Pocket Slider vs Dome Slider

[3mpire 0]

From this thread there was some conversation about a pocket slider or a dome slider.

Can someone explain the difference between the two?

From the context of the conversation a pocket slider sounds like a regular slider with perhaps an extra piece of material added to increase drag whereas a dome slider is an entirely different cut of material for the slider (I'm envisioning an inverted ice cream cone).

My google fu was unable to find images or detailed explanations of either.

(on a side note searching for pocket sliders did lead me to hand bags made from old parachutes. oh la la!)

So of course I understand what a "normal" slider looks like and how it functions. Can anyone show me a picture of what a pocket slider and a dome slider look like, and maybe a little about how they're different in terms of affecting the opening sequence of a square main?

[pchapman 279]

A couple slider pockets.
(Normally they are fully open except for the pouches being sewn down at the center line, but these have been sewn partially shut to adjust and reduce their effect. I've even seen one that was built "so open" that it would invert and be nearly totally useless. The owner was going to sell the canopy, but a minute of sewing closed it up a little and now he likes the canopy.)

Pro: Easy to add on to existing slider
Con: Still takes quite a bit of time to build.
Pocket sliders may not be quite as reliable in catching air the same way consistently, compared to a domed slider.

[inline pocket1.jpg]

[inline pocket2.jpg]

[skydiverek 63]

Domed slider shown here:

http://www.youtube.com/watch?v=vZB0sNdUOcs

[3mpire 0]

pchapman

Pro: Easy to add on to existing slider
Con: Still takes quite a bit of time to build.
Pocket sliders may not be quite as reliable in catching air the same way consistently, compared to a domed slider.

Ah I get it. That makes sense. So basically the pocket is attached to the back (tail) of the slider and adds more drag causing the slider to come down more slowly, correct? Is the goal to have it actually inflate almost like a cell or just billow out like another mini slider?

In terms of reliability, do you mean that it might not inflate until the slider is already partially down the lines? What effect would that have on the opening? Just not as smooth?

Is a pocket slider always a custom addition or are there some designs from the factory that have this configuration or would they just go with a bigger slider or a dome slider?

skydiverek

Domed slider shown here:

http://www.youtube.com/watch?v=vZB0sNdUOcs

Ah that's a clever design. The idea is by having the material only connected to the front and back "edge" of the slider (what do you call that btw?) you can have more material creating more surface area and therefore more drag, right? Basically you get a bigger slider effect within the same dimensions of a smaller slider? What purpose would having mesh between the left and right edge and the center material serve versus just open? reduced risk of a toggle fire getting threaded through the slider?

[JerryBaumchen 1,373]

Hi 3,

Quote

the pocket is attached to the back (tail) of the slider

Peter has his photos upside-down. Unless someone has developed something that I don't know about ( always possible ), the pocket is on the front edge of the slider.

JerryBaumchen

[airtwardo 7]

JerryBaumchen

Hi 3,

Quote

the pocket is attached to the back (tail) of the slider

Peter has his photos upside-down. Unless someone has developed something that I don't know about ( always possible ), the pocket is on the front edge of the slider.

JerryBaumchen

That's the way mine is...on the front, and it has 3 separate sections.

I've had & used both domed and pocket sliders, MY preference is a pocket slider. For whatever reason the openings are more consistent.

~ If you choke a Smurf, what color does it turn? ~

[JerryBaumchen 1,373]

Hi 3,

Quote

Peter has his photos upside-down.

Let me rephrase that: His photos are as you would see the slider while under canopy.

Does that make more/less sense?

JerryBaumchen

[3mpire 0]

Yes that makes sense - now that I look at the photo more closely I see that it is on the front. I'm assuming its on the front so you have easier access to draw strings not because it matters during deployment?

[monkycndo 0]

3mpire

Yes that makes sense - now that I look at the photo more closely I see that it is on the front. I'm assuming its on the front so you have easier access to draw strings not because it matters during deployment?

