Horizontal Separation

[skr 1]

Well, I did read to the end of the thread, but I'm responding
to Bill's post out of years of habit on this subject :-) :-)

[ Insert standard soapbox here:
[ OPEC changed the oil prices in 1973.
[ Multiple groups per pass started shortly after that.
[ It's now 30 years later and we're *still* ...

I do see signs of progress though. Not only are lots of people
concerned about the lack of training on this issue, but more
people are talking in terms of horizontal separation instead of
elapsed time.

Cool.

>However, one method of ensuring good exit separation is to
>look at the _ground_ and simply exit when you've covered
>1000 feet or so.

Yes, I agree with that, except that the 1,000 ft was a round
canopy intuition and after the discussions went on for a while
I finally realized how much distance squares travel in only a
few seconds and changed to 1,500 ft for small groups.

>To do this you have to be a good spotter

I used to think in terms of spotting too because I've done
a lot of it, but I now think that this term scares people off.

People at turbine drop zones don't get to spot, so asking
them to use that skill for exit separation doesn't work.

I tell them about looking at the horizon and then straight
down too, but reassure them that seeing the picture change
by 1,500 ft before exiting is what counts, and you can soon
learn to do that even if you're not looking quite straight down.

Just looking down in a consistent way and seeing the picture
change by 1,500 ft is enough.

John and others have correctly pointed out that the ground
is irrelevant, it's the layer of wind at opening altitude that
matters.

But you can't see that layer of wind, you can only see the
ground. We have ground winds opposite or different than
the uppers most of the time in Colorado.

Also, in playing with John's model I saw that it takes a while
after entering the new layer of wind for your horizontal drift
to match the new layer, so if the wind shear is at 5 or 6,000
ft you only have to stretch your exit separation by a little bit.



USPA's role in this training is almost non existant because
USPA moslty reacts to grass roots ground swells instead of
leading. So if you guys want any action out of USPA you will
need to write to the safety and training committee and also
ask your regional director to ask them to put it on the agenda
for the next board meeting.

Skr

[LouDiamond 1]

OK, I said I wouldn't get involved again but I can't help it. If it sinks into one persons head I will feel better. This convo is like all the others we've had on this same subject but this one does seem a bit more sane than the others, thank God. My first points I'd like to make and then you can take it or leave it or tell me to pack sand, your choice.

1. Ground speed is relavant. That is why I posted the excel cheat sheet with ground speed/sec between groups back in the beginning.

2. Spotting isn't hard to do but grasping the concept for some is next to quantum physics for some. I am here to tell you that I can teach any one to spot correctly with a table and 3 pennies and about 30 mins of explanation. There is no reason why "we" shouldn't be doing this at our DZ's or even in the student course.

3. Calculating winds on the ground is something I never hear anyone talking about. I posted 2 power point presentations that explain how to do this so you can correctly calculate for freefall and canopy drift(do a search on "do bad spots exist" if your interested) Even if you have incompatable winds or doglegs, you can still calculate for the spot and use the ground speed chart to help determine the seperation between groups. While learning and understanding how to Calc winds isn't the easiest thing to do for everyone there is an even easier solution that I'm surprised no one has latched onto or even mentioned here. Garmin makes software called jumpmaster for the Vista series designed for Military HALO(skydives) jumps. The GPS actually does the calculations I described in the PP presentations for you. All you have to do is call AWAS and get the winds and input them into the GPS and you get a calculated High altitude release point(HARP).

We are fortunate the the sky is as big as it is, otherwise I know that there would be more people running into each other in freefall than we have running into each other under canopy. The bottom line is you need to know the ground speed, you need to know what the seperation time between groups are for a given ground speed and worst case scenario if you don't have the ground speed availiable you need to know what 1500 ft across the ground, from altitude, looks like. Spotting is useless if you don't know how to do it correctly and you must actually have a spot on the ground your looking for to initiate the first group to leave the A/C. To do that you need to calc the winds. SWAG is the answer on many DZs and thats why we're having this conversation. Sometimes the SWAG is just that Guessing.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[riddler 0]

And since we're talking about 1500 feet of separation here, I would like to harken back to Chris's point about getting out over the runway. 1500 feet is about 1/3 of many runways. If jump run starts at one end of the runway, that really allows only four groups to get out before the end of the runway. If you stretch to outside the runway, you might be able to get 6 groups out.

