bigbearfng 18 #26 September 23, 2003 Lead dislodgement-I really feel this possibility is negligible- even a 10G pull on a wire that light....just can't see it-if you've ever handled a pacer lead-it is very light. The device itself moving....it would have to displace a lot to pull on the leads! And some actual movement in the subq space where it sits is normal. Skin has to be able to move around a bit....Once the area is healed, it shouldn't shift-even under some significant forces.... As previously mentioned-if the pacer ends up being under the harness-pad the jumpsuit for comfort, and I would try to adjust things so that it isn't directly under. I've never seen a pacer damaged by an airbag....so I really don't see a pacer as being an exclusion to skydiving! If your Doc tries to say no, I'd really like to know his specific reasoning..... Blue skies! Quote Share this post Link to post Share on other sites
billvon 2,822 #27 September 23, 2003 >Anyone who has had a 10G opening, describe the what/where/why/how's > of it, because my wildest imagination can't come up with something that > would make an opening pull 10Gs. Bill Beaver had an opening close to 20G's; they know it was that high because it bent the rings on his harness, and knowing his weight and the deformation load of the rings they worked backwards. It destroyed his main (a Sabre 1) and rendered him semiconscious. He landed safely but didn't jump for a while after that. I had a few tandem openings that left me grayed out and passing blood; I suspect they were close to 10G's. Quote Share this post Link to post Share on other sites
Kramer 0 #28 September 23, 2003 Interesting. But still I don't get it. What is it that goes wrong during deployment that causes a 10G rush? -Kramer The FAKE KRAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAMER!!!!!!!!! Quote Share this post Link to post Share on other sites
mr2mk1g 10 #29 September 23, 2003 QuoteInteresting. But still I don't get it. What is it that goes wrong during deployment that causes a 10G rush? -Kramer From reading numerous threads on this subject I think the general consensus is... "shit"... ie "it happens". The opinion of a lot of very experianced jumpers, some of whom have technical knowledge through their work, appears to be that there is simply a low instance of slammer openings that just happen no matter how careful the packing is. I dont even pretend to understand why - I would have thought that there has to be a reason for the slammer, but then I am also aware of chaos theory, and... well, theres a lot of random things that can go on in a burble that can effect your canopy when its opening. Quote Share this post Link to post Share on other sites
darkwing 4 #30 September 23, 2003 I suspect that jumpers are very poor judges of how many gees an opening was. They know soft, brisk, hard, and slammer, but any numbers they put on them are unreliable, unless they have a lot of test jumps with accelerometers (maybe Gary Peek and a few others). Years ago I did some research (reading) about tests done by NASA and others in the late 1950s. It was fascinating reading (lots of hurt people and dead pigs), and what remains in my mind is enough to make me say the "20 Gs will kill you" statement above. -- Jeff My Skydiving History Quote Share this post Link to post Share on other sites
vonSanta 0 #31 September 23, 2003 Depends on the time the g-s are endured. There was this crazy doctor in the US Air Force who put himself up on a rocket sled, fired it up and then came to a sudden stop in water. He pulled several times 20g's - but only for a very short time period. And survived. Santa Von GrossenArsch I only come in one flavour ohwaitthatcanbemisunderst Quote Share this post Link to post Share on other sites
skydiverek 61 #32 September 23, 2003 QuoteDepends on the time the g-s are endured. There was this crazy doctor in the US Air Force who put himself up on a rocket sled, fired it up and then came to a sudden stop in water. He pulled several times 20g's - but only for a very short time period. And survived. I read in a Guinness Book of Records that the record number of "G"s survived is 170 (yes, 170 "G"s). Basically some racecar driver crashed into the wall and decelerated from 100mph to 0mph on a distance of 3 feet. He was pretty messed up but survived. Some other guy was using sleds and putting himself through 80 "G"s (that was some kind of military experiment). Quote Share this post Link to post Share on other sites
darkwing 4 #33 September 23, 2003 it was 45 g's and he was better protected than a jumper in a harness. -- Jeff My Skydiving History Quote Share this post Link to post Share on other sites
