winsor

You don't have an entry for my category. My dilemma is to vote for him or throw away a vote on whoever runs on the Libertarian ticket. If he signs renewal of the firearms ban, I'm going Libertarian. I will die of old age before voting for a Democrat, and at this point the only thing dubya has going for him is that he might keep a Democrat out of office. I'm wildly unimpressed with any of the options (as usual). Blue skies, Winsor

How many skydivers do you know that have this understanding? Actually, rather a few - the sport is rife with techies. In most technical degree programs Physics 101 or its equivalent is a Freshman course. Anybody with an Bachelor of Science degree should have covered this material at some time early in their educational curriculum (if not in High School). I suppose I learned this stuff enough decades ago that I really don't remember what it's like not to understand it, and don't have much patience for people who demonstrate ignorance of things that I assume are simple. Dr. Ralph Heller, a professor at my alma mater, was reputed to have once told a Freshman class "I've been teaching this subject for thirty five years - you should understand it by now!" His students weren't amused, but I know how he felt. Blue skies, Winsor

Yes. Good. Are we agreed that if the winds at exit altitude (13,000 ft) are say 50 kts, and they drop to 0 kts at 5000 ft. you cannot calculate exit seperation based purely on airspeed? While the balloon example shows that ground speed counts for jack shit when it comes to seperation, the space ball example shows that air speed is not the answer either. I just hope that people will take the time to figure out what is going on. Dave I hope you include yourself among the people who need to take the time to figure out what is going on. We are not agreed that you cannot calculate exit separation based purely on airspeed, so long as you can calculate the exit speed relative to the airmass at opening altitude. If all you have is exit airspeed and groundspeed, you can still make a good estimate of an appropriate exit interval that will ensure horizontal separation between exit and opening altitude. A clear understanding of the kinematics involved is pivotal, but apparently elusive. Blue skies, Winsor

Errr... does that not mean they will be moving towards each other at 60 kts? Yes.

If you criticized the racist agenda of Al Sharpton and Jesse Jackson with equal enthusiasm I might pay attention. As it is, I get the impression that "Progressives" are unable to distinguish between an underdog and a loser. Blue skies, Winsor

I should not have implied that there was any change to the approach to spotting on the basis of my treatise on the subject (or Fred Leslie's or John Kallend's, for that matter), since that wasn't the point. Given the tools that are available to a jump pilot, ground speed gives the only measure that is useful for determining separation at opening, and I don't know anyone who does a better job - regardless of how they go about it. I considered a response of "okay, that's legitimate" to the theory behind the physical models that we use to be as close to a change of standpoint as I meant to convey. Up until that point, there was no suggestion that any other model had merit. I am by constitution a semanticist, and do make a distinction between theory and practice. For theory I'll turn to Doctors Leslie and Kallend, but in practice nobody is better than Mike Mullins. It will be a cold day in hell that I presume to tell Mike Mullins how to fly an airplane.... Blue skies, Winsor

For a second, I thought we were going to get through a separation thread without seeing this falsehood. The 45 degree rule doesn't/can't work. I..... see hahahaa care to elaborate? Sure thing. When you step out the door you are subject to two effects that come to mind - gravity and wind resistance. Gravity applies a constant force in the down direction, and wind resistance applies a force proportional to the square of airspeed in a direction opposite airspeed. Right out the door airspeed is often close to terminal, so you can expect almost 1 g of acceleration directly aft from wind resistance (drag); add to that orthogonal (right angle) acceleration downward, and it turns out you follow close to a 45 degree path out of the door. Thus, the angle of departure is a poor parameter upon which to base exit timing. Bill's suggestion that 7 seconds to start with from an Otter is a minimum between groups is a good one - I'm prone to count off 5 seconds before climb-out. BTW, if you're putting out a series of solos who can be trusted to stick to their column of air, you can shorten it up significantly. While playing Army, we used to hook our reserve under the main of the guy closer to the door and run out. We could clear out a C-130 like it was a tube of toothpaste that got stepped on. In retrospect that was none too fucking bright, but it sure was fun. Blue skies, Winsor

If they don't send me back to Serbia first, I'll be there.

You really don't get it, and it is frightening to note how consistently and insistently wide of the mark you are. In the years that I taught Physics I don't think I had a student who was so opposed to figuring it out, so I don't know what approach is likely to get through. I'm not sure to what I should attribute this intransigence. Given your writing I doubt if stupidity is the issue, so my guess is some combination of ignorance and denial. In this sport, ignorance and denial can be fatal singly and even more so in combination. A big problem is that someone else's ignorance and denial may get ME killed, and I'm not okay with that. To a certain extent I don't mind if people don't understand the theory as long as their practice is safe. I do, however, draw the line when people put forth comic-book physics to explain their decisions. Perhaps you're playing Devil's Advocate, with the intent of putting to rest some common misconceptions, though I doubt it. When all is said and done, people who don't understand lose track of which model was valid and which one was tripe, so it tends to be a bad approach. There are plenty of people in the sport with a thorough understanding of the physics of skydiving. A simple litmus test is to see if they agree with your arguments put forth in this thread - if they do, they're clueless. Blue skies, Winsor

