pchapman

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Everything posted by pchapman

  1. The cartoon "This Modern World" has taken care of the graphics already, fairly much in line with your thoughts. Obama has been playing the long game and now, at the last moment, shows that all the conspiracy theories are true: https://www.thenation.com/article/president-obamas-last-confession/
  2. Edited for clarity: For the "cautionary tale for the original poster", you started on that canopy very soon after student status, right Keith? Thanks for sharing.
  3. Brilliant idea, can't believe nobody thought of it before. Heck, we do it all the time. Just walk up to one of the security guards and tell them you want the elevator to the top floor, because you're a fucking skydiver! Some of them are a little hesitant, even when you walk in with a skydiving rig and cool jumpsuit. So DON'T TAKE NO FOR AN ANSWER. Tell him if he doesn't, he must be some kind of cock sucker. Mouth off about killing their stupid royal family, if they let those cool towers be built yet not let you jump them. Be a man and put those people in their places! They LOVE that take-charge shit over there. Remember to tighten your googles before the jump. Sometimes there's sand in the air there. You want to be safe, right? I'm impressed with your creative idea of deploying a student canopy at 550m (~1200 ft) AND using an AAD for safety. Whatever dropzone you jump at, your out-of-the-box thinking will make an impression on many. People won't forget you like some newbie are! As another suggestion, hang gliding naked off Everest is pretty cool too, especially if you're high on weed. But I admit I stole that idea from a movie. [Aside to other skydivers: Maybe then he'll be off the internet for some years.]
  4. True.. in general, within certain limits, under certain conditions. False... in particular. The Crossfire isn't a PD product and has relatively small nose openings. It and other canopies with similar noses may not be suitable at low wing loadings. As degeneration stated, Icarus themselves do not recommend it. If you were an experienced jumper / had canopy courses / had read DZ.com for the last 10 years, you'd know already. Openings: Hours in the tunnel may help with the pull position. (If you actually practiced holding the pull position.) It can't help much with dealing with the dynamics of opening or flaring out from a track. Anyway, good luck. You may well do OK. If nothing goes wrong, you know your emergency procedures, you're never caught in heavy traffic approaching landing, and you have a good sense for flaring, you could be fine. But you're doing yourself a disservice by downsizing so quickly. (Edit: I double checked archive.org for icaruscanopies. Initially they recommended 1.0 - 2.0 WL for the Crossfire "1", but later changed to 1.4 - 2.1. So the 1.4 value as seen for the Crossfire 2 still holds for the previous model.)
  5. Yes, and in the same way, it is simpler to define the angle of attack using that same bottom skin. Of course, to measure an angle, one has to look at that line relative to something else. For trim angle (or angle of incidence) that is the horizon. For angle of attack, it is the relative wind. So we should be on the same page. Yes in one sense it is, sure, one can choose that as one's convention. But the standard aerospace usage is different. You'll never find any engineering publication about the characteristics of airfoils that redefines the chord line (and thus angle of attack reference point) every time a control surface deflects. It would be a nightmare of changing references. One wants to know the angle the air is coming at the airfoil relative to some fixed reference angle through the airfoil. I guess if I were describing what happens when a jumper pulls down the brakes, I would say that the increased camber, especially at the aft end, will result in increased lift. The angle of attack does not change until the canopy pitches or otherwise changes its flight path. But for a skydiver trying to imagine what's happening, yes one can think of it as if the angle of attack has suddenly increased, since the line from nose to tail had changed. These kind of discussions do get at the usages of language and what terms mean and what is considered proper in what communities. We get "porosity" checks on canopies when technically someone can always chip in to say that "permeability" is the proper term. A skydiver might think of Lift as an upwards force, when the proper definition of lift is the force perpendicular to the line of flight... which for a descending skydiver is tilted somewhat away from the vertical. We always have some messiness when it comes to common usage versus technical terminology, and there's no single perfect answer.
