crazy

I completely agree. Maybe some people think that a lightly loaded canopy will collapse more easily because they give more bumpy rides. It's hard to understand that in some cases, more bumpy means safer. -- Come Skydive Asia

Everybody already said it: there are different criteria (speed, glide, reactivity...), few of them scale linearly. In addition, lots of factors can't be measured accurately, so, even for a specific criteria you can't get a formula. However, maybe it's possible, at a chosen wingloading, to estimate the variation for some criteria. To be more specific on Quade's point, if you use a scale factor of 1.4, here are the variation of some important factors: - chord, span and thikness: 1.4 each - area of the canopy: 2 (1.4^2) - area of the nose: 2 - volume of the canopy: 2.8 (1.4^3) - length of the lines: 1.4 - weight of the pilot: 2 (to keep the same wing loading) - height of the pilot: 1.3 (cubic root of 2 in an idealized world) - frontal area of the pilot: 1.6 From these elements, you can get some information about the flight characteristics. The volume of the canopy and the area of the nose gives the time needed to inflate or deflate the canopy at a given speed. The larger canopy will inflate (about 1.4 times) slower; the openings might be softer. Conversely, for a given turbulence it might be more stable. The lift is proportional to the area, the angle of attack and the square of the air speed, so, as a first approximation, the air speed is the same if you don't change the wingloading. The length of the lines and the frontal area of the pilot give the parasit drag of the lines and the pilot respectively. As the lift and the drag of the canopy vary with the area (at a given speed and angle of attack), the ratio lift/drag is better on the large canopy. It might have a better glide ratio, a better flare and longer swoops. As a consequence it might be easier to land. Another consequence is that the larger canopy should allow a faster recovery from a dive. This doesn't necessarily mean a shorter natural recovery rate. The radius of a turn (in a spiral), at a given bank angle, will be almost the same because the difference between the lines can be neglected compared to the radius. The small canopy will be more responsive because there is less inertia (needs less time to swing the body). As a consequence it might be less forgiving on low turns (more risk to stall while digging out). All of these can be neglected most of the time because if you take two pilots, the difference in skills, style and morphology will probably be much more significant than the difference of flight characteristics, whatever the difference in weight. -- Come Skydive Asia

Assuming that both places are dry, the speed at ground level will be ~3% higher. This is approx half a mile per hour at full glide, probably not something that you can objectively notice. As a comparison, a variation of temperature of ~30 degrees fahrenheit woud make an equivalent difference. Now, if you PLF, the impact will be ~7% stronger. As a weak comparison it would be like a PLF with ~10 pounds of lead. -- Come Skydive Asia

If they planned things properly, the weather has to be like shit on the last day (after an attempt hold for 1 second on the previous day) and they will complete it during a miraculous break in the clouds at the last minute before packing. We all know they can do it and they have to be creative to keep the thrill untill the end -- Come Skydive Asia

Of course his math is right! 1/83 chance to make a mistake means 82/83 chances to make it right. This is for every skydiver. Put 300 skydivers together, the chances that everybody make it right on a given record attempt is (82/83)^300 ~= 2.6%. This also means that there is 97.4% chances of failure on each record attempt. The chances that all the 24 attempts fail are 0.974^24 ~= 53%. Hence, the chance that at least one of the attemps is an actual record is 47%, close enough to 50%. Is this nerdy enough? Or shall we also study the impact of individual skill levels on the overall chances of success? -- Come Skydive Asia

Your statement is so shocking that i had to check. I went on the BASE fatalities list and here are the numbers: - 67 fatalities listed - 9 females (this is 13%) but maybe i missed a few (10, 15, 24, 27, 30, 35, 43, 52, 60) - 1 references (43) where you mention the relationship - 1 reference (27) where the "pretty girl thing" is mentionned as a side issue Obviously, there are some hidden informations that you have and that i don't. So what's the explanation for the huge difference between your claims ("35% of student accidents happen to women" and "girlfriends die") and the info in the fatalities list ("13% of reported fatalities happen to women" and "2 reported fatality where the relationship might be a side issue"). 2 fatalities out of 67 is 3%. If there are more than 3% of the BASE students who are pretty girls or starting with their bf as BASE instructor, then it would mean that pretty girls and girlfriends survive. So what's the missing information? bb -- Come Skydive Asia

