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Exit Order Safety Article

 

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BrianSGermain  (D 11154)

Mar 26, 2012, 2:14 PM
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Exit Order Safety Article Can't Post

Exit Order Safety
by Brian Germain

There are many different views on exit order, although only some of them are based in science. The following exit order plan is based on the principle of "prop blast penetration": the degree to which a jumper remains under the aircraft based on the drag produced by their body position. When a jumper assumed a log drag body position, head down for instance, they follow a longer arc through the sky on their way to vertical descent.
The fastest falling skydivers are freefliers, which means that they remain under the aircraft longest. If freefliers exit the aircraft first, their trajectory will take them toward, and often beyond the trajectory of flat flyers exiting after them. This fact has been proven time and again in the numerous close calls that have led to the creation of this exit order model. Therefore, the best way to create maximum separation between jumpers at deployment time is to have the RW "flat" jumpers exit before the freefliers, regardless of deployment altitude.
Beyond this, we must also consider formation size when planning exit order. Since the last groups out of the airplane are more likely to land off the dropzone, large groups tend to exit before small groups based on the "needs of the many outweigh the needs of the few" principle of human civilization. I concur that this is a good plan, but for another set of reasons. Large groups tend to open lower than small groups due to task fixation and the need for adequate tracking time to create safe separation. This means participants of large formations should open closer to the dropzone. Further, smaller groups have the option of breaking off early, tracking perpendicular to the jumprun and pulling high to compensate for long spots, while the complexity of building a large formation makes it difficult to take such steps toward safety due to the peer pressure associated with the situation.
So this brings us to the preliminary plan of sending the flat flyers out first, in groups largest to smallest, then the freefliers. However, since inexperienced freefliers most often remain under the aircraft for a shorter period of time than vertically oriented freefliers performing perfect zero angle of attack exits, the order should be lowest experience to highest. This also allows the more experienced freefliers to observe the exits of the novices, giving them the opportunity to give helpful advice, and to provide extra time in the door if necessary. If the previous skydiver or group is still under the airplane, do not jump. When in doubt, wait longer.
Following the flats and then the vertical skydivers, we have the students and tandems. The order can be varied here, although there are some reasons to support sending the tandems out last. First, landing a tandem off the dz is safer than landing a student into an unknown location. Second, students can sometimes get open lower than planned, which not only increases their risks of landing off, but puts the instructors at risk of landing off even more as they open lower than their students. Tandems on the other hand have the option of pulling whenever they see fit, which allows the camera flyer to get open high as well.
The last groups to consider are those involved in horizontal skydives, such as tracking, "atmonauti" or steep tracking, and wingsuit pilots. The truth is, experienced horizontal skydivers can safety get out of the way of other jumpers quite easily, and can exit in any part of the order. However, in the case of two or more horizontal skydiving groups, plans must be created and followed with vigilance. For instance, one tracking group can exit first and track out and up the right side of the jumprun, while another group can exit last and offset toward the left side of the jumprun. Three horizontal groups on the same aircraft are best handled by adding a second pass, although there is a great deal of room for creative answers when wingsuit pilots are involved.
The amount of time between groups must vary based on the groundspeed of the aircraft. On a windy day, with an into-the-wind jump-run, the aircraft may move quite slowly across the ground, reducing separation between jumpers. This requires significant time between exits, perhaps as much as 10 seconds or more on a windy day or a slow airplane. The separation between groups can be increased quite easily on windy days by crabbing the aircraft with respect to the upper level winds, a practice that has become increasingly common at large dropzones.
The bottom line is, keep talking. Every load is a brand new set of circumstances, and requires a good deal of thought. Make sure everyone arrives at the loading area at the ten minute call to allow for good planning and preparation. Many close calls could have been easily avoided by skydivers talking to skydivers, and skydivers talking to pilots. Take your time in the door, keep your eyes open and look for each other. It is a big sky up there, and if we work together, we can use all of it to create safe, fun skydives.


