pchapman

Slightly odd risers indeed. There's probably some other explanation, but those risers with 3 legs to them would work for a ParaFlite Evolution, that had spanwise cascades and used similar risers with 3 legs. The middle riser would connect to the B lines only, and the dive loop on it would make it easy to do a B-line stall (as it is termed in the paragliding world) - a relatively controllable stall with the wing staying roughly in place and not collapsing. Or, pulling on one side only, as described in the Evolution manual, would produce a very quick turn. While putting those risers and an Evolution together makes sense, I'm not sure why such a nice new looking set of risers would have been put together with an old, rare, quirky, out of production canopy like the Evolution. I suppose one could use those same risers with any continuous line canopy without cascades. (Like a Xaos, right?) But why, I'm not sure. Pulling the front riser dive loop on such a 3 riser system would only pull down the A lines, not the A and B like on a normal setup. Pulling just the A's makes it very easy to tuck the nose under. It's all fun and games with a moderate sized Evolution up high, but deadly down low if one wanted to use front risers to set up for a swoop with a tiny canopy. (And yes the term "triple risers" has confusingly been used both for risers with 3 full legs, and those that have the brake lines coming off an offshoot on the normal rear riser. I'm not sure if clearer terminology is available.)

Better in Florida nearer the equator than in the UK. And when someone has a turn on landing, maybe it can be blamed on coriolis forces. :) But seriously, to add to the other useful stuff in the thread: A PLF is handy when there's vertical speed to dissipate, if you drop it in from some height. Slides are good for taking care of horizontal speed, unless the terrain is uneven enough that you might catch a foot and break an ankle. But to slide you do have to be down low, not planed out a foot above the ground. You need to be down where you lift your feet a bit and then just put them down for ground contact. Keeping the plane out low avoids both any vertical drop at the end, and allows for a low body center of gravity so you don't pitch forward while trying to slide with feet out in front. (Or if you are the stage with a canopy where you can't guarantee the plane out is at a precise height, X inches off the ground, you can pretty much plane out but with a very gradual descent so that some time during the flare process you get to the desired height and finish the flare.) It is hard to run out a landing if you have any significant vertical velocity on landing -- If you touch down running, one foot touches first, and it will take a lot of the vertical energy shock on its own. Easy to hurt yourself that way. A slide also allows for a more gradual transition from flying to not flying. As weight transfers to your feet from the canopy, you are effectively loading the canopy less, allowing it to keep flying to a lower speed. As for getting your rig dirty in a PLF, if you really need to, you just do it. Better than slamming in on your wrists and face as people do when they are unprepared for whatever excess speed they have on landing. I'm not sure how to best describe it, but getting ready to twist on landing is helpful. You need to twist if you are going to PLF rather than fall face forward, and if you are going to slide it in, you need to do it to be less likely to drop it straight in on your tailbone and spine.

The "marionette" problem! For the orig. poster: Having a loosened chest strap also helps get your body more upright while the canopy is behind you during the flare. A loose chest strap is not just for cool swoopers. (But someone new should get a briefing on loosening the chest strap because there are a couple small concerns about distraction or cutaways after opening.)

Yeah the simple approximation method only works when dealing with low probabilities, and few enough repetitions that the cumulative probability stays low. So it is close enough if one looks at 2000 jumps and 1/100k jumps having the bad event happening. But it doesn't work for your example, as you showed, for 100,000 jumps because it gives a 100% chance of the bad event happening. (And 200% for 200,000 jumps...) Nor does it work for coin tosses, where we're talking about large chances of a chosen event happening. After two coin tosses, the chance of getting heads at least once clearly isn't .5 * 2 = 100%. So there are plenty of cases where one has to use the proper way to calculate the theoretical risk, e.g., using the chance of staying alive per jump to the power of the number of jumps = the chance to live through every jump. For some more fun philosophy of risk, one can think about the risk per participant per year. If you normally jump 100 times a year, what do you do if one year you can only make 10 jumps. Do you figure you can pull low and hook it irresponsibly, because you can be 10 times more dangerous per jump and still maintain your comfortable average risk per year?

