skr

Members
  • Content

    595
  • Joined

  • Last visited

  • Days Won

    1
  • Feedback

    0%

Everything posted by skr

  1. I remember how confusing the airspeed/groundspeed debate on rec.skydiving was, and I remember the aha moment when I saw billvon formulating it as differently moving layers of air and realized that my confusion came from unconsciously applying my ground based, common, solid frame of reference intuition to the moving layers situation. I think by the way this question keeps coming up that we, experienced jumpers, DZO's, and USPA, are not doing very well at explaining this to new jumpers. A few days ago I added a bit to the second paragraph of an email I had sent to a young friend of mine and sent it off to the Safety and Training committee. So if Winsor comes across this and doesn't grumble too loudly, then I'll consider it safe for home use :-) :-) Why Groundspeed? Sun 2012-4-1 ---------------- ------------ With typical winds, stronger on top, pretty much the same direction and gradually decreasing on the way down, a group in a higher, faster moving layer of air will spend the whole freefall moving closer to a group in a lower, slower moving layer. Bill Von Novak is the first person I saw explain the situation in those words, and this is something I wrote to a young friend of mine on stretching her intuition to feel comfortable with this. Mockup Intuition to Layers of Air Intuition ------------------------------------------- The name of the game here is to learn how to think so that what physically happens with upper winds appears natural. Once we have that, once our intuition has expanded, the various approaches to leaving exit separation will be easier to understand. Specifically I'm talking about going from the intuition for leaving exit separation at the mockup, with the ground as a solid and common frame of reference, to the intuition for leaving exit separation on jumprun, where different groups will be in different layers of air which are moving relative to each other. At the mockup, if the first group gets out and walks a certain distance away, and then stops, and then we step out, and then we all just stand there, falling straight down, we will still be the same distance apart 60 seconds later. That's how life on the ground works, and we have a lifetime of experience and deeply ingrained habit thinking that way. If there were no winds we could do the same thing on jumprun. When the first group has fallen far enough behind the plane, we can jump out, and that initial separation will still be there down at opening altitude. But with uppers we have to teach ourselves to automatically see something new, and that is that during the freefall we will be in a higher layer of wind than the group in front of us, and our layer will be moving faster than their layer. The initial separation at exit will be there, but we will spend the whole freefall gradually moving closer to them. In order to have the separation at the bottom for opening, we have to start with that separation plus enough more to account for the relative motion of our two different layers of air. Once that new way of thinking feels natural the various approaches to leaving more time between exits for upper winds will be easier to understand. Practical Difficulties ---------------------- At this point we hit the first set of practical difficulties. The obvious, intuitive way of leaving separation, looking out the door at the group ahead of us, and leaving enough room for the desired separation at opening plus enough for the different layers effect, doesn't work because - We don't know the speeds of the different layers - We can't accurately judge the horizontal separation from a group that could be thousands of feet below us at exit if the uppers are strong - Training - We can't do the large amount of training required for every new jumper even if we did know the speed of the layers and could judge the distances. That's why we turn to the more indirect method of time between exits. But even here there are practical difficulties - Trying to state a procedure that would work for combinations of all different sizes of groups is too complicated - And for really strong uppers the very concept of exit separation becomes meaningless because the first group could be practically at opening altitude before we get enough horizontal separation. (I'm thinking here of a King-Air load where the GPS showed a groundspeed of 12 knots.) So the time between exits approach only works for smaller numbers and light to medium uppers. Everything else is case by case. More Intuition -------------- The final intuitive part to become comfortable with is that people standing - in the door - on the layer of air at exit altitude - on the layer of air at opening altitude - on the ground are all looking at the same situation, and all seeing something different because of their relative motion. The discomfort comes from our lifetime habit of automatically applying our ground based, mockup intuition where everything happens in a common, solid frame of reference, to this new situation with lots of moving parts. The comfort will come from practicing, and getting used to seeing the situation with all its moving parts, from each point of view. First fly over and sit down on an air molecule in the jumprun layer and watch