Hooknswoop 19 #1 October 29, 2003 Several factors or combinations of these factors can cause hard openings. 1) Slider not up against the stops. If the slider is not completely against the stops o opening, the canopy is not reefed in as much as it should be allowing the bottom skin to inflate too much, overpowering the slider. 2) Initial pressurization of the canopy is too high, expanding the canopy too much, exposing too much bottom skin while still falling at terminal. 3) Deployment speed. Very few people actually flat track, or slow their vertical speed while tracking. If the jumper does not take the time to slow down after their diving track, their deployment speed can cause a hard opening. Also for free flyers, if they do not allow enough time to slow down from free fly speeds they can experience a hard opening. 4) Bag dump. It is possible, but rare, for the canopy to be pulled from the D-bag prior to line stretch, resulting in a hard opening. I have seen lots of videos of deployments, but I have never seen video of bag dump. If loose stows or line dump (not locking stows), caused hard openings, then every deployment with a 'no-stow' D-bag or coiling the lines in the bottom of the main pack tray would result in a hard opening. It doesn't. I have deployed several main canopies from free-bag style D-bag (with a pouch for all the lines except the locking stows) and except for intentional line-overs, have not experienced a hard opening with loose line stows. As long as the locking stows remain in place until they are pulled out at line stretch, the canopy will open normally. I have seen lots and lots of videos of deploying canopies. Some of them were very hard openings. I have never seen video of bag dump. Bag Dump What is it? Bag dump is when the pilot chute pulls hard enough on the bad and/or the line stows that hold the bag closed are loose and or small enough that the canopy is yanked out of the bag before the lines are taut. The canopy begins to inflate and then the jumper falls to the ends of the lines, resulting in an extremely hard opening. The opening could result in injury and/or equipment damage (broken lines, torn fabric, etc) For this to happen, the line stows that hold the deployment bag shut must be released before the line tension would release them normally. If the other, non-locking stows released early, the only difference should be a faster, not harder opening. How loose would the locking stows have to be? That depends. Size of the deployment bag, distance between the locking stows, weight of the bag, amount of force the pilot chute delivers at your opening speed are all factors. The heavier the line, the bigger the PC, and the farther apart the stows are, the bigger the problem. Taking some measurements on an old Sun Path Javelin J3 main deployment bag, the locking stows are 5 inches apart. If you make 2 inch stows, there is 8 inches of line outside the stows and 5 inches between the stows. The line outside the stows is heavier and high acceleration of the deployment bag does not tend to create bag dump. Acceleration tends to hold the stows in place until line tension pulls them out. Only if the locking stows were to break allowing the canopy to come out of the bag could the canopy open hard. Looking at a Sun Path Javelin J3 reserve free-bag, the locking stows are only 4 inches apart. With 2 inch locking stows, there is 8 inches of line outboard of each stow and 4 inches of line between stows. There an less weight inboard of the stows. So even loose stows shouldn't result in line dump and a hard opening. Looking at reserve packing instructions, I found the Dolphin manual says 2-3 inch locking stows, the Mirage manual says 2 inches for micro-line and up to 3 inches foe Dacron line, and the Reflex manual says 1 ½ inch locking stows." I believe canopies inflate in 3 "stages" Stage 1- once he canopy is out of the bag, it will "snivel" until the nose catches a bit of air and it begins to pressurize, making the bottom skin slightly larger than the slider. (I removed the ribs and top skin from a canopy and jumped it in a free-bag style D-bag. The bottom skin never inflated.) Stage 2- The bottom skin begins to inflate, out-pacing the pressurization of the canopy. The slider slides down the lines. Stage 3- Canopy pressurization. This happens last and accounts for closed end cells. Derek Quote Share this post Link to post Share on other sites
mouth 0 #2 October 30, 2003 QuoteStage 3- Canopy pressurization. This happens last and accounts for closed end cells. So explain what the cause of end cell closure is and how can you aviod it? I know to pump my risers to get them to inflate. What I want to know is how to stop it before it happens. -- Hot Mama At least you know where you stand even if it is in a pile of shit. Quote Share this post Link to post Share on other sites
