pchapman

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.

I saw one where the student didn't mind that the slider came down, but when she couldn't get it to go back up, even after pumping the brakes, that's when things got scary and she cut away.

... you knew that having cool colours on your rig and canopy required dye and a laundry tub. ... you knew that the way to get a really hot canopy was with a pair of scissors. ... you had a pair of frenchies. ... you dearched before cutting away

Good point. I've seen such pockets too. One presumably worked well, while another did absolutely nothing significant according to the jumper (but it was a bit of an unusual canopy). One pocket I built for myself ended up being too big, so I sewed a portion of the mouth closed. But it was easier to build big and reduce, than to start small and find I had wasted my time on a pocket that didn't work. I'll accept others' experience that things like a new larger slider or a domed slider may be superior, but a pocket can be sufficient. I had a customer who was literally going to dump his canopy on the bonfire but was happy with it after I added a pocket. At the extreme opposite end of the wide-tape-pocket, there's the two foot long slider pocket on my Parafoil that during packing goes outside the canopy roll and wraps around it, and looks like a Superman cape when the slider is stowed behind one's head after opening. With that "flag" slider pocket, I have no problems going to terminal, unlike some other Parafoil jumpers. (I think the pocket is susceptible to line burns and it perhaps has some negative effect on overall opening reliability.)

Holiday season = Northern hemisphere winter and denser colder air slowing canopies down. So a few extra pounds just evens things out for true airspeeds. :) Seriously, yes some jumpers do get concerned about their wing loading and weight changes, if they put on significant weight (not just 5-10 lbs) and are already loading their canopy up at some personal comfortable limit. If anything, this issue gives jumpers a good incentive to stay fitter and keep weight off.

I don't work in a big rigging shop or anything so I don't know any "right way" to build a pocket. I just made something up. But here are some pics of two I built and one someone else did. Differences exist in whether the center sewn down point of the flap is supported by a lengthwise or crosswise piece of tape. Also there is one set of rough plans available on dz.com from '03. Search "slider pocket" and "rigging65". He cut the flap material flared wider, so that when folded and sewn, it bulges to catch air more reliably. It seems a sound idea but making everything squared off works too.

Might as well finish this thread off. Tri160 was pretty close. The airplane is apparently a Handley Page HP 33 "Clive". It all looks a bit messy as there were similar HP 33's, 35's, 36's, with bomber versions and troop transport versions. Anyway, one of the military transports ended up civilian registered, sold to Alan Cobham's travelling aerial circus. That's the plane in the photo. So unlike most photos of drag-offs from similar planes, that could well be a civilian jumper. (As for the later photo of a sheep in a parachute, it is unrelated, and was from the Italian military resupplying their troops with fresh meat by air in Ethiopia.)

Nothing against what you are saying, but one can sarcastically say that yes, it had nothing to do with experience --- as they evidently didn't use that experience to set up properly and avoid a simple communication error that newbies might make. :-) Just another Bridge Day.

Also seen rigs built that way for style jumpers. Less intrusive during a tight style tuck.