I completely agree. Focusing on "flying the canopy during the opening" makes it more difficult to estimate the appropriate input. In addition it can induce delays in the reactions and make things worse. Focusing on the stability of the body allows much faster and accurate reactions. This is just my opinion and i have never jumped a x-braced. bb -- Come Skydive Asia

You're right, sounds even much better than water. Assuming that the density of sand is ~2, a 4 inches long cylinder should have the appropriate falling rate. bb -- Come Skydive Asia

Emergency recovery from a (too) low turn? I wouldn't do or even think about using the rear risers. Survival expectations would be insignificant if i stall the canopy. If i already turned too low, means that my judgement is somewhat impaired, i might misjudge the input on the rear risers as well, stall the canopy and finish to kill myself. Not to mention that i would definitely freak out if i was too low to recover with gentle and smooth toggle input. bb -- Come Skydive Asia

AVN short range is probably what you want z = 23000 * log(P0/Pz) z = altitude in feet P0 = Pressure at sea level in millibars (1013 if no actual value) Pz = Pressure at altitude z in millibars 1 millibar = 0.02953 inches of mercury (you'll need it to convert the pressure at sea level). yes. The jumprun as well. In addition to the time for 100ft, 500ft and 1000ft, there should be the optimal jumprun with the begining and the end. Of course, this has to take into account the winds from opening altitude to the ground. Once you have all of this, you could turn it into a simulator (or ask John Kallend if you can use this to improve his excellent simulator). A bit nerdy but it's a pretty cool idea. Not sure if it would be of any practical use at the DZ, but probably a very useful tool to explain spotting and exit separation with realistic data. bb -- Come Skydive Asia

How do you know that it is a 45 degree track? bb -- Come Skydive Asia

Don't change your beliefs about this one! The deploying canopy sees the relative wind and doesn't really care about the direction. The thing is that the relative wind when you are tracking is slower than the relative wind when you are falling vertically. See Paul Quade's post or mine for suggested values. Kallend, Livendive and HookAndSwoop are also emphasizing on the total speed, not only the vertical speed. You're absolutely right. the deceleration is in the direction of the airflow. If the airflow has an horizontal component, the deceleration has one as well. Don't buy it. I don't think that anyone on this thread emphasizes on the vertical speed only. Most people agree that it's the air speed, whatever the direction. If you had a hard opening in track, it might be that you were unlucky, or that you were in a bad track position when you did it. As the relative wind in track is slower than in normal belly to earth vertical freefall, openings in track should be softer (and actually they seem to be softer). bb -- Come Skydive Asia

Well, but you are going to accept this 1/500 chance of having the "wild" unplanned ride each time you will jump. If you do 1000 jumps, you take the 1/500 chance 1000 times. Alltogether, deciding to skydive is a much bigger risk than deciding to do one intentional cutaway. I'll do the (bad) math for you: chances to have a malfunctioning main = 1/500 chance to die on a wild unplanned main malfunction = 1/1000 (approximately, from the fatalities stat) chances to die from a planned cutaway = 1/10000 (roughly, because it's planned, so you get rid of lots of shit, like cross checking the rigger's job, reducing the risk of blown cells and broken lines, more altitude, less stress, clear handles, no disorientation, no injuries...) Assume 500 jumps/year and 1 intentional cutaway/year. Statistically, the risk is: 1/1000 to die because of a main malfunction during your 500 jumps 1/10000 to die because of the intentional cutaway 1.1/1000 total risk for main/reserve malfunction Apparently, you have increased the risk by 10%, it's not really significant, given the error level of the assesment. You would easily change the figure with small details on a sloppy pack job for instance. The "if you don't trust your reserve, why do you jump in the first place" partially translate into: "if you don't accept the small (insignificant) risk increment of 1 intentional cutaway, why would you accept the huge risk of 500 jumps?". Now, imagine that the intentional cutaway has a real training value, and that it will train to better reactions to emergencies. For instance, you might have a more realistic feeling of the risks, anticipate more, pull a bit higher, get used to the idea to actually pull the reserve... In that case, your intentional cutaway could reduce significantly the risk associated to malfunctions, maybe 20% less, reducing it to 8/10000. Then the overall risk, including the risk of the training, is a bit less. You can't deny the training value of an intentional cutaway, the only thing is that it's quite difficult to quantify the effect on the overall safety. I'm not telling you that intentional cutaways should be part of your normal training, I'm just highlighting the fact that the evaluation of the risk is definitely nothing close to the blunt "an intentional cutaway is 500 times more dangerous than pulling the main". bb -- Come Skydive Asia