riggerrob 615 #34 September 23, 2003 The most common cause of hard openings is sloppy packing., ergo the chaos theory. Common packing problems are not having the slider all the way up and not having all the lines tight before the canopy catches air. Quote Share this post Link to post Share on other sites
The111 1 #35 September 23, 2003 IMO it's more than "G's" (acceleration) you have to worry about, it's jerk (change in acceleration). I don't know a lot about parachute openings, but I'd assume a hard one can have the effect of instantaneously changing you from a 0G load to one of say, 5G's for example. This would wreak a lot more havok on your body than sitting on a roller coaster with a smooth jerk rate that brings you steadily to an acceleration of 5G's. Someone asked if a 20G load wouldn't be just like bouncing? Not really... assuming (arbitraily) a bounce takes .275 second, your average deceleration over that interval would be 640 ft/s^2... about 20G's. You acceleration changed from 0 to 20G's in .275 second... your jerk was 73G/s. On the other hand, if you go on roller coaster than drove in circles (at a steady lateral acceleration rate) until it was going fast enough to accelerate you centripetally at 20G's... you might pass out, but this situation would CERTAINLY not have the same effect that impacting the ground after freefall would. The point of this, to the original poster, is that you can get jerked pretty hard regardless of what the deceleration rate is, but in reality the higher jerk values will occur in the harder openings which also have higher average decelerations. www.WingsuitPhotos.com Quote Share this post Link to post Share on other sites
quade 4 #36 September 23, 2003 Quote IMO it's more than "G's" (acceleration) you have to worry about, it's jerk (change in acceleration). (sigh) . . . it's all the exact same thing. Quote Really?quade - The World's Most Boring Skydiver Quote Share this post Link to post Share on other sites
mailin 0 #37 September 23, 2003 ok, with that being said.... I understand that hard openings are just something that can happen, as someone had mentioned - the chaos theory. But isn't it true that many of the newer canopies - when packed correctly have a 'smoother' opening than older models, thereby reducings the possibility of a higher G-Force impact? I spoke with a parachute rigger examiner today and this was the argument that he made. Any thoughts? JenniferArianna Frances Quote Share this post Link to post Share on other sites
Remster 27 #38 September 23, 2003 Quotethereby reducings the possibility As (either Bill or Quade... didnt look up 1st) mentioned, its a case of a hard opening always being possible, even with canopies known as snivelly.... Yes, some canopies are known for their smooth openings, but even they cam slam you.Remster Quote Share this post Link to post Share on other sites
The111 1 #39 September 23, 2003 Quote(sigh) . . . it's all the exact same thing. Jerk is extremely different than acceleration. Jerk can break your neck ("whiplash"), acceleration cannot. Why are you sighing at me?www.WingsuitPhotos.com Quote Share this post Link to post Share on other sites
quade 4 #40 September 23, 2003 QuoteJerk is extremely different than acceleration. No, it's not. It's all expressed in terms of g-loading. I will admit that from a materials standpoint different materials react differently to sustained g-loading as opposed to sudden g-loadings, but it's all g-loading.quade - The World's Most Boring Skydiver Quote Share this post Link to post Share on other sites
kallend 1,890 #41 September 23, 2003 QuoteQuote(sigh) . . . it's all the exact same thing. Jerk is extremely different than acceleration. Jerk can break your neck, acceleration cannot. Why are you sighing at me? I wasn't aware that the third derivative of position with respect to time was called "jerk". If anything, I would have called da/dx "jerk", like you'd get at rope stretch when being hanged. Learn something new every day. JK - Physics Prof.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
mailin 0 #42 September 23, 2003 Ok, now this has brought something new to the argument. Is how hard the 'jerk' a measure of total Gs or the difference between current rate of speed (MPH) and 0 mph - as you have to reach that point in order to change direction. Confused.... JenniferArianna Frances Quote Share this post Link to post Share on other sites
