DexterBase 0 #26 January 22, 2003 QuoteQuoteToilet paper works much better, and will dissapear in no time. Good call. I'll make sure to bring some along on our next outing. Actually, I know several people who bring toilet paper along on their jumps for an entirely different purpose. heh heh... Share this post Link to post Share on other sites
Faber 0 #27 January 23, 2003 Quote Actually, I know several people who bring toilet paper along on their jumps for an entirely different purpose. heh heh... I know aswell..they have to dry their eyes when they are running Stay safe Stefan Faber Share this post Link to post Share on other sites
Dd0g 0 #28 January 23, 2003 Quote I hope if you take 5 secs slider up from a 600' object, you are over water and wearing indestructible diapers. And if you take 5 secs slider "on", but not up, be prepared to land on 3 or 4 cells. be careful. Not necessarily. One thing I carry with me all the time (loaded in my Palm, and yes I'm a geek) is a fall rate chart. A five second delay until PC deployment is likely approximately six seconds to canopy pressurization. [note that this is a big assumption - despite the critical nature of post-PC extraction length calculations to anyone doing really low pulls, I've never seen a consensus on exactly how long after PC deployment until a given canopy is pressurized and flying. . . clearly, one would expect this number to vary depending on slider up/slider down, direct/indirect stow or no stow slider up, venting or unvented canopy, etc. . . however, as a general rule I've heard others talk about a standard, 1 second post-PC deployment delay until pressurization. . . mostly, those who play the low pull game develop a very good "gut feel" of how long until PC deployment is possible by doing lots of jumps and building a virtual model in their mind of where the fringe of the chart is and how close to the fringe is possible without going to the hospital or morgue. . . an interesting topic, at least to me.] A body falling for six seconds with no decceleration (either from aerodynamic drag or partial canopy extraction drag) would eat up 504 feet, and be going 94.09mph. One hundred feet of canopy time is not on the low end of the spectrum - I've seen (and partaken in) lower than this many times, even slider up. Which brings me to an important issue. First, it is important to actually have a good feel for the "fall rate chart," particularly when dealing with subterminal objects (less than about 850feet to deployment). I know several jumpers who have simply memorized the zero to seven second fall rate chart. While this is (obviously) a continuous function, some data points extracted from the curve are: 1 10.91 16 2 31.36 62 3 51.81 138 4 70.91 242 5 84.54 366 6 94.09 504 7 100.91 652 8 terminal 808 9 terminal 971 Note that the distance travelled in freefall is far from linear; in fact, it's approximately geometric until about 7 seconds. This is why, in my opionion, timing delays accurately between 2 and 6 seconds is an advanced BASE skill mastered by few folks. Things happen fast in that zone- acceleration and distance fallen are increasing at an increasing rate (humans think mostly in linear terms, so most folks don't naturally cotton to this math). It takes alot of jumps to get a feel for how this curve really unfolds in freefall. This is, of course, particularly relevant when "low pulling." Taking 4 seconds off a 440 foot object requires pretty good timing, for example. Take five (assuming the opening didn't break your back slider off), and you'll likely impact at line stretch. Take three, and well you are wasting valuable freefall time If we are not using laser rangefinders (or if the exit is underhung and makes a laser reading impossible without climbing gear to set an anchor and partially rappel off the exit for a clean line of sight), then the way to see how high an object is (and thus what delay is possible, assuming no glide to landing area problems, etc.) is by rock drop. [B]WARNING Doing rock drops incorrectly can result in substantively incorrect readings and potential fatalities! A rock - in order to overcome aerodynamic inertia - must be (by conventional wisdom) at least as big as a softball and roughly spherical. A smaller rock - or one with a flatter shape - will slow down and hit "terminal" much earlier than a falling human body before transition to track (and without a wingsuit). Thus, throwing a flat or small rock off a cliff, timing (with a watch) eight seconds, and planning a 5 second slider up delay is a likely fatality. The object may well be only 500 feet or so high - and a 5 second slider up delay off that will result in impact at line stretch most likely. Fatality. Also remember that "lighter" rocks (like volcanic tuft) will float no matter how big they are, within reason. Their density is too low to offer accurate rock drops. I've seen many experienced jumpers make these rock drop mistakes, thereby systematically over-estimating how high cliff exits are. This is extremely dangerous. Yes, low pulls are a dangerous game. It is stupid - why would anyone do it? Don't do low pulls. In other words, do as a I say and not as I do (as in so many other areas). Peace, D-d0g [email protected] http://www.wrinko.com+~+~+~+~ But this, surely, was the glory that no spirits, canine or human, had ever clearly seen, the light that never was on land or sea, and yet is glimpsed by the quickened mind everywhere. Share this post Link to post Share on other sites
Dd0g 0 #29 January 24, 2003 Dwain has been gracious enough to step in and correct some inaccuracies in my statements above. I've excerpted elements from his correspondence to me, with his permission: Hey I just read your dropzone.com post regarding delay/distance. There are a couple of minor inaccuracies (in my opinion) which add up to a big inaccuracy if taken literally. First of all MotherHucker wrote: "I hope if you take 5 secs slider up from a 600' object, you are over water and wearing indestructible diapers. " This is true 95% of the time. "And if you take 5 secs slider "on", but not up, be prepared to land on 3 or 4 cells. " This is not true. "Be prepared to land with a broken neck" is more accurate. You wrote: "A five second delay until PC deployment is likely approximately six seconds to canopy pressurization." This is totally wrong. [emphasis added] From memory if you release a p/c at about the 5 second mark you will hit LINE STRETCH at about 6.2 - 6.3 seconds after exit (it takes about 1.3 seconds from p/c release to line stretch at that speed, from memory - it's definitely more than a second). This means you will you will begin to decelerate at about 60 - 70 feet above the ground while travelling at about 97 miles per hour downwards. In this instance MH's first statement is correct. You will hit the ground very hard during deployment. . . As to the other 5% of the time: I have a video of myself jumping a 590 ft cliff and taking very close to a 5 second delay slider up (brakes off, nice flare landing with a few secs canopy time). This doesn't work according to the math. However this is possible due to a number of factors (I believe): 1. The canopy deployment was unusually fast for slider up, and I'm relatively light so I don't use as much height for deployment. 