What you are thinking of is this: Chance of getting killed 1 in 100,000 per event (=jump). Therefore chance of not getting killed is 0.99999. To make 1000 jumps, you need to get "not killed" 1000 times in a row. So it is .99999 for one jump, times .99999 for the next jump... and so on. (Like a coin flip: .5 to get heads. So to get heads 3 times in a row it is .5 * .5 * .5 = 1/8 chance.) So for the jumping, it is .99999 to the power 1000 = .9900497 to not get killed. Subtract that from 1.0 for the chance to get killed, = .00995 = 0.995 % chance. This is very close to the approximation where one just multiples 1 in 100,000 by 1000, equals 1 in 100, equals 1 %. The approximation only works when calculating events that are highly unlikely. (When one gets into calculating something like how many malfunctions will I have in 2,000 jumps if people have a mal on average 1 in 500 jumps, that's a little different. One can still look at the simple average and say "4" as an approximation, but the real math gets a little messier, into binomial theorem stuff, because one is looking at the number of mals, which can vary, not whether or not one has a mal at all. In the death case, one only cares if one gets killed once as that puts the stop to further chances of jumping and getting killed again...)

I hesitate to get involved in this as there are so many factors, and the subject has so often been discussed before. Look for the USPA annual fatality summary published in their mag, The Powerpoint version may be online. They show some info on the number of jumps per year in the US, as well as fatalities. (Just watch for the issue of students vs. non students in the numbers.) Lately the 1 fatality per 100k jumps sounds like a reasonable starting point. If a somewhat active recreational jumper makes 100 jumps per year, that's a 1 in 1000 chance of getting killed per year. (Yes statistically one can't just multiply like that, but it is close for small probabilities.) Over 20 years of skydiving that's 1 in 50, or 2%. While not like a lifetime of Himalayan mountaineering, that's still appreciable. One might choose not to go to a restaurant if one knows someone is going to walk in and randomly kill one of the 50 people inside. One in 50 also gets into the territory of "someone you know is going to die in the sport" if one is around long enough. Sure one can say one won't be like the average jumper, but there are those risks that are hard to avoid -- aircraft crashes, hit from behind under canopy, and so on. Also, just about everyone thinks they are going to survive their next swoop... but some don't. We are all stupid at some point, so it is hard to expect the stats to not apply at all to oneself because of how smart and safe one is. (Not to be fatalistic... one should still try to be better than average.) As for comments about statistics not "catching up": They sure do for cumulative risk. If the dice are fair the chance of rolling snake eyes on 2d6 is the same 1/36 as usual even if one has rolled a hundred times without, but the total risk of rolling snake eyes keeps rising each time you roll. While playing with a few risk numbers isn't what will keep one alive on one's next jump, and good data is hard to get, I think it is still worth looking at stats to get some idea in one's mind about the long term risks of the sport.

I'd guess 1200 fpm is reasonable, for only slightly turning flight with no brakes. Sharper turns are of course much faster, while hanging out in brakes can be quite a bit slower. (I've flight tested a few main canopies and was getting about 1000 fpm for big student stuff, 1200-1300 fpm for a 160 and 135, older squarish non-ground hungry designs, at say 170 lbs weight.) Even if I'm off on my numbers, your friend seems to have been a bit on the low side.

Thankfully, no. :) I suppose some riggers have gotten used to packing those Raven MZ's? Since ZP front skin BASE canopies exist, it isn't out of the question that ZP last chance parachutes can be packed neatly. It's just that personally I haven't seen or repacked an MZ in a decade. (My question is separate from the original poster's question, although it fits under the subject of ZP reserves in general.)

Since you think things through I guess you'll also realize the little problem with lead being over 11 times more dense than water. (Spherical shot of course won't attain the same ratio.) A 34" long water belt that's 6" high and a chunky 1.5" thick is going to only get to 11 lbs of water. "I'm sinking on the formation... pull the emergency dump valve!" [edit for typo]

I've only done CRW with tandem canopies the safer way -- jettison your passengers first.

Phenolics, delrin, all these sorts of options -- it would be interesting to see what the strength calculations work out to be. I'm not knocking the idea, just saying that could be part of the process. Carbon fibre may be overkill. The related issue is what strength is required. It's not like there's a lot of research into the loads on slider grommets, both for normal and abnormal openings. Putting a normal #8 brass grommet into a tensile test machine would at least give a baseline of what is an old standard in skydiving, whether or not it is structurally overbuilt.