Do you have any data to backup this claim? The vertical speed of a belly flyer at 2500 feet is around 125mph. The vertical speed of most good trackers will be close to 75mph at 2500 feet (this is easy to check, ask a good tracker what is his lowest average speed on the protrack). As long as his horizontal speed is lower than 100mph, the velocity of the tracker is lower than the velocity of the belly flyer (75*75 + 100*100 = 125*125). Do you have any evidence that a tracker can go faster than 100mph horizontally? My personal experience shows much less than this. Experience done with a pro-track set at 7000 and 3000 feet. I spotted at both altitudes and measured the distance. I admit, it's very inaccurate, but it was much less than 1 mile. More like 4000 feet. I got the same kind of measurement from 2 other people. One guy once claimed he got a glide ratio of 1.2, but he never gave me all the data. If you are a good tracker, make the experiment yourself to be really convinced. If you're not that good, pay a beer to a tracker nearby to organize more track jumps . BTW, I've dumped in track hundreds of time at wingloadings from 1.4 to 2.5 (never tried with a cobalt, an air-locked or a x-braced). Always had very soft openings. bb -- Come Skydive Asia

While i have no doubt that an extremely hard opening can cause serious injury, i am wondering why opening in track would cause hard openings. As long as you don't really know the detail of the hard opening, it's quite difficult to speculate on any solution. What's wrong with dumping in a track? bb -- Come Skydive Asia

I'll do as soon as i'll know why Winsor's offensive behavior is not negative. -- Come Skydive Asia

It's not about jumping the reserve or the main on every single jump for 5000 jumps. It's about one reserve ride and evaluating the risk of that specific reserve ride in different contexts. The first case is the intentional cutaway/reserve in a controlled environment, the second case is the wild reserve ride that you will most probably have within the next 500 jumps. Obviously, the first one is significantly less hazardous. So, if you think that accepting the first one is a stupid mistake, then you ought to have a very good reason to accept the second one. If your only reason is that you are an adrenaline junkie and that you are craving for these 500 jumps, well, admit that you're disjointed on this one and keep the fun skydiving. If you like stats, compare the risk to kill yourself, for instance landing your main, with the risk to die because the reserve failed (a real reserve failure, like blown cells or broken lines, not an entanglement, a horseshoe or a no pull), particularly after an intentional cataway. Don't be too surprised if the conclusion is that an intentional cutaway is not significantly more dangerous than landing a main (depending on the source, might even seem safer). Besides, overestimating the risk of a reserve ride to a ridiculously irrealistic level (5000 times more dangerous) might compromise your own safety: you might try to fix a serious problem with your main or your PC for a too long time before deciding to use your reserve. Then it will be too late. If you don't trust your reserve, why jump in the first place? bb -- Come Skydive Asia

Why do you think Treetop's offensive behavior is negative, while Winsor's hideous political incorrectness is ok? Treetop, would you mind having a proper haircut and give up these fancy sun glasses? Not that i'm suggesting you're gay or something, but it would give a much less negative image. bb -- Come Skydive Asia

even with 3 canopies you would have no promise to survive. It's not about certainty, it's about evaluating risks and deciding which are acceptable. If you think that a cutaway/reserve in the perfect conditions (stable, very low speed, high altitude...) is not an acceptable risk, then why would you do something that will put you in such a deep shit that you will need that reserve in much worse conditions (high speed, low altitude, unstable...)? The other thing is the value of a cutaway and reserve ride in a skydiver's experience. Again, it's a personal evaluation. You can dismiss it and claim that it has no real value. Some people think differently (a cutaway can even be a requirement for some tandem ratings). In most cases, it's almost impossible to get a proper setup with 3 canopies, so there are not many other choices than your own rig, when your reserve is due for repack. bb -- Come Skydive Asia