2. I jumped up on the launch a fair way so that probably squeezed an extra 1/2 second or more out of the freefall (charts are based on just dropping straight down - nobody does that unless you do a hanging exit - notice how quickly you go down when you do a hanging exit from [that B we jump alot that is about 340 feet to impact] - you have way less time). Same goes for the way you exit - you launch up and out, so you tend to get more freefall time. If you wanted to relate it to the freefall charts you'd have to start timing at the top of your arc during freefall, not when your feet leave the exit point. 3. I was slow falling the whole way getting max air resistance. I've noticed that the freefall charts don't apply to myself that much because I can really float in freefall. This is how I can get 7.5 secs from a 930' cliff in Australia whereas others are smoking it way down on deep sixes. You wrote: "I've never seen a consensus on exactly how long after PC deployment until a given canopy is pressurized and flying" Well time isn't as important as distance travelled from pc release to reaching full pressurization (but I know this is what you meant). There isn't a general consensus because this is so highly variable. Say you and KS were jumping the same canopy, same packjob, same wingloading, (ie. your canopy would be more than twice the size of hers), etc etc and you deployed side by side. You will always open way lower than her because it will always take way more energy to decelerate you (M*V squared). Therefore KS will always be able to dump lower than you (providing other things remain constant). Being heavy means your p/c tosses must always be higher. You'll never win (and live) a low pull comp against someone lighter (if they are good) whereas you may win a lowest deployment comp. Same goes for really low freefalls. You require more energy (and therefore more height) to decelerate. This is all academic though and I know you already know this. Loose the weight fat boy if you want to dump/exit ultra low. ;-) [ha ha - thanks Dwain! ] You wrote: "however, as a general rule I've heard others talk about a standard, 1 second post-PC deployment delay until pressurization" One second isn't a valid time to apply under any set of circumstances (from my research). On a one sec delay it takes 2 secs from p/c release to line stretch. On a 2 sec delay it takes 1.6 secs from p/c release to line stretch (all averages). It seems to stabilize out at about 1.1 - 1.2 secs from p/c release to line stretch at terminal (from memory - I did all these figures 6 or 7 years ago and my memory a little rusty). Full pressurization eats up a LOT more altitude and is highly variable on a huge range of things. Once again this is mostly academic. Your delay usually should depend upon eyeballing the ground, not counting. No matter how badly you want to take a 5 secs from 600ft (saying that you just drop off the exit - not jump up) I'm sure you'll have the pc out before 4.5 secs because your survival instinct will kick in. Basically my point is that the charts aren't valid unless you measure freefall time from the top of the arc on exit. The other point is the way we measure freefall time in BASE is stupid. It would be much more meaningful to measure from the time that we start moving downwards to the time we start decelerating (ie. hit line stretch). This is more relevant to the actual act we are performing. Timing exit to pc release just describes what the jumper did, it doesn't tell the full (and more relevant) picture of what actually happened in terms of distance travelled and speed obtained. But the standards are set and there is no way it will ever be changed. Also my brain is so wired in to the current system I don't think I could change. My thanks to Dwain for the clarifications; I hope folks appreciate the years of experience that stand behind his statements. . . well, all except for the "fat boy" quip Peace, D-d0g [email protected] http://www.wrinko.com +~+~+~+~ But this, surely, was the glory that no spirits, canine or human, had ever clearly seen, the light that never was on land or sea, and yet is glimpsed by the quickened mind everywhere. Share this post Link to post Share on other sites
Faber 0 #30 January 24, 2003 Quote This is, of course, particularly relevant when "low pulling." Taking 4 seconds off a 440 foot object requires pretty good timing, for example. Take five (assuming the opening didn't break your back slider off), and you'll likely impact at line stretch. Take three, and well you are wasting valuable freefall time You could always chop it and take the restWhat i want to say is that,dont go lower than you are comfomtabel whit. While im an newbie,and still mean that 400ft is an exelent altitude and not so much stess by pulling "high",making the hole jump a bit safer.It will all come when the person fell for it. But wery interesting. Dwain could you please contact me,i have some Q´s for YOU only. Stay safe Stefan Faber Share this post Link to post Share on other sites
Lolie 0 #31 November 26, 2003 QuoteQuoteIf you are gonna "burn" a site you might as well go all out. I think if any of our sites get burned we should set fire to them, since, really, if you can't jump it then it becomes totally useless. And remember, fire is cool! Fire is cool. Arson isn’t. Show a little respect to the owners/environment, dude. Most objects aren’t just there to be jumped from, believe it or not. Okay, I know this is an old thread, but I was doing a search just now and found this post--I DEFINITELY didn't write it! I have no idea who did, but I use a lot of computer labs and friends' computers, so I guess it shouldn't surprise me. Just wanted to let all y'all know I have a sense of humor (albeit on that goes unappreciated by most... ) Alright, nothing more to see here, folks; move it along... -Miranda you shall above all things be glad and young / For if you're young,whatever life you wear it will become you;and if you are glad / whatever's living will yourself become. Share this post Link to post Share on other sites
