Isn't it time for a serious talk about exit timing??

[winsor 185]

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Hey Winsor, can you elaborate on this one?

A ship with an airspeed of 160MPH, might have a ground speed of 80MPH. To get the necessary separation between groups shouldn't we rely on the ground speed? A ship could have an airspeed of 160MPH and not cover any ground, in which case we'd have groups getting out literally on top of each other. Why does airspeed matter?

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

[Jimbo 0]

You're right, my mistake. I understand completely now.

-
Jim

"Like" - The modern day comma
Good bye, my friends. You are missed.

[murps2000 86]

Do you really think that if you were flying jumpers with an airspeed of 160mph into uppers that were blowing at you at 160mph (giving you a groundspeed of 0 mph) that you would do anything but drop them all right on top of each other? Sure they would be separated by some 240 ft. for each second between exits at first, but at some point they would get off the hill and be falling straight down, except for the horizontal vector imparted to them by the winds they fell through. They would all drift in freefall to the same point when they reached opening altitude. In this hypothetical situation, and, in fact, all other situations, airspeed would be irrelevant.

[murps2000 86]

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here's some examples to worry about:

1) Airspeed = 160, headwinds at altitude = 80, so groundspeed at altitude = 80. Winds at 2000ft = 5

2) Airspeed = 160, headwinds at altitude = 80, so groundspeed at altitude = 80. winds at 2000ft = 40

3) Airspeed = 160, headwinds at altitude = 80, so groundspeed at altitude = 80. Winds at 2000ft = -30 (opposite uppers)

Now, when you find yourself under an open canopy at 2000ft, will your separation from other canopies (from other groups) be the same in all three cases? The jumprun groundspeed is the same for all three.

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.

[winsor 185]

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Do you really think that if you were flying jumpers with an airspeed of 160mph into uppers that were blowing at you at 160mph (giving you a groundspeed of 0 mph) that you would do anything but drop them all right on top of each other? Sure they would be separated by some 240 ft. for each second between exits at first, but at some point they would get off the hill and be falling straight down, except for the horizontal vector imparted to them by the winds they fell through. They would all drift in freefall to the same point when they reached opening altitude. In this hypothetical situation, and, in fact, all other situations, airspeed would be irrelevant.

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

[winsor 185]

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here's some examples to worry about:

1) Airspeed = 160, headwinds at altitude = 80, so groundspeed at altitude = 80. Winds at 2000ft = 5

2) Airspeed = 160, headwinds at altitude = 80, so groundspeed at altitude = 80. winds at 2000ft = 40

3) Airspeed = 160, headwinds at altitude = 80, so groundspeed at altitude = 80. Winds at 2000ft = -30 (opposite uppers)

Now, when you find yourself under an open canopy at 2000ft, will your separation from other canopies (from other groups) be the same in all three cases? The jumprun groundspeed is the same for all three.

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

[murps2000 86]

Nice link, with an obvious great deal of effort put into it. I disagree with the conclusions you draw, however, particularly in case 2, figure 1. The figure shows the tethered balloon, which is the same condition as the one I described in which airspeed and upper winds cancel each other out. Each jumper exits and arrives at the same opening point. they follow the same light trail. Where the smoke goes is irrellevant because the smoke is not falling. If the first jumper hangs around under canopy at the same point above the ground where he opened, the next jumper's opening point will be right over top of him.

Think of it this way. If you are in a boat travelling at 20 fps up a stream that is flowing at 20 fps (in effect moving 0fps over the bottom of the stream), and start dropping fishing bobbers into the water, they will be separated by 20 feet for each second of interval between them. They will remain separated this way because they will remain under the influence of the fluid medium in which they are placed indefinitely. If you start dropping fishing weights into the water, and they take 5 seconds to sink to the bottom, they will all travel 100 ft. downstream as they descend and hit bottom at the same point. Can you explain to me how they would travel to anywhere else?

Also, if airspeed is what should determine exit interval, then exit interval should be the same for each jump run on every day, regardless of the change in wind conditions, as long jump run is flown at the same airspeed. To my knowledge, I have only recently, and for the first time, visited a DZ that operates this way. Upper winds and ground speed are usually taken into account. Why is this? Is the majority of the skydiving community as ignorant of basic physics as I appear to be to you?

[billvon 2,381]

>>will your separation from other canopies (from other groups) be the same in all three cases?

>Answer: Yes it would.

It definitely will not.

>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.

