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

[Douva 0]

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>I'm not great at physics, so I'm probably just not grasping the way this video was setup . ..

A camera in the front bottom corner of the door pointed down at exactly 45 degrees.


>I've never seen jumpers look like they were even close to 45
>degrees as quickly after exiting as that video shows.

That's because people can't accurately judge a 45 degree angle without help. It takes people a while to learn even how to look straight down.

So, if I'm understanding this correctly, the problem with the 45 degree rule is that degree does not necessarily denote distance--For instance, the preceding group could be 45 degrees down but only 100 feet apart horizontaly? That makes sense. A forty five degree angle is a lot steeper than most people probably imagine.

I don't have an M.D. or a law degree. I have bachelor's in kicking ass and taking names.

[kallend 1,625]

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>I'm not great at physics, so I'm probably just not grasping the way this video was setup . ..

A camera in the front bottom corner of the door pointed down at exactly 45 degrees.


>I've never seen jumpers look like they were even close to 45
>degrees as quickly after exiting as that video shows.

That's because people can't accurately judge a 45 degree angle without help. It takes people a while to learn even how to look straight down.

So, if I'm understanding this correctly, the problem with the 45 degree rule is that degree does not necessarily denote distance--For instance, the preceding group could be 45 degrees down but only 100 feet apart horizontaly? That makes sense. A forty five degree angle is a lot steeper than most people probably imagine.

The problem with the "rule" is that it is not based on any known law of physics. No-one seems to know from whence it came or how it was justified in the first place. The angle a jumper or group makes with the plane doesn't depend on distance or on wind conditions, it is difficult to estimate the angle by eye, and even if you can, the rate of change of angle is small so determining an exact criterion for exit would be impossible even if the "rule" were to be otherwise valid.

Other than that, it's just fine.

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

[rehmwa 2]

This is hilarious - 45 degrees, stick your head out and watch for horizontal sep. All this mean decision making is based on watching the previous group. That's the mistake.

1 - It's the same plane each time and the group is falling in the same air that the plane is in. So the angle is the same and separation of the people relative to the plane is the same - every single time (for specific fall rates.) You learn nothing watching the group that exits in front of you...(by angle, vertically, and horizontally)

2 - The issue is layers of winds from exit to ground. Watch John's simulator on his site or on www.omniskore.com - it's absolutely perfect in showing a simplified version of what really happens

3 - If you want an easy thumb rule - Look out the door at your penetration relative to the ground. If the plane is creeping along, then the uppers are fast and you can take a long time between groups. If the plane is smoking along (relative to the ground) then exit separation is shorter.

4 - This works most of the time but does assume the uppers and ground winds are in the same directions and the uppers are faster than the lower winds.......

5 - Nothing is a better substitute than knowing how to read the wind layers and then figuring it out that way. Many/most can't

6 - winds change during the day, so the thumb rule still isn't too bad most of the time.

It's not intuitive for most, so I won't respond to arguments except from those who've actually played with the simulator first.

Ignorance in this situation can be dangerous.

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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

[rehmwa 2]

I've never, ever seen a group even remotely looks like they are at 45 degrees....... Unless they jump up they might be there for a moment.

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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

[rehmwa 2]

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p'faw - "Physics", it's all spin anyway....

If that's a quantum mechanics joke, it's pretty damn funny....

Not really funny, but that's the intent. Nerdiness is really a lost art. (You hear about the physicist who went out to the Italian restaraunt? He wouldn't eat pasta and anti-pasta in the same meal for fear of destroying the universe and giving off crouton particles.) Please, don't kick me, here's my lunch money.

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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

[diverdriver 5]

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Please, don't kick me, here's my lunch money.

[rehmwa 2]

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Please, don't kick me, here's my lunch money.

and rightly so..

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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

[peacefuljeffrey 0]

I guess I would have to see a seminar on this to properly grasp what you're saying doesn't work about the "45 Degree Rule."

I have been told to use exactly that on several occasions, mostly from experienced jumpers who still view me (with 79 jumps) as someone who should still be watched and reminded about various safety concerns (and I like that and I have no problem with it). So now and then someone will remind me about not getting too far downwind when the wind is blowing out to the lake, or to exercise caution on landing, or to keep on the lookout for alternate landing fields, etc. I'd rather have people treating me like I don't know enough than to assume I know stuff I may not know, if the up-side of it is they'll keep coming at me with good knowledge to share.