So what exactly is the minimum and should it be modified based on group sizes? For a four-way RW formation that breaks off at 3,500 and deploys at 2,500, given the results of tracking contests it is conceivable that a radical tracker could get nearly 600 ft. from the center of the formation by pull time (average 100 fps for 6 seconds). If you cut that in half for an average recreational jumper, and double it to get the results of people from two groups flying toward each other, you have the same 600 feet. Figure an 80 knot TAS jumprun, which gives you something like 130 fps. Five seconds separation is 650 feet, which can have people from subsequent groups opening in each other's faces - if not quite hitting each other in freefall. If your group size is larger and you're tracking longer, you'd best increase your delay between groups. This assumes that neither group was sliding around, of course. Going from bellyfliers to head-downers you don't need quite as much delay in general, since the fast fallers get separation from their increased throw (it's significant if there is a great difference in fall rates). If your airplane is slower, bump up the times accordingly; out of the Jet you have separation whether you like it or not. Oh, and the groundspeed part of the deal? If you have enough headwind to keep you in "green light territory" longer (lower groundspeed), use the extra time on target to get extra separation between groups. More is better. It's better to land out than to risk freefall or canopy collisions. It's a lot easier to plan for a safe off-DZ landing than to hope that you either don't collide or survive the collision. So my personal minimum is like 5 seconds between RW groups, maybe a solid 3 before the first head-downers should follow. If we're doing RW 12-ways in succession, an 8 to 10 second delay is not a bad idea for starts. If you have more time, use it. Blue skies, Winsor

You really don't get it. The smoke traces the path through the airmass, and indicates the effect of the extra dimension - time - in the problem. The distance between the smoke trails is the horizontal separation between jumpers IN THE AIR, even though they will land at the same point, all else being equal. If the jumper hangs out under canopy, they're being blown downwind and will have the same horizontal separation as in freefall. Even at opening altitude the jumper is at the mercy of the wind, and their motion with regard to the ground is irrelevant. Again, you aren't paying attention. I make no such claim, and your model has no bearing on the issue at hand, which is exit timing to maintain separation in freefall. Read the article, and pay attention. I get into the whys and wherefores at the end. The minimum is the minimum, and anything you can get above that you should take. A headwind allows you more time on target, so you have more time with which to work. Divvy it up between the groups. Unfortunately, many are. There is a large part of the skydiving population that has a solid technical background in the relevant subject matter, and there are no significant differences among us - beyond preferences regarding presentation format and whatnot. There are, however, many people out there with lots of jumps and as garbled a concept of the physical realities as you exhibit. Some of these are Big Names, who mistake luck for ability and understanding. Three seconds delay between groups? Somebody's clueless. Blue skies, Winsor

Answer: Yes it would. You and all who exited before and after you would be affected identically by the variances in wind direction and velocity that you encountered as you descended. In short, you would all drift the same amount. Wrong again. The most critical parameter for ensuring freefall separation is the speed of the aircraft with regard to the airmass at opening altitude. If you work out the trajectories in each of the cases noted by Prof. Kallend, you'll find that the separation at opening altitude is hardly constant. Blue skies, Winsor

Wrong - in this case, like all others, airspeed (and relative airspeed) is the only relevant factor. I suggest that you peruse the notes from the Spotting and Separation Seminar at the WFFC at the following URL: click here It's likely overkill, but the treatment is legitimate. The ignorance I encounter regarding the Physics involved scares me. Having people occupying the sky with me, armed with such misinformation is truly frightening. Blue skies, Winsor

I actually find it frightening that you ask this in all seriousness. If you're doing 160 mph airspeed, each group is getting blown aft accordingly. There is no way in hell that you could have groups exiting such that they're on top of each other - at terminal, groups are separated by 240 some-odd feet for every second of delay between them. What the ground is doing, in and of itself, means precisely nothing until you reach it. Blue skies, Winsor

Take Physics 101 and pay attention to the "frames of reference" section. Mike was wrong then, and has since updated his stance. You're wrong now. Blue skies, Winsor

First, a ground speed of 160mph ... Ground speed is entirely irrlevant to separation in the air. Airspeed is what gives you freefall separation, groundspeed *contributes* to separation between groups on landing. Big, big difference. Blue skies, Winsor

That was pretty much my progression, with the substitution of a 5 second delay for the full-altitude jump. 1st square jump - XLCloud w/FXC, IAD PRCP. 2nd square jump - DeltaCloud w/FXC, throwout. 3rd square jump - CruisAir, no AAD (my rig), throwout. 4th square jump - same rig, 5 sec. delay. etc. Yeah, I'm a pilot as well. I didn't bounce, either. Blue skies, Winsor