That statement is correct. Hence, when you change the wind vector at a given altitude, all jumpers are affected similarly. Often, this has the effect of causing jumpers to end up closer to each other when they open.

As a thought experiment - imagine you are in freefall over someone who is 1000 feet below you. The winds are dropping off as you descend; you are upwind of him. You will see him creep towards you, since he's always in less wind than you are (he's 1000 feet lower.) Even though you are both seeing exactly the same wind at the same point in your trajectory, you are not seeing it at the same _time_ - so he slides closer to you.

[winsor 185]

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Nice link, with an obvious great deal of effort put into it. I disagree with the conclusions you draw, however, particularly in case 2, figure 1. The figure shows the tethered balloon, which is the same condition as the one I described in which airspeed and upper winds cancel each other out. Each jumper exits and arrives at the same opening point. they follow the same light trail. Where the smoke goes is irrellevant because the smoke is not falling.

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.

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If the first jumper hangs around under canopy at the same point above the ground where he opened, the next jumper's opening point will be right over top of him.

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.

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Think of it this way. If you are in a boat travelling at 20 fps up a stream that is flowing at 20 fps (in effect moving 0fps over the bottom of the stream), and start dropping fishing bobbers into the water, they will be separated by 20 feet for each second of interval between them. They will remain separated this way because they will remain under the influence of the fluid medium in which they are placed indefinitely. If you start dropping fishing weights into the water, and they take 5 seconds to sink to the bottom, they will all travel 100 ft. downstream as they descend and hit bottom at the same point. Can you explain to me how they would travel to anywhere else?

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.

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Also, if airspeed is what should determine exit interval, then exit interval should be the same for each jump run on every day, regardless of the change in wind conditions, as long jump run is flown at the same airspeed. To my knowledge, I have only recently, and for the first time, visited a DZ that operates this way. Upper winds and ground speed are usually taken into account. Why is this?

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.

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Is the majority of the skydiving community as ignorant of basic physics as I appear to be to you?

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

[billvon 2,381]

>Upper winds and ground speed are usually taken into account. Why
> is this?

Because normally, winds at 3000 feet are from a similar direction as the winds at 12,000 feet, but aren't as strong. Under these conditions, using ground speed alone is a sufficiently safe approximation. As long as you understand where that approximation fails (i.e. if the winds at opening are in the opposite direction) it's a reasonably safe approximation to use.

>Is the majority of the skydiving community as ignorant of basic
> physics as I appear to be to you?

Heck, some are worse! Many believe the 45-degree-angle thing, which is about as accurate as counting the number of windows in the plane and using that as a separation in seconds.

[DBCOOPER 1]

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The minimum is the minimum, and anything you can get above that you should take

So what exactly is the minimum and should it be modified based on group sizes?

Replying to: Re: Stall On Jump Run Emergency Procedure? by billvon

If the plane is unrecoverable then exiting is a very very good idea.

[pchapman 261]

Winsor replyin to murps2000:

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If the first jumper hangs around under canopy at the same point above the ground where he opened, the next jumper's opening point will be right over top of him.

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.

BEHAVIOUR AFTER OPENING:

While generally I'll trust Winsor, there's a detail to be careful of here--

When murps mentions "hanging out under canopy" I think he doesn't mean someone circling around gently, drifing with the wind, but someone faced into the wind, staying over the same point on the ground. Maybe that's because the jumper is doing their wind checks, or just wants to make sure he doesn't get drifted too far downwind.

It seems to me that the assumption of what the jumpers do after opening isn't always made explicit or emphasized enough in these separation discussions!

When first thinking through the physics, it is simplest to think of jumpers drifting under unsteerable round chutes. An exit separation that's good enough for them may not be when adding in the unpredictable flying of parachutists at 25-45 mph under canopy.

Some jumpers might tend to stay in one spot over the ground, therefore reducing the separation from the next group. On the other hand, fast canopy pilots who are less concerned about the wind, may make a beeline back downwind to the DZ. This will increase separation from the next group.

This suggests that in the case of a load with a lot of groups being dropped, longer separation is more important for the first groups dropped. Someone who was in one of the early groups to drop is more likely to have the previous group flying upwind to make it back to the DZ.

The last few groups out of the plane may be safer, all else being equal, as each previous group will be more likely to turn to fly downwind after opening.

All this assumes 'normal' wind conditions, not some strange 180 degree wind shift between jumprun and opening.