But I can't yet visualize what you are saying would not work with the 45 second rule. When I saw the table about there being like .2 seconds between groups, I found myself saying, "Well, if 45 seconds really dictated such a paltry amount of time, I would think normal people would not actually exit that quickly. It's like if a light turned green but there were still cars screaming by across an intersection, I would not just jet out into them simply because green told me to go." Likewise, I think that there is some intuition and observation that must go into separating groups. I usually do a combination of looking at the previous group/individual, counting a good five seconds at least, THEN getting up in the door and within a second or two releasing. I have not had any issues with proximity to other freefallers nor openings. Is it luck or prudence?
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-Jeffrey
"With tha thoughts of a militant mind... Hard line, hard line after hard line!"

[kallend 1,625]

The ostensible purpose is to ensure proper separation between jumpers or groups of jumpers at opening time.

The problems are:

1. There is no correlation whatsoever between angle made with the plane and separation between jumpers at opening time.

2. No-one can accurately gauge 45 degrees by eye from a moving plane.

3. In almost all cases, the angle never actually makes 45 degrees anyway once the group has left the door, so people are interpreting it wrongly.

4. Separation between jumpers depends sensitively on the winds aloft. Angle made with the plane does not.

5. If you are a belly flier following a freeflier you need more spacing than a freeflier following a freeflier. However, both jumpers would see the exact same angle for the freeflier ahead of them.


See

www.dropzone.com/cgi-bin/forum/gforum.cgi?post=990220#990220

and

www.dropzone.com/cgi-bin/forum/gforum.cgi?post=990950#990950

and
www.iit.edu/~kallend/skydive/

...

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

[AFFI 0]

Even more 45 degree rule information...

[ozzy13 0]

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This is hilarious - 45 degrees, stick your head out and watch for horizontal sep. All this mean decision making is based on watching the previous group. That's the mistake.

1 - It's the same plane each time and the group is falling in the same air that the plane is in. So the angle is the same and separation of the people relative to the plane is the same - every single time (for specific fall rates.) You learn nothing watching the group that exits in front of you...(by angle, vertically, and horizontally)

2 - The issue is layers of winds from exit to ground. Watch John's simulator on his site or on www.omniskore.com - it's absolutely perfect in showing a simplified version of what really happens

That is good but we dont have one of them on the plane.

3 - If you want an easy thumb rule - Look out the door at your penetration relative to the ground. If the plane is creeping along, then the uppers are fast and you can take a long time between groups. If the plane is smoking along (relative to the ground) then exit separation is shorter.

This is also good but try telling this to someone with 15 jumps and they will look at you like you have two heads.

4 - This works most of the time but does assume the uppers and ground winds are in the same directions and the uppers are faster than the lower winds.......

This is the problem. Winds are different on every load. so how can you make a rule up that is changing every time.


5 - Nothing is a better substitute than knowing how to read the wind layers and then figuring it out that way. Many/most can't

I know students wont be able too

6 - winds change during the day, so the thumb rule still isn't too bad most of the time.

I dont want to bet my life on a guess.

It's not intuitive for most, so I won't respond to arguments except from those who've actually played with the simulator first.

Ignorance in this situation can be dangerous.

I replied to your post because I think the best why for this is experience. You have much more then me that is clear. I dont think the 45 deg rule works and I also dont think the counting thing works. So with that said.

I think you need to work with the newer jumpers and show them what is safe and whats not. Things change every time you exit the plane. Just to give them a rule that fits all is just plan stupid in my eyes. This last part of my post is not directed any one person so dont take it that way

Never give the gates up and always trust your rears!

[kallend 1,625]

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This is hilarious - 45 degrees, stick your head out and watch for horizontal sep. All this mean decision making is based on watching the previous group. That's the mistake.

1 - It's the same plane each time and the group is falling in the same air that the plane is in. So the angle is the same and separation of the people relative to the plane is the same - every single time (for specific fall rates.) You learn nothing watching the group that exits in front of you...(by angle, vertically, and horizontally)

2 - The issue is layers of winds from exit to ground. Watch John's simulator on his site or on www.omniskore.com - it's absolutely perfect in showing a simplified version of what really happens

That is good but we dont have one of them on the plane.

3 - If you want an easy thumb rule - Look out the door at your penetration relative to the ground. If the plane is creeping along, then the uppers are fast and you can take a long time between groups. If the plane is smoking along (relative to the ground) then exit separation is shorter.

This is also good but try telling this to someone with 15 jumps and they will look at you like you have two heads.

4 - This works most of the time but does assume the uppers and ground winds are in the same directions and the uppers are faster than the lower winds.......

This is the problem. Winds are different on every load. so how can you make a rule up that is changing every time.


5 - Nothing is a better substitute than knowing how to read the wind layers and then figuring it out that way. Many/most can't

I know students wont be able too

6 - winds change during the day, so the thumb rule still isn't too bad most of the time.

