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The "45 degree rule" for exit separation DOES NOT WORK

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kallend  (D 23151)

Dec 11, 2005, 2:03 PM
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 The "45 degree rule" for exit separation DOES NOT WORK Can't Post

Given the discussion going on in the "Incidents" forum, it is time to mention this again.

Anyone who wishes to dispute the statement is welcome to argue with me.

(This post was edited by kallend on Dec 11, 2005, 2:04 PM)

NelKel  (D 25024)

Dec 11, 2005, 2:23 PM
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 Re: [kallend] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post
I do not want to argue, but could you explain, with out descent, what exactly is the rule?

kallend  (D 23151)

Dec 11, 2005, 2:35 PM
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I do not want to argue, but could you explain, with out descent, what exactly is the rule?

Not sure what you mean by "without descent"?

Some people (including some instructors) mistakenly believe that you can achieve adequate exit separation from a group leaving the plane ahead of you by watching for that group to make a 45 degree angle behind the plane.

It does not work. Physics can be used to prove conclusively that it does not work, and because some people don't believe in physics, it has been proven by actual measurements that the physics is correct, and the "rule" does not work.

Dec 11, 2005, 2:40 PM
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...And I downloaded a program from your website that not only proves it, but illustrates what you mean
in visual terms even a neophyte like me can understand!

Dec 11, 2005, 4:01 PM
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 Re: [airtwardo] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post
...And I downloaded a program from your website that not only proves it, but illustrates what you mean
in visual terms even a neophyte like me can understand!

"programs" prove nothing, ever. All they do is provide an illustration of what the underlying theory is. The only thing that proves a theory is observation.

If there are assumptions implicit in the theory, or aspects overlooked, then those wont be reflected in the program, so the program doesn't prove the theory.

The mathemeatics here, and the non validity of the 45 degree angle are failry simple and easy to illustrate.

Sadly, even with a big document about the invalidity of the 45 degree angle posted right outside manifest at Eloy by S&TA Brian Burke, I STILL heard an instructor there tell an inexperienced solo jumper on the plane to give a 45 degree angle.

OSOK  (A 48456)

Dec 11, 2005, 4:36 PM
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Maybe he said something like "wait for the other group to be at least 45 degs from the plane" ??

mark  (D 6108)

Dec 11, 2005, 4:53 PM
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Maybe he said something like "wait for the other group to be at least 45 degs from the plane" ??

Wouldn't have mattered if he did, it would still be wrong.

The only way to get 45 degrees or more is for the vertical speed of the jumper to be less than the horizontal speed of the airplane. That occurs twice: once immediately at exit, and second after canopy deployment. Using the first occurence of 45 degrees is unsafe; using the second is uneconomical.

Mark

MB38  (A 48618)

Dec 11, 2005, 4:57 PM
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Understanding and accepting that the "45 degree rule" does not work, lets talk about what does.

I've heard a lot of things from other jumpers and instructors. One of them was the 45 degree rule. Another is to wait as many seconds as half of the upper wind strength. 40mph uppers? Wait 20 seconds. Another is to wait until it just "looks like there's enough" separation, but as a tremendously inexperienced jumper, I can't make that judgment.

So how should I judge separation? I still ask more experienced jumpers pretty much every time, trust their judgment and try to learn from it, but I'd love to have the "formula" in my head.

[don't worry, I've done searches on it before and I have a decent idea... I'm pretty much just trying to steer the conversation and learn from it]

LouDiamond  (D 25931)
Moderator
Dec 11, 2005, 5:38 PM
Post #9 of 364 (9941 views)
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Quote:
but I'd love to have the "formula" in my head.

Then print this out and tape it to your helmet or better yet, tape it right beside the lights by the door. In order for this to work the pilot must give you the groundspeed while on jumprun.
Attachments: Exit Separation.xls (16.5 KB)

popsjumper  (D 999999999)

Dec 11, 2005, 5:55 PM
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 Re: [LouDiamond] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post
You mean that I shouldn't necessarily go when the TIs start screaming????

billvon  (D 16479)
Moderator
Dec 11, 2005, 6:15 PM
Post #11 of 364 (9911 views)
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> lets talk about what does.