What can one say? Some say better safe than sorry, get it done. Figure out where it fits into ones overall skydiving budget. Others wait until something breaks. How can one tell what the limits are unless one finds them? One has to figure in how much of a risk of loss there is, if one has to chop the canopy, e.g., whether the DZ is surrounded by trees or not. In your case you may not have a very accurate idea of the number of jumps on the line set already, which is also a factor in people's decisions. Another factor is how easy it is to get the set replaced. Maybe not for you, but for some it means sending a canopy away to another country, so if one doesn't send it away one off-season, one will want to put another full season's jumping on the canopy. One can see when a line starts to look really fuzzy, with many loose ends sticking out, that one figures will do something to the strength. But really, how often does one see a line tested to its limit? At a smaller DZ, one may only have someone break a line every few years, and if one isn't at the DZ that day, one might never see what it looks like. So one's actual experience base in seeing lines that have broken may be almost zero, making it tougher to make a decision. (Brake lines are another matter and clearly require more care. Also, while lines may in general break on opening, there is the issue of lines breaking during a high G approach rather than during a very soft opening. Rare but it has happened.)

For that "crazy airshow trick" - Anyone have an idea who or where it was? It shows someone doing a drag off from the top wing of a Jenny biplane, at what appears to be a racetrack, with the caption just saying that it was in Canada in 1972. The sleeveless canopy is just opening, but the reinforcing bands in it seem to crisscross every which way, not like the usual gore style parachute. More like a Hoffman Triangle or ??? Even in '72 a jump and aircraft like that would be extremely rare! [Edit: added hours later:] It seems the photo was mislabelled. There are a bunch more in the sequence, but with different tags. Between the other photos and searching of car race websites, those distinctive stands were the ones at the California Motor Speedway, at Ontario, California. It was out in agricultural land then, but is all covered by malls and the like now. Looks like the jumper went without a reserve, as far as I can see in the photos.

Here in Canada, where we went to 180 days some years ago, I didn't see much change in repack prices. Maybe a rigger bumped the price up by $5, figuring if it was time for a modest increase, now was a good a time as any. While with 180 days a rigger might have to deal with more wear and tear on rigs, in some way it made it easier to recommend work to be done. There was perhaps less of a feeling that something could wait for the next repack in a few months. For some, 180 days is a full season.

Interesting, Mark! Like you originally, I missed that reference in the 105.45 tandem section. But the FAA really tries to confuse us. In the doc Howard provided, the FAA specifically stated that the rule changes have nothing to do with tandems: "Another commenter stated that this rule should also apply to the main parachute of a dual harness/dual parachute (tandem) system and that ‘‘the 180 day requirement should be applied to such systems to give at least the same level of control as single harness/dual parachute systems.’’ Although this comment may have some merit, it too is beyond the narrow scope of this rulemaking, which addresses only single harness, dual parachute systems. The FAA will consider this issue for possible inclusion into future rulemaking."

Just musing, no good answers for the original poster: Carbon fibre composite rings (epoxy and fibre) still sound pretty good due to the strength that is possible, compared to say some plastic. Properly, they'd be disks so one can have a few holes next to the main one, to attach the slider fabric to. (In the manner of some RDS rings or Russian slider grommets.) I don't know how they'd hold up, but I don't see that there would be that much wear over a few jumps. On the other hand, the local heat buildup due to line friction on opening could be more than expected. Light lubrication probably helps, even if lubrication isn't generally liked in skydiving due to dirt trapping. One would of course want to test that slider descent rate is still OK given the different weight of the slider and drag of the grommets on lines. The question is whether there really is some existing product out there that is suitable, some engineered product hidden in an industrial catalogue. As opposed to going to a composites shop and having them make a mold and lay the rings up by hand, or learning composites techniques yourself. For strength one wants them built with the fibres going circumferentially around the circle, not just cutting a donut out of a flat sheet of carbon composite.

Just to get this straight: 1) Tandems stay at 120 days. However the FAA says it will look at the matter. (The FAA loves to say in response to a lot of questions that something is "beyond the narrow scope of this rulemaking".) 2) Earlier suggestions in dz.com threads were made that previous pack jobs would be only good for 120, yet I don't see language that prevents old pack jobs from automatically becoming good for 180.

