Forums: Skydiving: Safety and Training:
The "45 degree rule" for exit separation DOES NOT WORK

 

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Premier Remster  (C License)

Jun 26, 2011, 8:13 AM
Post #326 of 364 (1989 views)
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Re: [rehmwa] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

Quote:
I doubt you or anyone can "guarantee"

We're not defensive... Really.. Now STFU!!!!! Wink

Seriously, you are right. As long as people are people, some guy or gall may slip through the cracks when it comes to making sure they really understand something. What worries me if "the lot at Eloy" part of his statement. One bad apple is one thing, a basket full of them another...

I'll have a chat with Ian and Brian next weekend, and see if we can have another pass at educating people. Maybe we think it's a dead matter since this was explained and institutionalized se well a few years ago, but, it may be time for a refresher...


Scrumpot  (D License)

Jun 27, 2011, 2:35 PM
Post #327 of 364 (1942 views)
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Re: [rehmwa] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

Lat time I heard it uttered, it was at Perris. ....And, by a Perris local. - Just sayin'


champu  (D 28302)

Jun 27, 2011, 5:46 PM
Post #328 of 364 (1916 views)
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Re: [Remster] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

What's tricky is that when you overhear it, it's not always at a time where you can drop what you're doing, convince both the person who said it and the person they said it to to drop what they're doing, and hold an impromptu lesson in physics.

I've found that the people who perpetuate things like the 45 degree rule also happen to be the people who like to yell a dozen reminders about god-knows-what in the middle of jump run when everyone has their helmet on, the door is open, people are trying to climb out, and they ought to just shut up (unless, of course, there is actually an emergency.)


skr  (D 981)

Jun 29, 2011, 7:04 PM
Post #329 of 364 (1862 views)
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Re: [kallend] Re:The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

> Why are we still discussing this? Newtonian physics hasn't changed in the last few years.

Because it's a social and psychological problem,
not a physics problem.

I think one root of the problem is that our intuition
about how stuff works developed down here on the ground
where we have a fixed frame of reference (the ground) and
stuff doesn't move around.

Trees don't move around, houses don't move around.

If someone steps out of the mockup and walks away
for 10 seconds and stands still, and then I step out
and stand still, we don't move around, we stay the
same distance apart.

We have a lifetime of experience that that's how
the world works.

So when we go up and jump out and try to apply that
intuition when my layer of air is moving relative
to his layer of air we get the wrong answer.

I look out the door and watch him fall behind the
plane for 10 seconds and then jump out and use the
intuition that we're going to stay that same horizontal
distance apart all the way down, just like we did
when we stepped out of the mockup.


To see it otherwise means I have to make the effort
(uh oh :-) :-) to expand my intuition to this new
situation and practice new ways of thinking.


I remember how confusing it was when I first ran
into this question.

My first reaction was to imagine my self standing
4 or 5 miles off to one side watching a jump run
with two people getting out 1000 feet apart.

You just take the first trajectory and move the whole
thing, top to bottom, 1000 feet up wind.

You separate opening points by separating exit points.

1000 feet was just an easy number to think about,
and you have to allow for tracking and canopy motion
on the bottom and upper winds on the top to get a
real answer.


The confusing part was when I looked at the same
situation from the door.

If he's 1000 feet behind me when I get out then
why isn't he 1000 feet away when I open?

I've worked so hard to expand my intuition that
it's now hard to remember how confusing that was,
and it took a long time to realize what was tripping
me up, which was the intuition about how it works
when we step out of the mockup on the ground.

I even went up and tried following groups out
with high uppers to watch it happen, but it was
only when I read a post by billvon where he was
talking about the relative motion of the two layers
on the way down that I was able to verbalize it.


So I think that's the psychological part.

The social part is that there is no unified,
system-wide voice training the people who train
people so we still have all this embedded misinformation
like the 45 degree rule floating around.

Changing that would take effort too.