(This issue has been about a jumper under canopy endangering the NEXT group to have jumped. Normally nobody under canopy can endanger anyone in a PREVIOUS group. One exception is the head downer after a flat RW guy. The head downer opens first despite leaving the airplane later, and immediately flies downwind along the jump run, rushing towards the point where the flat RW guy is about to deploy. )

I'm not usually at a big-aircraft DZ, so I don't know what people usually get told at such DZ's (or boogies). If one is the person in one's group who happened to track upwind, it might be best to turn back downwind once open. Still, as the exit separation may only be a matter of 5 seconds, that's not a lot of time for the person under canopy to do much.

It's probably better to rely on longer exit time separtion, than on evasive canopy maneuvering for safety...

As for many skydivers not understanding the basic physics, that's true. But even for those of us who like to think (correctly or not) that we can get our head around the issue, some rules of thumb and simplifications for different situations are helpful so that we don't have to work out the equations while on jumprun.

[kallend 1,621]

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> Many believe the 45-degree-angle thing, which is about as accurate as counting the number of windows in the plane and using that as a separation in seconds.

Hmmm I think I'll use that in my lecture (with appropriate attribution, of course)

...

The only sure way to survive a canopy collision is not to have one.

[kallend 1,621]

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(This issue has been about a jumper under canopy endangering the NEXT group to have jumped. Normally nobody under canopy can endanger anyone in a PREVIOUS group. One exception is the head downer after a flat RW guy. The head downer opens first despite leaving the airplane later, and immediately flies downwind along the jump run, rushing towards the point where the flat RW guy is about to deploy. )

.

What about those who have premature deployments?

...

The only sure way to survive a canopy collision is not to have one.

[winsor 185]

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The minimum is the minimum, and anything you can get above that you should take

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

[murps2000 86]

Look, I went to Kallend's website (which was quite nice), and plugged in the values for the three scenarios that he depicted. All things being equal, that is, no difference in fall rates between each group, the distance between opening points remained constant at 1000 ft. for each situation. Each jumper drifted the same amount during freefall. The only thing that increased the distance between the parachutists was the downwind drift of the first jumper under an open canopy, while the second jumper finished freefall. This would lead one to assume that the jumpers in the program were on rounds, and at the mercy of the winds after opening. Last I checked, people don't jump rounds much any more, so counting on the previous jumper to automatically drift downwind would be relying on chance, IMO.

Next, I tried plugging in some other values to see what I would come up with. Leaving the airspeed on jump run constant at 80kts, I plugged in upper wind values of 0, 20, 40, 60, and 80 kts. I left ground winds at 0 to simplify. What I noted was that the distance between opening points steadily decreased with each increase in upper wind values (which one could equate to a reduction in groundspeed on jumprun). Further, I found that, in order to maintain the same separation between opening points, exit intervals needed to increase exponentially with each increase in upper wind velocity. Then, I tried plugging in the same values as a tailwind, which would simulate an even greater groundspeed. Distances between opening points increased further. Remember, airspeed remained the same. Try this yourself, and see what you come up with.

[billvon 2,381]

>The only thing that increased the distance between the parachutists
>was the downwind drift of the first jumper under an open canopy,
>while the second jumper finished freefall.

Exactly! Hence the issue.

>This would lead one to assume that the jumpers in the program were
> on rounds, and at the mercy of the winds after opening.

No, it is expected that each jumper will face outwards and fly away from the center for, say, 5 seconds. This is exactly what you _should_ do as a safe RW jumper. In that way we are worse than rounds, because we spread out more by the time the next group comes along. And if you're facing downwind in a 20kt wind, you're going to be motoring along at 40kts. You have to take that into account when choosing exit separation. Having a plan that only works when the previous group opens and instantly turns into the wind to avoid drift is a poor plan, and will lead to close calls and collisions - both on the previous group and between it and the second group.

>Last I checked, people don't jump rounds much any more, so
> counting on the previous jumper to automatically drift downwind
> would be relying on chance, IMO.

Not chance; it is what he must do to be a safe skydiver. You must choose an exit separation such that you have, say, 200 feet of separation from the two closest trackers, both of whom will be tracking (and flying their parachutes) away from the center. That 200 feet must include tracking distance, freefall drift and canopy flight; that's why the minimum distance I recommend between groups is 1000 feet at opening time. You can go shorter on small groups, but you run a greater risk of tracking into someone.

1000 feet isn't all that hard to do, either. In an aircraft flying at 90kts in a 20kt headwind, and no wind at opening altitude, it's only 7 seconds. Most 4-ways can't check the spot, get into position, give the count and go in much less than 7 seconds.

