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Let's talk about exit seperation

 

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airdvr  (D 10977)

Sep 26, 2010, 10:58 AM
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Let's talk about exit seperation Can't Post

I think we need to re-visit how that works. Anyone care to lead off?




Premier LouDiamond  (D 25931)
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Sep 26, 2010, 11:27 AM
Post #3 of 79 (2323 views)
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Re: [airdvr] Let's talk about exit seperation [In reply to] Can't Post

In reply to:
I think we need to re-visit how that works. Anyone care to lead off?


How about doing a search on the topic first and providing links to all the threads already created on the topic in this thread? That way people would have a frame of reference to refer to and we wouldn't have to rehash all the same arguments once again before moving forward with something new. Just food for thought. Smile


airdvr  (D 10977)

Sep 26, 2010, 11:36 AM
Post #4 of 79 (2316 views)
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Re: [LouDiamond] Let's talk about exit seperation [In reply to] Can't Post

In reply to:
In reply to:
I think we need to re-visit how that works. Anyone care to lead off?


How about doing a search on the topic first and providing links to all the threads already created on the topic in this thread? That way people would have a frame of reference to refer to and we wouldn't have to rehash all the same arguments once again before moving forward with something new. Just food for thought. Smile

Or we could have a fresh conversation for those who've forgotten the advice. More food for thought. Smile

Heaven forbid we'd want to use up bandwidth in the Safety and Training forum to discuss exit seperation. That bandwidth could be put to better use over in the incident forum.


davelepka  (D 21448)

Sep 26, 2010, 11:44 AM
Post #5 of 79 (2306 views)
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Re: [airdvr] Let's talk about exit seperation [In reply to] Can't Post

Quote:
I think we need to re-visit how that works

Why?

If this is in relation to the incident in Aus, exit seperation is not neccessarily to blame for the collision. If you were to establish enough seperation that no jumpers from two different groups could ever converge under any circumstances, then you would have to make multiple passes on every load, or have a jumprun that is 3 miles long.

The incident in question involved two jumpers trakcing in exactly the wrong direction, that being either up or down the jumprun. Proper exit seperation 'should' dictate that this 'should' never be a problem, but in certain circumstances overlap of the airspace can occur.

If an RW jump should funnel towards the bottom end, or otherwise be comprimised, it wouldn't be unusual for a jumper to track off a little early. Even 500 ft above break off could make the difference.

If a jumper is very light, and an excellent tracker, they would have the ability to cover more ground than the average jumper. Let's say this same jumper tracks up the jump run, gets further than most, and then has a hard opening. The end result is an open canopy that is higher, and further up jump run than anyone expected.

If the group had stayed together until break-off, the jumper would not have been able to track as far up jump run. If the canopy had not opened instantly, it would have been open 500 or 600ft lower.

Now if you turn and look at the following group, you can apply the same logic. If another light-weight, accomplished tracker happened to head down the jumprun after a high breakoff, and had a PC hesitaiton followed by a 1000ft snivel, you have the potential for a collision.

If you remove any of the above factors from either jumper in either group, you have no collision. To attempt to account for all of these factors on every jump is impossible, and would require a great deal of exit seperation, more than is practical on a day-to-day basis.

The real solution is to not track up or down the jumprun. This is easier said than done in some cases, but it does work itself out in some ways.

For example, a lower time jumper who may not be able to recognize the direction of jumprun by break off probably isn't going to have the tracking skills to overcome the exit sepereaiton. As jumpers gain expereience, and become better trackers, they need to become more aware of their surroundings.

In the case of bigger-ways, where they need the full 360 degress out from the center to get everyone clear, of course increased exit seperation is needed. Again, things work themselves out because if you have a 15-way leaving an Otter on a day with average winds, the remaining 5 or 7 people in the plane can give the big way a good 15 or 20 seconds before resuming exits. The plane should still be close enough to the DZ to allow normal exit seperation for the remaining jumpers while still making it back to the DZ.