Your first suggestion was a decent one - divide the upper winds (in knots) by 2 and wait that number of seconds. Or divide by 3 if the airplane is a fast one (i.e. King Air.) In light winds always give at least 5-7 seconds.

The "wait until it looks OK" can work if you can judge distances over the ground. If you wait until the plane has covered 1000 feet then go, you will generally get 1000 feet or more of separation from the previous group. One way to do this is use landmarks. With a 2000 foot runway you can put one group out over one end, one over the middle, and one over the far end and have an easy 'yardstick' to use.

A final method, the one we started with at Brown years back, was to always start at about 10 seconds, then reduce it if it gives too much separation, increase it if it gives you too little. There are obvious problems with this though.

kallend  (D 23151)

Dec 11, 2005, 7:47 PM
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 Re: [apoil] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post
...And I downloaded a program from your website that not only proves it, but illustrates what you mean
in visual terms even a neophyte like me can understand!

"programs" prove nothing, ever. All they do is provide an illustration of what the underlying theory is. The only thing that proves a theory is observation.

If there are assumptions implicit in the theory, or aspects overlooked, then those wont be reflected in the program, so the program doesn't prove the theory.

.

Not disagreeing with your statement, but all that are needed to model the situation are Newton's Laws.
Newton's laws have been well validated over the centuries when applied to situations like skydiving. Relativity and quantum mechanics are not required. I've found that a visual model to illustrate the point helps non physicists to get it.

Dec 11, 2005, 9:23 PM
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If I was a Supreme Court Justice I would not hear this case seeing there is lack of new evidence presented.

This argument was settled mid 2004 by undisputable evidence provided by the application of science. Not only the application of technology was used, computers, but the careful explanation of the events of two objects dropped from an aircraft in flight in two simulation, one being time base which equals distance, and the 45 degree rule.

For those of you needing or wanting to learn about this subject, may I suggest you search the Form Archives and read the past posts.

(This post was edited by lug on Dec 11, 2005, 9:28 PM)

FrogNog  (C 34484)

Dec 11, 2005, 10:31 PM
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The thing I like about using time is it's about the easiest value to reliably get the stick/group/jumper after you to give before following you out. I can trust most people to count 10 seconds, somewhat reliably, if I make them swear to me in the plane that they will do so after I jump.

nathaniel

Dec 11, 2005, 10:57 PM
Post #15 of 364 (9790 views)
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The only thing that proves a theory is observation.

That's quite an epistemological theory you've got there. How would you prove it?

BIGUN  (D 23385)

Dec 12, 2005, 4:26 AM
Post #16 of 364 (9702 views)
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 Re: [kallend] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post
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The "45 degree rule" for exit separation DOES NOT WORK.

Neither does not posting LouDiamond's chart on the back of the aircraft, nor the pilot not communicating the ground speed. I like BillVon's approach to /2, but there is still that commmunication gap. I'm thinking every plane ought to have a bullhorn like Mullins bird... He comes on and tells ya, exit, exit, exit and I noticed at WFFC last year, he was giving separation times between groups.

<Makes note of another bullet item for safety day>

Anvilbrother  (C 39168)

Dec 12, 2005, 6:04 AM
Post #17 of 364 (9657 views)
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I was impressed with the fact that he gave separation times.

kallend  (D 23151)

Dec 12, 2005, 8:19 AM
Post #18 of 364 (9588 views)
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If I was a Supreme Court Justice I would not hear this case seeing there is lack of new evidence presented.

This argument was settled mid 2004 by undisputable evidence provided by the application of science. Not only the application of technology was used, computers, but the careful explanation of the events of two objects dropped from an aircraft in flight in two simulation, one being time base which equals distance, and the 45 degree rule.

For those of you needing or wanting to learn about this subject, may I suggest you search the Form Archives and read the past posts.

Well, this is not the Supreme Court and the purpose was not to hear fresh evidence, but to bring existing evidence before a new crop of unbelievers.