A King Air can easily hold 8 groups, if there are some solos on board. If everyone gives 1500 feet of separation, does it make sense that the DZ should plan on making two passes? It does to me. Will dropzones go for that idea, since it costs more fuel and time? Probably not.

[diverdriver 5]

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And since we're talking about 1500 feet of separation here, I would like to harken back to Chris's point about getting out over the runway. 1500 feet is about 1/3 of many runways. If jump run starts at one end of the runway, that really allows only four groups to get out before the end of the runway. If you stretch to outside the runway, you might be able to get 6 groups out.

A King Air can easily hold 8 groups, if there are some solos on board. If everyone gives 1500 feet of separation, does it make sense that the DZ should plan on making two passes? It does to me. Will dropzones go for that idea, since it costs more fuel and time? Probably not.

What I figure on is if ther is absolutely no wind any experienced jumper should be able to make it to the main landing area from a distance of .8 miles at 2,000 feet fully opened altitude. Tandems can make it from almost 1.5 in no wind. If there is a camera man then I try not to go that far. This, however, is all based on an understanding with the regular jumpers at SDC. I don't think I would spring this on a DZ without letting them know what I planned first.

Chris Schindler
www.diverdriver.com
ATP/D-19012
FB #4125

[phoenixlpr 0]

There are some small tricks. Ive heard that the plain(L410~20jumpers) is flying on level, but making a slite curve around the airfield according to the situation of the wind.

[billvon 2,384]

>I finally realized how much distance squares travel in only a
>few seconds and changed to 1,500 ft for small groups.

Hmm, I agree that more distance is generally better, but I'm not sure that 1500 feet is neccessary. Even a napkin of a canopy won't do more than about 40fps in brakes, and most 4-way tracks seem to cover a few hundred feet. That means that, at 1000 feet, you end up with two canopies facing each other and each has 5 seconds to avoid a collision - and that's worst case.

In terms of real-world experience, I seem to have acquired a lot of experience jumping from otters under conditions of 10-30kt headwinds; a windless day is rare, as is a downwind jump run. Under those conditions you'd need 13 seconds per group to get 1500 feet separation. And while that sort of spacing is definitely appropriate for larger groups, I've done a lot of 4-way with 8 seconds of separation at those speeds and not had any problems with separation, outside the odd ones (i.e. a freeflyer tracks over us and opens on the other side.)

I have no problem taking a second pass to get everyone out safely, but consistent 13+ exit separations might give you three or more passes in some places, and then you have other problems (i.e. interfering with the next load, rapid 180's resulting in people opening over the people on the last pass.)

[skr 1]

>If jump run starts at one end of the runway,

The rule of thumb that I use is that these days
a lot of people are in the saddle at 2,500 ft,
and from 2,500 ft you can go about a mile on
a no wind day.

That means you have about a two mile interval
for stringing out the groups.

The more wind there is the more that two mile
interval shifts up wind.

Also when I have several solos that I'm helping
with their exit spacing I use more like 1,000 ft
and hope that the big sky theory will neutralize
their natural tendancy to slide toward each other
in freefall and then open facing each other both
with line twists.

Skr

[kallend 1,621]

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>I finally realized how much distance squares travel in only a
>few seconds and changed to 1,500 ft for small groups.

Hmm, I agree that more distance is generally better, but I'm not sure that 1500 feet is neccessary. Even a napkin of a canopy won't do more than about 40fps in brakes, and most 4-way tracks seem to cover a few hundred feet. That means that, at 1000 feet, you end up with two canopies facing each other and each has 5 seconds to avoid a collision - and that's worst case.