  6. Sorry everyone else, here's my big reply: I'll have to disagree there. Yes that is the normal definition, you are quite right. However, for wind tunnel studies or simulations or whatever, everything is calculated relative to the wing with zero deflection on a control surface. That way one can say for example, "OK, this wing is at 2 degrees angle of attack. Let's graph the lift changes when we deflect the aileron 5 degree." You get the new lift values and plot the value for 2 degrees. So you see how the wing acts relative to the base case. If you redefined the angle of attack each time, then you'd have to rotate the model in your real or simulated wind tunnel. To give an example with made up numbers: "Let's see, the aileron is 20% of the chord length, and a 5 degree deflection down now puts the trailing edge 3.4% of the chord down and 0.4% of the chord forward from where it was, which corresponds to a 1.6 degree change in the angle of attack, so we are really measuring not for 2 degrees angle of attack but 3.6 degrees relative to the new reference line." Anyway, it would get quite messy. So again, the definition is correct as you were taught... But to make things practical, in any aerodynamics textbook or paper, the reference line is not changed when a control surface is deflected. In skydiving, I guess we can talk about it in either way because there's no mandatory aerodynamics training: a) Not very technical , but is still useful for practical understanding: "Dude, I pulled down on the toggles, so the back of the canopy went down, so the angle of attack went way up... and the canopy created a lot more lift" or b) The technical way: "The airfoil with toggles pulled, is still defined as being at the same angle of attack. But due to the increased curvature, it is generating a lot more lift at that angle." Yes indeed. Normally one uses "leading edge to trailing edge" as the zero reference line, but one can also do it relative to the whatever angle actually gives gives zero lift for that airfoil or wing. That can be handy to use as a definition when talking with skydivers, as it is more intuitive to understand that "the lift goes negative when the angle of attack goes negative", rather than having to explain why there still may be positive lift at supposedly zero angle of attack, that was defined along some easy to see line between points on the airfoil. In skydiving I also sometimes see the zero angle of attack line done along the bottom surface of the airfoil -- because it often happens to be fairly flat and the "nose is cut off" for a typical skydiving airfoil. That's handy when doing diagrams. If one draws the line in conventional airfoil fashion, from the very nose to tail, which will be from the cutoff point at the top of the nose inlets, that is technically correct too, although would tend to result in angle of attack numbers that are hard to compare to an airplane's airfoil. (Axis Flight School used that definition, I saw in a diagram of theirs.) These differences are often glossed over, both in instructional material and to some degree by myself, when explaining aerodynamics to skydivers. Sometimes that avoids confusion, but at other times a fuller explanation is required to avoid confusion when getting into more detail.
  7. For the thread: It's the picky people posting now! So "Glide Ratio" is normally defined for the aerial vehicle through the air mass. No ground, no wind, no up or downdrafts. As far as I can tell in aviation there is no really convenient universal notation for the glide ratio "relative to the ground" or "over ground" or "with wind". One just spells that out or makes sure that it is clear from the context. Calling it "relative glide" might be OK as an abbreviation, but one shouldn't define it as a key term as in the Parachutist article. Then one should at least call it "relative glide ratio", indicating it isn't just a pure glide ratio but relative to something else in context. (A quick look on the web shows no evidence that "relative glide" is a term that is used. Other than by the Axis Flight School, who wrote that Parachutist article. Well, at least make it clear that "glide ratio" is the proper term for the situation without winds.)