The parachute part of the deal is pivotal to any aspect of the sport to which you may gravitate. No matter how great your freefly or RW skills, if you can't successfully bring your parachute to a nice, safe landing time and again, your skydiving career is subject to ending abruptly. In the static line progression the focus is first and foremost on the part of the endeavor that will save your life. Only when you have the parachute part of the deal wired do you begin to add freefall skills to your bag of tricks. AFF is, as the name implies, a freefall intensive training method. The parachute part of the deal is given short shrift by comparison to learning the nuances of freefall. After 100 jumps it doesn't make a hell of a lot of difference which route you took from the standpoint of freefall skills, if developing them is your goal. If you don't develop the canopy skills right up front, you may not make it to 100 jumps. My impression is that more AFF trained jumpers exhibit mediochre canopy skills later in their skydiving careers than do those who started with static line. Since it is under canopy that we now have by far the most casualties, I strongly suggest going with the training method that does the most to enhance your safety. If you decide to go AFF, please do everything you can to learn to fly your parachute safely. You will be welcomed into POPS in 21 years if you stick with it and keep it safe in the meantime. Blue skies, Winsor

Actually, I traded my PC for Hank's 7-TU for a jump. Since they were connected to many of the same lines, I decided to use the toggles instead of honking down on the rear risers like with the PC. Bad plan. I rediscovered that burying the toggles on a cheapo is how you put it into a sink. Oops... To the original poster - yes, you can flare a PC. If you want, I have copies of the Paracommander Manual that gets into the process. Though landings on my RWPC don't really need much input, brisk application of rear risers before touchdown does make standups routine. Blue skies, Winsor

No one has the right to brag. "It ain't bragging if you can do it." Dizzy Dean Blue skies, Winsor

This summer at Rantoul I organized an 8-way RW group at the end of a weather hold. There were still more clouds than holes, and we agreed to have an EXTREMELY experienced jumper near the door clear the spot. When the green light came on, we got continued shaking of the head from our spotter. No good. People behind us were yelling "GO!" I started out responding "NO!" and rapidly switched to "FUCK YOU!" When our group's part of the jump run had elapsed, we let the people behind us go, so they were not delayed by our decision not to jump and exited just where they would have if we'd gone on the green. Everyone on my group agreed to eat a jump ticket to avoid punching a cloud with a group, but we got a go-around (thanks, Paul!) and had a great jump. Even though I couldn't see out the door, I wouldn't second guess someone with years of experience who was making the call. I did apologize for yelling "FUCK YOU!" at those pressing us to go, since I didn't consider how unhappy it was likely to make tandem students at the time. Nevertheless, I greatly appreciated having someone in the door looking out for me. I jump with Bill. I trust his instincts, and defer to his expertise in areas where he has experience and I don't. I would be more comfortable jumping after he had given the all clear than simply on the basis of GPS. I bet if you had simply said "excuse me," he would have made way if it was safe, or indicated his concern if it wasn't. I think you are reading much more into this than circumstances warrant. Blue skies, Winsor

6,015 days - so far, so good.

Skydiving can be characterized as committing suicide - but changing your mind at the last moment. If you either fail to intervene, or the lifesaving procedures themselves fail, you are dead as a doornail. What part of flinging yourself bodily at the Earth from a couple of miles up strikes you as "safe?" The fact that you have some very expensive nylon on hand, replete with the latest automation? Playing with cobras may seem safe if they haven't seen fit to bite you yet. To blithely assume that the antivenin you have on hand affords you impunity in the event they do is dangerously naive. Denial isn't a river in Egypt. If you have to lie to yourself that skydiving isn't dangerous in order to participate, you would be well advised to take up another hobby. When you are given irrefutable evidence that a rethink is in order, it is usually in a particularly nasty fashion. In this sport, safety is never more than a "so far, so good" kind of thing. 1) You have to bat a thousand. 2) Nobody bats a thousand. Blue skies, black death, Winsor

Sounds like Steve "Deadman" Morrell. His first jump on the main was from 600'. IIRC, it was a Precision Interceptor. His second was supposed to be from 250', but the plane lost some altitude on jump run. It took less than 10 seconds between letting go of the strut to hitting the peas. I still have pictures of that jump somewhere. I just kept him in frame with the camera in continuous mode, and it used less than a roll of film. Much of what Steve did fell into the "don't try this at home" category. Blue skies, Winsor

I haven't had any problems jumping in Europe, but I believe you have to have an AAD to jump in France these days. As long as you don't play the Ugly American, you'll be fine with just English. Gap is outstanding, as is Lapalisse. Skydiving is close to a national sport in France, and it's a great place to jump. My home DZ in Germany is in the Black Forest, so I doubt that would be of much use. I don't have the link for German DZs handy, but I'm sure someone will post it. The Euro is doing extremely well these days, so brace yourself for sticker shock. The overhead is serious for a DZ in Europe, so the prices are accordingly steep. When you have time free, Empuribrava (sp?) in Spain sounds like a great deal, and Texcel in Holland was a happening place. lf you're stuck there at the appropriate time, the Hercules Boogie in Sweden and the Espace Boogie in France get high marks. Espace was in Vichy when I was there, but had moved to Lapalisse from what I heard. The Army-sponsored parachute club in Bad Tolz has been closed for over 10 years, but there may be one still in existence. People like the Golden Knights tend to be a good resource for finding military-sponsored clubs; if you contact them, they can point you in the right direction. In any event, you should have fun with the parachuting part. All the way, Winsor