I dont want to bet my life on a guess.

It's not intuitive for most, so I won't respond to arguments except from those who've actually played with the simulator first.

Ignorance in this situation can be dangerous.

I replied to your post because I think the best why for this is experience. You have much more then me that is clear. I dont think the 45 deg rule works and I also dont think the counting thing works. So with that said.

I think you need to work with the newer jumpers and show them what is safe and whats not. Things change every time you exit the plane. Just to give them a rule that fits all is just plan stupid in my eyes. This last part of my post is not directed any one person so dont take it that way

So what exactly are you proposing is safe, and what is not safe, to show these newer jumpers?

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

[Meux 0]

As an alternative,

What if the pilot announced on each load what the ground speed on jump run is forecast to be and from that told each group how many seconds to take.

Does any body know their ground speed on jump run?

If the pilot doesn't tell me, I can only guess based on what it was last week, or if this is a Caravan then my speed must be XXknots.

Does anyone ever debrief exit spacing. i.e. the video guy in the second group has his camera on and records the time of the first group leaving, HACK, how many seconds later does his group leave. Was it enough, or not enough?

Is normal climb out for groups enough?

What about your solo student at the end?

Great discussion, thanks for bringing it up Professor.

Mo

[JohnMitchell 14]

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I also dont think the counting thing works. So with that said.

How else do you keep track of time in the door? I count in my head "1-1000, 2-1000, . . . " after the first group leaves and we begin our climbout. Most RW exits take about 7-8 seconds to get in the door, count and go. So I count to "3-1000" and start the climbout. I'm usually on "9-1000" as we begin our exit count.

At the bottom of the jump, under canopy, I check the spacing between the groups. I don't turn towards the DZ until I spot the following group opening up. If anything seems tighter than it should be, I talk to the groups on the ground about using more separation.
Staying alive. It's not just a job, it's an adventure.

[riddler 0]

It's good that these topics get reposted once in a while. I still occasionally hear students that I coach say 45-degrees. Fortunately, I don't think it's coming from the instructors - they seem to be hearing the message. I ask the students where they heard that, and it's usually from up-jumpers that have been around a while.

Trapped on the surface of a sphere. XKCD

[pilotdave 0]

I think THIS is what prompted the bump of this thread. Apparently the word hasn't gotten out at every dropzone about the 45-degree rule (see the comments). But at least any mention of it online gets shot down. Different story at dropzones though. I've heard it within the last couple years at a few dropzones from an instructor, a coach, and an RW organizer. Can't really discuss it when you hear an instructor explain it to their student on the plane.

Dave

[rehmwa 2]

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I think you need to work with the newer jumpers and show them what is safe and whats not.

I don't think anyone teaches 45 because they are intentionally hoping to kill someone. They genuinely "believe" it is safe and that's why they teach it. They are just wrong - in a deadly way.

So your comment doesn't fly with me in that aspect. Good intentions based on stupid theory can still have terrible results. Look at politicians - they are pretty well wrong every single decision they make. And maybe even 2% of them have good intentions (at least on the local level).

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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

[ozzy13 0]

Well you are the one with more experience. You tell me. I just don't think there is one rule that works in all situations. I think working closely with students in the door showing them is the best way. It all depends on ground speed and uppers as well as lowers so to make one rule for all those variables is not the smartest thing to tell students. The next thing you will hear is my Instructor told me that this works all the time.

Never give the gates up and always trust your rears!

[kallend 1,625]

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Well you are the one with more experience. You tell me. I just don't think there is one rule that works in all situations. I think working closely with students in the door showing them is the best way. It all depends on ground speed and uppers as well as lowers so to make one rule for all those variables is not the smartest thing to tell students. The next thing you will hear is my Instructor told me that this works all the time.

I think the method suggested by Billvon, myself and others DOES take into account the winds (upper and lower). What is your objection to it? When do you think it will fail?

Have you ACTUALLY read my article (or Bill's)?

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

[billvon 2,400]

>What if the pilot announced on each load what the ground speed on
>jump run is forecast to be and from that told each group how many
>seconds to take.

Well, all he really has to do is tell people how much time to take, right? That's _usually_ related to ground speed. The one exception is if the lower winds are opposite, which happens out here during Santa Anas.

>If the pilot doesn't tell me, I can only guess based on what it was
>last week, or if this is a Caravan then my speed must be XXknots.

I usually just ask either the pilots or someone else who's been spotting.

"What are the uppers doing?"
"How much time did you give last time, and was it enough?"