In terms of real-world experience, I seem to have acquired a lot of experience jumping from otters under conditions of 10-30kt headwinds; a windless day is rare, as is a downwind jump run. Under those conditions you'd need 13 seconds per group to get 1500 feet separation. And while that sort of spacing is definitely appropriate for larger groups, I've done a lot of 4-way with 8 seconds of separation at those speeds and not had any problems with separation, outside the odd ones (i.e. a freeflyer tracks over us and opens on the other side.)

I have no problem taking a second pass to get everyone out safely, but consistent 13+ exit separations might give you three or more passes in some places, and then you have other problems (i.e. interfering with the next load, rapid 180's resulting in people opening over the people on the last pass.)

There are some graphics illustrating the influence of group size on separation on the "Separation" presentation at www.iit.edu/~kallend/skydive/

...

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

[mjosparky 3]

***I used to think in terms of spotting too because I've done
a lot of it, but I now think that this term scares people off

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It's sad, but today many jumpers think spotting is being the first one to see the green light come on.

My idea of a fair fight is clubbing baby seals

• Quote

[winsor 186]

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WOW, this issue is like a social disease, it always comes back. I will say that if you want to read all about this to do a search and you can spend hours reading people argue about it. Frankly, it's scary how many people don't have a clue on this issue. I've attached a Excel doc that you can download, print and laminate and tape next to the door of your A/C for reference. It is quick and easy to use and ends debates on the A/C.

"For every complex problem, there exists a solution that is simple, elegant - and wrong." H. L. Mencken

Nice spreadsheet, but the physics are fundamentally flawed. What the ground is doing is entirely irrelevant with regard to separation IN THE AIR. It only matters in terms of where you land.

If you wish to pick a critical speed, it is that of the aircraft with regard to the airmass at opening altitude.

An introductory treatment of exit separation can be found here: http://dogyks.home.netcom.com/jumprun/jmprun~1.htm.


Blue skies,

Winsor

[PhillyKev 0]

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What the ground is doing is entirely irrelevant with regard to separation IN THE AIR.

Hmmm.....that brings up a good question. It's often said that longer time between groups is necessary when jump run is into a strong wind. But wouldn't the jumpers exiting the plane be in that same wind? Essentially, the airspeed of the plane is unchanged. The distance traveled in the air over a 6 second period of time is the same no matter what the wind is doing. So, when the first jumper exits, they will be whisked away downwind from the plane much faster when there is a strong wind. So why is it necessary to change the separation time between groups? After 6 seconds, they should be just as far "downstream" from the plane regardless of ground speed. No?

[winsor 186]

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What the ground is doing is entirely irrelevant with regard to separation IN THE AIR.

Hmmm.....that brings up a good question. It's often said that longer time between groups is necessary when jump run is into a strong wind. But wouldn't the jumpers exiting the plane be in that same wind? Essentially, the airspeed of the plane is unchanged. The distance traveled in the air over a 6 second period of time is the same no matter what the wind is doing. So, when the first jumper exits, they will be whisked away downwind from the plane much faster when there is a strong wind. So why is it necessary to change the separation time between groups? After 6 seconds, they should be just as far "downstream" from the plane regardless of ground speed. No?

This is a classic "frames of reference" scenario that gives Freshmen fits (at least those in a rigorous technical program presupposing a solid basis in Physics).

The airspeed of concern to jumpers just after exit is the true airspeed of the jump aircraft. In a free balloon you're looking straight down at whoever just left, regardless of what the ground is doing.

The benefit that a headwind provides is the ability to take more time between groups and still have everybody get back (groundspeed only affects WHERE YOU LAND). Thus, with honking headwinds at altitude you can greatly increase horizontal separation between groups above the minimum, without anyone getting hosed (assuming that the person spotting has some understanding of the physics involved there, as well).