johnny1488 1 #3 October 30, 2003 From what I have seen, it has nothing to do with packing, and has to do with the airpressure in the canopy. I have seen it more on lightly loaded canopy but I have no real evidence to support my outrageous claims. Johnny --"This ain't no book club, we're all gonna die!" Mike Rome Quote Share this post Link to post Share on other sites
mouth 0 #4 October 30, 2003 I load my Sabre2 at 1.04:1 so I don't heavily load it at all. I have the same loading on my Spectre and don't really see closed end cell often. -- Hot Mama At least you know where you stand even if it is in a pile of shit. Quote Share this post Link to post Share on other sites
rigging65 0 #5 October 30, 2003 QuoteI know to pump my risers to get them to inflate. What I want to know is how to stop it before it happens. Why do you want to stop it before it happens?? Closed end cells are almost always associated with soft openings...don't you like soft openings?!?!?! As a canopy is pulled through the air during inflation, a combination of events are occurring. First, air is being rammed in the nose. Second, as more air is rammed in there is a pressure increase. The excess pressure is shunted away to other cells via the crossports. As the pressure inflates the more outboard cells, the bottom skin gathers air and spreads itself out (also aiding in topskin inflation). This spreading causes pressure on the slider, trying to force it down the lines as they spread. The slider catches air, effectively slowing its descent. On a very slow opening (one that might result in closed end cells), the bottom skin inflates so slowly that the pressure in the cells themselves is not enough to force open the canopy. This is mostly due to the slider doing its job, as well as the trim of the canopy controlling how much air is forced in the nose. The canopy slows its descent slowly and smoothly until the slider is no longer effective. But, since there was no rapid bottom skin inflation, nor massive influx or air going into the nose (because the slider is doing its job holding the snivel together) there is not "adequate" pressure pushing through the crossports to push the outboard cells into shape...hence, the last cells don't get fully pressurized. By laying on your rear risers, or toggles, you're increasing the pressure inside the canopy, thus extra air is pushed through the crossports and helps inflate the end cells. Repeat after me..."Slow openings are good...we like slow openings..." If you don't agree, I have an old original sabre 210 I'd love to sell you.... "...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
johnny1488 1 #6 October 30, 2003 QuoteBy laying on your rear risers, or toggles, you're increasing the pressure inside the canopy, This is the only part I wouldnt agree with. I think by laying on the rears or toggles, you are lowering the airpressure in the canopy, slowing the canopy down enough so the force of the pressure inside the canopy can overcome the force of the relative wind holding the endcells closed. Johnny --"This ain't no book club, we're all gonna die!" Mike Rome Quote Share this post Link to post Share on other sites
mouth 0 #7 October 30, 2003 Basically because these same slow opening end cell closures also seem to cause off heading openings when they are not symetrical. -- Hot Mama At least you know where you stand even if it is in a pile of shit. Quote Share this post Link to post Share on other sites
mjosparky 4 #8 October 30, 2003 Quote there is not "adequate" pressure pushing through the crossports to push the outboard cells into shape...hence, the last cells don't get fully pressurized How do you explain how canopies opened before crossports?My idea of a fair fight is clubbing baby seals Quote Share this post Link to post Share on other sites
nacmacfeegle 0 #9 October 30, 2003 Hey Derek. Can slider size, design, and packing method significantly alter fast/slow openings. One way I used to tame my Angry Butterfly (monarch) was to pull more of the slider out at the front, dunno if this was urban myth or real. Cheers.-------------------- He who receives an idea from me, receives instruction himself without lessening mine; as he who lights his taper at mine, receives light without darkening me. Thomas Jefferson Quote Share this post Link to post Share on other sites
ZigZag 0 #10 October 30, 2003 One item I would like to agree with is stowage of lines. The years prior to becoming a rigger were spent packing main or tandem canopies, on various dropzones, and as such I was exposed to a variety of methods. Just about all of them worked well, provided the suspension lines were even, the slider was placed correctly, the stabilizers were oriented(flaked) outboards, the steering lines not pulled or placed in front of the nose!, clean even bights with good tension between the stows and an appropriate length of line left to prevent an uneven extraction of the d-bag. Basics!!! So much for convention. As a rigger one almost always stowes lines in the pocket provided (free stowing) on the free-bag, unless the system requires an alternate method, as with rounds, and I cannot remember a jumper complaining about an excessively hard opening, other than those that experienced asymmetrical deployments or excessive speeds during deployment.