Premier billvon  (D 16479)
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Mar 26, 2012, 3:17 PM
Post #2 of 86 (4157 views)
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Re: [BrianSGermain] Exit Order Safety Article [In reply to] Can't Post

>The fastest falling skydivers are freefliers, which means that they remain under
>the aircraft longest. If freefliers exit the aircraft first, their trajectory will take them
>toward, and often beyond the trajectory of flat flyers exiting after them.

Throw is a very minor variable, accounting for (at most) a hundred yards or so of separation. Wind drift is a much larger factor. Fortunately for into the wind jump runs both factors favor belly-first, so there's no question that it's the right thing to do.

>On a windy day, with an into-the-wind jump-run, the aircraft may move quite slowly
>across the ground, reducing separation between jumpers. This requires significant time
>between exits, perhaps as much as 10 seconds or more on a windy day or a slow
>airplane.

Windy days may require more than that. A good _minimum_ is 7 seconds between groups; this gives groups about 1000 feet of separation at opening time. With 30kt uppers that could be as long as 15 seconds.


BrianSGermain  (D 11154)

Mar 26, 2012, 3:29 PM
Post #3 of 86 (4143 views)
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Re: [billvon] Exit Order Safety Article [In reply to] Can't Post

I appreciate you adding thoughts to the conversation, Bill.

I agree with your points, although in my experience as a freeflyer, forward throw is not a minor concern at all. Back in the good old days of freaks out first, I remember opening up on the other side of the flat groups on more than one occasion, including light wind conditions. A head down flyer can continue to have horizontal movement for a very long time.

Regarding the point about 10 seconds being not enough on a windy day, I agree completely. I suppose I should have used stronger wording than "10 seconds or more", stressing the "more" part.

Again, I really appreciate the input Bil.

Blue Skies!
Brian


BrianSGermain  (D 11154)

Mar 26, 2012, 8:46 PM
Post #4 of 86 (4044 views)
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Re: [billvon] Exit Order Safety Article [In reply to] Can't Post

One more point of clarification regarding Bill's astute comments: When we speak of freefall drift, the amount of time spent in freefall is what most profoundly changes the distance that a skydiver or group drifts with the wind. Freeflyers spend less time in freefall, which means that they drift back toward the dz less. Add this to the greater prop blast penetration, and you have a very different story than the flat groups.

-BG

In reply to:
>The fastest falling skydivers are freefliers, which means that they remain under
>the aircraft longest. If freefliers exit the aircraft first, their trajectory will take them
>toward, and often beyond the trajectory of flat flyers exiting after them.

Throw is a very minor variable, accounting for (at most) a hundred yards or so of separation. Wind drift is a much larger factor. Fortunately for into the wind jump runs both factors favor belly-first, so there's no question that it's the right thing to do.

>On a windy day, with an into-the-wind jump-run, the aircraft may move quite slowly
>across the ground, reducing separation between jumpers. This requires significant time
>between exits, perhaps as much as 10 seconds or more on a windy day or a slow
>airplane.

Windy days may require more than that. A good _minimum_ is 7 seconds between groups; this gives groups about 1000 feet of separation at opening time. With 30kt uppers that could be as long as 15 seconds.


jcbfly  (D 30546)

Mar 26, 2012, 8:50 PM
Post #5 of 86 (4043 views)
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Re: [BrianSGermain] Exit Order Safety Article [In reply to] Can't Post

Hey Brian,
What do you think about the often heard rule of thumb for exit separation that states that for into the wind jump runs, you should divide the speed of the wind on jump run in half, and wait that number of seconds between exits?
JC


popsjumper  (D 999999999)

Mar 26, 2012, 9:25 PM
Post #6 of 86 (4023 views)
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Re: [billvon] Exit Order Safety Article [In reply to] Can't Post

In reply to:
>The fastest falling skydivers are freefliers, which means that they remain under
>the aircraft longest. If freefliers exit the aircraft first, their trajectory will take them
>toward, and often beyond the trajectory of flat flyers exiting after them.
As Bill said, this is a function of freefall drift. Why complicate matters with the trivia? With proper separation your body position on exit matters not.