So in essence, it is more like a new sermon on an old sin.

(This post was edited by kallend on Dec 12, 2005, 8:23 AM)

kallend  (D 23151)

Dec 12, 2005, 8:21 AM
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Quote:
The only thing that proves a theory is observation.

That's quite an epistemological theory you've got there. How would you prove it?

The year 1976 saw a complete solution to the Four Colour Conjecture when it was to become the Four Colour Theorem for the second, and last, time. The proof was achieved by Appel and Haken, basing their methods on reducibility using Kempe chains. They carried through the ideas of Heesch and eventually they constructed an unavoidable set with around 1500 configurations. They managed to keep the boundary ring size down to 14 making computations easier that for the Heesch case. There was a long period where they essentially used trial and error together with unbelievable intuition to modify their unavoidable set and their discharging procedure. Appel and Haken used 1200 hours of computer time to work through the details of the final proof. Koch assisted Appel and Haken with the computer calculations.

The Four Colour Theorem was the first major theorem to be proved using a computer, having a proof that could not be verified directly by other mathematicians. Despite some worries about this initially, independent verification soon convinced everyone that the Four Colour Theorem had finally been proved. Details of the proof appeared in two articles in 1977. Recent work has led to improvements in the algorithm.

tso-d_chris

Dec 12, 2005, 1:45 PM
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. . . The Four Colour Theorem was the first major theorem to be proved using a computer. . .

Didn't that have something to do with being able to make a map of territories with no bordering territories sharing a color, and that only four different colors were required?

Dec 12, 2005, 1:51 PM
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 Re: [tso-d_chris] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post
You forgot to put a winky-face after that statement, Chris.

Hint: RBYG

But prof, in all seriousness though... What is white?
Also, I always hesitate quoting any "science" from the mid to late 70's. Seems to me as I remember a particular Popular Science edition about that time purportedly "proving" (or at least touting) Global COOLING ...and the very near impending coming of the next (by 2015) ICE AGE. 1977 scientific conclusions? Hmmmm.... Careful there.

-Grant

phoenixlpr  (D 3049)

Dec 12, 2005, 4:12 PM
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It seems we had something common in our studies like the The Four Colour Theorem.:)

Dec 12, 2005, 4:30 PM
Post #23 of 364 (9398 views)
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 Re: [kallend] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post
Not disagreeing with your statement, but all that are needed to model the situation are Newton's Laws.
Newton's laws have been well validated over the centuries when applied to situations like skydiving. Relativity and quantum mechanics are not required. I've found that a visual model to illustrate the point helps non physicists to get it.

I knew you'd understand what I'm saying.
In this case it's probably fine.
But just saying Newton's Laws is a bit general and doesn't mean you have a complete model in your program. Remember high school physics when we neglected friction and wind resistance? Well there's a lot of wind resistance going on in skydiving.

Also Newton's laws still govern highly complex dynamic systems (aka chaotic systems). As the number of variables increases the ability to predict becomes severely limited.

Basically, just because the program does what you say it will, it doesn't necessarily follow that reality will do what you say it will, so a program is simply an illustration and not a proof.

nathaniel

Dec 12, 2005, 5:11 PM
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a program is simply an illustration and not a proof.

Well then, lets start from scratch. What justification do we have for believing the 45-degree rule to begin with? Other than you heard someone else say that it works, of course.

I believe the 45-degree rule might "work" because it will take a reasonable person at least 5-7 seconds staring blankly out the door before they realize they have no freaking clue where a 45-degree angle line might be, and that's often enough time to survive.

I'd prefer they actually counted off seconds in accordance with the ground speed...but there's a lot of risk in this sport, eh?

Dec 12, 2005, 5:50 PM
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"just because the program does what you say it will..."

Then can we just say that it's at least better than someone staring out the plane at the previous group without a clue about groundspeed?

Also, how difficult is it to figure out wind resistance? Tell me how much you weigh and I'll tell you your very own force for drag.

I'll trust Mr. Kallend to have taken such things into account. There aren't any black holes here so I'm pretty this is all straight-forward.

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