the plane come toward you. When the plane is even with you and the first jumper goes, reach down and color that molecule bright red. Now watch, the plane flies away at the airspeed of the plane, the first jumper starts to move away from you as she falls through progressively slower layers of air, and then the second jumper goes. The second jumper also starts moving away from you, but not as fast as the jumper in the lower and slower layer. They are actually getting closer together, but it's hard to see that because they are getting too far away. -- Now fly down to the opening layer and replay that last jump. When the first jumper goes, mark that bit of sky, and a molecule directly under it in the opening layer, as "exit point", and do the same when the second jumper goes. When they open, mark the corresponding molecules in the opening layer as "opening points". Now notice a crucial fact: The trajectory of the second jumper is exactly the same as the trajectory of the first jumper, just displaced up wind by the distance between exit points. The distance between opening points is exactly the same as the distance between exit points. We can separate opening points by separating exit points. When there are uppers, the distance the plane must fly through the air in the exit layer is from the red molecule, which has moved some distance down wind, to the second exit point. That's airspeed, and that's the distance someone looking out the door at the first jumper would have to leave to account for the moving layers effect. But for separation at opening, the meaningful speed, the speed we can use to separate exit points, is the speed we see from the opening layer. It's airspeed minus the speed of the exit layer. It's slower than the airspeed, that's why it takes more time to go from exit point to exit point on windy days. Feeling at ease with all these view points and moving parts takes practice because our old, ground based habits are deeply ingrained, and they tend to take over in the stress and excitement of jumprun and exit. If you practice a little on the ride up, you will get used to it all and it will start to feel normal. More Practical Difficulties --------------------------- If we could see the exit points in the opening layer we could just look down and jump out as we pass over them. But we can't, plus the opening layer keeps moving relative to the dropzone, which is where we want to land, so we would have to have a staff member up there dragging them back into place before each load. We could use the aviation winds aloft forecast to calculate the speed of the plane relative to the opening layer, but that forecast is only done every 6 hours and local conditions can vary. The military does this but they have a larger budget for special equipment than most dropzones. So probably the most common separation technique is that on the first load, jumpers make a guess based on what's usually needed for the current conditions, and then make adjustments from there. With the advent of GPS we have another possibility because we can know the groundspeed of the plane on jumprun. If the uppers are in the same direction all the way down, and not too strong at opening altitude, so that the meaningful speed of the plane relative to the opening layer is close to the groundspeed, then using groundspeed to calculate time between exits is a good estimate. And it has the advantage of being accurate at the time of the jump. That's how "groundspeed" gets into these exit separation discussions. Conclusion ---------- The best situation is where the experienced jumpers talk about how much time to leave between exits at the loading area, and they know how much because the dropzone posts the current groundspeed by the chart of Time Between Exits at the manifest or the loading area. From there it goes downhill to denial of the very concept, just leave 5 seconds and go, with the tandem masters and cameras screaming "Go! Go! Go!", and we are saved from more disasters by Bryan Burke's Big Sky Theory. This email was about intuition and conceptual framework. My last efforts to talk about concrete details are here: http://indra.net/~bdaniels/ftw/sg_skr_coach_weekend.html http://indra.net/~bdaniels/ftw/sg_skr_dealing_1_uppers.html http://indra.net/~bdaniels/ftw/sg_skr_dealing_2_tables.html If you're feeling hard core you can skip over the arithmetic and scan some of the words for more ideas :-) :-) Down at the bottom of http://indra.net/~bdaniels/ftw/index.html are some links to some of Bryan Burke's and Bill Von Novak's early writing. Both guys are very good thinkers about all kinds of stuff (Google). And finally, the link to John Kallend's Simulation Program http://mypages.iit.edu/~kallend/skydive/ still works and it's helpful in visualizing all these moving parts. He's also a good thinker. So all this is pretty confusing when you first run into it, but I think that if you can get your intuition used to the moving layers you can find your way through. Skr