Blue skies,

Winsor

[PhillyKev 0]

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The benefit that a headwind provides is the ability to take more time between groups and still have everybody get back

But if you stretch out the time between groups, you're also stretching out the horizontal separation in the air. In strong wind, that means the first groups to exit will probably be downwind of the dz.

Don't you want the same amount of total horizontal space between the first and last groups to be sure everyone can get back? And if increasing the time between groups increases separation unnecessarily, wouldn't that be a bad thing?

I'm going to have to take notice and see if there are more off landings during strong head wind when everyone's taking more time between groups.

[billvon 2,384]

>After 6 seconds, they should be just as far "downstream" from the
>plane regardless of ground speed. No?

If the wind stayed the same from exit to opening, then you would be correct. However, it usually does not. Usually it is much closer to zero at opening altitude than at exit altitude. This is why ground speed is a better number than airspeed to use - because ground speed is a good approximation of what the speed of the aircraft is relative to the winds at opening altitude, which is what you care about.

If you want to be picky, though, it's absolute airspeed of the plane minus (minus in a vector sense) the windspeed at opening altitude that is the critical parameter.

[LouDiamond 1]

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Nice spreadsheet, but the physics are fundamentally flawed. What the ground is doing is entirely irrelevant with regard to separation IN THE AIR. It only matters in terms of where you land.

Please explain to me how it's wrong so I can tell the Military. If I know how fast the airplane is moving through the air at a given moment and I know what the winds are at altitude(becasue I did my wind calcs and got the winds) I have a general idea of how much the wind is affecting not only the aircraft but the people leaving the aircraft. Hence the calculation of forward throw when computing the HARP. Once I know all of that I can use the ground speed as a reference to figure out the seperation between groups after the first group exits. I may not be a physics teacher but I have calc'd enough winds and put people out of both STOL and High performance aircraft to know that it works in the real world.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[winsor 186]

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Nice spreadsheet, but the physics are fundamentally flawed. What the ground is doing is entirely irrelevant with regard to separation IN THE AIR. It only matters in terms of where you land.

Please explain to me how it's wrong so I can tell the Military. If I know how fast the airplane is moving through the air at a given moment and I know what the winds are at altitude(becasue I did my wind calcs and got the winds) I have a general idea of how much the wind is affecting not only the aircraft but the people leaving the aircraft. Hence the calculation of forward throw when computing the HARP. Once I know all of that I can use the ground speed as a reference to figure out the seperation between groups after the first group exits. I may not be a physics teacher but I have calc'd enough winds and put people out of both STOL and High performance aircraft to know that it works in the real world.

Read the article to which I posted the url. I have made a living as a Physics Instructor.

The Military is hardly monolithic, and I assure you that there are plenty of people in The Military that already understand the fundamentals. You don't (nothing personal, but it's the truth).


Blue skies,

Winsor

[winsor 186]

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The benefit that a headwind provides is the ability to take more time between groups and still have everybody get back

But if you stretch out the time between groups, you're also stretching out the horizontal separation in the air. In strong wind, that means the first groups to exit will probably be downwind of the dz.

Don't you want the same amount of total horizontal space between the first and last groups to be sure everyone can get back? And if increasing the time between groups increases separation unnecessarily, wouldn't that be a bad thing?

I'm going to have to take notice and see if there are more off landings during strong head wind when everyone's taking more time between groups.

How far apart you are in the air is simply the product of airspeed and time between exits (e.g., 150 fps * 5 seconds between exits = 750 feet horizontal between groups).

The distance between no-drift landing points (like with round parachutes) is the product of groundspeed and time between exits (e.g., (150 fps airspeed - 50 fps headwind) * 5 seconds between exits = 500 feet.

In the case above, which is like a 90 kt jumprun into a 30 kt headwind (typical), you can have a total of a mile and a half of horizontal separation in the air with only a mile track over the ground.

Looking at it another way, assuming you have constant winds from the ground on up (you don't, but it makes it easier to visualize), the first group and the last group are separated by a mile and a half in the air. Between the time the first group lands and the last group lands, the last group will have drifted half a mile, so their landing points are only a mile apart.