[winsor 185]

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Look, I went to Kallend's website (which was quite nice), and plugged in the values for the three scenarios that he depicted.

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

[kallend 1,621]

The points you are missing:

You have to account for the individual who deploys, and then fiddles around with his slider, cheststrap and booties while drifting with the wind.

You have to account for the Stiletto that opens on a random heading. On average for the first few seconds of flight, they drift with the wind.

You have to account for the average behavior of the group, each of whom may be facing out from the center but whose center point drifts with the wind.

People don't just deploy and, when open, instantly turn into the optimum direction for collision avoidance. Sometimes they turn in the worst direction for collision avoidance and the wind drift makes it even worse.

And, you may be surprised to know, some people have round reserves!

...

The only sure way to survive a canopy collision is not to have one.

[skydiventom 0]

Winsor,
It's other skydivers like the one you've been talking to that scare me. I firmly believe that some just should stay on the ground. This guy's gonna get hurt and will probly hurt someone else in the process.

Kind'a makes me glad I fly camera and have a "birds eye" view and can choose where to fly and open.

Blue Skies!

"Time flies like an arrow, fruit flies like a banana" -Groucho Marx- "Tom flies like a rock" -Tom Carson-

[DBCOOPER 1]

So lets see.Standard rate turn 3 degrees per second.60 seconds for a 180.Downwind at True airspeed plus what ever the uppers are,give it say 30 seconds.Another standard rate turn,another jump run.Another 3 and a half minutes of operating cost.Now I have no idea what it cost to operate a Casa or an Otter,but I would be willing to pick up my share for a guarantee of my own colulm of air and separation.

Replying to: Re: Stall On Jump Run Emergency Procedure? by billvon

If the plane is unrecoverable then exiting is a very very good idea.

[murps2000 86]

***The points you are missing:

You have to account for the individual who deploys, and then fiddles around with his slider, cheststrap and booties while drifting with the wind.

You have to account for the Stiletto that opens on a random heading. On average for the first few seconds of flight, they drift with the wind.

You have to account for the average behavior of the group, each of whom may be facing out from the center but whose center point drifts with the wind.

People don't just deploy and, when open, instantly turn into the optimum direction for collision avoidance. Sometimes they turn in the worst direction for collision avoidance and the wind drift makes it even worse.


-

Thank you, Kallend. These points are exactly what I am missing. Your ability to see my obstacle to accepting what I am being told in the midst of this debate over whether or not I understand the physics involved is one that must serve you well as an instructor. And I now see what Billvon and Winsor are trying to get through my thick skull. If opening and behavioral anomalies experienced by jumpers under ram-air canopies average out such that they behave like rounds, then canopy drift should be taken into account when determining exit interval. Whether or not jumpers end up opening at the same point in space because their exit point is stationary over the ground is, in fact, inconsequential because of the time delay (which Billvon and Winsor did attempt to tell me), and the fact that the ram-air pilot who, after opening, holds in the wind at the point at which he opened (albeit lower, of course) is essentially flying back up the line of flight. As Billvon appropriately pointed out, this is a decidedly unsafe thing to do, and can defeat the beast laid plan of anyone determining exit interval.

And, you may be surprised to know, some people have round reserves!

This is no surprise, but I would be surprised if you said they used them on every jump. Nevertheless, I’m familiar with the school of thought that says you should spot for your reserve.

[murps2000 86]

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----------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.

So I take it this means you won’t forget me?

Well let’s see… perhaps to get myself to agree with you I should approach this topic in a different way. Say, in the manner of a simple geometric proof.

Now, if I accept as postulate that if Kallend says something, it must be right, and Kallend’s position is the same as yours, and your position (and therefore Kallend’s) differs from mine, it must follow, then, that I am wrong, right? Dang!

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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.

Err… thanks… I think. Actually, engaging in heated debate with you, Kallend and Billvon? It’s probably stupidity. Don’t mistake the gift of the gab for intelligence. I believe the intransigence you speak of was something I most likely mistook for tenacity.

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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.

Well then, you have nothing to worry about from me. As you can see, I’m merely stupid. In addition, I doubt seriously that I will ever be in a position to make a decision that will jeopardize your safety. You already know that I will give you way more time than three seconds if I’m exiting after you, regardless of my motive for doing so, and I don’t think I could force you to exit an aircraft at a time that you deem unsafe. You already know that I’m aware that I should track perpendicular to the line of flight whenever possible, so I will probably not commit an incursion into your airspace after exit. You also know that I think holding at my opening point is a bad idea, so I doubt I’ll be under canopy below you in freefall.

