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BrianSGermain

Exit Order Safety Article

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>longer net delay for the two big groups that'll be tracking a ton. the 2 way does have
>the option to track perp to jump run.

Problem there:

8 way climbs out takes 12 seconds
2 way gets in the door goes in 6 seconds
next 8 way goes in 12 seconds

Now you have an 8 way tracking a ton towards a 2 way that is very close to them.

If they were a low experience 2 way pulling high I'd put them out last, because they will take a while in the door and vertical separation helps a bit. If they're high experience I'd put them out first IF they're OK with the shorter spot (i.e. winds are a bit high but they have faster canopies.)

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>Now you have an 8 way tracking a ton towards a 2 way that is very close to them.



your solution? have two 8ways tracking at each other in the same scenario?

1 - there shouldn't be an overlap, so it shouldn't matter for groups of similar fall rates on any exit order
2 - however, if there is an overlap (great trackers, bad execution of exit delays, etc) - this reduces the number bodies in the overlap

I don't really see how you refuse to get this.


your example is cherry picked - if the delay between (exits, not climbouts) is 12 seconds, then it's 12 seconds.

8 way climbs out (9) and count (3) takes 12 seconds, good job
2 way climbout 3 seconds + 3 sec exit count (6 sec) - they got out too fast didn't they - if they went last, they'd have the exact same problem with the 2nd 8way - wouldn't they
next 8 way climb + count in 12 seconds (good job, so what)

your two way screwed up - teach them correctly, don't account for errors and let them continue to get away with it without retrain, they'll think they are doing it right



I agree with a lot of your other specific scenario points (that weren't part of the discussion, but good to consider)

If your only point is, "it depends", sure, I agree with you. Know your jumpers.

...
Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants

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Some modeling shows that the forward throw (relative to airmass) for a headdown jumper can be 200m (~650ft) greater than that of a belly jumper at jumprun airspeed of ~80kts (and even more at higher airspeeds, obviously).



Thanks Yuri, I never considered that. Even though Chris is shitting on your model, it makes sense.

It was counter-intuitive until I thought about it, looked at your chart, and realized that even after an HD flyer has hit terminal, her body would still be along way from vertical, as the relative wind would still contain a strong horizontal component. Indeed, for the case in the chart, the body would never be completely vertical and only get "close" after about 1200m or so.
It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

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>1 - there shouldn't be an overlap, so it shouldn't matter for groups of similar fall rates
>on any exit order

If they obey the minimum exit timing, yes. The problem is sometimes people don't. One of the reasons is that they are under pressure from the people behind them, and while such pressure should always be ignored, low timers have more trouble doing this.

We can help ease this pressure by putting smaller low experience groups at the end. And if they are opening higher, then a long spot does not affect them as badly.

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Solution = all exit at same time.
flat, verts, AFF, tandems. Throw in CRW and wingsuiters just for fun. Might only get to do it once but it'd make for an awesome photo :)



Bwahahaha! Well, while I was on coach status we had an 8 way go out of the king air. That was basically everyone in the plane! All that was left was me, my coach and one wingsuit guy.

We DID have plenty of time for exit separation after they left!
I'm trying to teach myself how to set things on fire with my mind. Hey... is it hot in here?

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wow, old thread


well, if every group on the load is doing the same discipline, I'd still put a little way between a couple big ways instead of largest to smallest,

for example - two 8-ways and a 2-way

longer net delay for the two big groups that'll be tracking a ton. the 2 way does have the option to track perp to jump run.

Of course, if we calc the correct delay, it's kind of a moot point, so I'm just adding to safety margin. delay between groups and exit order matter so much more than everything else, I hate to bog up on any other factor than the big two



Or just make sure manifest puts the two 8 ways on different loads and fills the remaining seats with tandems thus maximizing profits!:ph34r:

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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.



Some modeling shows that the forward throw (relative to airmass) for a headdown jumper can be 200m (~650ft) greater than that of a belly jumper at jumprun airspeed of ~80kts (and even more at higher airspeeds, obviously).



