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Everything posted by skr

  1. > From Bryan Burke at Skydive Arizona. I think these analyses and formulations of situations that he does are real milestones in the evolution of skydiving. Skr
  2. I read to the bottom of Bryan Burke's article and tried to add a comment, but it doesn't show up. I was able to rate it by clicking on one of the little gold stars but couldn't add a comment. Skr
  3. skr

    The Horizontal Flight Problem

    Thanks Bryan. These analyses and formulations of situations that you do are real milestones in the evolution of skydiving. Skr
  4. > One type of dive you can do is where you do nothing in freefall ... except feel the air. I still do that fairly often, just go out by myself and feel the amazing feeling of being in Freefall. Sixty seconds is a really long time! Skr
  5. Besides all the other good answers above I find it helpful to get on Google Maps and practice seeing how the runways, surrounding ground features and so on look. I look at the dropzone from various altitudes then look away and practice visualizing it. I do that enough times that I can see the runways and know their numbers, and can see the river, highway, town, railroad track, race track, or whatever, and know which way north, south, east and west are. That helps me assimilate the avalanche of other new stuff I will encounter at a new dropzone. Skr
  6. > Writing to us the 'old' jumpers Skratch! Yes, some of the gear, airplanes, and common practices have changed, but lots of his stories revolve around human nature, motives, quirks, bravado .. How many young guys get in trouble doing something weird these days because underneath it all they were just trying to get noticed by all the pretty girls? :-) :-) I remember a story about them jumping a watermelon - a Texas sized watermelon. Right away I'm visualizing something the size of a small tank, with handles dangling off the ends (how'd they get that thing into and out of a 195?). And immediately upon exit the watermelon goes supersonic, with two jumpers fluttering in the breeze, leaving the camera and third jumper stranded in freefall at exit altitude. So they seek wisdom far into the night, and decide to try it with a mattress the next day. A mattress?? From a 195?? But I can see that story happening today. The jumpsuits and gear and airplanes may have changed but ... The "old days" really were different in some ways, and I'm glad I got to see it, but under the surface a lot is still the same. Kind of scary thinking there's lots of young guys out there now with attitudes like ours were back then, isn't it? :-) :-) Skr
  7. Aha! I thought there might be more to the story than appeared in Parachutist :-) :-) It was good to see the uncut version, but I agree with Guru312 that your stories reveal even more. So if you happen to fall into a reminiscing reverie from time to time ... You'll be writing to us, the jumpers, not to some Parachutist editor, so you can just kind of let go and ... Skr
  8. Clarice just forwarded this email from Brian Williams: Date: Sun, 5 Aug 2012 19:48:02 -0700 (PDT) From: Brian Williams Subject: Bill Newell gone I'm sad to say, but Bill passed on sometime after 6:00 P.M. today. He battled the Grim Reaper to the very end. I've known this Great Guy for 49 years and will miss him terribly. Brian Williams
  9. > They are from way back in the Casa Grande era Way back? Whaddya mean *way back*?! It seems like just day before yesterday. I ran into Bob Schaeffer in Oklahoma in 1980 when I was helping Hillsy at Skydance, but I haven't seen Mike in a long time. Those guys really knew how to run a drop zone. Thanks, Gary. It's good to know Mike is still active and flying. Skr
  10. Worst DZO? I've been jumping at Snohomish for the last four years and I have a different impression of Tyson. He reminds me of Bryan Burke down at Eloy who looks at the whole system and how the various components fit into the overall situation and tries to let people do as much as they can without endangering others. And I'm sure he would like to be doing some wingsuit jumps himself. But I think he's up against the question of how to coordinate really different flight modes, like swooping with regular canopy flight this is wingsuits with straight downers and high pulling tandems. And I think the real sticking point is the effort it would take to keep new wingsuiters out of the straight downer airspace. Multiple landing zones and airplanes add to the complication, but I think the training to keep the airspaces separated is probably the stumbling block. Didn't Mark Twain say something about people who do what's right even when it's inconvenient and unpopular? Something like aggravating some and astonishing the rest? :-) :-) Skr
  11. > our mom was to say the least, one of a kind. Most of the people she jumped with were unique and colorful characters, but yes, she stood out even in that crowd, and not just because we were nearly all guys and she was a really pretty girl :-) :-) I wasn't there for her malfunction, but now that you mention it I remember it happening. I remember her being on the Fairchild jumps at Oceanside. I was jumping at Oceanside, Elsinore, Taft, Arvin, Lancaster and California City, and ran into her at several places, but I imagine that I noticed her much more than she noticed me. People are fading fast. It's good that you have so many memories of her. Skr