Moving back down to the 15 way on break off, if you figure they will have a higher break off altitude than normal, this will give them more time in their track. During this time, the jumpers can locate the DZ and establish the jumprun. If they find that they are heading up jumprun, they can veer off a few degrees in either direction. As the track progresses, the seperation between the jumpers increases, allowng more room for 'adjustment'.


9,999,999 times out of 10 million, the above works and there are no collisions. How it came to be on that day that two jumpers with a reported 20,000+ jumps betwen them both tracked the wrong direction for the wrong length of time is anyones guess. Even if the exit seperation for the day was correct, and the second group rushed the exit, the jumper in the second group would have known that, and should have been even more aware of not heading back down jumprun on break off.


Premier LouDiamond  (D 25931)
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Sep 26, 2010, 11:48 AM
Post #6 of 79 (2305 views)
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Re: [airdvr] Let's talk about exit seperation [In reply to] Can't Post

In reply to:
In reply to:
In reply to:
I think we need to re-visit how that works. Anyone care to lead off?


How about doing a search on the topic first and providing links to all the threads already created on the topic in this thread? That way people would have a frame of reference to refer to and we wouldn't have to rehash all the same arguments once again before moving forward with something new. Just food for thought. Smile

Or we could have a fresh conversation for those who've forgotten the advice. More food for thought. Smile

Heaven forbid we'd want to use up bandwidth in the Safety and Training forum to discuss exit seperation. That bandwidth could be put to better use over in the incident forum.


You missed the point entirely. My post wasn't to suggest we not discuss the topic, only to provide access to the history that already exists so that others could re-visit those threads easily to educate themselves and allow fresh topics of discussion to be posted in this thread.


kallend  (D 23151)

Sep 26, 2010, 1:11 PM
Post #7 of 79 (2250 views)
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Re: [airdvr] Let's talk about exit seperation [In reply to] Can't Post

 
http://mypages.iit.edu/...d/skydive/#resources

for a comprehensive discussion.


Premier billvon  (D 16479)
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Sep 26, 2010, 6:08 PM
Post #8 of 79 (2138 views)
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Re: [airdvr] Let's talk about exit seperation [In reply to] Can't Post

A few basic rules:

Leave more time when flying into a headwind.

Leave less time when flying downwind.

Worst possible case is flying into a strong wind with OPPOSITE winds at opening time.

Putting RWers out first increases exit separation when you are flying into the wind.

Basic formula for separation is (groundspeed+winds at opening altitude)*time in seconds. So 80 feet per second groundspeed, 10 feet per second winds at opening altitude (same direction) ten seconds separation gives you 700 feet.

One way to achieve it is to always wait seven seconds. If the winds are strong, divide them by 2 and wait that number of seconds. If you're in a fast airplane, divide them by 3.

Another good way is just to look. Wait until the airplane covers 700 feet over the ground, then go.


obelixtim  (D 84)

Sep 26, 2010, 6:58 PM
Post #9 of 79 (2115 views)
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Re: [davelepka] Let's talk about exit seperation [In reply to] Can't Post

 
Yep, you can plan and figure it all out, but no matter who you are and whatever your experience and ability, if you open the door when the reaper knocks, thats about it.

Shit happens.


erdnarob  (D 364)

Sep 26, 2010, 9:00 PM
Post #10 of 79 (2058 views)
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Re: [airdvr] Let's talk about exit seperation [In reply to] Can't Post

Say a typical DZ landing area measurements are 1000 ft x 1500 ft. Now a canopy opens at 3000 ft with a glide ratio of 2 to 1 (I am conservative here). That means without any wind a canopy can fly horizontally twice its height which makes 6000 ft.
OTOH an airplane flying at 85 MPH is doing 125 ft/sec. If the separation is 10 seconds between groups, the horizontal travel of the airplane is 125 x 10 = 1250 feet.
Lets suppose now there are 5 groups with no wind.
Group 1 is dropped (before with respect to the jump run) at 3000 ft before the center of the landing area
Group 2 is dropped 10 seconds after the group 1 which means 1750 feet before the center of the landing area
Group 3 is dropped 10 seconds after group 2 which is 500 feet before the center of the landing area
Group 4 is dropped 10 seconds after group 3 which is 750 feet after the center of the landing area
group 5 jumps 10 seconds after group 4 which is 2000 feet after the center of the landing area

If there is now a medium wind. Well we have to do some calculations but I can see that the whole process will be moved upwind.