The pocket is mounted on the front for other than having access to the lines that collapse the slider. Slowing the opening is done two ways. Keeping the slider against the stops until the inflating canopy forces the slider down the lines. The pocket on the nose of the slider will slightly deflect some of the air entering the nose of the canopy, when combined with the increased drag of the pocket holding the slider against the stops, keeps the canopy snivelling longer and the opening is softer.

50 donations so far. Give it a try.

You know you want to spank it
Jump an Infinity

[3mpire 0]

Interesting - that makes a lot of sense. It's interesting to me that even a little extra fabric can have a measured affect on how the air hits and opens the canopy.

[JerryBaumchen 1,373]

Hi 3,

Quote

I'm assuming its on the front so you have easier access to draw strings not because it matters during deployment?

My personal experience is that sliders almost always come down with the front edge higher than the rear edge; with the eexception of those 'slammer' openings; BTDT.

Gary Peek ( known as peek on here ) has done some studies that increasing the front to back dimension of a slider is the most effective way of reducing opening shock.

In effect IMO this is what the pockets do; increase that front to rear dimension. Yes, I know that as pockets they also catch air better ( no pms please ).

You might do a Search for 'peek' and see if you can get copies of his studies on sliders vs opening shock.

JerryBaumchen

PS) Take a read on this thread in Gear & Rigging: Gear and Rigging: sabre 1 hard opening fix

[3mpire 0]

Quote

In effect IMO this is what the pockets do; increase that front to rear dimension.

Makes sense -- I'll look for the studies and keep learning. thanks for the explanation and the tip!

[3mpire 0]

JerryBaumchen

Gary Peek ( known as peek on here ) has done some studies that increasing the front to back dimension of a slider is the most effective way of reducing opening shock.

Thanks Jerry for the tip, I found the study I believe you were referring to here:

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

I wanted to post the link in this thread in case someone in the future finds it via search and wanted to read the linked information as well.

Thanks again everyone, I appreciate the shared knowledge!

Edited: I've been informed that the link above is not accessible to all, so for the sake of future visitors I've excerpted a portion of the content so you get the main points:

Quote

First of all: Read the Manual!

Make sure you are doing everything the manufacturer suggests to slow down the opening.

The advent of zero porosity canopies and suspension lines that stretch very little, e.g., Spectra, has created many opportunities for variations and errors in packing to cause hard openings on these canopies. It has taken a while for information about how to prevent errors in packing to reach everyone, but now, there is no reason to be making obvious packing errors when so much is known about these problems.

Personal Experiences and Research:

Strong Enterprises Z-PO 150:

I purchased a Z-PO 150 when the design was quite new and had rather hard openings from the beginning. Stong Enterprises had no particular advice on how to slow down the openings, only that they had not yet gotten much feedback about hard openings. I suggested to Bill Morrissey of Strong Enterprises that we try a larger slider, a solution which has "traditionally" been assumed to make canopies open slower. (This may or may not be the case any more, as I will explain below.) He sent me a slider designed for a Strong Tandem 425 canopy. It is quite large of course, but on the Strong Z-Po canopy it made very little difference. (The Strong Z-PO was not constructed with a tuck in the nose as are many canopies.) Since that time, Strong Enterprises has found the solution of using a "pocket slider" on this canopy as well as other canopies that they make.

Performance Designs Sabre 150:

I purchased a new PD Sabre 150 (original Sabre, not the Sabre 2) that nearly always opened quite hard, as many Sabres seem to do. It seemed that many people had no problems whatsoever with hard openings on this particular canopy model (not particularly related to size) but occasionally someone would get one that opened unacceptably hard on most jumps, and eveything that they tried would not slow down the opening. This seemed to be the case with the Sabre 150 that I got. I discussed the problem with John LeBlanc of PD and even had him pack this canopy for me at the World Freefall Convention when we were both there, but even this pack job changed the opening very little.

Around this time, many people were purchasing Sabres and some were having hard openings no matter what they tried. This was also around the time that John LeBlanc published the document about hard openings, because it was believed that many of the problems people were having were due to errors in packing. I knew that this was not the case with my packing, so after dealing with two different zero-porosity canopies that opened much faster than I wanted, I decided to try to find another solution.