(Bless them) The locking stows on a freebag are quite secure, as the pull forces load them evenly, until the tension (load path) of the suspension lines reaches the first bight, initiating release from the stow. Some years ago, PARAFLIGHT conducted a study that addressed this issue with satisfactory results. So it can be interpolated, that the new method of freestowing the suspension lines in d-bags utilizing free stow methods is effective.(Provided the locking stows are done correctly). That said, we need to ask ourselves how much time and effort we have spent analyzing hard openings in relation to rubber bands, tube-stows and bungees (shock-cord), and the various configurations of d-bags and their attachment points for rubberbands! Pilot-chute size plays a significant role as well, in addition to the condition of the fabric of the p/c and the kill-line length. Too small a p/c for a large canopy may exhibit long delay times for openings due to reduced snatch forces.( Really nice soft openings). Too large a p/c for small canopies may result in increased snatch force. Shrunken kill-lines will adversely affect the p/c's effectiveness. Mfg's are aware of this and generally ship p/c's of appropriate size with their containers. But since p/c's and their associated parts (bridle & d-bag) are easily interchanged by jumpers, one might infer, that some hard openings could be attributed to mis-configurations of certain components. Maintenance is another issue, naturally! But to absolve all those that do their job correctly and pack their canopies with the utmost of attention: WARNING: Even a properly packed canopy may result in a malfunction, causing injury or even death! Do not ever forget the risk that you accept. The smallest molecule of air can have unintended results on your deployment, somewhat overstated, but you get my drift. Consistent hard openings do require an investigation by a rigger or the mfg. Just remember, that there are many factors that can cause a hard opening, and pin-pointing the cause is difficult. Free-fall body position may be another factor, or just plainly a bad design, which is rare these days. Lets keep this issue open, an ongoing investigation, from which mfg's can improve their designs, and let's keep an open mind. Quote Share this post Link to post Share on other sites
Hooknswoop 19 #11 October 30, 2003 QuoteCan slider size, design, and packing method significantly alter fast/slow openings. Slider size, disgin of the canopy make a significant difference in how a canopy opens. Pulling the slider out the front, rolling the tail tight, etc can change how a canopy opens, but not too much, in my experience. I think a canopy tends to open a certain way and that can be affected by packing technique, but not drastically changed. Of course packing errors can definately change how a canoy opens. Derek Quote Share this post Link to post Share on other sites
sunshine 2 #12 October 30, 2003 What about when a canopy is out of trim? ___________________________________________ meow I get a Mike hug! I get a Mike hug! Quote Share this post Link to post Share on other sites
Hooknswoop 19 #13 October 30, 2003 If the canopy is out of trim, all bets are off. Mostly, I've seen canopys open harder and off heading once they get out of trim. People are always amazed at how well a canopy opens and flys after being re-lined from out of trim. The difference from jump to jump is so small, but it adds up. Derek Quote Share this post Link to post Share on other sites
DBCOOPER 5 #14 October 30, 2003 QuoteThe excess pressure is shunted away to other cells via the crossports How about the Cobalts?Replying to: Re: Stall On Jump Run Emergency Procedure? by billvon If the plane is unrecoverable then exiting is a very very good idea. Quote Share this post Link to post Share on other sites
PhreeZone 20 #15 October 30, 2003 >How do you explain how canopies opened before crossports? Before crossposts the noses were'nt as closed off as they are today. The older designs the nose would catch enough air all the way across the nose to inflate the canopy. With more and more closed noses the crossports are assisting more in the opening then before.Yesterday is history And tomorrow is a mystery Parachutemanuals.com Quote Share this post Link to post Share on other sites
VectorBoy 0 #16 October 30, 2003 QuoteQuoteThe excess pressure is shunted away to other cells via the crossports How about the Cobalts? Cobalts do have crossports in the 3rd and 6th cell its just that they are about one half the area of the rest of the crossports, thereby metering a smaller amount of cross ventilation inflation. Quote Share this post Link to post Share on other sites
rmsmith 1 #17 October 30, 2003 QuoteCan slider size, design, and packing method significantly alter fast/slow openings. My 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. Quote Share this post Link to post Share on other sites