What I am trying to explain here is that very often people are reluctant to wait a well measured 10 seconds after the precedent group. Most of the airplanes are just traveling 1250 feet during those 10 seconds while your canopy is able to travel 6000 ft and more when open at 3000 feet.
The problem arises when winds are high. Spot are then more touchy.
Figures do not lie.Cool


NWPoul  (D 178119)

Sep 26, 2010, 9:59 PM
Post #11 of 79 (2040 views)
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Re: [billvon] Let's talk about exit seperation [In reply to] Can't Post

In reply to:
A few basic rules:
...
Putting RWers out first increases exit separation when you are flying into the wind.
...
When there are wind shift (i.e. strong wind) I am tired of this "modern and correct" method when it applyed as default at any circumstances=/
Without a significant wind shift midair this method just doesn't work and all what we get - opening the 15 way formation (exit first) and FF (exit after 15-17 sec delay at the same time at same altitude=/


popsjumper  (D 999999999)

Sep 26, 2010, 11:25 PM
Post #12 of 79 (2021 views)
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Re: [NWPoul] Let's talk about exit seperation [In reply to] Can't Post

In reply to:
When there are wind shift (i.e. strong wind) I am tired of this "modern and correct" method when it applyed as default at any circumstances=/
Without a significant wind shift midair this method just doesn't work and all what we get - opening the 15 way formation (exit first) and FF (exit after 15-17 sec delay at the same time at same altitude=/

You lost me somewhere in there.


kuai43  (C License)

Sep 27, 2010, 1:29 AM
Post #13 of 79 (1998 views)
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Re: [popsjumper] Let's talk about exit seperation [In reply to] Can't Post

In reply to:
In reply to:
When there are wind shift (i.e. strong wind) I am tired of this "modern and correct" method when it applyed as default at any circumstances=/
Without a significant wind shift midair this method just doesn't work and all what we get - opening the 15 way formation (exit first) and FF (exit after 15-17 sec delay at the same time at same altitude=/

You lost me somewhere in there.

I'll take a shot at it... I think he's saying that the difference in the flat/freeflyers freefall times are roughly equal to the delay they take, so both groups will be opening at the same approximate time & altitude, resulting in a chance that jumpers from the two groups could find themselves crowding the same altitude under canopy.

I suppose he believes the freeflyers going first would allow them to have a 15 second head start under canopy (as if that would make much difference). I don't know about anyone else, but I don't lose significant altitude immediately after opening.


If he's referring to the recent tragedy in Australia, it doesn't seem to have any pertinence.

That incident seems to be at the fringes of a "canopy collision" description if the given account is accurate. Sniveling (still a freefall component) from above into an open canopy is not the same animal as most other recent collision incidents.

This appears to be an exit separation/tracking direction issue. Both jumpers have been categorized as extremely competent bigway jumpers with top of the line tracking abilities, and at least one of whom is on record as emphasizing long, strong tracks. Rather than flying into each other under open canopies, they tracked into each other's group's 'air-space' - essentially the equivalent of a head-on car collision.

At the risk of complicating things beyond the air-awareness of of some lesser-experienced jumpers, perhaps the recommendation should be "track like hell off jumprun, but if you're unlucky enough to be 'forced' into having to track up or down jumprun, de-tune your max-track."