  12. I don't know. Danger wasn't why I started jumping. I wanted to go out in space and be weightless, but I was inconveniently born a couple centuries before that became commonly available. And I wanted to fly, like a bird. And when I was a kid I played WW-II pilot getting shot down over Germany so I would have to bail out, and I would fall and fall and fall. And for a couple summers I spent all day jumping off the 24 ft diving platform, accumulating several days worth of freefall one second at a time :-) :-) And when I finally did start I was really, really scared until I got stable (11th jump), and that wasn't fun. And the times after that when I would get in some situation and be really shit scared weren't fun either. On the other hand .. That danger introduced me to intense focus, and forethought, and paying attention, and I found that I really liked that. And I remember, in the late 70's, when life was starting to transition, wondering why I had to jump in order to focus like that. Well, of course you don't. People have known that for thousands of years. That led to a big thrash of reading spiritual and meditation books. And as I became more self aware, or maybe honest, over the years I found that I was drawn to situations of concentration and paying attention. I remember, working at the Academy of Science in Beijing a few years ago, the first time I decided to try taking a taxi and get further than walking distance from my apartment. It was like the pre-jump jitters of my first jump, reviewing how to say where I wanted to go, pinchecking everything I was taking with me, going to the bathroom again .. And when I got to the subway and started down the steps into the vast unknown of god-knows-what my heart was racing like on any jumprun. So I guess I'd change my answer from not sure to about the same as it is now. I don't like being afraid but I like what I've learned from it. Skr
  13. Well all the words floating around in my mind seem kind of trite and inadequate. He used to jump at Oceanside, near Camp Pendleton, in the early 60's, and when I'd run into him here and there over the years he always seemed like the same guy - a little more weather beaten, but the same, quiet guy. And he was always in such good shape I guess I thought he'd just kind of go on forever. Damn .. Well, thanks for posting this. Skr
  14. Hi Al, > The old crowd seems to be shrinking at an alarming rate now. I don't know if you've seen Bill Newell's latest post (5-5-12) on Air Trash but it snapped me back to reality. I didn't know about that. Thanks for telling me. I should apologize for pulling in your face before it's too late. It's just that I was used to pulling at two rather than breaking at two. I actually saw you, but by the time it registered my right hand was going for the ripcord and it pulled before I could shift gears. And then when you said I should be able to handle myself at 1,500 ft I knew you were right but I was too embarrassed to say so. It's funny the stuff you remember. Skr
  15. I got so involved in drawing that ascii diagram that I forgot about this part: > Why is this not true in your example: > When J1 passes through, it will take him horizontally farther away from J2 and when J2 pass through it will take him horizontally closer to J1, back to the original horizontal separation at exit. > > J1 will see J2 first moving horizontally away from him and then horizontally closer to him. Except that I woke up a couple mornings later thinking "No, he's right. That apparent extra separation disappears right there in the forward throw layer." So then I started trying to think where I got off the track, thinking I would come back here and say something, but I can't seem to concentrate on this right now. This is especially annoying because I used to think what you just said, and even posted about it. rec.skydiving Sept 1999: > One way I retrain my intuition is to practice standing in the door > with my primary focus being my relation to the ground and my motion > across it. With high uppers I can see that I am not moving very much > and the previous group is being swept away by the upper wind. When > I step out I too will be swept away by that same wind and will end > up pretty close on top of them. > > With no uppers, I am covering distance across the ground and basically > leaving the previous group where they got out (except for forward throw) > and moving away from them. Bryan Burke has a number of pithy sayings, one of which is "Minds are like parachutes. "Sometimes they just don't work. So this effort foundered on poorly formulated physics, but I'll be back sometime later and start a new thread. I know that 98% of the attention these days needs to be developing customs that allow different kinds of canopy flying to coexist, but I'd just like to have a nice, clean exposition that takes new jumpers from their initial intuition of looking out the door and leaving room, to why that doesn't work with uppers, to when groundspeed is a good technique and when conditions are in unsolved territory. Skr
  16. I mostly hear "hard deck" when people are talking about when to stop trying to fix it and start taking steps to get a reserve out. But there are all kinds of "mental gear shift" points. When do I decide I can't make it over the freeway or alligator farm and land over here? When do I decide I'm not going to make it to shore and start preparing for a water landing? If I have a canopy collision when am I too low to cutaway? ---- One thing about "trying to fix it" is that it's really easy to get focused on trying to fix it, and forget how fast you're coming down. So to me practicing and ingraining that "Try once, try twice" reaction is really important. Skr