This is a FOUR dimensional problem - time is an important element.


Blue skies,

Winsor

[LouDiamond 1]

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I have made a living as a Physics Instructor.

And I make a living of jumping out of airplanes and more specifically putting people out of them safely. I looked at your paper and the only part that I can assume that your prior post would be applicable to would be jumping from a stationary object.

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The Military is hardly monolithic, and I assure you that there are plenty of people in The Military that already understand the fundamentals. You don't (nothing personal, but it's the truth).

Yes there people who understand and I happen to be one of them. Otherwise the military wouldn't of seen fit to award me the responsibility of jumpmastering people into combat. While I don't write the doctrine, there are people who do. We will assume that they are the "ones" you claim to know the fundamentals. What I and every other HALO jumpmaster do every time we jump is what those who "know" have seen fit to make doctrine. Which goes pages beyond what can be said for sport skydiving, which is too bad. You keep teaching physics in the classroom and I will keep putting people out of airplanes the military way, wheather or not you agree with the military method. Funny how we don't seem to have these seperation issues in the military?

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[winsor 186]

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I have made a living as a Physics Instructor.

And I make a living of jumping out of airplanes and more specifically putting people out of them safely. I looked at your paper and the only part that I can assume that your prior post would be applicable to would be jumping from a stationary object.

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The Military is hardly monolithic, and I assure you that there are plenty of people in The Military that already understand the fundamentals. You don't (nothing personal, but it's the truth).

Yes there people who understand and I happen to be one of them. Otherwise the military wouldn't of seen fit to award me the responsibility of jumpmastering people into combat. While I don't write the doctrine, there are people who do. We will assume that they are the "ones" you claim to know the fundamentals. What I and every other HALO jumpmaster do every time we jump is what those who "know" have seen fit to make doctrine. Which goes pages beyond what can be said for sport skydiving, which is too bad. You keep teaching physics in the classroom and I will keep putting people out of airplanes the military way, wheather or not you agree with the military method. Funny how we don't seem to have these seperation issues in the military?

Your understanding, such as it is, is the classic "good enough for Government work." You simply don't know enough to have any idea how little you know.

The Excel spreadsheet you tout illustrates at a glance the level of your ignorance. It's like the Soviets trying to bluff the West into thinking that their new jet bomber was supersonic without any understanding of the Area Rule - it only took one fast look to classify it as a subsonic flight platform.

Your procedure is not inherently dangerous, and is better than nothing, but the physical model you use displays a fundamental lack of comprehension - as does your defense of your methodology.

Be advised, you're out of your league.


Blue skies,

Winsor

[LouDiamond 1]

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Your understanding, such as it is, is the classic "good enough for Government work." You simply don't know enough to have any idea how little you know.

Dude, I many not be a physics teacher but I have a 4 year degree so don't try to insult my intelligence with your passive aggresive replies. All your accomplishing is making yourself look like an ass. If you want to talk, then talk like a man, don't act better than thou.

The term "good enought for Gov't work" doesn't hack it in my world. In SF, if it's not done right people die so it's never "good enough" it HAS to be done right, there is no margin for error. You are confusing that term with civillian gov't workers, who use that as their motto.

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The Excel spreadsheet you tout illustrates at a glance the level of your ignorance.

Did you even bother to look at the power point presentations? The excel spread sheet I posted is part of a bigger equation. However,civillian skydivers don't calc winds so the only thing one can do to try and be as safe as possible is to use a method safer than the 45 degree method or the 4 sec method. If you have a better way of ensuring seperation then put your money where your mouth is and show the rest of us "ignorant" people. Up until this point all you've done is waste bandwidth.

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Your procedure is not inherently dangerous, and is better than nothing, but the physical model you use displays a fundamental lack of comprehension - as does your defense of your methodology.