*edit - with respect to davelepka, read entire thread before posting Wink


(This post was edited by kuai43 on Sep 27, 2010, 1:35 AM)


Andy9o8  (D License)

Sep 27, 2010, 3:31 AM
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Re: [kuai43] Let's talk about exit seperation [In reply to] Can't Post

In reply to:
"track like hell off jumprun, but if you're unlucky enough to be 'forced' into having to track up or down jumprun, de-tune your max-track."

One reason why yelling "Go!" at the group in the door should be a grounding offense.


jumpwally  (D License)

Sep 27, 2010, 4:47 AM
Post #15 of 79 (1948 views)
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Re: [Andy9o8] Let's talk about exit seperation [In reply to] Can't Post

    +1 some a-hole did that on several loads at a Freak Brother convention,,,,he stopped after i pulled his reserve handle as he suited up in the packing area...


NWPoul  (D 178119)

Sep 27, 2010, 5:04 AM
Post #16 of 79 (1944 views)
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Re: [kuai43] Let's talk about exit seperation [In reply to] Can't Post

In reply to:
I'll take a shot at it... I think he's saying that the difference in the flat/freeflyers freefall times are roughly equal to the delay they take, so both groups will be opening at the same approximate time & altitude, resulting in a chance that jumpers from the two groups could find themselves crowding the same altitude under canopy.
Yep! This is exatctly what I mean

In reply to:
I suppose he believes the freeflyers going first would allow them to have a 15 second head start under canopy (as if that would make much difference). I don't know about anyone else, but I don't lose significant altitude immediately after opening.
H-mm but i usually works, when FF comes first than canopies are distributed by altitude and all load landing in order (if there no spiraling monkeys)

In reply to:
If he's referring to the recent tragedy in Australia, it doesn't seem to have any pertinence.
No I refer only to that "Slow exit first, fastest exit after" and "wind drift/overlay" stuff


davelepka  (D 21448)

Sep 27, 2010, 5:17 AM
Post #17 of 79 (1935 views)
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Re: [NWPoul] Let's talk about exit seperation [In reply to] Can't Post

Quote:
Without a significant wind shift midair this method just doesn't work and all what we get - opening the 15 way formation (exit first) and FF (exit after 15-17 sec delay at the same time at same altitude=/

What's wrong with opening at the same time/altittude? Soemtimes I'm in the first group of freeflyers after the RW groups, and I open before the group before me (not by much, but before). Always with plenty of horizontal seperation, but sometimes before.

Given the figures qupted above, 15 seconds would equal 1875 ft of seperation. Even if you figure that a jumper from each group could track 400ft up or down jumprun, they would still be openiing over 1000ft from each other.

Higher airspeed, in this case, does not dictate who goes first. I've been freeflying since before we figured this out, and has my share of RW guys freefalling past my open canopy. It wasn't all that bad at my home DZ becasue the plane was small, and the groups took their time getting out. My worst expereince was at Perris Valley in the mid-90s when there was a close enough call that the two jumpers almost came to blows in the packing area.

The longer time in freefall for RW groups exposes them to the upper winds for a longer period of time, resulting in increaed dift in freefall. Provided that the jumprun is flown into the wind, this drift pushes them back down jumprun. If the freeflyers exit first with a shorter freefall and less drift, followed by an RW group with greater drift, the freeflyers will be open first with an RW drifting right over the top of them.

Don't try to re-invent the wheel. We all did the wrong way for several years, and then caught on to our mistake. Since reversing the order,there have been very few RW canopy / freeflyer freefall close calls, and every one (that I've seen) could be traced back to the freeflyers rushing the exit in the door (as comfirmed by footage from a tandem vidiot in the plane).


