kallend 2,117 #26 November 2, 2003 QuoteQuoteMy new Sabre2-210 was opening too fast, IMHO. I talked to PD about it, and they made another slider that was 3-inches longer in the chord dimension only. I've only got 4-jumps using the larger slider, but the results were a significant improvement. Just tagging onto this for educational purposes: "Bigger" is a general term. When changing the square footage of a slider, it's very important that certain things are taken into consideration. Since most common folks won't build their own sliders, this is mostly left up to canopy mfgs., but, increasing the width or length of the slider just to get surface area can open up other problems on opening. It can expose more bottom skin, change the pressure the lines place upon the slider, etc...these things can actually make matters worse. I know a guy who had a new FX (or VX?) that was acting up and knocking his around on nearly every jump, so Icarus sent him a new slider. It was actually smaller in surface area, but controlled the hard openings because it was proportioned very differently from his last, larger slider. Shape is as important (if not more so) than square footage! Just some interesting things to think about when you can't sleep!... I have a Stiletto 150 that gave consistently hard openings for several hundred jumps. Eventually I sent it back to PD. They kept it for over 2 months,. then sent it back with an adjustment to one stabilizer line attachment and a new slider (about 1 inch larger in each dimension). Now it opens beautifully.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
kallend 2,117 #27 November 2, 2003 Quote Stage 3- Canopy pressurization. This happens last and accounts for closed end cells. Derek I believe this may be the issue with Stilettos and their reputation for off-heading openings. Mine usually stays nicely on-heading until the very end of the opening sequence, and then if one end cell inflates before the other (which is fairly frequent) it turns sharply. I noticed on the Crossfire 1 a similar tendency for uneven end cell inflation, but that canopy did not turn as a result.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
Jonsmann 0 #28 November 2, 2003 A quick comment on this thread. In many posts it is stated that the canopy pressurises. While this is true (very small overpressure), it is not the reason for the opening of the canopy. The pressure inside the canopy is never very high, but the pressure above the canopy is very low. In fact the canopy is sucked open rather than blown open (don't get me wrong!). The underpressure on the topskin seeks to open the canopy, but the lack of air inside the canopy prevents it (and of course the slider). In full flight the overpressure inside the canopy is indeed very low (most people would be scared to know! I think). Often I hear people say that the pressure inside the canopy is very high, but that is simply not true. What "pressurises" the canopy is the underpressure at the outside of the canopy, rather than the overpressure inside. - Jacques Quote Share this post Link to post Share on other sites
rigging65 0 #29 November 3, 2003 QuoteIn full flight the overpressure inside the canopy is indeed very low (most people would be scared to know! I think). Often I hear people say that the pressure inside the canopy is very high, but that is simply not true. That's true, as anyone with any CRW experience will tell you.... QuoteWhat "pressurises" the canopy is the underpressure at the outside of the canopy, rather than the overpressure inside. I don't think anyone was eluding to the fact that the pressure was super high inside the canopy, it's just higher than it's surroundings. True, the reduction in pressure above the topskin does a lot to help this along, but what needs to be understood that the pressure inside the canopy is significantly higher than the pressure outside the canopy. "...and once you had tasted flight, you will walk the earth with your eyes turned skyward. For there you have been, and there you long to return..." Quote Share this post Link to post Share on other sites
Jonsmann 0 #30 November 3, 2003 So we agree, thats nice! :-) Quote ... what needs to be understood that the pressure inside the canopy is significantly higher than the pressure outside the canopy. You are right, this level of understanding of canopy pressurisation is adequate for most skydivers. Still the fact is that the overpressure inside the canopy is appx. +0.001 Bar, while the underpressure on the topskin is appx. -0.4 bar, both pressures relative to athmospheric pressure (appx. 1 Bar). For low speed flight it is very hard to make a high overpressure (depends only on speed), but easy to make an underpressure. So what really controls canopy pressurisation is the underpressure outside the canopy, the overpressure inside is insignificant. This is important because this thread is about openings and not canopy stability. A correct understanding of openings, require that you know that it is the underpressure that is the dominant factor. - Jacques Quote Share this post Link to post Share on other sites
rigging65 0 #31 November 3, 2003 QuoteA correct understanding of openings, require that you know that it is the underpressure that is the dominant factor. It is a factor, absolutely. But so is knowing about the relationship of slider dimension (both cord and span) as compared to exposed bottom skin area, drag as established by the pilot chute, drag as established by the canopy, trim angle of the canopy, line length, descent speed, etc... Some are more important than others (depending on what stage of the opening you're talking about), but it takes all of them to make it work. It's all important to know! "...and once you had tasted flight, you will walk the earth with your eyes turned skyward. For there you have been, and there you long to return..." Quote Share this post Link to post Share on other sites
kallend 2,117 #32 November 4, 2003 QuoteSo we agree, thats nice! :-) Quote ... what needs to be understood that the pressure inside the canopy is significantly higher than the pressure outside the canopy. You are right, this level of understanding of canopy pressurisation is adequate for most skydivers. Still the fact is that the overpressure inside the canopy is appx. +0.001 Bar, while the underpressure on the topskin is appx. -0.4 bar, both pressures relative to athmospheric pressure (appx. 1 Bar). - Jacques If that were true, the force across the topskin on a 150sqft canopy would be around 130,000 pounds. I find that hard to believe. I would believe an underpressure of around 150Pa to be in the right ballpark.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
Jonsmann 0 #33 November 4, 2003 QuoteIf that were true, the force across the topskin on a 150sqft canopy would be around 130,000 pounds. I find that hard to believe. I would believe an underpressure of around 150Pa to be in the right ballpark. Ok, I got a little carried away to bring my point across. The 150 Pa you mention seems a reasonable pressure difference between top and bottom skin when the canopy is in full flight. The absolute pressure is quite a bit lower though. Not the 0.4 bar, I will grant you that! My mind was on inflation pressures, not full flight pressures. Quote Share this post Link to post Share on other sites