John LeBlanc suggested that a slightly larger slider might help in this particular case but that he was hesitant to suggest this solution to very many people. He thought that eventually someone would eventually solve their packing problems that were causing their fast openings, and then have a Sabre with a big slider that snivels for a long time, another undesirable type of opening.

I began measuring the slider sizes of many Sabres in order to find one that I could use that was bigger, but found that all of the sliders from canopies sizes ranging from 135 to 210 were within an inch of each other. The size I measured was about 30 inches by 19 inches. (Discussion about why different size canopies have the same slider size is a lengthy topic in itself.)

Experiments:

So, I tried a "radical" experiment: I put the Strong Tandem 425 slider on the Sabre 150. I opened high on the test jump in case it sniveled severely, however, the opening was very good, and continued to be good no matter what packing technique was used. I eventually sold this canopy, but the person I sold it to jumped it the way it was for a long time, and until having it relined, kept the Tandem slider on it.
After observing my success in getting my Sabre openings slowed down, people that I know began asking me to make them larger sliders for their Sabres, so I made several different sizes as "demo" sliders to see what size is really neccessary to work well without being too large.

Conclusions:

What seems to slow down Sabre openings reasonably well is a slider that is 2 inches wider and 10 inches bigger from front to back: (32" wide by 29") (This assumes that Sabre sliders are still 30" by 19".) Note: All of the sliders that I built used number 8 grommets even though many canopies with small lines have stock sliders with smaller grommets.

[JerryBaumchen 1,373]

Hi 3,

Quote

I wanted to post the link in this thread in case someone in the future finds it via search and wanted to read the linked information as well.

To me, this is what the internet is all about; the sharing of information.

Now you know more than when you first posted; to me, that is a very good thing.

And thanks for the link; if it helps just one other person all of our efforts have been worth it.

JerryBaumchen

[pchapman 279]

I found a photo of a really large slider pocket, although it doesn't show it well. The large white cape thing is the slider pocket on my Parafoil 282. (It's a model from maybe 15 years back. I didn't put the pocket on and don't know if the factory did or not.)

The slider addition basically has a pocket formed on the last 6", with a total length of a couple feet. In packing, it can be used to wrap the whole canopy roll, and on inflation the large amount of material may work to delay getting air into the cells, in addition to the pocket effect on the slider.

Openings can still be snappy and not symmetrical at times, but does make the Foil OK to take to terminal.

[inline large_slider_pocket_-_on_Parafoil_in_flight.jpg]

[3mpire 0]

That is gnarly!! Wow. I'm not familiar with the Parafoil is that a canopy that is not designed to go to terminal, thus requiring a pocket that large? I'm thinking maybe accuracy given its size and the body position in the photo, so sub terminal hop and pop style exits right?

[pchapman 279]

Yes the Parafoil is an accuracy canopy, and people often didn't want to take them terminal. There have however been variations in design and construction over the years. Most have just a normal slider and the latest probably just have a big slider. So that huge slider pocket is a bit of an exception.

[airtwardo 7]

pchapman

Yes the Parafoil is an accuracy canopy, and people often didn't want to take them terminal. There have however been variations in design and construction over the years. Most have just a normal slider and the latest probably just have a big slider. So that huge slider pocket is a bit of an exception.

Years ago they came with the 'spider slider' that was just a big X of webbing with the pilot chute attached to it - line going up through the center of the canopy. Pilot chute controlled reefing system. . . worked great- when it worked!

~ If you choke a Smurf, what color does it turn? ~

[3mpire 0]

Interesting -- so as the slider comes down the pilot chute essentially retracted? Or was there still some bridle between the pilot chute and the line to the spider slider? Were the pilot chutes a lot bigger?

[RiggerLee 61]

The idea is still around. Look at some of the new CRW canopies.

Lee

Lee
lee@velocitysportswear.com
www.velocitysportswear.com