You see, thats where your wrong. Becasue I don't have to defend the methodology, because what you think is not relevant to what I do. The physical model I use works in real life as I stated. We don't have this seperation issue in military skydiving. Can you explain that?

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Be advised, you're out of your league

Did you forget to put the smileys next to that? Becasue that has got to be the most pompous, cliche thing to say. Your joking right?


Show me what you have to solve this problem or stop wasting everyones time.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[kallend 1,621]

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Your understanding, such as it is, is the classic "good enough for Government work." You simply don't know enough to have any idea how little you know.

Dude, I many not be a physics teacher but I have a 4 year degree so don't try to insult my intelligence with your passive aggresive replies. All your accomplishing is making yourself look like an ass. If you want to talk, then talk like a man, don't act better than thou.

The term "good enought for Gov't work" doesn't hack it in my world. In SF, if it's not done right people die so it's never "good enough" it HAS to be done right, there is no margin for error. You are confusing that term with civillian gov't workers, who use that as their motto.

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The Excel spreadsheet you tout illustrates at a glance the level of your ignorance.

Did you even bother to look at the power point presentations? The excel spread sheet I posted is part of a bigger equation. However,civillian skydivers don't calc winds so the only thing one can do to try and be as safe as possible is to use a method safer than the 45 degree method or the 4 sec method. If you have a better way of ensuring seperation then put your money where your mouth is and show the rest of us "ignorant" people. Up until this point all you've done is waste bandwidth.

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Your procedure is not inherently dangerous, and is better than nothing, but the physical model you use displays a fundamental lack of comprehension - as does your defense of your methodology.

You see, thats where your wrong. Becasue I don't have to defend the methodology, because what you think is not relevant to what I do. The physical model I use works in real life as I stated. We don't have this seperation issue in military skydiving. Can you explain that?

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Be advised, you're out of your league

Did you forget to put the smileys next to that? Becasue that has got to be the most pompous, cliche thing to say. Your joking right?


Show me what you have to solve this problem or stop wasting everyones time.

Newton's laws have been tested much more thoroughly than your jumpmastering. Winsor is right.

...

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

[billvon 2,384]

>You simply don't know enough to have any idea how little you know.

Winsor, Scott, cut it out. You both have really valuable inputs here (Winsor from the theoretical side, Scott from the practical side) and they can be presented without going after each other.

[masher 1]

Have any of you actually done the calcs?

The desired goal is to have 1000' (300m) of horizontal seperation at opening altitude (~3k).

The calculations presented by LouDiamond are from the military, and I'm guessing that the SF don't do head-down HALO insertions, so this is all for flatfly. If everyone is flatflying, they will all drift the same. Therefore, the only thing that will give seperation is the plane moving forward.

The 1000' seperation is designed to incorporate buffers for tracking and canopies opening, so I am neglecting that in my analysis. The 1000' is, I look up at one jumper, run 1000', and look up at the next jumper, so it's seperation with respect to the ground, so you're interested in groundspeed.

So, from LD's excel sheet:

Ground       time between

speed             exits

kn                    s

125                 5

115                 5

...

35                  18

25                  25

Tada! Those numbers correspond to a horizontal seperation of 1000'!!!

--
Arching is overrated - Marlies

[mjosparky 3]

I would tend to question advise that is prefaced by:
DISCLAIMER: THE AUTHOR(S) MAKE NO WARRANTIES OR REPRESENTATIONS AND ASSUMES NO LIABILITY CONCERNING THE VALIDITY OF ANY ADVICE, OPINION, OR RECOMMENDATION EXPRESSED IN THE MATERIAL. ALL INDIVIDUALS RELYING UPON THE MATERIAL DO SO AT THEIR OWN RISK.

My idea of a fair fight is clubbing baby seals

[wmw999 2,116]

I'm very glad you did that. There are too many pissing matches on S&T right now.

Wendy W.

There is nothing more dangerous than breaking a basic safety rule and getting away with it. It removes fear of the consequences and builds false confidence. (tbrown)