Skr


popsjumper  (D 999999999)

Mar 27, 2012, 12:33 AM
Post #330 of 364 (1720 views)
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Re: [kallend] Re:The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

In reply to:
Why are we still discussing this? Newtonian physics hasn't changed in the last few years.

Evidently, geometry and trigonometry has put the smack-down on physics....

Brain Germaine just posted this in another thread:

"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."

Go figure.

I hope he was just joking.


Fearjoburg  (A 7079)

Mar 27, 2012, 5:53 AM
Post #331 of 364 (1684 views)
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Re: [popsjumper] Re:The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

Hi Pops

I am relatively new to the sport but what Brain said make a lot of sense to me.

Surely if you can see that the jumper/jump group is behind the plane irrespective their angle to the horizon it should be relative save to exit?

Also doesn't it take around 3 - 5 seconds for the jump group to exit?

So if the group before you is already behind the plane and you take about 3-5 seconds to exit, it should be safe to jump?


pchapman  (D 1014)

Mar 27, 2012, 6:49 AM
Post #332 of 364 (1653 views)
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Re: [popsjumper] Re:The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

Someone got the link to the one 45 degree video, the one helping dispel the 45 degree idea?

I've lost it among the long 45 degree rule threads.

It would be great if someone else made a video too so there would be some independent evidence.
(I don't believe in the 45 degree rule, but it would be useful to have more evidence to confirm the argument.)


popsjumper  (D 999999999)

Mar 27, 2012, 7:05 AM
Post #333 of 364 (1645 views)
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Re: [Fearjoburg] Re:The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

In reply to:
Hi Pops

I am relatively new to the sport but what Brain said make a lot of sense to me.

Surely if you can see that the jumper/jump group is behind the plane irrespective their angle to the horizon it should be relative save to exit?

Also doesn't it take around 3 - 5 seconds for the jump group to exit?

So if the group before you is already behind the plane and you take about 3-5 seconds to exit, it should be safe to jump?

You may want to read this thread. I know it's a lot of fluff to wade through but it will help you understand.

Also, go to John Kallend's page here:
http://mypages.iit.edu/~kallend/skydive/

...and download his freefall modelling program to look at his animated demo for exit order, exit separation and freefall drift. Play with it for different scenarios.

It's almost the de facto bible for all that.


rehmwa  (D 12816)

Mar 27, 2012, 7:35 AM
Post #334 of 364 (1624 views)
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Re: [pchapman] Re:The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

In reply to:
Someone got the link to the one 45 degree video, the one helping dispel the 45 degree idea?

I've lost it among the long 45 degree rule threads.

It would be great if someone else made a video too so there would be some independent evidence.
(I don't believe in the 45 degree rule, but it would be useful to have more evidence to confirm the argument.)

Billvon did that video - I suspect you can find it on u-tube - try a search.

good luck


Premier billvon  (D 16479)
Moderator
Mar 27, 2012, 11:55 AM
Post #335 of 364 (1568 views)
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Re: [Fearjoburg] Re:The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

>Surely if you can see that the jumper/jump group is behind the plane irrespective their
>angle to the horizon it should be relative save to exit?

Nope. Picture the following:

Winds are 50kts on the nose at 10,000 feet , then they decrease to 10kts as you get to 2000 feet. That means the winds are dropping off by 5kts every 1000 feet.

You wait 10 seconds before exiting and see that nice angle to the group before you. You exit. You watch the group below you - and they're moving! They are slowly moving under you, but they're not tracking! How is that happening?

Then you realize they are 1000 feet below you, and thus you are always in wind that is 5kts stronger than the wind they are in. You are getting blown over the top of them - even though at exit time it looked like it would be OK.


kallend  (D 23151)

Aug 25, 2012, 8:13 AM
Post #336 of 364 (1290 views)
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Re: [kallend] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

Bump.