The111 1 #43 September 23, 2003 QuoteQuoteJerk is extremely different than acceleration. No, it's not. It's all expressed in terms of g-loading. I will admit that from a materials standpoint different materials react differently to sustained g-loading as opposed to sudden g-loadings, but it's all g-loading. Acceleration is expressed in distance per time^2. It can more easily be expressed by a "G factor", the relation of that acceleration to the acceleration caused by earth's gravity. Jerk is expressed in distance per time^3. OR, acceleration per time. I understand your point that when considering mechanical tensile failure of most materials, the absolute load is the most important thing to consider, and not the rate of load. But, you have said twice that jerk and acceleration are the same, and they're not. That's the equivalent of saying speed and acceleration are the same. The reason I'm focusing on this? (besides the fact that I hate to see physics misrepresented) QuoteThe two things he'll be worried about are device, lead dislogment and pressure on the device from straps. When considering lead dislodgment, jerk plays a much larger role than acceleration.www.WingsuitPhotos.com Quote Share this post Link to post Share on other sites
The111 1 #44 September 23, 2003 QuoteIf anything, I would have called da/dx "jerk", like you'd get at rope stretch when being hanged. You mean da/dt? www.WingsuitPhotos.com Quote Share this post Link to post Share on other sites
billvon 2,822 #45 September 23, 2003 >Is how hard the 'jerk' a measure of total Gs or the difference > between current rate of speed (MPH) and 0 mph - as you have to > reach that point in order to change direction. Uh oh, derivatives enter the discussion! When you're freefalling, you're just constantly changing your position (on a linear scale) with time. You could say your speed is the difference in position over the difference in time - in, say, feet per second. This is the first derivative of distance with respect to time. The second derivative of distance is acceleration. That's how fast your speed is _changing._ For example, 1G of acceleration will change your speed 32 feet per second every second, or 32 feet per second squared. The third derivative is jerk. That's how fast your acceleration is changing. A "jerk" of 1G per second would be expressed as 32 feet per second cubed. Basically a hard impact (like a car crash) has a very high jerk; a constant but strong acceleration (like a shuttle launch) has a very low jerk (except for the moment they shut off the engines at the end of boost.) Quote Share this post Link to post Share on other sites
The111 1 #46 September 23, 2003 QuoteOk, now this has brought something new to the argument. Is how hard the 'jerk' a measure of total Gs or the difference between current rate of speed (MPH) and 0 mph - as you have to reach that point in order to change direction. Confused.... Jennifer In simple real life terms... Drive your car down the road, and take a sharp corner, but do it smoothly. You will feel your body leaning against the seatbelt. This is acceleration ("G's"). If you do it smoothly you will feel forces, but they won't cause you to jerk around. Now take a bunch of consecutive left and right turns, but don't do it smoothly. Yank the wheel to the left and right as fast as you can. Your head will get jerked around and you'll give yourself whiplash if you do it hard enough. Or, in the lateral case.... Jerk is what you feel when you are a passenger of one of those shitty drivers who constantly alternates between gas and brake, as your accelerations bounces back and forth around zero.www.WingsuitPhotos.com Quote Share this post Link to post Share on other sites
billvon 2,822 #47 September 23, 2003 >But isn't it true that many of the newer canopies - when packed > correctly have a 'smoother' opening than older models, thereby > reducings the possibility of a higher G-Force impact? That's true. A spectre, for example, can reduce (but not eliminate) the odds of a hard opening. Quote Share this post Link to post Share on other sites
kallend 1,890 #48 September 23, 2003 QuoteQuoteIf anything, I would have called da/dx "jerk", like you'd get at rope stretch when being hanged. You mean da/dt? NO I don't. Your head has a different "a" than the rest of your body at t=const, and the difference in force acting on each gives a net force between the parts, which is transmitted by the neck, thus snapping it.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
The111 1 #49 September 23, 2003 That a(x) curve would be spiky. www.WingsuitPhotos.com Quote Share this post Link to post Share on other sites
kallend 1,890 #50 September 23, 2003 So Jerk = d3x/dt3 No-one seems to have told Halliday and Resnick... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
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