  17. Well that's hard to hear. He really was one of the good guys. He used to come over to Hillsy's dropzone in Oklahoma. He was not only really good with students, he was colorful, entertaining, a good story teller, and deep. A very perceptive guy. One by one, they're leaving, one by one. Skr
  18. > It STILL seems as though you are saying that J1 didn't pass through that same higher, faster moving layer. Right. This region during and right after exit is hard to get into words. The bottom is easy. J1 arrives at O1; a little while later J2 arrives at O2. Once you can control opening points you can talk about group centers and tracking and canopy motion and so on. And the middle is easy. Each jumper is falling straight down in his little patch of air, and the higher patch is moving slowly toward the lower patch. But the exit stage is hard. It's not linear, and J1 and J2 are in corresponding parts of their trajectory at different times, and so on. I find myself fantasizing about taking John's program and modifying it to have one jumper exit, and then some time later a similar jumper exit, and plot, or somehow display, a history of their horizontal separation. He's already done all the heavy lifting, selecting the drag law, the numerical integration technique, step size, and so on. But I know I'm not going to do that. I'm just a couple g's short of floating off to ... otherwhere. But maybe there's some energetic math or physics student out there who could be enticed by the fame and glory of finally resolving the notorious separation debate :-) :-) And then students could all look at that program. And we experienced jumpers, too. I'd like to run a bunch of different scenarios and get a clearer idea of exactly how the distances play out. ---- But! To your question: J1 and J2 are not interchangeable. It's not symmetric. If we start the video running when J1 exits, then J2's path doesn't look like J1's. It has an extra, horizontal piece on the front end. The freefall parts of the trajectories have the same shape, but when you're comparing J1 and J2 moment by moment you're comparing points on two dissimilar paths. UPPERS ------ >
  19. Well! That wasn't the discussion I was expecting from that first post. I know .. Expectations .. I thought we were going to talk about training students. But I'm worn out, so I'm going to restate the central point, and go have a beer or something. When jumper 2 exits: || is the separation of exit points || is the separation jumper 2 sees UPPERS ----------- > < ----------- AIRPLANE || EP2 EP1 || . . J1 . . . . . . . . . . . . . . . . . . . . OP2 OP1 . . .. . . . . . . . . # # # # # GROUND # # # # # # # GROUND # # # # # The relevance of this is that almost everybody's first intuition for leaving separation is to look out the door, see || for separation, and expect that to still be there at opening time. That's the ground based, mockup intuition of how the world works. They need to understand that they're going to spend all but the first and last bits of the freefall in a steady state situation where jumper 2 is in a higher, faster moving layer, and that they're going to end up with || at the bottom. And I think it's possible for experienced jumpers and USPA and the Safety and Training Committee to explain this to new jumpers. I know .. "Look Martha! Hand me my camera! There's an idealistic optimist!" :-) :-) Skr
  20. Hey, Walt, I've read this 3 times trying to get why you're saying this. An aerodynamic, plutonium brick will take longer than a feather, but they both get to 80 knots. The sideways motion is independent of the downward motion. Unless .. Do you mean by this: > As the angle from vertical increases, it tells-reflects the amount of effect the moving medium has on it. that the motion is asymptotic, that it gets closer and closer to 80 but never actually gets there? Skr
  21. > Why should the position over the ground have any significance at all? I really don't get it. You're right. As a question on a physics test, tossing spherical, isotropic skydivers off the tailgate and watching their horizontal separation evolve over time, the ground is irrelevant. And actually, in the rec.skydiving discussions several people kept pointing this out. When a new example or theory was being put forth, they would wait until the jumpers were in freefall and then bring out this giant yellow Caterpillar tractor and start hauling the dropzone around under the jumpers. At the time I found this annoying because I was still trying to understand how both airspeed and groundspeed arguments could seem so convincing. You would have been one of those guys :-) :-) I finally pulled back from trying to follow other people's arguments and sat down to think it through from a standing start for myself. I found that if I imagined standing on the ground, a couple miles off to one side, and watched a jumprun unfold, I could see all the parts in a way that I knew the physics was correct. The exit points on the ground, the corresponding points in the space above the ground, the opening points, the patches of air in the exit layer where people exited, the way those patches moved across the sky with that layer of wind, the patches where they opened and the way they