Aug 2, 2007, 8:29 PM
Post #1 of 13
I have been thinking a bit lately on how the slider slows the opening. I know it chokes the lines to the canopy to control how fast it inflates, but my question is 'what is the slowest sized slider?'
Let me explain a bit further. Initially I thought that a smaller slider would cause slower opening due to more 'choking' force, but after searching and reading here I have found that a smaller slider will cause faster opening, I guess because due to smaller size there more force pushing it down.
So at what size does the slowest opening occur? Obviously there must be some point where a bigger slider will actually cause a faster opening, take the extreme example, if the slider was the same size as the canopy there would be no 'choking' at all so the canopy would open as if there was no slider. Does the slowest opening happen when the slider is a set size, say 1/10th as wide as the distance from outermost lines, or does it vary from canopy to canopy?
There is no real reason behind this question, I am just curious about the physics behind opening.
There are a number of forces acting on a slider during the opening sequence.
Just after the canopy comes out of the d-bag, you're still descending vertically. The canopy is trying to inflate -> lines move further apart, pushing down the slider. In opposition to this is the force created by the air on the slider, holding the slider up the lines.
As you decelerate, the force holding the slider up the lines decreases (because the force from the air is less) and the slider moves down, allowing the canopy to continue to inflate.
As to the "one true size", I don't think there's one. But then I'm not a parachute designer.
As a side note a bigger slider doesn't mean a slow opening. If the slider is to big then more of the canopy when it get out of the bag can inflate before it has to work against the slider. You get a very hard snatch force but the rest of the opening will be quite slow.
The ideal solution would be to create a small slider (lots of reefing effect) but with the drag of a bigger one (longer snivels). That’s why pockets and domes work so well, they combine the best of both (reefing of small and drag of larger).
I know first hand tha a dome slider (of equal size to factory slider) works great on a problem canopies. For example a sabre 1. MEL (skyworks rigging) explained it to me once - a dome slider is "self correcting" so it will never stand on an edge and come rocketing down the lines like a regular or pocket slider can.
if the slider was the same size as the canopy there would be no 'choking' at all so the canopy would open as if there was no slider.
In my limited experience I would say that wouldn't happen. The canopy will stay in the burble of the slider and thus choking it off. I experienced this while jumping a R.A.G.E. (107?) by Paratec. I did some jumps on that and every time I pulled, the slider was so huge that it didn't even let the canopy inflate. Of course when I started yanking on the yonkles the slider started coming down.