  8. To try to be more precise, a) It would be questionable whether the canopy would stall DUE to the angle of attack changing too FAST. (Air reacts very fast to changes so a sudden change in wing shape on our timescale shouldn't make it harder for the air to adhere to a wing surface.) b) But it will stall if the angle of attack is too HIGH. c) And if input is applied too fast, it can be easier to get to high an angle of attack, and stall the canopy, before the canopy has time to react and change its pitch and adjust to the new input. (For example, with front risers, pulling them too suddenly on a canopy where they are light, can cause a problem by getting the nose to zero angle of attack, even if the hand position is no lower than what is OK when front risering more slowly) In any case, rear risers don't cause as much pitching motion as using toggles, and the distance one has to pull rear risers until the canopy stalls is much lower than for toggles. So it is easy to stall a canopy on rears, and they are less useful for pulling out of a dive. That's why they joke "always trust your rears", because in reality, you shouldn't, when trying for a sudden dive recovery. Similarly, people have stalled their non-swooping canopies when trying to land entirely on rear risers. That isn't because they pulled too FAST, but they pulled too FAR (and if you are pulling fast, it is easy to go too far). When I was new at swooping (and the swoop course was over land) I recall my FX 88 bucking wildly as I was on the edge of, or partially in, a rear riser stall, because I was trying to pull out too quickly on rears. All was OK when I transitioned to toggles. Rear riser stalls tend to be more benign than toggle stalls, in that the canopy doesn't tend to collapse nearly as much. One isn't dragging the tips down & in with full arm movement. So the transition between stalled and unstalled is not as violent, making it easier to transition back from a stall. Still, if done at high speed, any stall is going to be more violent than at slower speed. =============== Aside about definitions of angle of attack: Rears are a little confusing when it comes to 'angle of attack' as they aren't really changing the angle of attack relative to the original location of the airfoil, but are only changing the airfoil shape. After all, in aero engineering, if one deflects an aileron or flap, one doesn't redefine the trailing edge of the airfoil to be where the deflected flap is. One still defines the angle of attack relative to the undeflected airfoil. But I don't expect skydivers to follow the exact same conventions, so I'm ok with the idea of saying that pulling on rears changes the angle of attack. It does if one is defining the airfoil zero angle as being between the nose and the deflected tail.
  9. 1. Indeed the "glide ratio" for an aerial vehicle is defined without any wind or reference to the ground. So there's no technical need to keep saying "glide ratio ... without wind". But skydivers aren't all trained aero engineers or pilots so inevitably someone is unclear whether someone else is talking about wind or no wind conditions, so in practice we sometime have to remind someone, "I'm talking about the real glide ratio of the parachute... no wind... and not talking about what happens in a wind." (In which case, the best glide ratio canopy would be the slowest descending one, flying downwind in a hurricane...) 2. Hybrid parachutes-paragliders have been around as a concept for a long time, but have never really found a civilian market. RevoFly was mentioned by Piisfish -- and RevoFly mention Nervures being involved, people who were working on that stuff two decades ago. [eg, Paramag did an article on them in 1998]. Even Paraflite / Airborne systems has some high glide military canopies that look like early paragliders. And I jumped a couple experimental PD canopies in the mid 1990s that were easily getting 4.5:1 glide ratio, although squirrely on opening. 3. Want a really high glide production skydiving canopy? Bigger canopies tend to do better because the payload under them is smaller and less draggy in relative terms. So while a Stiletto is probably great in a medium to small size, an efficient student canopy like the Navigator might have an even better glide ratio. Not sure of that, but just my impression.
  10. While everything is debatable, here's my quick take: Cypres 1 is worth zero. The small rebate deal when replacing it with a new Cypres was only for ones within 1 year after expiry. Some rigger might want to play with it though. The PD reserve is a PD reserve and worth a fair bit, and has plenty of repack life left. Some riggers still don't like stuff 20+ years old, so that's a factor, but that often was more of of a factor for weird old technology gear. How much people take into account that it will be 30 years old after 8 more years, I don't know. A PD reserve is still considered a gold standard in North America. (Ok, the PD Optimum might be Platinum, if the regular PD is still Gold) Turbo Z - nobody newer will recognize it. Out of production nearly (?) 20 years by a company out of the civilian market for that long. Which means replacing lines could be a real hassle. If it doesn't open too hard, and the lines aren't shot, it might be worth a few hundred for a newer jumper. Their actual flying was OK at moderate wing loading as you know. Vector II -- Worth a hundred or two maybe, I dunno, for someone needing a spare rig or first rig. But these days people may expect everything on the load to be more freefly friendly, so spending money on rigging mods would almost be expected. (Maybe less so if sold to someone experienced who knows the limitations.) Which makes it only worth it if picked up super cheap.
