45 degree rule?

[moth 0]

so to bring this debate from another thread whats the pros and whats the con? i dont know. Ive heard for, from jumpers with 4000 jumps plus and against from equally experienced jumpers so what does it all mean?

[wildcard451 0]

please do a search and read.

[JohnMitchell 14]

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so to bring this debate from another thread whats the pros and whats the con?

Pros are that it is so simple an idiot can use it.

Cons are that it is meaningless for safe separation and only idiots use it.

Use time between exits for safety. The factors that make the previous group appear or not appear at a 45 degree angle have nothing to do with separation. It's more to do with jumprun speed and the sectional density of the jumpers.


There, the debate is now finished.

[kallend 1,619]

www.iit.edu/~ugcol/separation.zip

...

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

[moth 0]

why do a search? its a current issue that someone has bought up and i feel it would be benificial to get some attention again. please remember that not everyone has read every post on this forum, and some issues are not forefront in everyones mind, so it sometimes does good to bring them up again. it certainly does no harm!

[Samurai136 0]

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why do a search? its a current issue that someone has bought up and i feel it would be benificial to get some attention again. please remember that not everyone has read every post on this forum, and some issues are not forefront in everyones mind, so it sometimes does good to bring them up again. it certainly does no harm!

http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=1111597;search_string=45%20degree%20rule;#1111597
http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=1049154;search_string=45%20degree%20rule;#1049154
http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=1971076;search_string=45%20degree%20rule;#1971076
http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=866964;search_string=45%20degree%20rule;#866964
http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=988627;search_string=45%20degree%20rule;#988627

Here's at least 5 threads on the topic. There may be other nested links to other threads in there.

Most of the skydivers who frequently post about the flaws of the "45 degree rule" are physicists and engineers.

There's really nothing new to say about this topic.

"Buttons aren't toys." - Trillian
Ken

[billvon 2,379]

Short answer:

The 45 degree angle does not work at all. I took a bunch of pictures of people exiting during both upwind (long delay required) and downwind (short delay required) jump runs, and there's no difference. Heck, they never even reached 45 degrees under any conditions.

The reason people THINK it works is it makes them stick their head outside the plane and try to figure out what 45 degrees looks like. After a few seconds they either:

1) decide they think the group is at 45 degrees, even though it isn't

2) give up because they don't want to look stupid

3) give up because everyone else is screaming "GO! GO!"

But in all 3 cases, they waste 5-10 seconds, and that's enough (usually) to give them safe separation.

[AFFI 0]

First Off:
You have a great question and it is fantastic that you want to learn more about this topic.

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why do a search?

Why?
Because this issue has been discussed in-depthzilla ad-nauseam not to mention that it is a rule/policy of DZ.com.
(Use existing threads on your topic to continue a discussion rather than starting a new one.).

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not everyone has read every post on this forum, and some issues are not forefront in everyones mind

That is exactly why there is a search function, so those that have not read about a topic can easily gain access to the information.
It was not that long ago since this issue was at the fore-font and discussed thoroughly form a variety of diversified opinions.

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Its a current issue that someone has bought up and i feel it would be benificial to get some attention again.

Then what you should have done (DZ.com Forum Rules and Policies)is a search on the topic. Then, after adding your comments the thread would have been brought to the top, thus placing it in front of everyone’s eyes again.

I did not create the rules and policies of this forum but I imagine this rule was put into place to reduce repetitive postings that complicate the system which in turn make it more difficult to conduct searches because there are multiple threads on the same topic.

It would make searches easier if people complied with this policy.
A month from now someone is going to actually perform a search on this topic and get bogged down because they have to read many multiple threads rather than a single repository of information.
This is one rule I wished was enforced and complied with more.

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Use existing threads on your topic to continue a discussion rather than starting a new one.

The Forum Rules and Policies are found here:
http://dropzone.com/cgi-bin/forum/gforum.cgi?post=142088

This one had been locked:
http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=1049154;search_string=45%20degree%20rule;#1049154 (Note the Last entry)

Mykel AFF-I10
Skydiving Priorities: 1) Open Canopy. 2) Land Safely. 3) Don’t hurt anyone. 4) Repeat…

[slotperfect 7]

Well said.

Everyone: please use the threads here and in Bonfire that AFFI has resurrected to educate yourselves and - if you wish - add content that has not already been discussed. Please do not use them to spin up and recover old ground on this well-discussed (but very important) subject.

