the way it was supposed to. 

Take a plastic bag, and rush it through the air 100 times in a row. How many times does it inflate the way you want it to?

Now cut out a rectangular segment from that plastic bag, give it just a few inches of slack, and rush it through the air 100 times in a row. How many times does it inflate the way you want it to?

 

The point i’m getting at, is maybe slider modifications that help a slider catch air better aren’t only for canopies that open too hard. Maybe instead of only domed sliders on Sabre 1’s, that domed sliders on spectre’s, pilot’s, and safire’s wouldn’t be such a bad idea. If they make a canopy open TOO slow, then maybe a smaller domed slider is better than a larger normal/flat slider. 

 

Sliders obviously don’t have to fill up to the size of a basketball, but maybe just having an extra two or three inches of slack in the fabric could make a world of difference when it comes to less than desirable openings, and would probably only increase opening time by 1-3 hundred feet. 

 

How often do you hear of a hard opening with a pocket slider or domed slider? Far less often than with regular canopies.

 

Thoughts? 

it seems that dome sliders do work, I jumped a canopy from Paratec and noticed that the slider was not rectangular but domed shape, it really had an affect on the openings, a few years later packing tamdems I saw a dome slider on the sigmas and they had great opening. looking at todays canopies and their crossport designs and tapered leading edges on high perf canopies, manufactures are doing great things with openings.So its hard to say whether it's canopy design with today's tech. that's allowing canopies to open slower or is it slider design. After a few years in the sport I learned that even if you think you have the best opening canopy, you may have that one opening that will zap you, whether it be from air temp, or cond in the air or whatever it may be

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SOFTERMAN!!! 

In the 2000's there was a guy who's real name I never knew.  He had ad's in Parachutist for a year or more.  He gave a seminar at a PIA symposium that was a sales pitch for an after market domed slider that he promoted as a new lifesaving device.  He jumped into the seminar wearing a super hero tights out fit as 'SOFTERMAN'.  He thought a domed slider on everything was his idea for the next big skydiving thing.  Really had no real testing info or other supporting information.  He was so silly nobody that I know took him seriously let alone bought one of the things.  By the way I don't believe he ever called it a slider but some other sort of 'device'.  BTW we never let him give another seminar because it wasn't educational, just a sales pitch which are not allowed as a Symposium seminar.

IF a domed slider provided more consistent opening I guarantee the major canopy manufacturers would be installing them.  Clearly cost of construction is no longer an issue in the market.

I agree (sometimes, like now) with Mark that the everything is in line with the relative wind.  I believe a slider made to try to ease a hard opening would only make every other opening much too slow.

But keep thinking.

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PD is a company that has done a lot of fiddling or research with slider design, and while they have some domed sliders, the variety of slider designs they use suggests that domed sliders are not the answer to every problem.

Most PD sliders are flat, but PD uses domed sliders on the Sigma tandem mains. They also have Katana canopies of certain sizes with mesh at the outside of the slider, divorcing the grommet spacing from the actual sail slider fabric size. Those sliders are also domed. They also have canopies with I guess flat sliders, that have snaps to hold the slider in place, and that's whether it is a high end swooping canopy or a giant-nosed accuracy canopy.

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15 hours ago, JerryBaumchen said:

Hi gb1,

^^^^^ This.

As someone said to me a few years ago, 'If it weren't for people like XXX, we would all still be jumping gutter gear.'

Jerry Baumchen

Jerry, you have a good memory. Sheeks could be one of those people. Always good to hear your comments.  Obvious you are one of the more wise people on this site.   Jim T

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When I worked at Para-Flite we did lots of work with domed sliders and also lipped sliders. As a matter of fact we used them on our cargo delivery systems in the mid to late1970s up until the time I left in 1995.  Now having lines dump due to bad rubber bands this can cause an out of sequence opening and no slider will prevent that.  If the canopy is out of the bag before line stretch it can spread. Without tension on the lines the slider cannot contain/restrict the opening as the canopy has started to inflate. Domed sliders can increase the snatch force create  a spike in felt opening shock. I had many instrumented jumps measuring g forces some with very low g forces felt harder than much higher g force openings due to the length of time the forces were occurring. Out of sequence opening can kill or injure.

 

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On 3/6/2019 at 9:07 PM, sheeks said:

....... assuming that it’s properly quartered in the first place .....

hah!

Hah!

Watch more people pack and count how many times they perfectly pack their sliders ...... versus just shoving it into the middle of the canopy.

I jumped Sabre 1s hundreds of times - with factory stock sliders - and they only slammed me when I lost control of the slider while “bagging” them.

 

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