  2. Thanks Amy. The first memory that popped into mind was the almost comical effect she had on the guys at the dropzone. There were very few women jumping then. The guys would be out there doing our best to be wild and crazy and adventurous, with more than a dash of uncouth, and when she would show up you could almost see people sort of mentally taking a shower and combing their hair and standing up straighter :-) :-) And I remember the Fairchild jumps when Lyle was wanting pictures of people climbing all over it for the magazine. People were up on top, and hanging from the steps underneath and up on the wheels right behind the prop, and there was Suzie, standing in the door with a great big smile. She was a good influence, added a lot of class to the scene. Skr
  3. > the Oceanside City Council agreed last night in a closed session hearing to grant Tsunami Skydivers Inc. a lease ageeement for the Oceanside Municipal Airport. Good work! I jumped at Oceanside from 1964 until it closed due to flooding (on Google maps it looks like the dropzone was just past where the golf course is now). It was a wonderful place and a wonderful scene. I hope you guys can add some good lines to its logbook! Skr
  4. > because it doesn't fit under Wing suiting, or canopy, or anywhere else. That's a good sign. Every time the official world thinks they've got it surrounded, categorized, and ready for some standard, compulsory maneuvers, someone steps outside the framework and goes somewhere else :-) :-) Skr
  5. And remember that you have to explain to the pilot what you are trying to do, and especially what he has to do. When you throw it the plane has to circle so that you can keep it in sight until it hits the ground. I used yellow crepe paper because it was easy to see against a green tree background. The plane has to stay fairly close and you have to keep your eye on it. If the plane gets too far away, or you look somewhere else and then back again it can be hard to find. And if the plane banks too much and the wing blocks your view of it it can also be hard to find. And once it hits it's good to get to a place that's 90 degrees from what the jump run is going to be so you can get a good view of where the opening point is (like other land marks besides just the place where it landed). The pilot has to fly as if he were the one watching it and keeping it in sight and deciding where the opening and exit points are. It could be good to do some wind streamer dirt dives with the pilot. Trying to make it all happen in real time with an oblivious pilot is a recipe for jump stories :-) :-) Skr
  6. > What would be some of the ways that cause this Usually it's lack of symmetry plus stiffness. Stiffness comes from fear and lack of knowledge. Fear is a good sign. It means you're paying attention, and realize that you are doing something totally fucking insane that mammals didn't evolve to do. What to do is find some instruction that you have some rapport with and make a whole bunch of jumps fairly close together. What you need is some experience with how your body and the air going by work together in freefall, plus some first hand experience that your parachute is going to open. That enables you to start to relax and begin to feel some control, which starts to remove the fear, and pretty soon you'll realize that it's a glorious insanity! So go make a bunch of jumps and report back with some jump stories :-) :-) Skr
  7. > Marisan: Certainly is. Eeeeee .. He was a good guy. I always meant to get back down there but it never worked out. > Obelixtim: That 10 way meet was talked about quite a bit back in the day when getting a 10 way together was a big deal. It felt like a big deal. They invited every country that had made a 10-man, and some kind of connection between us all was formed. Funny that it was 4 Commonwealth countries and one renegade colony. I used to wonder if that said something about the British spirit. There had been talk of some kind of world meet but New Zealand was the one that did it. Skr
  8. I made about 900 jumps on PC's and always used a sleeve, but the guys in Florida at that time used bags so maybe the idea is to find some Florida old timers and get details on packing techniques. PC's are complicated parachutes. You've got the center line from the apex down to the back risers, and steering lines that go up and then branch out to a bunch of steering slots, and down around the skirt you've got stabilizers that are not attached to the skirt, and they flail around during deployment looking for convenient steering lines or even a center line to snag. With a sleeve I never worried about the crown lines, but with a bag you have to stow them in some kind of organized fashion. I guess a nylon bag might be OK but I heard about nylon sleeves burning canopies so I wouldn't do that. 60 inches is a major short-line. I never heard of anybody doing any more than that. The accuracy people were doing that. I believe the theory was something about the jumper and canopy being a more closely connected system with less pendulum effect and with the jumper and canopy staying more closely related during turns. Knowing jumpers I'm sure some people did more than 60 inches, but short-lining tended to make the canopy snivel and people probably figured out that 60 inches was about as much as you could get away with. As far as bag size goes there must be some tables with cubic inches somewhere in one of Dan Poynter's books. Bill Booth is on here sometimes and he probably still remembers those figures. I remember one night at a Z-hills Thanksgiving meet watching John Sherman cram a PC into a bag that looked like it had about 3 cubic inches of space. I couldn't believe he was going to get it in there, but he did. I was afraid it was going to implode and become a black hole :-) :-) Give him a call at the Jump Shack, he probably still remembers those cubic inch numbers, too. Just pack the center line, steering lines and stabilizer section so that it stays organized when the canopy comes out of the bag and hits the wind. PC's were really pretty amazing chutes. Skr