moved relative to the ground, and so on. Once I had that I could listen as others layed out their current theory and I could follow it, and I could see if I agreed or exactly where I might disagree. That's when I saw that the second freefall trajectory was exactly the same as the first, just displaced upwind, and you could separate opening points by separating exit points. So my answer was, when the first person goes, look down at the ground and see where they got out, go a certain distance across the ground, and go. It was neither airspeed nor groundspeed, it was all spatial distance. So I posted about that and advocated that for several years. But I gradually saw that it's not practical. I had spotted a lot in the past, but these days lots of people never get the chance to spot any. -------- Once I had that I could see how, when the first jumper get's out, the plane flies upwind from that point in space, and the first jumper blows downwind from that point in space. And the second jumper sees a large distance to the first jumper at exit, while at the same time separating exit points by a smaller distance. That excess distance is what disappears from the moving layers effect. -------- (I guess I'm actually now responding to later posts in (the thread, not just to strop45. Some time back John asked why we're still talking about this since Newton's laws haven't changed in several hundred years, and I said because the current problem is psychological and social rather than physics. Almost everybody's initial intuition for leaving separation is to look out the door and leave some room between jumpers. Now you can say "Use groundspeed", and some people are happy with that. That's all they want to know. But! They won't know why, and they won't know the conditions under which it's appropriate. And there are plenty of people around who don't accept proof by authority, they want to think for themselves and know how it works. And for those people we need to explain the genesis and limits of that initial intuition, and some ways to see the more complicated situation of winds, and the approximation and limits of groundspeed. That's what the initial post in this thread was about. I think John and Bill and others are doing a good job of simplifying a complicated situation. ---- Billvon, it's a good thing your 80 knot example wasn't 120 mph with the jumper falling away from the plane at 45 degrees for the whole jump. That would have really stirred things up :-) :-) Skr
  22. > Scratch has now explained explained that he was only discussing the "45 degree angle rule" No, I am not. I am talking about the initial intuition that leads people, when they first encounter the separation question, to look out the door and leave what looks like good opening separation between them and the person that went in front of them. And how that leads us astray. And how to expand that intuition so that what actually, physically happens seems normal. In the hopes that when enough new people have been taught this, it will become concensus reality and this whole separation discussion will recede into history. I remember when I first encountered this, Pope Valley, 1970's, Bill Dause told us one morning that we were going to start putting multiple big groups out of the DC3. There was horrified silence and a vast reluctance :-) :-) But none of us discussed how to do it, we just looked out the door and left a whole lot of room between us and the group in front of us. I was elsewhere in the 80's and didn't see that part of the evolution. My next encounter was the legendary airspeed-groundspeed debate on rec.skydiving around 1995. After reading a thread of wildly varying views and really clever arguments going in every which direction I was really confused. The arguments were so convincing, and the conclusions were so contradictory. If I imagined standing on the ground watching a jumprun, then separating opening points by separating exit points was obviously right. And I got better and better at the physics of it all. But I couldn't shake the feeling that if I looked out the door and left separation that that was also obviously right. It was only when I saw billvon formulating the situation as moving layers that I realized that I was unconsciously using a ground based intuition about how the world works in a situation with a lot of moving parts where it didn't apply. And I think, by the way people talk about it, that a lot of other people are falling into the same trap. That's what the original post was about. I'm not trying to solve a question of skydiving technique, I'm trying to solve a sociology problem, which is the never-ending separation discussion. I haven't been over to look at Brian's stuff yet, but I'm sure that if he ever stumbled across this thread he would understand immediately what I'm trying to do. Skr