If you are at the point where body position on exit is a determining factor, you have other, more serious problems.

In reply to:
Windy days may require more than that. A good _minimum_ is 7 seconds between groups; this gives groups about 1000 feet of separation at opening time. With 30kt uppers that could be as long as 15 seconds.
Well, yes and no. Let's be more clear here. Suggesting a "good _minimum_ is 7 seconds between groups" is misleading. That number depends on wind direction, wind speed, jump run direction with respect to wind direction, ground speed, etc, etc, etc.

For everyone. It's simple. Really it is. Do the math. Avoid generalizations and "rules of thumb".

I have AFF students who can pinpoint a perfect spot. They can calculate exit separation. They can determine when and where the first groups should leave and when the last group should leave both for rounds and squares. I do not entertain the idea that an experienced jumper can't do that too. The simple matter of it is that they won't make the effort to learn and do the math.

Now before you go off your rocket, yes, the math is only as good as the information you put into it and we all know that winds aloft and many of those variables cannot be determined as precisely as we would like. But is sure beats the hell out of guessing, generalizing and getting all complicated with the minor details.


Premier LouDiamond  (D 25931)
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Mar 26, 2012, 9:25 PM
Post #7 of 86 (4022 views)
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Re: [jcbfly] Exit Order Safety Article [In reply to] Can't Post

HERE's an excel chart that can be printed out and taped to the side of the door or carried inside a helmet for reference on how long to wait between groups.


Squeak  (E 1313)

Mar 26, 2012, 9:39 PM
Post #8 of 86 (4015 views)
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Re: [LouDiamond] Exit Order Safety Article [In reply to] Can't Post

In reply to:
HERE's an excel chart that can be printed out and taped to the side of the door or carried inside a helmet for reference on how long to wait between groups.
We have a similar chart inside our plane, but ours is based on knots of wind on the nose, not ground speed. Our plane speed run in is always the same.


Premier billvon  (D 16479)
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Mar 26, 2012, 10:07 PM
Post #9 of 86 (4009 views)
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Re: [popsjumper] Exit Order Safety Article [In reply to] Can't Post

>Suggesting a "good _minimum_ is 7 seconds between groups" is misleading. That
>number depends on wind direction, wind speed, jump run direction with respect to
>wind direction, ground speed, etc, etc, etc.

Agreed. But it should never be less than 7 seconds.


popsjumper  (D 999999999)

Mar 26, 2012, 10:17 PM
Post #10 of 86 (4004 views)
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Re: [billvon] Exit Order Safety Article [In reply to] Can't Post

In reply to:
>Suggesting a "good _minimum_ is 7 seconds between groups" is misleading. That
>number depends on wind direction, wind speed, jump run direction with respect to
>wind direction, ground speed, etc, etc, etc.

Agreed. But it should never be less than 7 seconds.
Are you sure about that? What's your airspeed? Your wind speed? Your ground speed? What plane are you jumping - an AN2 or a B-17 or a high-speed pass on whatever?

Did you see Lou's chart?


popsjumper  (D 999999999)

Mar 26, 2012, 10:28 PM
Post #11 of 86 (3999 views)
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Re: [Squeak] Exit Order Safety Article [In reply to] Can't Post

In reply to:
We have a similar chart inside our plane, but ours is based on knots of wind on the nose, not ground speed. Our plane speed run in is always the same.
Well yes, air speed as a constant translates to ground speed well because the ground speed is a sum of airspeed and wind speed. It simplifies calculations throughout the day for sure.

As you already know, I'm sure, the calculations simply determine horizontal distance at a given ground speed which in turn translates to feet of horizontal separation required per seconds to cover that distance over the ground.