  11. That little? I know you have a lot of experience with lines and that's surprising. What kind of lifetimes have you seen? The criteria for replacement is tricky, as for how fuzzy is too fuzzy.
  12. The CSPA no longer does Style for its nationals, and I think that's a recent change in the last few years. So someone must have the ground video equipment. Don't know if the CSPA owns it or some S&A jumpers. It's a long shot but one could dig around and see if anyone wants to sell.
  13. You need to be hanging out at a DZ chatting!... There's a lot to learn. You can go to a big online skydiving site like Chuting Star or Square 1 or Paragear. Most carry most of the big name full face helmets. The Z1 is quite an older design. Newer designs tend to be bigger around the face. The ones that came out in more recent years, the G3, Aero, and Kiss for example are the ones without a big lump of frame infront of the mouth. In effect, getting rid of the "Darth Vader" breathing ports, which in prior designs used to be important for keeping the visor from fogging. So it is those newer designs that allow for seeing the mouth by another jumper. But that doesn't mean an older design helmet isn't any good. There's no clear best helmet out there; skydivers can endlessly debate the different designs for their liner, strap system, visor closing & opening method, shell material, popularity, cutaway system, etc.
  14. So you wouldn't go up in Virgin Galactic's Spaceship even if you won a seat, because suborbital doesn't cut it for you?
  15. Looking at the measurements, it looks like the only suspension line that really stands out as being "of concern" is the Right A-4. That is the A line at the Stab on the right. It is -1 inch. What disturbs me is the fact that they have a -1" measurement of that line, but the attached B4 is +5/8". I may be totally confused about their relative measurements like A4-B4, but the way I see things, the number are really weird: So the the A shrunk by 1", and the difference between the A and B is now 5/8" too high (relative to the A since it is A4-B4). The B in relative terms would be +1" now if nothing happened to it, but instead is +5/8 relative to A, which means it shrunk by only 3/8. If B for example didn't shrink at all above the cascade, then all that 3/8 is in the common A/B line below the cascade. But that means A shrunk by 3/8 below the cascade, and a whole 5/8 above?? The A4-B4 measurements seem a bit odd, but what about A3-B3, where the increase in the B number is more than how much the A shrank: A3 shrunk by 3/8" (at least compared to spec) but A3-B3 is +7/8". So +3/8 of that is just because "A moved away from B", meaning that B3 stretched by 5/8? And if some of A's loss was below the cascade, where A & B would shorten together, then B would have to stretch above the cascade even more to make up for it! Is there a lot more variation in construction standards and measurement of lines than one might suppose, that makes these numbers a mess to try to interpret? I'm still a little miffed that PD has never (that I know) mentioned this line trim issue. Some of us are used to the idea that a Spectra lined canopy will go seriously out of trim (enough to ground it!) in hundreds of jumps, but not suspecting that a handful* of jumps is enough to do it. * the OP reported 5 jumps on the 1993 PD 126. Skimming the thread, I'm not sure if it was always his since new or not. Still, one isn't going to have hundreds of jumps on the canopy.
  16. Well in that case, 1 K only means one unit of temperature (Kelvin). So how does one distinguish the k = 1000 vs. k = 1024? I used to throw on a subscript denoting the base, 10 or 2, but that's nonstandard. FWIW wikipedia says: Looks like the 1000 definition is supposed to be the correct one now. Still it is messy when one looks at the free space on a hard drive or something, and two different sources give different numbers...
