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

[rehmwa 2]

Quote

At the risk of repeating myself:
www.iit.edu/~ugcol/separation.zip

repetition is how people learn things
repetition is how people learn things
repetition is how people learn things

further, I don't think you've ever had any issue repeating yourself

...
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

[david3 0]

Quote

Quote

At the risk of repeating myself:
www.iit.edu/~ugcol/separation.zip

I think they should put that into the SIM.
But then, being the cynical fuck that I am, how many actually read the SIM these days.

What is this SIM you speak of?

Edit to add

[GreenLight 7]

Quote

I might be wrong here but I don't think I am. No one reading this thread is concerned with getting a degree, they just want to get out of the aircraft, make it back to the DZ and not fall through one another while in freefall. Most people don't know how their TV works but they know what buttons to push to get it to do what they want.

Thanks for that LouDiamond. I have read the first 7 pages and now have a tremendous headache. I'm interested in this thread due to an incident that happened last week. Scared the bejesus out of the entire otter load as we all opened up in the same column of air barely missing each other and we have lots of video to show it. We are talking lots of near misses of only a couple of feet.

After over twenty years of jumping this is the scariest jump I have lived through. 1st load of the day. On the way up we asked the pilot for uppers. 10 out of the west was the answer. It was wrong. He got the uppers at a lower altitude than jump run altitude. At altitude we later found out they were 130 knots. Needless to say we all ended up on top of each other and it was a miricle no one was injured or killed.

I have always used my own eyes and my own math to figure out seperation and it has worked well over the years. I tend to go with Bill Von on this one. Of course you need GOOD information for any of this to work.

My main point is that no one is too experienced to die and no one is too old to learn. We all made a potentially disasterous mistake that day and if not for plain luck, you might be reading about the most horrific free fall accident in history now instead of this post. So I am very motivated to learn all I can from this thread and others like it.

Now for the next 5 pages...

Green Light
"Harry, why did you land all the way out there? Nobody else landed out there."
"Your statement answered your question."

[Squeak 17]

Quote

***After over twenty years of jumping this is the scariest jump I have lived through. 1st load of the day. On the way up we asked the pilot for uppers. 10 out of the west was the answer. It was wrong. He got the uppers at a lower altitude than jump run altitude. At altitude we later found out they were 130 knots. Needless to say we all ended up on top of each other and it was a miricle no one was injured or killed.

No one actually LOOKED at the ground and said, Um we're going a bit slower than we should be for 10knotts?

You are not now, nor will you ever be, good enough to not die in this sport (Sparky)
My Life ROCKS!
How's yours doing?

[GreenLight 7]

Quote

Quote

***After over twenty years of jumping this is the scariest jump I have lived through. 1st load of the day. On the way up we asked the pilot for uppers. 10 out of the west was the answer. It was wrong. He got the uppers at a lower altitude than jump run altitude. At altitude we later found out they were 130 knots. Needless to say we all ended up on top of each other and it was a miricle no one was injured or killed.

No one actually LOOKED at the ground and said, Um we're going a bit slower than we should be for 10knotts?

Exactly... We were second group out of an otter. 4 way including camera. Almost fatal mistake on our part. Obviously no one behind us looked either. We had a little pow wow in the LZ immediately after. Again we were very lucky... Here are both vids to show you just how lucky we were. Watch the canopies come up. We all felt pretty stupid and very lucky afterwards.

http://www.youtube.com/watch?v=wG99kloOhi8

http://www.youtube.com/watch?v=5a9t8Bu0yl8

Green Light
"Harry, why did you land all the way out there? Nobody else landed out there."
"Your statement answered your question."

[champu 1]

Quote

Quote

On the way up we asked the pilot for uppers. 10 out of the west was the answer. It was wrong. He got the uppers at a lower altitude than jump run altitude. At altitude we later found out they were 130 knots.

No one actually LOOKED at the ground and said, Um we're going a bit slower than we should be for 10 knots?

"Yeah, and on top of that, the ground is going by in the wrong direction."

[GreenLight 7]

Quote

"Yeah, and on top of that, the ground is going by in the wrong direction."

Actually if the plane had been going backwards we might have had some seperation LOL. Those videos are of the same dive. We all went zinging through canopies on opening. We normally always look at the exit before us. I don't know what happened this time.

Green Light
"Harry, why did you land all the way out there? Nobody else landed out there."
"Your statement answered your question."

[Sadist 0]

Frikken scary.