  9. Is this the same Jon Butterworth that was jumping in the late 60's? One of the organizers of the first world 10-man star meet in 1970? I'm not on facebook so I can't see that page. Skr
  10. > So, when you're a beginner, and during the landing the flare still leaves you with a fair amount of horizontal speed (and some vertical speed) should you run it out, slide (baseball style) or PLF? I always PLF. But you need to find someone who can teach you how to do a PLF, and then practice it in all directions about a zillion times. Sliding seems like a bad idea because there are sticks, rocks, and other weird stuff to hit when you land, plus it wears your gear out. I try to gauge my landing so that I come to a stop with my feet about a quarter inch from the ground, and then calmly place my feet on the ground. That's hard to do with no wind, but if I have to take more than a couple steps, I just PLF because for me it's easier. I've made it through quite a few less than graceful landings because I'm really good at PLF's. Skr
  11. > How many jumps did you all have before your first 8 way. I don't know. One day a letter showed up with a patch and a photocopied letter from Bill Newell saying that he was honoring Bob Buquor and sending this patch to the 20 people who had been in an 8 man. I hit a thousand some time in 1967 so it was several hundred. Skr
  12. > Is the angle from me in the air down to the ground, or the angle from the ground up to me??? They're both the same size so you think in terms of whichever helps you the most. It's hard to come up with a simple rule so instead you have to take advantage of your brain's amazing ability to see patterns as you accumulate landing experiences, so try approaching each jump like this: Before the jump watch the wind socks and what other jumpers are doing and make a plan. Use an aerial photo if you need to. The plan is something like this: In these conditions I'll start my downwind leg here and go to here, turn 90 and fly my cross wind leg to here, turn 90 and fly my upwind leg from here to the target. Of course when you're starting there's a lot of guess work, plus other jumpers get in the way, the wind changes and so on. But the point is that having a concrete plan and trying to fly it really helps you see all the stuff that comes up that pushes you off of your planned path, and that helps your pattern detecting brain to start sorting out what's causing what. So basically this is the universe telling you to make as many jumps as you can right away :-) :-) Besides paying attention another thing that really helps is to find some good role models to hang out with. Skr
  13. > portable flux capacitors? No, they could never get those to work right. The latest stuff has levitator crystals mixed in to the coating that makes the canopies zero porosity. But even the Strato Star created lift. It's just that canopy design is one place where gear has really evolved forward. The new canopies come from a lot of research, engineering, test jumping and experience. Skr
  14. What about going to both places for a day of watching and listening and see which place strikes you as the most comfortable to start? While you're there you can get the details of how they would want to get you current. Once you're back in you can jump at both places see what develops. Some things have changed over the years. The airplanes are way better, and squares have come a long way since the Strato Star days. Human nature hasn't changed, though. You still get that feeling when you jump out into freefall, and the newer jumpers are just as enthusiastic as always, and people still drink beer and embellish their stories, and you still see young guys doing stupid shit to impress the few girls around :-) :-) Once you're around every weekend you can start tuning in to appropriate gear. I jump at Snohomish so I know they do a good job of guiding their newer jumpers. Pitt Meadows just north of the border is also a really good dropzone, but the dollar has lost so much value that Canadian prices are way up there. Shelton is a really long drive for me so I haven't been there, but I know people who jump there and you would be OK there, too. So really, you can't go wrong at any of those places. Skr
  15. If you lay on the ground and arch you can feel the muscles in your butt and lower back that are causing that pelvis down position, and those muscles are how you get pelvis down in freefall. But relaxing is also key. If you're tense and asymmetric you'll probably turn, which makes you even more tense, and you get a feedback loop going the wrong way. A half hour in a wind tunnel will take away the mystery of a body in airflow, which will help you feel more in control when you jump out, which will help you relax and get that feedback loop going the other way. Remember though that freefall happens in the framework of a parachute jump and all that rigging, packing, spotting, tracking, weather, canopy flying, judgement, and being in the air with others takes hundreds of jumps even for people who are making an effort. So find some good influences to hang out with while you're playing around in freefall. Skr