Arrive Safely

John

[DBCOOPER 1]

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Short answer:

The reason people THINK it works is it makes them stick their head outside the plane and try to figure out what 45 degrees looks like. After a few seconds they either:

1) decide they think the group is at 45 degrees, even though it isn't

2) give up because they don't want to look stupid

3) give up because everyone else is screaming "GO! GO!"

But in all 3 cases, they waste 5-10 seconds, and that's enough (usually) to give them safe separation.

I knew there had to be a reason so many think it works

Replying to: Re: Stall On Jump Run Emergency Procedure? by billvon

If the plane is unrecoverable then exiting is a very very good idea.

[apoil 0]

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But in all 3 cases, they waste 5-10 seconds, and that's enough (usually) to give them safe separation.

--
I knew there had to be a reason so many think it works

So, ironically, waiting for a 45degree angle doesn't work but TELLING someone to wait until there's a 45 degree angle may well guarantee you the proper separation. The rest of the load gets hosed, but at least no one comes through your canopy.

It may even be more effective to tell them that than to tell them to wait 10 seconds. Nearly everyone counts seconds way too fast on jump run.

[kallend 1,619]

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But in all 3 cases, they waste 5-10 seconds, and that's enough (usually) to give them safe separation.

--
I knew there had to be a reason so many think it works

So, ironically, waiting for a 45degree angle doesn't work but TELLING someone to wait until there's a 45 degree angle may well guarantee you the proper separation. The rest of the load gets hosed, but at least no one comes through your canopy.

It may even be more effective to tell them that than to tell them to wait 10 seconds. Nearly everyone counts seconds way too fast on jump run.

Digital clocks are cheap. Why not velcro one by the door to solve that problem.

...

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

[billvon 2,379]

>Digital clocks are cheap.

How about just flashing the green light once a second? Would get people's attention better, as well.

[kallend 1,619]

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>Digital clocks are cheap.

How about just flashing the green light once a second? Would get people's attention better, as well.

Or you could recite:

"One flea found on Kallend's dog
Two fleas found on Kallend's dog
Three fleas found on Kallend's dog
Four fleas found on Kallend's dog
..."

...

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

[matthewcline 0]

The only issue with using a count is that "time" is not a guarantee of separation. Distance is though.

I don't dispute Bill or Kallend's knowledge and expertise just posting a tag along to their discussion.

An Instructors first concern is student safety.
So, start being safe, first!!!

[kallend 1,619]

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The only issue with using a count is that "time" is not a guarantee of separation. Distance is though.

I don't dispute Bill or Kallend's knowledge and expertise just posting a tag along to their discussion.

Distance with respect to what? Not the ground.

Winsor once made a very nice analysis of jumping from a balloon blowing along in a strong wind aloft. Although successive jumpers leave after appropriate DISTANCE over the ground has been covered, they all open in the same place.

Alternately, jumpers from a tethered balloon in the same wind all exit over the same spot on the ground, but have good separation on opening.

The only distance that counts is the distance with respect to the air at opening altitude, and you can't see that!

Edited to add link to Winsor's analysis:

www.koyn.com/clouddancer/articles/jmprun98.html

...

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

[JohnMitchell 14]

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The only distance that counts is the distance with respect to the air at opening altitude, and you can't see that!

How about with an aerodometer right nest to the door?

Seriously, I will stand by the door and count "one one thousand, two one thousand . . .", ticking it off on my fingers before the climbout. Remember, too, for most launches involving grips and counts and more than 2 people, a 5 second wait before climbing out should give you an easy 10 second separation, since it almost always take 5 seconds or more to climb out, get grips and give the count.

[kallend 1,619]

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The only distance that counts is the distance with respect to the air at opening altitude, and you can't see that!

How about with an aerodometer right nest to the door?

Seriously, I will stand by the door and count "one one thousand, two one thousand . . .", ticking it off on my fingers before the climbout. Remember, too, for most launches involving grips and counts and more than 2 people, a 5 second wait before climbing out should give you an easy 10 second separation, since it almost always take 5 seconds or more to climb out, get grips and give the count.

I think the issue is not that you can't count seconds accurately, but that some people can't when excited/stressed. Additionally, they may not know how long to wait anyway, or they have been given bad information and don't know it's bad.

In addition to hearing an instructor tell a group of newbies to use the 45 degree myth this year, I also was on a plane this year when the pilot told everyone to leave just a 3 second delay!

