Let's talk about exit seperation

[kallend 1,647]

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no wind situation = steady wind situation...

I'm not sure how you figure that. In no winds, all jumpers will fall straight down (more or less). When you introduce wind, jumpers being to drift. The two factors effecting how far they will drift are the speed of the winds, and the time exposed to those winds.

All jumpers will experience the same speed of the winds, but not all jumpers will have the same exposure to those winds, that depends on the length of freefall. This is where the slower speeds of RW equates to more drift as a result of longer exposure to those winds.

Wind - is the moving relative to the earth air mass
So in case of steady constant wind the object in freefall don't know about wind, until they refer to earth...
Yes, there will be drift but drift of skydivers relative to the earth not to each other, and as far as for skydivers at deployment time the distance between the groups of them has matter, not from DZ (from safety and collision point of view) steady constant wind does not matter

Very rarely is wind the same at all altitudes. Are you going to bet your life on something that hardly ever happens? Would you play Russian Roulette with only one empty chamber?

...

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

[erdnarob 1]

I agree with you. Freeflyers with higher vertical speed are exposed to the the winds aloft for a shorter time (with respect to the belly flyers) therefore they are drifting less. That's why generally they jump after the belly flyers.
At certain wind and aircraft (aloft) speeds, even with a 10 seconds delay, belly flyers jumping after freeflyers can have a trajectory crossing the freeflyers one near opening altitude. I made some calculations and drawings which show that. I have also seen an Internet site (5 years ago maybe) where you could see an animation with possibility of choosing delays and speeds. You could clearly see in some case the crossing paths I have mentioned.

Learn from others mistakes, you will never live long enough to make them all.

[NWPoul 1]

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Even in no-wind conditions, fast fallers get more forward throw from the speed of the plane. The difference between typical RW and FF fall rates is worth around 3 seconds of separation. (IOW, if a freeflier exits first, a following RW group should add 3 seconds to the normal separation interval).

How can it be caused only by vertical speed (fall speed) in case if there enough altitude for both fast and slow fallers to arrest the forward speed from the plane? Or you mean tha typical FF present less surface area to horisontal relative vind than tipycal RW? Possible, but 3 sec equivalent? You mean that if RW flyer will exit after 3 sec from FF than he overhand FFlyer after 10-12 sec (arresting of forward speed)?

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Very rarely is wind the same at all altitudes. Are you going to bet your life on something that hardly ever happens?

Exactly for this reason I talk about significant wind shift wich can be even if there no wind at ground, but at least here the enough wind shiftig (leading to noticed freefall drift of RW to FF group) is quite rare, So at our DZ we stoped playing blindly with "modern exit order" cos if there no shift it gives nothing to horisontal separation but provoke mess at landing pattern
When wind is strong or pilots detect significant wind shift - the modern order is applyed...
But for some reason they (DZ) continue throw the big (10+) formation first regardless of wind shift (just because the formation organisers likes to land first and be the first at door)

Why drink and drive, if you can smoke and fly?

[wmw999 2,148]

Turn a fan on low.

Crumple a piece of paper tightly, then drop it in front of a fan, followed by a less-crumpled piece of paper. See whether the less-crumpled piece of paper drifts to above where the more-crumpled piece was before it hit the ground.

Now reverse the order -- first the less-crumpled, then the more-crumpled. See whether the more-crumpled one reaches as far as the less-crumpled one.

For extra credit, stack the fans and have the papers go through multiple wind directions. Which one is more affected by the fan?

Wendy P.

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)

[NWPoul 1]

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I agree with you. Freeflyers with higher vertical speed are exposed to the the winds aloft for a shorter time (with respect to the belly flyers) therefore they are drifting less.