>Does anyone ever debrief exit spacing

Generally only if they start getting too close.

[ozzy13 0]

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I think you need to work with the newer jumpers and show them what is safe and whats not.

I don't think anyone teaches 45 because they are intentionally hoping to kill someone. They genuinely "believe" it is safe and that's why they teach it. They are just wrong - in a deadly way.

So your comment doesn't fly with me in that aspect. Good intentions based on stupid theory can still have terrible results. Look at politicians - they are pretty well wrong every single decision they make. And maybe even 2% of them have good intentions (at least on the local level).

I'm not sure whats not fling with you but I never said the 45 deg works. I said working with the student in the door showing them what is safe for that day is the best way. So please tell what part of that you don't like and please fill me in on what you think is the best way. I am always open to opinions in helping myself teach

Never give the gates up and always trust your rears!

[pilotdave 0]

Trying to explain it in the plane doesn't work very well. It's too loud, your papers blow around when the door is open, and you might drop your laptop. It'd work much better to do the math on the ground using the winds aloft to come up with a time between groups, and then adjust it for group size, etc. It is more complicated than "wait 7 seconds." Unless 7 seconds happens to be the right number. But most of the time, when the winds aloft aren't doing anything funny like blowing in opposite directions at opening and exit altitudes, you can get a good guess using only wind speed at exit altitude.

But if you haven't checked the winds before boarding, what do you show when you're in the door to explain when it's safe to jump? You're not waiting for the 45-degree crap and you're not counting seconds. What are you looking for?

Dave

[ozzy13 0]

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I also dont think the counting thing works. So with that said.

How else do you keep track of time in the door? I count in my head "1-1000, 2-1000, . . . " after the first group leaves and we begin our climbout. Most RW exits take about 7-8 seconds to get in the door, count and go. So I count to "3-1000" and start the climbout. I'm usually on "9-1000" as we begin our exit count.

At the bottom of the jump, under canopy, I check the spacing between the groups. I don't turn towards the DZ until I spot the following group opening up. If anything seems tighter than it should be, I talk to the groups on the ground about using more separation.
Staying alive. It's not just a job, it's an adventure.

Ok I knew if I posted here this would happen. I don't think giving everyone on a load say 7 second works because lets say the first group is a 7way belly and the next to groups are free fliers 3 ways then some solo's. I would give the first group more time. So that say just to tell everyone leave 7 seconds doesn't work. Again most people here have experience so I hope we know this . I am trying to look at this from a student view and how to approach them with it. Telling a student leave 7 seconds between groups does not help them. Teaching them why they are leaving 7 seconds is. That all I am trying to say here :)

Never give the gates up and always trust your rears!

[kallend 1,625]

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I also dont think the counting thing works. So with that said.

How else do you keep track of time in the door? I count in my head "1-1000, 2-1000, . . . " after the first group leaves and we begin our climbout. Most RW exits take about 7-8 seconds to get in the door, count and go. So I count to "3-1000" and start the climbout. I'm usually on "9-1000" as we begin our exit count.

At the bottom of the jump, under canopy, I check the spacing between the groups. I don't turn towards the DZ until I spot the following group opening up. If anything seems tighter than it should be, I talk to the groups on the ground about using more separation.
Staying alive. It's not just a job, it's an adventure.

Ok I knew if I posted here this would happen. I don't think giving everyone on a load say 7 second works because lets say the first group is a 7way belly and the next to groups are free fliers 3 ways then some solo's. I would give the first group more time. So that say just to tell everyone leave 7 seconds doesn't work. Again most people here have experience so I hope we know this . I am trying to look at this from a student view and how to approach them with it. Telling a student leave 7 seconds between groups does not help them. Teaching them why they are leaving 7 seconds is. That all I am trying to say here :)

Take a look at www.iit.edu/~ugcol/separation.zip

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

[IanHarrop 37]

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I think THIS is what prompted the bump of this thread. Apparently the word hasn't gotten out at every dropzone about the 45-degree rule (see the comments). But at least any mention of it online gets shot down. Different story at dropzones though. I've heard it within the last couple years at a few dropzones from an instructor, a coach, and an RW organizer. Can't really discuss it when you hear an instructor explain it to their student on the plane.

You right, unfortunately the word has indeed not gotten to everyone. This past summer I heard a very experienced jumper/instructor tell a newbie the 45 degree rule. I was absolutely amazed. Unfortunately when I brought the topic up later with the instructor privately I was pretty much brushed off. He didn't want to discuss it.

So the 45 degree rule is still being taught by people that believe it works.

"Where troubles melt like lemon drops, away above the chimney tops, that's where you'll find me" Dorothy