  23. > Am I missing something here? Maybe it's that some words like "separation" are being used with different meanings in different parts of the conversation. "Exit point" used to just mean the place on the ground that you got out over. When these airspeed-groundspeed discussions came up, I'm not sure when, my first encounter was in the mid 90's, people started also meaning a corresponding point in the sky above the point on the ground. There could be 3 exit points, ground, opening layer, exit layer. And similarly for "opening point". Used that way separation between exit points translates directly to separation between opening points. But the intuitive way that almost everybody, before they encounter the airspeed-groundspeed discussion, first thinks of for leaving separation is to look out the door and leave some distance between you and the person who got out in front of you. In that case "separation at exit" means from you in the door to that person. If there were no winds that would work, BUT! :-) :-) With uppers the plane flies slowly upwind of the exit point, the first jumper blows downwind, and when you see what looks like the separation that you want at opening and go, you've really only separated the exit points by ... not enough. It's just that this conversation has been going on for so long among so many people that people get telegraphic and leave out background assumptions and sometimes it's hard to be sure you're actually both in the same conversation. It also depends on who you're talking to. I can say "groundspeed is a good technique" to you and we're probably then in the same conversation. If I'm talking to a new person it's really important that I lay out the conditons under which that's a true statement. The winds at opening altitude can't be very strong. And they need to be going in the same direction as the uppers. And the uppers can't be super strong either, especially with people pulling at such a variety of heights. A high puller could still be up there in the kill zone even 60 seconds later. It's a complicated situation and everybody including me would like a simple answer. Skr
  24. > commenting on your theory The theory I thought I was writing about is why so many people start out thinking you can leave exit separation based on how far the person in front of you has fallen behind the plane. It seems intuitive because that's how the world works down here on the ground where we use the ground as a common, rigid frame of reference. And then on through a number of reasons why that doesn't work with upper winds. The point was to help new jumpers stretch their intuitions to feel comfortable with the more complicated situation where the ground, the layer at opening altitude, all the layers on up to the exit layer, and the plane, are all moving relative to each other. Two jumpers in different layers of air may be falling straight down relative to their local patch of air, but the higher layer is moving relative to the lower one, so they are not staying the same distance apart like they would on the ground. They are not staying the same distance apart like they would if you had two planes, one following the other, and a jumper leaving each plane simultaneously. In that case the jumpers are in the same layer at the same time and the separation stays constant. But in the skydiving case the jumpers are separated in time as well as space. So that to do the initial, intuitive thing of leaving separation by looking at the jumper ahead of you, you have to leave the separation at opening altitude plus enough to account for the moving layers effect. The jumper in the door sees a distance that is roughly airspeed * exit interval, on the way down the moving layers effect subtracts enough that they end up with roughly groundspeed * exit interval. And each jumper after that sees the same thing. Someone standing on the ground would see distance between exit and opening points as the same but the jumper in the door sees something different. This is where the intuition needs stretching. The jumper in the door is measuring the exit separation in one frame of reference, and then opening separation in a different frame of reference, and the frames are moving relative to each other. And then the theory goes from there to why it's hard to do things that way and that's why people often start out with an educated guess for the first load and then adjust. Unless a GPS is present. With that you have the possibility, under certain conditions, of estimating exit interval using groundspeed. So the theory is about how our initial, ground based intuition leads us astray, and how to learn to think so that our intuition gives us good answers in the upper winds situation. I can't connect the rest of your objection to what I thought I was talking about. I first heard of the 45 degree rule long ago at Quincy from John Mathews. For about an hour I walked around feeling great relief that we finally had a simple answer to the endless exit separation question. Then suddenly it was like "Hey! Wait a minute! That's the classic airspeed approach! Shit! We have to keep on thinking!" I don't get around much anymore, just the local dropzone at Snohomhish, because I'm kind of fading into other... into otherness I guess. I didn't see Brian's stuff, but if he's having to explain that the 45 degree idea doesn't work with uppers that tells me that we experienced jumpers aren't getting the word out very well. And you're right about the King Air :-) :-) Skr
  25. Oh, Hi Walt, I see it lost some formatting, I should have enclosed it in a couple "pre" tags. If you're standing on the opening layer the exit and opening points look to be the same distance apart. If your standing in the door leaving separation by looking at the distance from you to where the first jumper got out, the distance to the red molecule, then you're measuring that distance in the upper layer but measuring distance between opening points down in the opening layer, which is a different coordinate system. I'll see if I can say it in another way when I get back. Skr