Premier billvon  (D 16479)
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Mar 26, 2012, 10:29 PM
Post #12 of 86 (3997 views)
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Re: [popsjumper] Exit Order Safety Article [In reply to] Can't Post

>Are you sure about that?

Pretty sure, yes.

>What's your airspeed? Your wind speed? Your ground speed? What plane are you
>jumping - an AN2 or a B-17 or a high-speed pass on whatever?

Any aircraft with an 80ish kt exit airspeed (i.e. most of em.)

>Did you see Lou's chart?

Yep.


popsjumper  (D 999999999)

Mar 26, 2012, 10:53 PM
Post #13 of 86 (3987 views)
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Re: [billvon] Exit Order Safety Article [In reply to] Can't Post

In reply to:
>Any aircraft with an 80ish kt exit airspeed (i.e. most of em.)
Yep. And therein lies one qualifier for the clarity. And for even more clarity, that's for zero wind speed at jump run altitude.
Please keep in mind that when we put out generalizations that youngsters are reading and we need to be clear on what we are presenting....and that, and only that, was the reason for my the questioning...no more, no less.
Smile


BrianSGermain  (D 11154)

Mar 26, 2012, 11:17 PM
Post #14 of 86 (3979 views)
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Re: [jcbfly] Exit Order Safety Article [In reply to] Can't Post

Interesting, JC, but most likely a bit over simplified. At a glance, 30 mph uppers giving 15 seconds of separation may work for the average jumprun speed, although a slower plane will require more, and a faster one less. It is a reasonable rule of thumb however, and I think it might be a good way to give students a good idea of the time between groups.

I prefer to use my eyes and wait until I see the previous group behind the airplane drift to at least a 45 degree angle. It probably works out to be a similar split that the half-ing rule, but visual confirmation couldn't hurt.

Nice one, thank you!

BG


popsjumper  (D 999999999)

Mar 27, 2012, 12:25 AM
Post #15 of 86 (3972 views)
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Re: [BrianSGermain] Exit Order Safety Article [In reply to] Can't Post

In reply to:
I prefer to use my eyes and wait until I see the previous group behind the airplane drift to at least a 45 degree angle.
????????????????????????????????????
Unbelievable.

You want to get it right? Do the math.


piisfish

Mar 27, 2012, 12:51 AM
Post #16 of 86 (3960 views)
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Re: [popsjumper] Exit Order Safety Article [In reply to] Can't Post

In reply to:
In reply to:
I prefer to use my eyes and wait until I see the previous group behind the airplane drift to at least a 45 degree angle.
????????????????????????????????????
Unbelievable.

You want to get it right? Do the math.
define 45 Crazy


BrianSGermain  (D 11154)

Mar 27, 2012, 1:09 AM
Post #17 of 86 (3956 views)
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Re: [piisfish] Exit Order Safety Article [In reply to] Can't Post

In reply to:
In reply to:
In reply to:
I prefer to use my eyes and wait until I see the previous group behind the airplane drift to at least a 45 degree angle.
????????????????????????????????????
Unbelievable.

You want to get it right? Do the math.
define 45 Crazy[/reply

Relative to the horizon.


Premier skydiverek  (C 41769)

Mar 27, 2012, 3:19 AM
Post #18 of 86 (3939 views)
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Re: [BrianSGermain] Exit Order Safety Article [In reply to] Can't Post

In reply to:
I prefer to use my eyes and wait until I see the previous group behind the airplane drift to at least a 45 degree angle.
????????????????????????????????????
Unbelievable.

You want to get it right? Do the math.define 45 Crazy
Relative to the horizon.
Brian - imagine a jumplane flying with an airspeed of 100 mph INTO the 100 mph headwind. The jumprun feels normal - one can stick his hand outside of the door and feel the 100mph wind on it. But, in reality, the airplane is covering 0 feet per second (ground speed).