[rehmwa 2]

Quote

At altitude we later found out they were 130 knots. Needless to say we all ended up on top of each other and it was a miricle no one was injured or killed.

here's the really neat thing -

if it was 10 knots - the view of the group before you would look EXACTLY the same as if it was 130 knots - as you know, the exact thing that's wrong about any visual reference concept such as 45DegRule - dramatic wind days like this are a great time to demonstrate the falsity.

just two weeks ago, I noted the dive angle to a formation and how it was extra nice due to a good launch of the base (funnels are steeper due to the extra throw). One rather experienced jumpers noted that it was 'really' due to the high uppers, not the exit - another jumper supported this. one got mad when I tried to explain reality that we all were leaving from the same plane, so the uppers had nothing to do with it - so I just gave up and walked away

...
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

[GreenLight 7]

Quote

if it was 10 knots - the view of the group before you would look EXACTLY the same as if it was 130 knots - as you know, the exact thing that's wrong about any visual reference concept such as 45DegRule - dramatic wind days like this are a great time to demonstrate the falsity.

I believe you. Im going to be watching with different amounts of upper winds just to satisfy my curiosity now as I have always relied on the visual effect plus some counting. My group is reading this entire thread along with me and we are going to discuss it this weekend. Sort of an emergency safety day. From now on it's the time calcs that we will be using such as what Billvon spoke of.

Thanks all for this thread.

By the way. Yesterday I happened to go outside to watch the sunset and overheard one of the packers talking to a newbie and explaining the importance of using the 45 degree rule. What a coincidence eh?

Green Light
"Harry, why did you land all the way out there? Nobody else landed out there."
"Your statement answered your question."

[Remster 30]

Quote

overheard one of the packers

Did you slap him across the back of the head? Or maybe even better, tell the newbie the real deal?


By the way, props for posting your mistake. As you said, fortunately, no one died, and it would have been easy to make this a non issue by checking the spot/speed looking out the door. We all can be reminded of that once in a while...

Remster

[rehmwa 2]

a legit "visual reference" is the ground - you can estimate ground speed and gage "time between groups". But this has a lot of assumptions associated with it (lower grounds than uppers, relative wind directions, etc etc etc)

...
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

[LouDiamond 1]

WOW, this issue is like a social disease, it always comes back. I will say that if you want to read all about this to do a search and you can spend hours reading people argue about it. Frankly, it's scary how many people don't have a clue on this issue. I've attached a Excel doc that you can download, print and laminate and tape next to the door of your A/C for reference. It is quick and easy to use and ends debates on the A/C.


Excel sheet can be seen HERE

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[Southern_Man 0]

Quote

I've attached a Excel doc that you can download, print and laminate and tape next to the door of your A/C for reference. It is quick and easy to use and ends debates on the A/C.

We have a chart like this (maybe even this exact one but I can't be sure without it in front of me) next to the door of our Otter. Works great, Thanks!

"What if there were no hypothetical questions?"

[rehmwa 2]

since most RW and FF teams can't even do their little "pause, shake, pause, breathe, compose, shake, GO" thing in less than 10 seconds anyway, we're pretty safe unless it's really honking up top anyway

...
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

[GreenLight 7]

Quote

Quote

overheard one of the packers

Did you slap him across the back of the head? Or maybe even better, tell the newbie the real deal?


By the way, props for posting your mistake. As you said, fortunately, no one died, and it would have been easy to make this a non issue by checking the spot/speed looking out the door. We all can be reminded of that once in a while...

I really felt like doing that but I am one of those "old guys" who doesn't have a clue as far as he is concerned. Not having an instructors rating I would be shot down in flames immediately.

I was a little leary of posting our mistake for all to see but I really don't want other skydivers to have to learn this the hard way as we did. This could have been disasterous so I'm not ashamed to admit our mistake. I hope we can all learn from this.

Now I'm going to download that PDF file, and thanks again for all the info. I will be talking to our DZO about this as well.

Green Light
"Harry, why did you land all the way out there? Nobody else landed out there."
"Your statement answered your question."

[winsor 236]

Quote

WOW, this issue is like a social disease, it always comes back. I will say that if you want to read all about this to do a search and you can spend hours reading people argue about it. Frankly, it's scary how many people don't have a clue on this issue. I've attached a Excel doc that you can download, print and laminate and tape next to the door of your A/C for reference. It is quick and easy to use and ends debates on the A/C.


Excel sheet can be seen HERE

Ground speed works okay for normal operations (jump run into the wind, winds constand direction and increasing with altitude), and it is "close enough for Government work," but I still flinch at its fundamental theoretical inaccuracy.