For separation at deployment time (amticollision wise) the fast fallers exposed to the wind the same time as slowfallers (if FF doesn't fly to the derection of jumprun before the next group start opening)

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At certain wind and aircraft (aloft) speeds, even with a 10 seconds delay, belly flyers jumping after freeflyers can have a trajectory crossing the freeflyers one near opening altitude. I made some calculations and drawings which show that. I have also seen an Internet site (5 years ago maybe) where you could see an animation with possibility of choosing delays and speeds. You could clearly see in some case the crossing paths I have mentioned.

This coused by wind shifting! not the wind itself! But yes the strong upper wind often means significant shifting

Why drink and drive, if you can smoke and fly?

[NWPoul 1]

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Turn a fan on low.

Crumple a piece of paper tightly, then drop it in front of a fan, followed by a less-crumpled piece of paper. See whether the less-crumpled piece of paper drifts to above where the more-crumpled piece was before it hit the ground.
Now reverse the order -- first the less-crumpled, then the more-crumpled. See whether the more-crumpled one reaches as far as the less-crumpled one.
For extra credit, stack the fans and have the papers go through multiple wind directions. Which one is more affected by the fan?
Wendy P.

Again, I refer to wind shifting (which made the difference) and steady constant wind (which does not impact on H separation)
Your examples about non constant wind or low altitude to both FF and LF object to accelerate to horisontal speed of air from the fan
And one fan in your examples - is equivalent to the initial speed from the plane, not wind
And crumpled paper vs non crumpled - is a bad example because they are differ not only in vertical freefall speed but has significant difference in weight/area ratio in general (i.e. has difference in reaction to horisontal component of wind) which not similar to FF and RW (FF usually has even more surface area in vertical crossection than Rw i.e. has more surface exposed to the H component of wind than RW:) )

Why drink and drive, if you can smoke and fly?

[davelepka 4]

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How can it be caused only by vertical speed (fall speed) in case if there enough altitude for both fast and slow fallers to arrest the forward speed from the plane?

Are you aware that the vertical speed is only being considered on the basis that it makes for a shorter freefall?

Nobody is saying that a person falling at a higher speed will also drift horizontally faster than a slow faller. If the freefall drift is 5 feet per second, that rate applies to both RW and freeliers. Rw jumpers will drift for 60 seconds, and freefliers will only drift for 45 seconds. The RW guys will drift 300ft, and the freefliers will only drift 225ft.

In that example, if the RW guys get out first, the total seperation is the time betwween groups plus the 75ft extra that the RW guys will drift. If you put the freefliers out first, the total seperation is the time between groups minus the extra 75ft that RW guys will drift back down the jumprun.

The numbers provided were for example only. In the real world the differences in drift can easily be enough to overcome the exit seperation and have two groups opening the same airspace.

[NWPoul 1]

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How can it be caused only by vertical speed (fall speed) in case if there enough altitude for both fast and slow fallers to arrest the forward speed from the plane?

Are you aware that the vertical speed is only being considered on the basis that it makes for a shorter freefall?I am ansvered on Mr.Kallend's "Even in no-wind conditions, fast fallers get more forward throw from the speed of the plane"

***Nobody is saying that a person falling at a higher speed will also drift horizontally faster than a slow faller. If the freefall drift is 5 feet per second, that rate applies to both RW and freeliers. Rw jumpers will drift for 60 seconds, and freefliers will only drift for 45 seconds. The RW guys will drift 300ft, and the freefliers will only drift 225ft.

The FF still be affected by the wind after deployment so He will drift the same 60 sec as RW flyer falls (+exit delay)
It is simple - if the wind is steady and constant, you in the sky cannot determinate if there a wind or not without groung reference... Say if you jump with groung covered by clouds you cannot determinate if there a wind using as referencr your canopy or any other skydiver (if he havent groung reference too) i.e. the winw does not affected on distance between you and other jumper

Why drink and drive, if you can smoke and fly?

[davelepka 4]

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The FF still be affected by the wind after deployment so He will drift the same 60 sec as RW flyer falls (+exit delay)

You're just missing the point left and right.