NWPoul  (D 178119)

Sep 27, 2010, 5:50 AM
Post #18 of 79 (1915 views)
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Re: [davelepka] Let's talk about exit seperation [In reply to] Can't Post

In reply to:
Quote:
Without a significant wind shift midair this method just doesn't work and all what we get - opening the 15 way formation (exit first) and FF (exit after 15-17 sec delay at the same time at same altitude=/
What's wrong with opening at the same time/altittude? Soemtimes I'm in the first group of freeflyers after the RW groups, and I open before the group before me (not by much, but before). Always with plenty of horizontal seperation, but sometimes before.
Given the figures qupted above, 15 seconds would equal 1875 ft of seperation. Even if you figure that a jumper from each group could track 400ft up or down jumprun, they would still be openiing over 1000ft from each other.
Yes we opened at good distance beetwen us, but than come to the LZ (I don't talk about small area close to packing hangar... just area where landing pattern should start) at the same time from different direction and it's came pretty crovded

In reply to:
The longer time in freefall for RW groups exposes them to the upper winds for a longer period of time, resulting in increaed dift in freefall. Provided that the jumprun is flown into the wind, this drift pushes them back down jumprun. If the freeflyers exit first with a shorter freefall and less drift, followed by an RW group with greater drift, the freeflyers will be open first with an RW drifting right over the top of them.
This is exactly what I am talking about this upper wind exposure and drift theory sounds pretty smart (and famous computer simulation quite spectacular) and the order "slow - first" sounds pretty smart and correct too... but in real word (at least at my earth semisphere)) ) this theory start work only when the upper wind is quite strong (and there is a wind shift) becouse without wind shift there simlpe no wind both for slow and fast fallers)

In reply to:
Don't try to re-invent the wheel. We all did the wrong way for several years, and then caught on to our mistake. Since reversing the order,there have been very few RW canopy / freeflyer freefall close calls, and every one (that I've seen) could be traced back to the freeflyers rushing the exit in the door (as comfirmed by footage from a tandem vidiot in the plane).
I just talk about what I see (left alone physics, which says that there now wind for object in the sky, until the wind is steady and object does not active flying relative to earth)


davelepka  (D 21448)

Sep 27, 2010, 6:17 AM
Post #19 of 79 (1901 views)
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Re: [NWPoul] Let's talk about exit seperation [In reply to] Can't Post

Quote:
Yes we opened at good distance beetwen us, but than come to the LZ (I don't talk about small area close to packing hangar... just area where landing pattern should start) at the same time from different direction and it's came pretty crovded

So what you're suggesting is that we trade a crowded pattern entry for possible freefall/canopy collisions?

It seems to me that jumpers have a far greater measure of control when all parties are under an open canopy as opposed to when one is in freefall and the other under canopy.


Quote:
in real word (at least at my earth semisphere)) ) this theory start work only when the upper wind is quite strong (and there is a wind shift) becouse without wind shift there simlpe no wind both for slow and fast fallers)

This is where you're wrong, no wind shift is required. Among jumpers falling at the same speed, the wind does have a 'net zero' effect, as they are all effected the same. When you have jumpers falling at two different speeds, the increased time exposed to the winds is what makes the difference between RW and freeflyers.

You are correct that in a no wind situation, the order becomes less important, but seeing as it is less important, we keep it the same for every day. This way the order is consistant, and nobody has to make the call as when the wind is strong enough to merit putting the RW groups out fisrt.


jumper03  (D License)

Sep 27, 2010, 6:29 AM
Post #20 of 79 (1894 views)
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Re: [NWPoul] Let's talk about exit seperation [In reply to] Can't Post

In reply to:
H-mm but i usually works, when FF comes first than canopies are distributed by altitude and all load landing in order (if there no spiraling monkeys)

I take exception with this statement. It is basically relying on vertical separation. If anyone in the first group has a premature deployment or if anyone in the second group has a high speed malfunction, this vertical separation is instantly negated.

Ask yourself how many premature deployments or high speed malfunctions happen each year. The only reason this is not a problem is because we put the slower falling (and therefore those that will drift more) out first.

If the trend of wanting to put FF out first due to the "altitude separation" continues, I predict there will be many more mid-air collisions at break off.