  16. > Seeing someone fly in front of me like that just blew my mind! It still does :-) :-) > how to maintain altitiude awareness when someone flying in front of you, making you feel like superman, or you're in the Matrix? The answer is to make a whole bunch of jumps right away so you can learn to do both at the same time. I practice a lot. I put a lot of effort into developing the habit of not letting too much time pass without glancing down at the ground. Learning to see the ground takes a lot of jumps spread over a period of time, and it takes intentional practice, like any skill that you develop. The first distinction you learn to see is: - Am I safe? Am I still above pull altitude? or - Should I pull right away? Maybe another way to say that is: - Am I way up there - 10 or 12,000 ft? or - Am I down in the lower part of the freefall - 5 or 6,000 ft? or - Should I pull right away? Another way is to see altitude (or lowness) as a cop in the rear view mirror. At first, when you're way up there, it's like driving down the freeway and you notice a cop maybe a half a mile back. So you don't obsess, you just kind of do what you are doing, but you don't forget he's back there, either, and you kind of glance in your mirror from time to time. Down towards the bottom it's like he's now two or three cars back so you're keeping closer track. At the end it's like he has now pulled in right behind you so you're really paying attention. It is a really good question. Skr
  17. > Who teaches students or new jumpers to practice reserve pull at terminal in freefall. I do something that includes that, which is to practice falling and feeling comfortable in the "pull position". The motivation is that pull time is maybe the most stressful time in a jump and it helps to develop a feeling of being in control. There are several versions depending on the student. One is to jump out and face each other, and then put your left hand and arm up above your head, arm straight and hand straight above your head. ("Above" is ambiguous in freefall, but when (we're standing there dirt diving your left hand (and arm are straight up above your head. Then, flying with one arm and hand and both legs, take your right hand and arm out of the slip stream. Put it on your chest or something. Now get used to flying with one arm and two legs. Sometimes we just hang out that way, depending on the student we may do 360's. Next is touching the main and cutaway handle and reserve handle. You don't take a grip, your hand is open and flat and just kind of pat each one and feel where it is and what it feels like. So maybe pat your main handle for 5 sec, then pat your cutaway handle for 5 sec, then your reserve handle. There are lots of variations depending on feedback from the student when you get down. We also do the mirror image, right hand above your head and patting an imaginary left handed main and then the reserve and the cutaway. Skr
  18. > Why are we still discussing this? Newtonian physics hasn't changed in the last few years. Because it's a social and psychological problem, not a physics problem. I think one root of the problem is that our intuition about how stuff works developed down here on the ground where we have a fixed frame of reference (the ground) and stuff doesn't move around. Trees don't move around, houses don't move around. If someone steps out of the mockup and walks away for 10 seconds and stands still, and then I step out and stand still, we don't move around, we stay the same distance apart. We have a lifetime of experience that that's how the world works. So when we go up and jump out and try to apply that intuition when my layer of air is moving relative to his layer of air we get the wrong answer. I look out the door and watch him fall behind the plane for 10 seconds and then jump out and use the intuition that we're going to stay that same horizontal distance apart all the way down, just like we did when we stepped out of the mockup. To see it otherwise means I have to make the effort (uh oh :-) :-) to expand my intuition to this new situation and practice new ways of thinking. I remember how confusing it was when I first ran into this question. My first reaction was to imagine my self standing 4 or 5 miles off to one side watching a jump run with two people getting out 1000 feet apart. You just take the first trajectory and move the whole thing, top to bottom, 1000 feet up wind. You separate opening points by separating exit points. 1000 feet was just an easy number to think about, and you have to allow for tracking and canopy motion on the bottom and upper winds on the top to get a real answer. The confusing part was when I looked at the same situation from the door. If he's 1000 feet behind me when I get out then why isn't he 1000 feet away when I open? I've worked so hard to expand my intuition that it's now hard to remember how confusing that was, and it took a long time to realize what was tripping me up, which was the intuition about how it works when we step out of the mockup on the ground. I even went up and tried following groups out with high uppers to watch it happen, but it was only when I read a post by billvon where he was talking about the relative motion of the two layers on the way down that I was able to verbalize it. So I think that's the psychological part. The social part is that there is no unified, system-wide voice training the people who train people so we still have all this embedded misinformation like the 45 degree rule floating around. Changing that would take effort too. Skr