Heard of this "rule" being recommended by a very experienced jumper just this year.


strop45  (D 957)

Aug 25, 2012, 3:22 PM
Post #337 of 364 (1228 views)
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Re: [kallend] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

In reply to:
Heard of this "rule" being recommended by a very experienced jumper just this year.
And when someone of my limited experience tries to explain the facts, its amazing how many 'experienced' jumpers argue that its does work and that they have been using it for years.

I guess 'experience' isn't always all its cracked up to be.


Quagmirian  (A 110392)

Aug 25, 2012, 3:32 PM
Post #338 of 364 (1226 views)
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Re: [strop45] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

*snigger*


mjosparky  (D 5476)

Aug 25, 2012, 9:51 PM
Post #339 of 364 (1145 views)
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Re: [strop45] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

In reply to:
In reply to:
Heard of this "rule" being recommended by a very experienced jumper just this year.
And when someone of my limited experience tries to explain the facts, its amazing how many 'experienced' jumpers argue that its does work and that they have been using it for years.

I guess 'experience' isn't always all its cracked up to be.

There is a difference between experience and knowledge.

Sparky


sundevil777  (D License)

Aug 25, 2012, 11:34 PM
Post #340 of 364 (1137 views)
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Re: [strop45] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

In reply to:
In reply to:
Heard of this "rule" being recommended by a very experienced jumper just this year.
And when someone of my limited experience tries to explain the facts, its amazing how many 'experienced' jumpers argue that its does work and that they have been using it for years.

I guess 'experience' isn't always all its cracked up to be.

It would be interesting to study which would give more separation between groups - telling people to wait 7 seconds, or until they spend time looking for 45 deg until finally giving up on it and figuring it has been long enough. Maybe it actually results in more separation (because they take so long looking for the 45), and that is why it has worked?


FastRon

Aug 26, 2012, 2:51 AM
Post #341 of 364 (1123 views)
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Re: [sundevil777] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

i don't know what-all about the 45 degree rule, but I'm obviously missing something- if it was a ballistics problem, unless conditions change, the separation between two 'targets' would be the separation at initiation (exit?) Conditions like: consistent speed and direction of winds, direction and altitude of (aircraft) similar ballistic (freefall) speed, and altitude of target. Of course (unguided) ballistic 'bodies' can't track down jump run...


kallend  (D 23151)

Aug 26, 2012, 7:14 AM
Post #342 of 364 (1087 views)
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Re: [sundevil777] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

In reply to:
In reply to:
In reply to:
Heard of this "rule" being recommended by a very experienced jumper just this year.
And when someone of my limited experience tries to explain the facts, its amazing how many 'experienced' jumpers argue that its does work and that they have been using it for years.

I guess 'experience' isn't always all its cracked up to be.

It would be interesting to study which would give more separation between groups - telling people to wait 7 seconds, or until they spend time looking for 45 deg until finally giving up on it and figuring it has been long enough. Maybe it actually results in more separation (because they take so long looking for the 45), and that is why it has worked?

Lots of ways to ensure passage of enough time before exiting.


d123  (B 6134)

Aug 26, 2012, 7:40 AM
Post #343 of 364 (1079 views)
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Re: [kallend] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

I am really inspired by your thinking but one reality that I see is that nobody can make skydivers smart when they are blocked by their ego.

I've worked on 1 DZ and been a regular to 3 more where they used 45 as the separation rule. I've stoped opening my 400 jumps mouth to the SO, AFFI or free-fly guru's that know it all.

I'm accepting stupidity as a trade off for having this experience called skydiving. I'm trying to be safe by asking the group after us to give 7-12 secs depending on whatever I get from the chat with the pilot on the winds and I give the same time to the group before me and that's it.

I wish that skydiving community was inspired by smart people and I salute your effort but the reality is that their models (or the people that they want to copy) have other strong points.

Maybe I'm circle-ing in the wrong DZ.


Premier billvon  (D 16479)
Moderator
Aug 26, 2012, 8:52 AM
Post #344 of 364 (1056 views)
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Re: [FastRon] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

> if it was a ballistics problem, unless conditions change, the separation between two
>'targets' would be the separation at initiation (exit?)