rigging65 0 #18 October 30, 2003 QuoteMy 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!... "...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
rigging65 0 #19 October 30, 2003 QuoteHow do you explain how canopies opened before crossports? Crossports aren't the only thing that lets a canopy open, they just help equalize and regularize (is that even a word???) the openings. Before crossports the nose did most all the work. And because of that, the leading edge on most canopies wasn't all the aerodynamic...at least not as compared with the shaped leading edges as found on some canopies today! This shaping is advantageous, as any pilot will tell you, because it's the first third of the wing that produces most of the lift...keeping it clean and smooth helps all that along. "...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
cssriggers 0 #20 October 31, 2003 What he said. Thanks for continuing to share your wisdom. Note to all - opening in a track can be painful. Be sure to pay attention to body position if you're having problems (hard and/or off-heading openings, line twists, etc.) Make sure you've slowed down and your shoulders are even. I agree with the line stow issue. The original "Berger Bag" - main Dbag with free-stowed lines - has no locking stows at all, just tuck tabs. (The prototype was built in our loft.) I've only seen video of deployments and heard reports from the field, but it seems to work very well. The videos were impressive; the bag almost looks anchored in the sky as lines release cleanly. I also think slider size and PC size/type/ condition are very important. I had a canopy that was really spanking me from time to time. I put it in a rig with an F-111 PC and the openings were immediately softer. We had a spate of problems in the past few years with some new canopies that were designed to have "inherently soft, sweet openings" putting newer jumpers down near Cypres-firing altis if they didn't watch it. After some trial and error smaller sliders solved all these problems. As for pressurization/crossports/line trim: Strong tandem mains don't have crossports and tend to have soft but not snivelly openings when new. Once they get some jumps on them we've found that they tend to snivel and have end cell closure, and it seems directly related to shrinkage of outboard lines. Of course this would seem obvious, and I'm not sure how this would relate to sport canopies. A question - I'd always heard/learned that older, high-jump # canopies - esp. F-111 - are supposed to open more snivelly as they lose porosity. But in experience it seems that old Sharpchuters, Rascals, Raiders, etc. seem to open hardest of all. Does anyone have an explanation for this? Would this be due to canopy design or tired fabric?Alpha Mike Foxtrot, JHL Quote Share this post Link to post Share on other sites
mjosparky 4 #21 October 31, 2003 QuoteA question - I'd always heard/learned that older, high-jump # canopies - esp. F-111 - are supposed to open more snivelly as they lose porosity. But in experience it seems that old Sharpchuters, Rascals, Raiders, etc. seem to open hardest of all. Does anyone have an explanation for this? Would this be due to canopy design or tired fabric? I agree with you that older sharpchuters open harder. I have 1500+ jumps on several of them and this always seems to be the case. They all had dacron lines and stayed pretty much in trim all the time. + - 1 inch. I have never been able to come with a reason.My idea of a fair fight is clubbing baby seals Quote Share this post Link to post Share on other sites
lazyfrog 0 #22 November 1, 2003 I had 2 hard openings witrh my saphire2 139 (I wheigh 75kg naked), never understood why... one hurt my back, the other one made me see stars (i had my video on the helmet for that one), the only thing you can see is when the bag is extracted (image moves a little) then the image "jumps" and you see my feet... but it normally takes 300 meters to open...---------- Fumer tue, péter pue ------------- ourson #10, Mosquito Uno, CBT 579 Quote Share this post Link to post Share on other sites
Hooknswoop 19 #23 November 1, 2003 If I had to guess, I would say most likely it was the slider not being against the slider stops on the stabilizers. Derek Quote Share this post Link to post Share on other sites
lazyfrog 0 #24 November 2, 2003 do you think it makes a difference if it's like 2 cm away ??? cause my slider was always up and open.---------- Fumer tue, péter pue ------------- ourson #10, Mosquito Uno, CBT 579 Quote Share this post Link to post Share on other sites
Hooknswoop 19 #25 November 2, 2003 Quotedo you think it makes a difference if it's like 2 cm away ??? cause my slider was always up and open. Yes, any little bit down the lines I think can make for a hard opening. Since your canopy nomally opens softly, leads me to suspect the slider. It isn't difficult for it to slip down the lines while putting the canopy into the D-bag. Derek Quote Share this post Link to post Share on other sites