I know quite a few people who regularly have an intentional cutaway/reserve ride with their usual rig and nohing else. These people are not specially daredevils nor irresponsible. They just trust their rigger and their equipment. I'm surprised that you got so much shit on this forun, for your question, first, because many skydivers do things much worse, second, because BASE seems welcome (and BASE is a few steps ahead of jumping a reserve). So, to answer your question, of course don't do it now, but in a few hundred jumps you will have the knowledge to make up your own decision. It's nothing specially silly; if it was that silly, it would be silly to go skydiving anyway. If you don't trust your reserve when everything is fine, how can you rely on it to save you when you are in deep shit? If you can't, why would you put yourself deliberately in a situation where you will need it (yes, reserve rides are a significant part of skydiving)? bb -- Come [beer adjudicator] skydiveasia.org

So, please, explain me how a newbie can accurately know how much altitude he looses, for instance in a 270 degrees turn? What error do you expect on the estimation, knowing that an altimeter is accurate at +- 100 feet at best, and that the newbie will probably never do the same turn twice. How is the beginner supposed to use this inaccurate information in his actual swoop training? Directly quoted from the first post of this thread: "Start w/ a simple 90 degrees" is the "best advice" from a DZ with "a lot of great swoopers" (sic). I think that at least one of these "great swoopers" is less than an impressive teacher. Focus on the turns when you teach swooping and be sure that some students will believe that you can "start w/ a simple 90 degrees". There are probably safer ways to teach swooping. bb -- Come

I don't call a perfect arc ending at 1000 feet a swoop. If it ends 20 feet above the ground, i call it a cockup. If it ends 6 feet below, it can be called a fatality. So, can you explain how the newbie with his perfect 360 front riser arc at 1000 feet will transfer safely this into swooping? I completely agree that learning to fly at altitude is important. I also completely agree that one of the requirements before learning to swoop is to have a good knowledge of the canopy and good skills to fly and land it. But i completely disagree when people claim that flying skills at altitude can safely transfer to the first steps of swooping. Training to do 270 front riser turns at altitude might even have the adverse effect to convince the newbie that a 90 degrees is an appropriate first step to learn swooping. This is already a dangerous lack of discipline, judgement and discernement. bb -- Come

That's an interesting concept but i'm not sure it's a very productive training method. At altitude, you can learn canopy control, but this is not specific to swooping. Anyway, you must be a skilled canopy pilot before even thinking about swooping. Swooping is not the ability to pull a riser or a toggle, it's a whole set of knowledge, abilities and skills on top of this. The big parts are planning the pattern (and the outs), flying the pattern (and knowing that you are), identifying the problems early, aborting and recovering safely, Few of these can be tried in a realistic way without the ground as a reference. Of course, there are some specific techniques that you might want to try up high, but not so many. bb -- Come

there is quite an informative web site: http://www.grc.nasa.gov/WWW/K-12/ To answer more specially your questions, the wing loading affects the flight characteristics but it's not the key factor; many other elements, such as the trim, the airfoil, the planform or the structure can have a more significant effect. Even for the speed, wingloading is not the key factor. -- Come

Great story. As altavista is a pain in the ass to translate a newsgroup, here is a short summary of the beginning of the thread (thanks to Marcus): - 1st post: Frank Besler (FB) claims that the FAA grounded all the nitros until the brake lines are replaced with spectra lines. The reason is an accident in Perris where a line with 250 jumps broke in a hook turn. - 2nd post: Pascal Lavielle (from Profile Research), after rebuking FB for his wrong info, explains that the guy had replaced his original lines (HMA 430), which had more than 1000 jumps, with much thinner ones (HMA 200). He also claims that, for reasons he wouldn't explain, the canopy and lines were not maintained by Profile Research or any authorised dealer. - 3rd post: Frank Besler corrects his own post: don't replace the lines, the broken line was cannibalized and didn't respect the manufacturer's requirements, the only grounded nitros are the 30 which were stolen to PR. I skip the other posts in the thread, not sure if there is any real info there, apart that there was 1 reported broken brake line with HMA 360, which is the reason why Profile Research upgraded to HMA 430, more than 3 years ago. So much for this horror story. It's still rumor mongering. Yes, there was an accident, but as soon as you check the facts, it's quite harsh and unfair to incriminate the line. I understand that lines breaking during landing are really scary, but please check the info before spreading rumors. If a skydiver goes against all the manufacturer's recommendations, makes stupid modifications and doen't maintain his equipment properly, he is the only one to blame in case of failure. Anyway, even though the HMA 430 was apparently good enough, as far as i know, now HiPeR use HMA (Technora) 750 for the steering lines. bb -- Come