My model pretty much agrees with that.
...

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

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We can help ease this pressure by putting smaller low experience groups at the end. And if they are opening higher, then a long spot does not affect them as badly.



so, yes, you were just saying "it depends" - and I understand and agree with most of those little tweaks

just like my note, we're just adding margin if people don't follow good separation - I don't see your option to be superior than mine since I'm playing with minimizing the number of bodies in a potential collision space, while you are playing with psychology assumption. different approaches - different results.

In the 8/8/2 or 8/2/8 scenarios we both end up with a 2way being two close one of the two 8ways due to their own fault. so flip a coin. In mine, we still have less landing congestion, but now it's just getting silly, that's not the goal


I'd rather teach them correctly and fix it when they do it wrong, rather than enable them to, in their ignorance, to not do exit separation correctly.

...
Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants

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Or just make sure manifest puts the two 8 ways on different loads and fills the remaining seats with tandems thus maximizing profits!:ph34r:



sorry, I know you already manifested, but two of the tandem$ want camera, so you have to wait a couple loads or turn the 8 way into a 7 way if you want on this load.... [:/]

...
Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants

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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.



Some modeling shows that the forward throw (relative to airmass) for a headdown jumper can be 200m (~650ft) greater than that of a belly jumper at jumprun airspeed of ~80kts (and even more at higher airspeeds, obviously).



My model pretty much agrees with that.




Yes, but it's a "model."

What I'm finding out is that in this world of individual flyers, this world of upside down cones of probability, is what you have pointed out in the first place and that is different groups can do different things...


Therefore....this is a highly variable disscussion and your modeling arguments can be used by anyone with an opposing viewpoint! In a sense it dosen't matter if freeflyers go before belly flyers, or belly flyers go before freeflyers. Because of the variability issues you raise apply to both groups equally!

You exit an aircraft that is moving at 144 feet per second? YES OR NO-----

What is the effect wind resistance wise on the ballistic trajectory???

This is a loaded question, because untill yo have actuall data...YOUR all just making a wag!!!



WAG = WILD ASS GUESS.

With affection to you all...:)
But what do I know, "I only have one tandem jump."

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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.



Some modeling shows that the forward throw (relative to airmass) for a headdown jumper can be 200m (~650ft) greater than that of a belly jumper at jumprun airspeed of ~80kts (and even more at higher airspeeds, obviously).



My model pretty much agrees with that.




Yes, but it's a "model."

What I'm finding out is that in this world of individual flyers, this world of upside down cones of probability, is what you have pointed out in the first place and that is different groups can do different things...


Therefore....this is a highly variable disscussion and your modeling arguments can be used by anyone with an opposing viewpoint! In a sense it dosen't matter if freeflyers go before belly flyers, or belly flyers go before freeflyers. Because of the variability issues you raise apply to both groups equally!

You exit an aircraft that is moving at 144 feet per second? YES OR NO-----

What is the effect wind resistance wise on the ballistic trajectory???

This is a loaded question, because untill yo have actuall data...YOUR all just making a wag!!!



WAG = WILD ASS GUESS.

With affection to you all...:)


Subsonic fluid dynamics is not a WAG, any more than Newton's laws. My model, and I'm sure Yuri's too, incorporate the effect of air resistance. Maybe you should do some research BEFORE posting.

If individuals choose to flail around and go off a ballistic trajectory as modified by air resistance, then even the experimental data you crave will just give probabilities.

Incidentally, Billvon's video of the "45 degree rule" in action agrees in every way with the predictions of the model.
...

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

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Yes, but it's a "model."

Yes, and a very good one. The world of engineering is full of models used to predict behaviors. :)
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What I'm finding out is that in this world of individual flyers, this world of upside down cones of probability, is what you have pointed out in the first place and that is different groups can do different things...

And these cones of variability say the belly flyers should go first.:P

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In a sense it dosen't matter if freeflyers go before belly flyers, or belly flyers go before freeflyers. Because of the variability issues you raise apply to both groups equally!