Given my choice of disciplines to pursue in skydiving, it's most likely that I will probably take myself out by way of a botched hook turn. If you and I are at the same DZ when it happens, I promise to do my utmost to avoid hitting you with the jagged end of my protruding femur.

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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.

Wait a second. What if said comic book physics still get you to make the right decision? You said yourself that if someone mandates three seconds between groups, they’re clueless, and I agree, but it seems to be for the wrong reasons.

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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.

I wasn’t, and the only misconceptions put to rest are my own. As far as the models are concerned, I wouldn’t worry too much. The only one so vociferously put forth was mine, and I believe it fairly well lies in ruin for all to see at the top of the illogical argument pile. It in itself was not incorrect, but, as you pointed out, it does not exactly apply. I see now that this is because it stops at what would be analogous to the opening point in a skydive, and more needs to be considered after that. Kallend’s assertion that a group of skydivers on ram-air canopies behaves, on average, as does a group on rounds is something I definitely failed to consider. I sort of figured this to be a purely random event, and this led me to believe that horizontal distance between opening points was necessary, regardless of time delay.

In the case where ground speed is zero and winds at deployment altitude are also zero (an admittedly highly unlikely scenario), collision issues will arise, but also I see now that this is not directly related to the fact that ground speed is zero. It is instead because the difference between airspeed at jump altitude and wind speed at deployment altitude happens to be the same as the difference between airspeed and ground speed, and is merely coincidental. I believe at one point you made a statement that should have clued me in to this. I believe it was this one:
The most critical parameter for ensuring freefall separation is the speed of the aircraft with regard to the airmass at opening altitude.

So you tried.

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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.

Well, now there’s one more, Winsor, even if it took all but the physical beating of the concepts into my head. And if Mike Mullins, whose ability to consistently and accurately put jumpers on target cannot be overstated, can admit he was wrong and change his position, than certainly I can, as well. I must say that it was quite gracious of you to attempt to educate me in these matters without charging me money. I hope I don’t see a bill.

Now, I think I’ll go wash this crow out of my mouth with a nice glass of shut the hell up.

Oh, and BTW, I’m still not going back to jump CASA’s at Lake Wales.

[michaelmullins 77]

With all due respect to Winsor (a friend and a very smart guy), I have not changed my position on this subject. Sorry, it is ground speed that determines the spacing that jumpers must be given. Other contributing factors, such as varying windspeed with altitude and jumpers turning a particular direction under canopy, must also be accounted for but the underlying basis for the spacing is ground speed. As many have argued ad nauseum over this question, I do not wish to open any more debate so this is all I will say on the subject. I will just continue to safely space the jumpers from my aircraft and put them on the target to the best of my ability.
Mike Mullins

[murps2000 86]

I will let it go as well. My original purpose for posting to this thread has been lost, anyway.

I would like to say, however, that when I visited your DZ for Halloween of 2001, you faced what I consider to be very challenging conditions for spotting. Surface winds were up considerably, and I assume uppers were quite fast. As I recall, you were very explicit in stating that there would be no set exit interval. Each group was to exit when you gave the go ahead. I remember waiting for as much as 20 seconds at the door after groups before me left. On one load, when I was last to exit, you flew jumprun in the shape of an L, and I had never seen this before. Yet no one landed off, and never did I witness anyone opening near each other. I assumed then, that because you likely flew jumprun at the same airspeed every time, groundspeed was of paramount concern to you in conducting operations this way, and I was more than a little impressed with the results.
When at Quincy once, I left your plane at 22,000 ft, and I could swear that I opened up right above the spot in the alternate landing area at which I intended to land. I remember taking a few seconds under canopy to ponder what a great shot it was from 4 miles up. And I also read with great interest the debate which took place in parachutist so many years ago. Your statements made perfect sense to me, and is a reason why I so vehemently clung to my position on this issue.

I have no aspirations to ever be a jump pilot, nor a load organizer, so for those who fear my ignorance, don't worry. I will have little influence over your safety in freefall.

If I'm riding in your King Air, Mike, I will do as you say, because you have proven to me that you can get the job done. If I am riding in anyone else's aircraft, I will do it the old fashioned way, and use my eyes. And if I don't like what I see when I get outside, I will, as I have on occasion, track for my life. It's what I had to do at Lake Wales.