After deployment, the drift becomes a wash as canopies will all drift the same, regardless of the type of freefall. Of course, there are different speed canopies, but they are all 'steerable' so the point is moot with regards to after opening.

Provided that all jumpers break off at 4000ft and pull at 2500ft, you could almost call it an even race from break off on down. Ignoring the higher speed of freeflyers entering the break-off, you can expect similar amounts of drift for all jumpers from break off on down.

The freefall portion, from exit to break off is where the differences are real, and they do occur. The freelfyers will spend less time going from exit to 4000ft, and as a function of that, will drift less than the RW jumper who spends more time in freefall between exit and 4000ft.

[NWPoul 1]

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The FF still be affected by the wind after deployment so He will drift the same 60 sec as RW flyer falls (+exit delay)

After deployment, the drift becomes a wash as canopies will all drift the same, regardless of the type of freefall. Of course, there are different speed canopies, but they are all 'steerable' so the point is moot with regards to after opening.

Provided that all jumpers break off at 4000ft and pull at 2500ft, you could almost call it an even race from break off on down. Ignoring the higher speed of freeflyers entering the break-off, you can expect similar amounts of drift for all jumpers from break off on down.

The freefall portion, from exit to break off is where the differences are real, and they do occur. The freelfyers will spend less time going from exit to 4000ft, and as a function of that, will drift less than the RW jumper who spends more time in freefall between exit and 4000ft.

You miss the point too, you say that th FF spend less time in freefall so he will drift less by the wind, but after deployement he will be still same affected by the wind at the same amuont of time wich he was less falling and therefore will drift horisontally the same way untill the RW came to deployment altitude... the fact tha canopy is stereble means only that you shouldn fly in derection of Jumprun (but even flying this way you are still affected by wind) the same as you should not tracking this way - it's regardless of wind and exit order
Once again, it is quite simple - if the wind is steady and constant, you in the sky cannot determinate if there a wind or not without groung reference... Say if you jump with groung covered by clouds you cannot determinate if there a wind using as referencr your canopy or any other skydiver i.e. the wind does not affected on distance between you and other jumper

Why drink and drive, if you can smoke and fly?

[377 21]

I've said it before, but GPS ground speed tells you VERY valuable info when you are at the door deciding how long to wait after the prior group has exited. Slow ground speed dictates long waits to exit after the prior jumpers. It's pretty simple physics.

I wish DZs would mount a GPS showing ground speed near the door. That info combined with your eyeballs and some common sense would eliminate a lot of hazards and misconceptions about exit separation.

I fooled around with a wrist mounted Garmin Summit GPS (it has a baro altimiter sensor and flux gate compass built in). I was trying to see if I could fly circles during descent and calculate winds aloft by looking at peaks and dips in ground speed indications during the turns. It was useful at the door also as I could see ground speed of the aircraft.

I was surprised one time over the Monterey CA DZ. Ground winds werent excessive but they were honking aloft. On jump run we were doing les than 10 knots ground speed. I waited a long tiime at the door and you could see that we were barely moving relative to the ground. Prior jumpers seemed to descend nearly straight down.

377

2018 marks half a century as a skydiver. Trained by the late Perry Stevens D-51 in 1968.

[davelepka 4]

You're just not right about this one. For some reason I can't seem to say it in a way that makes sense to you. Maybe someone else out there has a better example, or can just do a better job than I did.

In the end, put the RW groups out first, followed by the freeflyers. It's a proven method that gives everyone the best chance for maintaining good group seperation.

[kallend 1,647]

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Even in no-wind conditions, fast fallers get more forward throw from the speed of the plane. The difference between typical RW and FF fall rates is worth around 3 seconds of separation. (IOW, if a freeflier exits first, a following RW group should add 3 seconds to the normal separation interval).