NWPoul  (D 178119)

Sep 27, 2010, 6:38 AM
Post #21 of 79 (1893 views)
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Re: [davelepka] Let's talk about exit seperation [In reply to] Can't Post

In reply to:
Quote:
Yes we opened at good distance beetwen us, but than come to the LZ (I don't talk about small area close to packing hangar... just area where landing pattern should start) at the same time from different direction and it's came pretty crovded
So what you're suggesting is that we trade a crowded pattern entry for possible freefall/canopy collisions?
It seems to me that jumpers have a far greater measure of control when all parties are under an open canopy as opposed to when one is in freefall and the other under canopy.
No) I suggest to wise emplementation of any method tacking into account their pros and cons and the basics of their work instead of dumb "this modern methods is right! you RW now go first" (wich I saw once when the jump run was downwind!) I suggest to get both horisontal (which by all means the most important) and vertical separation

In reply to:
Quote:
in real word (at least at my earth semisphere)) ) this theory start work only when the upper wind is quite strong (and there is a wind shift) becouse without wind shift there simlpe no wind both for slow and fast fallers)
This is where you're wrong, no wind shift is required. Among jumpers falling at the same speed, the wind does have a 'net zero' effect, as they are all effected the same. When you have jumpers falling at two different speeds, the increased time exposed to the winds is what makes the difference between RW and freeflyers.
There is no differents as soon as both of them have enough frefall time to equal thier horisontal speed with air (ok a little difference can be during the defferense of slowdown Horisontal speed for RW anf FF but its quite minor compared to the exit separation) cos in case of steady wind you can consider them falling at no wind...
The famous computer simulation showed the pros of "slow - first" method also operate with wind shift

In reply to:
You are correct that in a no wind situation, the order becomes less important, but seeing as it is less important, we keep it the same for every day. This way the order is consistant, and nobody has to make the call as when the wind is strong enough to merit putting the RW groups out fisrt.
no wind situation = steady wind situation... even for a strong wind, but usually the strong wind has significant wind shift at altitude

Quote:

I take exception with this statement. It is basically relying on vertical separation. If anyone in the first group has a premature deployment or if anyone in the second group has a high speed malfunction, this vertical separation is instantly negated.
I am not refer/defend the vertical separation! The horisontal separation is the key for safety! I talk that improper use of "slow-first" method takes your vertical separation (as additional comfort) and crowd the landing area at landig time but does not give you any positive
There is no (at least at this side if planet) any significant overlapping of RW over FF without significant wind shift (if only FF does not fly thier canopies full flight upwind to DZ just after deployment)


(This post was edited by NWPoul on Sep 27, 2010, 6:52 AM)


Premier billvon  (D 16479)
Moderator
Sep 27, 2010, 9:16 AM
Post #22 of 79 (1812 views)
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Re: [NWPoul] Let's talk about exit seperation [In reply to] Can't Post

>Without a significant wind shift midair this method just doesn't work . . .

If you are flying into a headwind and the winds are stronger at altitude (which is the case about 95% of the time) then putting out belly first will always increase your separation. You do not need a "significant wind shift midair."

Let's take an example.

Plane flying 102 knots
Winds 20kts at altitude
Wind 8kts at opening

Case 1: Freefly out first, 5 second delay: Separation 150 feet
Case 2: RW out first, 5 second delay: Separation 1150 feet


davelepka  (D 21448)

Sep 27, 2010, 9:38 AM
Post #23 of 79 (1802 views)
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Re: [NWPoul] Let's talk about exit seperation [In reply to] Can't Post

Quote:
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.


NWPoul  (D 178119)

Sep 27, 2010, 10:12 AM
Post #24 of 79 (1782 views)
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Re: [davelepka] Let's talk about exit seperation [In reply to] Can't Post

In reply to:
Quote:
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


(This post was edited by NWPoul on Sep 27, 2010, 10:36 AM)


kallend  (D 23151)

Sep 27, 2010, 10:39 AM
Post #25 of 79 (1756 views)
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Re: [davelepka] Let's talk about exit seperation [In reply to] Can't Post

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).


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