First jumper leaves the airplane. You wait, let's say 20 to 30 seconds, until he reaches the "45 degrees". Second jumper exits. BUT both open above the SAME ground point.

" The "45 Degree Rule" for exit separation DOES NOT WORK ":

http://www.dropzone.com/..._latest_reply;so=ASC

http://www.dropzone.com/...post=1971076#1971076






(This post was edited by skydiverek on Mar 27, 2012, 6:15 AM)


Fearjoburg  (A 7079)

Mar 27, 2012, 5:43 AM
Post #19 of 86 (3875 views)
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Re: [skydiverek] Exit Order Safety Article [In reply to] Can't Post

Brian said when the group is behind the plane and at 45 degree angle.


chuckakers  (D 10855)

Mar 27, 2012, 6:06 AM
Post #20 of 86 (3855 views)
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Re: [BrianSGermain] Exit Order Safety Article [In reply to] Can't Post

In reply to:
I prefer to use my eyes and wait until I see the previous group behind the airplane drift to at least a 45 degree angle.

The 45 degree technique is ludicrous. I'm surprised you haven't found the obvious holes in the logic.

Or maybe I'm not surprised.


Premier skydiverek  (C 41769)

Mar 27, 2012, 6:12 AM
Post #21 of 86 (3849 views)
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Re: [Fearjoburg] Exit Order Safety Article [In reply to] Can't Post

In reply to:
Brian said when the group is behind the plane and at 45 degree angle.

I understand that. In my "100 mph" example the first jumper would also be behind the plane and at 45 degree angle.


Fearjoburg  (A 7079)

Mar 27, 2012, 6:19 AM
Post #22 of 86 (3841 views)
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Re: [skydiverek] Exit Order Safety Article [In reply to] Can't Post

So does the 100 mph headwind all of a sudden stop for the jumpers already out of the plane?

The jump group will continue to drift in the wind.

Sorry your argument doesn't make any sense to me.


Premier skydiverek  (C 41769)

Mar 27, 2012, 6:22 AM
Post #23 of 86 (3836 views)
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Re: [Fearjoburg] Exit Order Safety Article [In reply to] Can't Post

In reply to:
So does the 100 mph headwind all of a sudden stop for the jumpers already out of the plane?

The jump group will continue to drift in the wind.

Sorry your argument doesn't make any sense to me.

I will try to explain this to you:

1. Airplane has a GROUND speed of zero mph.
2. Airplane has an airspeed of 100 mph.
3. Both jumpers, in result, will exit over the SAME point on the ground, and will be "blown back" the same amout of feet.

Let me know if I need to explain further.


(This post was edited by skydiverek on Mar 27, 2012, 6:29 AM)


popsjumper  (D 999999999)

Mar 27, 2012, 6:43 AM
Post #24 of 86 (3812 views)
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Re: [Fearjoburg] Exit Order Safety Article [In reply to] Can't Post

In reply to:
So does the 100 mph headwind all of a sudden stop for the jumpers already out of the plane?

The jump group will continue to drift in the wind.

Sorry your argument doesn't make any sense to me.

Maybe you missed the part about "BUT both open above the SAME ground point. "

I'd suggest to all those who use the bogus 45-degree rule to search DZ.com forums for "45 degree" and read the posts on that. It has been explained time and time again....it doesn't work and has been proven to be bogus.

Brian...you've blown a major part of your credibility all to hell and back.


(This post was edited by popsjumper on Mar 27, 2012, 6:45 AM)


Premier skydiverek  (C 41769)

Mar 27, 2012, 6:56 AM
Post #25 of 86 (3797 views)
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Re: [Fearjoburg] Exit Order Safety Article [In reply to] Can't Post

In reply to:
Sorry your argument doesn't make any sense to me.

Read the first eight (blue) links on this website:

http://mypages.iit.edu/~kallend/skydive/


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