  17. I think the answers already given are decent, including those from before the thread bump. How your canopy moves over the ground in a given wind and given input is hard to know. Use the accuracy trick to see if you are doing any better. I don't recall anyone suggesting a particular percentage of canopy speed as a guideline. Similar to the previous poster: if you are up high then it is usually easier to find an alternate landing area (at least in the relatively uncluttered places I jump), rather than bothering to do a partial-chinup on the front risers for the next minute or two. The amount of extra distance you gain out of front risering may not be that much, given the bother. Serious front risering I would tend to do only if I really really need to make it forward a little more, like to make it over a tree line into a field (when I'm already low and committed).
  18. In addition to the issue about lying, I sometimes wonder if there's a basic personality thing involved in how people react to Trump. It's not just Dem/Rep or Left/Right. Some of us just don't like to work with the over-the-top personality type who acts like a big dumb idiot, a loudmouth jerk, a windbag, spouting crap and insulting people. That's "not one of us" normal people and makes it hard to give someone like that much attention. No matter what useful qualities the person might have behind the way they talk. It's not about being a precious snowflake needing ones safe space. And we all tend to accept different behaviour in different situations -- we may talk differently at the office than when with a bunch of skydivers drinking around the campfire. Still, some of us expect a little more attention to detail when dealing with big issues, and less shooting one's mouth off. We know there's a difference between politician' simplistic sound bites (or tweets now) and their actual plans, and that it can be tough to figure out what their actual plans and policies are, but Trump just takes everything to the extreme.
  19. That reminds me, I once was in a hangar watching a POPS bigway do a dirt dive. They practiced standing up, then they laid it out on their bellies, then the organizer told everyone to stand up again. The hangar filled with the sound of grunts and groans as they slooowly got back up again...
  20. Plenty of opinions possible on this issue. I note that an older PD reserve manual says that after 40 repacks / 25 deployments, the canopy must be sent in for "permeability testing", and "Subsequent to passing this testing, an additional label is affixed and the canopy is then returned into service." That's all that's listed that I noticed. So if I sent a canopy in I would tell them they are only authorized to conduct such mandatory testing, as was stated in the manual the canopy came with. They are NOT to assess its airworthiness in any other way. However, for informational purposes and their long term data collection, I would allow them to check trim, inspect the canopy, and report back to me. If the trim is out 3/8" and they can show me some test reports on how poorly such a canopy would open, yikes, I'll ground it myself. At the moment, however, most riggers probably haven't discussed small trim variations on reserves and the industry hasn't exactly made it an issue before. PD could be right... but I bet this is a pretty new issue for most skydivers & jumpers.
  21. So PD should do the Brian Germain thing* and tug some more on the appropriate lines? Measure immediately, record results, and ship out of the factory. Problem solved. How well that works, I'm not getting into. * Ref: thread named "Stretching lineset back to trim", # 4418737, 2012
  22. That's an issue, but maybe a rigger can sew the split center section part into one's existing slider. As long as the front to back distances are similar.
  23. Flag burners should take a page from US demo jumpers: It's not a FLAG, it is a BANNER that happens to look like the US flag. Or take a Sharpie to cover one of the stars before burning.
  24. Here's the pic, although it only gives a general idea of size and you'll have to figure out the exact dimensions yourself.
  25. This question has come up a few times before on DZ. A Paracommander works fine with a bag. Old timer purists might say a sleeve is better, less dumping-it-out-all-at-once, and they could be right. But later on in the era of PC's bags were used. On one PC of mine, I stowed the crown lines in elastics I installed on the inside top of the bag (although it was a bag with a velcro split, making it easier to access the inside top of the bag). Or as Riggerrob says, they can come through a big #8 grommet and be stored ontop of the bag. Looks like you already discovered that the Paracommander is bigger than a Parafoil 282. There's a photo I uploaded on dz.com somewhere, where I compare one of each, packed side by side, with a ruler to give some idea of scale.