How can it be caused only by vertical speed (fall speed) in case if there enough altitude for both fast and slow fallers to arrest the forward speed from the plane? Or you mean tha typical FF present less surface area to horisontal relative vind than tipycal RW? Possible, but 3 sec equivalent? You mean that if RW flyer will exit after 3 sec from FF than he overhand FFlyer after 10-12 sec (arresting of forward speed)?

That is exactly what I mean. Do the math/physics and convince yourself.

...

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

[dninness 4]

Crikey, its been awhile since I've seen one of these.

I'll go fire up the tractor.

NIN
D-19617, AFF-I '19

[popsjumper 2]

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You're just not right about this one. For some reason I can't seem to say it in a way that makes sense to you.

Well Dave, maybe his sig line is an indicator:
"Why drink and drive, if you can smoke and fly?"

And maybe we should all just leave the craziness to the Russians at his home DZ, Kasimovo.

It's good to know that I will not be making any trips there only to find out on arrival that I wouldn't jump there.

My reality and yours are quite different.
I think we're all Bozos on this bus.
Falcon5232, SCS8170, SCSA353, POPS9398, DS239

[NWPoul 1]

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You're just not right about this one. For some reason I can't seem to say it in a way that makes sense to you. Maybe someone else out there has a better example, or can just do a better job than I did.

It's depend on what you want to say:)
If you want to say that just wind cause any drift of one group frefallers relative to other - you are simple wrong (ask Mr. Kallend, hope his words make much more sence for you than mine:) )
I can draw a simple pics that could help you to understand the physics if you wish:)
If you want to say that this drift occurs when jumping in windy condition - you right but the reason is the wind shifting.

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In the end, put the RW groups out first, followed by the freeflyers. It's a proven method that gives everyone the best chance for maintaining good group seperation.

We know and anderstand and use this order... may be even a little bit better than you;) Coz we are anderstand and taking into account conditions when it work and when it don't work (also prooven by practice) :)

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Well Dave, maybe his sig line is an indicator:
"Why drink and drive, if you can smoke and fly?"

When smoking - wing does matter;)

Why drink and drive, if you can smoke and fly?

[billvon 2,433]

>If you want to say that just wind cause any drift of one group frefallers
>relative to other - you are simple wrong (ask Mr. Kallend, hope his words
> make much more sence for you than mine:) )

It's not just wind. It's also throw.

>We know and anderstand and use this order.

Cool, sounds like a good plan.

[NWPoul 1]

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It's not just wind. It's also throw.

Yep, but throw not affected by any wind, it's only matter of airspeed and specific of your body and the way as you present it to the relative air flow))

Why drink and drive, if you can smoke and fly?

[jono 0]

http://www.omniskore.com/freefall_drift2.html

Remember you don't stop laughing because you grow old, you grow old because you stop laughing.

[theonlyski 3]

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It's not just wind. It's also throw.

Yep, but throw not affected by any wind, it's only matter of airspeed and specific of your body and the way as you present it to the relative air flow))

So, if you were to exit an aircraft with a 90kt airspeed and 0kt windspeed, you would be 'thrown' as much as if you exited with a 90kt airspeed and a 50kt windspeed?

"I may be a dirty pirate hooker...but I'm not about to go stand on the corner." iluvtofly
DPH -7, TDS 578, Muff 5153, SCR 14890
I'm an asshole, and I approve this message

[pilotdave 0]

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So, if you were to exit an aircraft with a 90kt airspeed and 0kt windspeed, you would be 'thrown' as much as if you exited with a 90kt airspeed and a 50kt windspeed?

Over the ground, no. In relation to the plane you just jumped out of, yes, the throw will be the same.

I don't personally believe you can put much faith in the difference in throw between belly and freeflyers. It just depends on too many factors, such as exit body position and, well, success. A perfect headdown exit into the relative wind will create more throw, but a back-to-the-wind spread out sitfly exit probably won't.

I'd like to see NWPoul's graphics related to wind drift and exit separation to compare them to kallend's. I bet we could spot the difference in understanding real quick.