Nope, there is a certain immutable characteristic of the two groups, fall rate.


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You exit an aircraft that is moving at 144 feet per second? YES OR NO-----

Depends on the EXACT speed of the aircraft, duh! Most likely NO!




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What is the effect wind resistance wise on the ballistic trajectory???

This is a loaded question, because untill yo have actuall data...YOUR all just making a wag!!!



WAG = WILD ASS GUESS.

It's very easy for an engineer to calculate the ballistic coefficient of any object based on its terminal velocity in a known atmosphere. Certainly NOT a wag. :)

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And these cones of variability say the belly flyers should go first.:P



Exactly -

Chris - the worst abuse of statistics is when people say that nothing can be predicted because the error bands create enough uncertainty to invalidate the difference of the central trends you are comparing - that's a terrible application of the math. Typ (mean) RW vs FF rates are far enough apart, that the error bands certain will not invalidate that difference.

So go ahead and collect the data directly (go ahead and bias the data and throw in a handful of unstable RW and FF pretenders in the mix) and map out the 'cones' of probability (error bands). I'll bet dollars to donuts that the two data sets "cannot be shown to be equal with less than 95% probability". i.e., they don't overlap enough to pretend they act the same.


now THAT's how you serve up nerd talk...:D

...
Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants

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Ok...here goes. I find that many jumpers, experienced or otherwise...have a hard time grasping simple concepts like not crossing the wind line in the LZ. Are we expecting this same population of jumpers to apply calculations and physics equations in the door of an airplane, with a bunch of impatient knuckleheads pressuring them to Go Go Go 2 seconds after the group ahead? I'm sticking with BG's concept of using your eyes, brain, and experience to create the right separation between groups. I'll skip the scientific calculator and computer based drift models.

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I'm sticking with BG's concept of using your eyes, brain, and experience

Back in the 60's a lot of new B727 pilots used that method to calculate their descent profiles instead of following the books. Several fatal crashes made them go back to the scientifically calculated flight plans.

Time between groups has been proven to work, over and over again.

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Good god this is confusing. I'm always hearing people say different things about exit order. In the beginning of summer my dropzone was doing freeflyers and large groups first, and then one day out of nowhere they switched and were making me (noob, solo, belly) exit first. I just listen to the majority in the plane, but I'd really like to learn more about this.

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That's just because it's fun to watch the solo belly noobs sit next to the door and try to open it. Just wait until summer, they'll open that goddamn thing for 6000 feet with you just jammed right in there! ;)
I'm trying to teach myself how to set things on fire with my mind. Hey... is it hot in here?

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Tim: why don't you use the guidelines posted in the planes at SDAZ then?

They are based on those "models" and the chart Lou posted up on page 1, only simplified.



Remy, I guess what I'm saying...is I see and have experienced issues with people in our and other DZ's that get overloaded with too much created complexity while "in the moment"...and this isn't just isolated to skydiving. I think sometimes we try to over analyze things and create a workflow that essentially overwhelms people when things start happening fast. I think posting simple and easy to apply guidelines in aircraft is a great thing...but when we armchair this stuff with physics equations, it makes my eyes cross. I don't know how to work a slide rule, hence my dropping my major as a mechanical engineer one semester into college...

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I'm sticking with BG's concept of using your eyes, brain, and experience


Time between groups has been proven to work, over and over again.



Yes, time between groups...absolutely. I am agreeing with this completely...it's when we start expecting people to apply math equations in the door while a plane load of people are shouting Go, Go, Go is when things unravel...I just like to keep it simple, and count out a good delay. And yes, much longer when ground speed is slow...

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I think posting simple and easy to apply guidelines in aircraft is a great thing..

We do, and it works. :)
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.but when we armchair this stuff with physics equations, it makes my eyes cross.

The reason we're getting into all that stuff is that people keep denying the simple stuff, want to know "why?" and keep spouting this "45 degrees" BS. ;):P

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