(See the Gear and Rigging thread. )

The rate of descent itself won't change anything as long as the jumper isn't accelerating or decelerating. He's in equilibrium, in his own under-canopy terminal velocity so to speak. But lift does depend on the angle of descent. Lift isn't automatically "up", for it is defined as perpendicular to the direction of motion, and drag is parallel to that direction. So if you have a 200 lb skydiver + equipment, descending normally under a canopy giving a 2.5 to 1 glide ratio, the lift vector is tilted about 22 deg. off the vertical. There's only 186 lbs of lift. Since the 2.5:1 glide ratio also corresponds to the lift to drag ratio, there's about 74 lbs of drag. The jumper is being held up in the air (in constant motion without acceleration) by a combination of the 186 lbs of lift and the 74 lbs of drag. (If the same jumper is under a round chute that is descending vertically, he technically has zero lift and 200 lbs of drag.) When the jumper, back under a ram air, is flaring he will need to get the lift of the canopy to 200 lbs when planed out in level flight. [Edit: This is separate from the issue of increasing the actual load on the wing due to "pulling g" during a tight turn or the part of the flare where the jumper is pulling out from the canopy's descent. All that does increase the load that the wing feels.] It still makes sense in skydiving to usually just think about the 200 lbs as the load on the wing, even if we keep the whole lift & drag angles stuff in the back of our mind.

Yes one includes the weight of the main. But I could see one could also discuss a "payload weight", everything below the links or perhaps the connectors at the bottom of the risers. Just like "how much can I put in this airplane?" one could have "how much am I allowed to attach to this parachute?". But in practice it is simpler to deal with the all-up weight, which is also what is appropriate to wing loading calculations.

Ah, the poor ignorant skydiving novice! I can see how someone with about a hundred jumps might get confused. The novice knows that it is "normal" to hang outside an airplane like a C-182 or King Air, despite the danger to multiple people if a parachute is deployed at that point. The novice sees videos of 4-way or freefly teams doing transitions or maneuvers overtop of each other. The novice sees the cool photos of hybrid jumps with a jumper hanging below a couple belly flyers, and even better, of someone standing on top of the group. It is obviously something to aspire to, and accepted by national organizations like the USPA, CSPA, and BPA, all of which have shown hybrids on the cover of their official magazines in the last year or two. But if a novice mentions something similar with a tandem -- even when thinking about jumps with only experienced jumpers -- the novice is going to get slammed for even daring to think such wicked thoughts about obviously dangerous behaviour! Every society has its taboos and you just found out about one of ours. (But it is true that tandem rigs have additional complexities and dangers, and involving real students is much more frowned on.)

No TSO required. While less and less of such gear is around, it has allowed companies over the years to produce equipment in the Canadian market, like Niagara, Westway, ParaFab, Dionne, Parachutes Canada/Canadian Aerosports, and Flying High. Not all are still around. A couple companies did get TSOs on their later rigs, like Westway and Flying High. The lack of TSO requirement also allows for more freedom to modify gear. EXCEPTION in CAR 623.38: For demos requiring a demo rating. (That's the ones "over or into a built-up area or an open-air assembly of persons.") For those one needs TSO'd gear. But nobody checks, and few are likely to know the rule anyway. Unless I'm missing something, lack of a TSO requirement, or any gear rules from the government (as opposed to the CSPA) would allow one to conduct jumps with BASE rigs etc as long as it is outside of CSPA operations.

That's the surprising thing. It isn't as if he seems preoccupied with stability or practicing backloops. He seems to look forward and down, doing nothing until an unhurried waveoff and pull!

Last time I saw that debate come up on dz.com, there was no resolution that I recall. No proof that all chemicals (and pH especially) were compatible with nylon attachment tape and thus safe, yet no real evidence of actual harm occurring. Just guessing that marked tabs are probably fairly low on the list of things that will wear out and fail on a canopy over the next 2000 jumps.

Yup, I'm pretty sure I'm talking about you Lonnie. _IF_ that was Lonnie B, then he made plenty of BASE jumps before his injury (on a BASE jump), and I know he has made at least a couple since then, including a guyed tower he climbed. So he's not new to the game, and has some movement left in his legs.