Dave

[theonlyski 3]

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So, if you were to exit an aircraft with a 90kt airspeed and 0kt windspeed, you would be 'thrown' as much as if you exited with a 90kt airspeed and a 50kt windspeed?

Over the ground, no. In relation to the plane you just jumped out of, yes, the throw will be the same.

Isn't ground seperation the overall goal?

"I may be a dirty pirate hooker...but I'm not about to go stand on the corner." iluvtofly
DPH -7, TDS 578, Muff 5153, SCR 14890
I'm an asshole, and I approve this message

[NWPoul 1]

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So, if you were to exit an aircraft with a 90kt airspeed and 0kt windspeed, you would be 'thrown' as much as if you exited with a 90kt airspeed and a 50kt windspeed?

Over the ground, no. In relation to the plane you just jumped out of, yes, the throw will be the same.

more imprtant that it will be the same in rekation to the groups of skidivers

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I don't personally believe you can put much faith in the difference in throw between belly and freeflyers. It just depends on too many factors, such as exit body position and, well, success. A perfect headdown exit into the relative wind will create more throw, but a back-to-the-wind spread out sitfly exit probably won't.

This is exactly my consern regarding Mr. Kallend's "3 sec"

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I'd like to see NWPoul's graphics related to wind drift and exit separation to compare them to kallend's. I bet we could spot the difference in understanding real quick.

In given in Mr Kallens simulation conditions (wind shift) my graphics will be the same as Mr. Kallends coz it's based on simple calculation... may be I put some difference in very begining (those throw effect) but it's minor difference

Dave

[NWPoul 1]

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So, if you were to exit an aircraft with a 90kt airspeed and 0kt windspeed, you would be 'thrown' as much as if you exited with a 90kt airspeed and a 50kt windspeed?

Over the ground, no. In relation to the plane you just jumped out of, yes, the throw will be the same.

Isn't ground seperation the overall goal?

It's depend on what is your consern:)
If your consern is spot - than yes, ground distanse and groun speed you should taking into account
If your consern is the horisontal separation between the groups of skydivers (collision on deployment) - than air distanse and airspeed does matter
Why we should take extra time between exiting groups in high wing/low groundspeed jumprun? Becouse we can! Becouse usually you want both of safety on deployment time and not so far spot - you have to find compromise between amount of delay and distance covered by plane under the ground... when wind is high and groundspeed is low you just have oportunity to give more delay and get more separation between skydivers at deployment altitude for the same spot

Why drink and drive, if you can smoke and fly?

[pilotdave 0]

I think I'm starting to understand what you're saying, but I still don't agree with all of your points. As far as throw from the plane, we're generally in agreement. However, as unpredictable as the difference in throw from an RW group and a freefly group can be, it's likely that putting the slower fallers out first maximizes separation more often than not. Whether it's equivalent to a 3 second difference or a half second difference, I don't know. But putting freeflyers out first will put the groups closer together by the same amount, whatever it may be, except in less likely cases where the RW group gets more throw.

Now as far as time between groups... you're saying that separation at deployment isn't affected by wind speed, as long as the wind speed is steady, right? You're taking into account that after the first group opens, they will continue to drift with the wind away from the second group, so separation at the second group's deployment time is independent of wind speed. Personally, I wouldn't rely on wind drift under canopy for horizontal separation. Canopies are flying in all directions right after opening. If we all jumped non-steerable rounds, it'd be a different story and I might agree with you.

But now lets talk about order. You seem to advocate putting fast fallers out first to minimize canopy traffic. I'd like to see your graphics of the freefall trajectories and how exit order affects separation in freefall and at opening. Kallend's model clearly shows how, on an upwind jumprun, for any given exit separation and wind speed, putting out the fast fallers after the slow fallers maximizes separation. In fact, fast fallers out first tends to cause the slow falling group to cross paths with the fast falling group, risking a collision if the lower group has a premature deployment. Does your model look different?

Dave