For less than $20 you could get a cheapo digital clock or as Bill suggested, a flashing green light by the door.

...

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

[matthewcline 0]

I presumed distance between groups, for this discussion.

An Instructors first concern is student safety.
So, start being safe, first!!!

[billvon 2,379]

>The only issue with using a count is that "time" is not a guarantee of
>separation. Distance is though.

Definitely true. Distance is speed x time, so you have to know what speed you're moving with respect to the groups that have just opened to know how much time to leave. Which is why knowing the upper winds (and ideally the winds at opening altitude as well) is important.

[kallend 1,619]

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I presumed distance between groups, for this discussion.

OK, back to my question: measured WHERE? The only distance that matters is the one at opening altitude, and you can't measure that while still in the plane.

...

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

[matthewcline 0]

Distance at opening is the right as usual Prof.

I guess that is where we use SWAG.

Between you and I we have experience and can teach all the "tricks" to our students, as this discussion is proving (to me at least) that there is no exact science to it, but some good scientific applications.

I think I actually agree with you and Billvon, but must be missing how to state it right now.

An Instructors first concern is student safety.
So, start being safe, first!!!

[tdog 0]

A couple weekends ago... The uppers were so strong that we had nearly 1 minute pauses between climbouts - yet the winds at the ground were light and variable.

I joked that - if the uppers picked up any stronger, we would simply "backup the plane" onto jump run, slow it down a bit, and have a ground speed of negative something, and do a backwards jump run. Actually, with an otter's normal jumprun speed, this was a real possibility, but we were flying a king air.

Seriously though - this opened a whole new can of worms as a canopy can go pretty far in a minute, so a freefall/canopy collision became a concern if anyone opted to deploy considerably lower than another group that just flew "a hair" up jumprun. This opens a whole 'nother can of worms of discussion - with real long pauses and skydivers not taking into consideration how long the groups are waiting - how easy it is to fly in another skydivers freefall space. Typically with 10 seconds delays, you cant get your canopy that far... Within a minute, you better be setting up your landing especially with a canopy that is fast, so waiting in your own airspace for so long becomes difficult.

I did not appreciate all the risks until the end of the day and I started thinking it thru.

[billvon 2,379]

>so waiting in your own airspace for so long becomes difficult.

You shouldn't have to do that! Separation should take into account freefall drift and canopy flight away from the center of the formation at breakoff. If you find yourself having to 'steer away' from the next group - leave more time on the next jump. (Or more accurately ask them to leave more time.)

[tdog 0]

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>so waiting in your own airspace for so long becomes difficult.

You shouldn't have to do that! Separation should take into account freefall drift and canopy flight away from the center of the formation at break off. If you find yourself having to 'steer away' from the next group - leave more time on the next jump. (Or more accurately ask them to leave more time.)

Ya - but a canopy, in a minute, can fly almost the full length of a DZ landing area. If you opt to land at the peas, instead of right under where you opened - you are going to have to "invade" someone else's airspace eventually...

In a normal upper situation - you can fly off jump run until you are confident the next group is open, and you will see them open maybe 10 seconds later.

In a VERY high upper situation - if you fly off jump run for a minute waiting for the next group to open, you may be so far off the DZ that getting home is not an option. We are talking extremes here....

If the plane takes a minute to fight headwinds and cover 1000 horizontal feet on the ground/canopy opening altitude, and you like 1000 feet separation - then all of a sudden you need to take into consideration how far a canopy can fly in a minute - which is quite far - which means now each group might need many thousands of feet assuming...

Now, there becomes a point where the group before you has already landed (like a few weekends ago, where group one was already landed when my group was opening due to how long we waited between groups) - so unless you hum it so low your cypres is going to fire, you still are going to have separation on the vertical axis as the group below you is landing or on final...

BTW - I think our ground speed was 15 MPH (give or take) per the GPS. That is 45 seconds between groups for 1000 feet separation. That means the canopy at 3000 feet with no winds was actually flying faster over the ground up jump run than the plane fighting the super strong uppers! If I am not mistaken by high school level math - that means the first jumper out, if they wanted to, with a middle of the road 20MPH canopy could have flown up jump run and been completely under any group they wanted to be under - with the only limitation that eventually their own canopy must land eventually - because they were covering more ground than the plane. In this case, the only way to achieve absolute horizontal separation, regardless of which way canopies were going to randomly fly - would be to wait until the canopy landed.