  19. > Yes. > We perform better and learn faster when we are not stressed. ... ... :-) Great minds and all that. That's what I was going to say when I got the end of the thread. Skr
  20. Well I want to say something to acknowledge Kevin but I'm out of words. He was a good guy and such a long, steady presence and influence that ... Well, thanks Kevin. And thanks Sparky. Skr
  21. Ray was the first guy to sign up for the "tour group" going from Los Angeles to New Zealand for the first world 10-man meet in 1970. Clarice knew a jumper at Elsinore whose mother organized tour groups so he became the tour group leader and we spread the word. I can't think how we did that now since there was no internet yet. Every country who had made a 10-man was invited to send a team. That was Australia, New Zealand, Canada, the U.S. and England. Ray was a really colorful and interesting guy. We crossed paths many times at various boogies and other shindigs over the years. I bet the Great Party in the Sky up yonder just got a lot more interesting :-) :-) Skr
  22. > How often do you check your reserve pin? Before every jump. I have a standard gear check pattern that is the same for every jump. Over time it evolves, but between changes it's a rut that I can do even when tired, dehydrated, distracted, interrupted or whatever. I remember once at a long, hot midwestern boogie catching myself gear checking on auto-pilot. My hands were doing all the right moves, my eyes were aimed in the right direction, but my brain was not engaged. I was just going through the moves. That told me that I was dangerously dehydrated, as well as hot, tired, etc, and probably shouldn't even be jumping. Skr
  23. > I've always felt that was why people come out the DZ in the first place. They want to "jump out of an airplane." Me too, and maybe now with youtube and skydiving being fairly mainstream they want to do some of the stuff they see. I just think that in the course of focusing on Commercialization, Disneylandification, AFF, Base jumps, Wingsuits, Swooping, and all the other stuff, that our consensus reality has somehow lost sight of the fact that while jumping out is a wonderful and far out thing to do, making a parachute jump is a fairly complex activity. It's the foundation for all the rest of the stuff, and if I were Emperor of the Universe I would have people getting 100 jumps worth of serious training on rigging, packing, spotting, tracking, canopy flying, and so on, as well as a parallel sidebar introducing them to the other stuff. Of course if I were Emperor I would also change the ratio of men to women from 85/15 to 50/50 because that would balance out a lot of other stuff :-) :-) Skr
  24. Here's an email I just sent to a young friend of mine: OK, next topic. How do you decide whether to go or not? How do you sort through winds and weather, how late you stayed up, how much you want to jump, peer pressure, and so on? Hang out with good jumpers, make lots of jumps at a variety of dropzones, pay attention to what happened on each jump, think about it all the time, ... That's all good advice, but I've never had a simple phrase that captured a way to think about it. A phrase like "wings level" for canopy flying, or "skydance" for freefall. But a few days ago Mike put up an essay about "margin of influence" which feels definitive: http://michigansuits.com/blog/2011/01/an-organic-approach-to-risk-assessment/ It's a good conceptual axis around which to organize the multitude of factors. I think it even covers the case of getting in over your head, trying something too advanced too soon and losing your margin of influence, although I don't remember him saying that. ---- Mike has recently been using the phrase "Organic Skydiving". This may have some of its roots in his reaction to Skydive University, which was that what we really need is Skydive Highschool. An unintended consequence of switching from static line to AFF as the doorway in is that the current social structure is to plunge into freefall activities and pretty much skip over learning how to make a parachute jump. I wrote something about that once: http://indra.net/~bdaniels/ftw/soc_ev_skydiving.html So part of your assignment is to stop by Deland some time on your way to anywhere and hang out with Mike for a week or so and make a bunch of jumps. ---- The last little bit is that I had to laugh when he described his sequence for checking his gear. I've seen lots of people do it that way, there are many correct ways to pack, check gear, and so on. I'm a symmetry person, checking both sides in parallel. The main thing is to find a correct way that suits you and practice it until you can do it when it's cold and windy and you've been up all night and you're in charge of a demo into a ridiculously tight area and you're trying to gear up and keep track of everybody else and six people are standing there asking you stupid questions. (to be cont)