You answered your own question there. You are literally correct but conditions DO change for jumpers on their way down - they pass through different layers of wind with different velocities.

If people jumped in wind conditions that were constant all the way down, then you're right; exit separation is equal to separation at opening time. Most of the time, though, winds are stronger at altitude.


FastRon

Aug 27, 2012, 12:54 AM
Post #345 of 364 (994 views)
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Re: [billvon] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

  Most of my skydives were from Cessna 170's, 180's, 182's... So we rearely had two 'groups' of jumpers. I'm trying to get a handle on the the issue(s) but 'ballistically' as it were, I would think that unless winds aloft changed in the time it took to launch the next group, they would affect all jumpers the same pretty much if they have similar fall rates. If we dropped say 4 same sized/weight watermelons 7 seconds apart, shouldn't they impact in a rough line parallel jump run about aircraft ground speed (in ft./sec.) times 7 seconds apart?


phoenixlpr  (D 3049)

Aug 27, 2012, 1:07 AM
Post #346 of 364 (993 views)
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Re: [FastRon] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

In reply to:
If we dropped say 4 same sized/weight watermelons 7 seconds apart, shouldn't they impact in a rough line parallel jump run about aircraft ground speed (in ft./sec.) times 7 seconds apart?

You don't seem to have the concept of separation.
How much separation do you get if you drop jumpers with 7 seconds of delay, the plane flies with 80kts into the wind and the wind is 10, 40, 70 kts?


kallend  (D 23151)

Aug 27, 2012, 9:05 AM
Post #347 of 364 (921 views)
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Re: [FastRon] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

In reply to:
Most of my skydives were from Cessna 170's, 180's, 182's... So we rearely had two 'groups' of jumpers. I'm trying to get a handle on the the issue(s) but 'ballistically' as it were, I would think that unless winds aloft changed in the time it took to launch the next group, they would affect all jumpers the same pretty much if they have similar fall rates. If we dropped say 4 same sized/weight watermelons 7 seconds apart, shouldn't they impact in a rough line parallel jump run about aircraft ground speed (in ft./sec.) times 7 seconds apart?

Yes, but when skydiving we don't normally wish to impact the ground. The concern is: how far apart are we at opening altitude?


Premier billvon  (D 16479)
Moderator
Aug 27, 2012, 9:42 AM
Post #348 of 364 (908 views)
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Re: [FastRon] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

> If we dropped say 4 same sized/weight watermelons 7 seconds apart, shouldn't they
>impact in a rough line parallel jump run about aircraft ground speed (in ft./sec.) times
>7 seconds apart?

They will impact about 7 seconds apart.

Now take the case where the wind is 70kts at altitude and the plane is flying straight into it. Your groundspeed is zero. Winds on the ground are light and variable. Now you do the experiment again. How far apart will the watermelons be when they hit the ground?


Divalent  (C 40494)

Aug 27, 2012, 10:33 AM
Post #349 of 364 (884 views)
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Re: [billvon] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

In reply to:
> If we dropped say 4 same sized/weight watermelons 7 seconds apart, shouldn't they
>impact in a rough line parallel jump run about aircraft ground speed (in ft./sec.) times 7 seconds apart?


They will impact about 7 seconds apart.

Now take the case where the wind is 70kts at altitude and the plane is flying straight into it. Your groundspeed is zero. Winds on the ground are light and variable. Now you do the experiment again. How far apart will the watermelons be when they hit the ground?

He gave the answer in his question: ground speed (in ft/sec) times 7 seconds.


Premier billvon  (D 16479)
Moderator
Aug 27, 2012, 11:14 AM
Post #350 of 364 (862 views)
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Re: [Divalent] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

>He gave the answer in his question: ground speed (in ft/sec) times 7 seconds.

Which, in a nutshell, is why it doesn't work.


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