Admitted, it is better than the "45 degree rule," but there are cases where it is just plain wrong, and could get you into trouble if you used groundspeed as your sole basis - which the spreadsheet does.

I suppose dumbing down the process has much to recommend it, and it could be argued that it's better than nothing, but I would prefer a treatment where the fundamentals are presented, and the fast and dirty approach is given with appropriate disclaimers.

The Excel spreadsheet is a fast and dirty approximation that works reasonably well most of the time. There are, however, very real circumstances where is is entirely inaccurate.


BSBD,

Winsor

[rehmwa 2]

Quote

Ground speed works okay for normal operations (jump run into the wind, winds constant direction and increasing with altitude),

those are the assumptions......

still nice to train everyone on the why's, so they can adjust when the conditions aren't like this (many places, those conditions are true 90+% of the time - others? not as much....)

that said, I like that chart anyway

...
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

[pchapman 279]

Quote

The Excel spreadsheet is a fast and dirty approximation that works reasonably well most of the time. There are, however, very real circumstances where is is entirely inaccurate.

Maybe then we just need a short list of caveats to be added to the spreadsheet.

Something like: "Do not use table, and consult DZ management if: 1. Jump run is not upwind, 2. ...."

It's common enough for math to describe a real world situation accurately enough, but only within certain boundaries -- and we often forget those boundaries and assumptions.

[GreenLight 7]

Question... Is it the GPS that tell's the pilot the ground speed?

Green Light
"Harry, why did you land all the way out there? Nobody else landed out there."
"Your statement answered your question."

[rehmwa 2]

Quote

Question... Is it the GPS that tell's the pilot the ground speed?

If they have GPS, I suspect that's a good source.

It doesn't hurt to be able to look out the door and be able to gage it yourself. A little practice at this helped me a lot. "Hey guys, we're really crawling along - take about 15 (20, 30, 45) between" "Hey, we're screaming. You can climb out normal right away." etc

Our pilot calls out ground speed, but I still always check (out the door or out the window) anyway.

...
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

[popsjumper 2]

Quote

Ground speed works okay for normal operations (jump run into the wind, winds constand direction and increasing with altitude), and it is "close enough for Government work," but I still flinch at its fundamental theoretical inaccuracy.

Maybe you could give examples, including the math, of why it doesn't work for other conditions?

Basically, if I exit with 1000 ft separation from the previous group, how is it that I won't be 1000ft away at opening?
(Assume same discipline, same fall rate, same opening altitude)

My reality and yours are quite different.
I think we're all Bozos on this bus.
Falcon5232, SCS8170, SCSA353, POPS9398, DS239

[popsjumper 2]

Quote

Question... Is it the GPS that tell's the pilot the ground speed?

Or, you could stick your head out the door and see that it took X seconds to travel Y feet over the ground.

My reality and yours are quite different.
I think we're all Bozos on this bus.
Falcon5232, SCS8170, SCSA353, POPS9398, DS239

[winsor 236]

Quote

Quote

Ground speed works okay for normal operations (jump run into the wind, winds constand direction and increasing with altitude), and it is "close enough for Government work," but I still flinch at its fundamental theoretical inaccuracy.

Maybe you could give examples, including the math, of why it doesn't work for other conditions?

Basically, if I exit with 1000 ft separation from the previous group, how is it that I won't be 1000ft away at opening?
(Assume same discipline, same fall rate, same opening altitude)

Since it is a four-dimensional continuum mechanics problem, the math would not be all that useful to anyone whose math & physics background is short of a solid master's.

Here is Tammy Koyns transcription of my Descent Kinematics seminar notes, where I tried to use graphical representation of limiting cases to get the point across.

John Kallend did a marvelous job of addressing the subject, so I did not develop it further.

The bottom line is that:

1) There is a finite minimum time that groups should take between exits at a given airspeed to provide sufficient horizontal separation out the door.

2) Additional time may be ADDED to account for lower speed of the aircraft with regard to the airmass at opening altitude.

3) What the ground is doing is, in and of itself, irrelevant to what objects are doing in freefall. Groundspeed may be used on a "rule of thumb" basis, but its physical relationship to maintaining separation is incidental.


BSBD,

Winsor

[rehmwa 2]

Quote

Since it is a four-dimensional continuum mechanics problem, the math would not be all that useful to anyone whose math & physics background is short of a solid master's.Nonsense, it's just bookkeeping of wind layers and directions to track drift of groups that leave at different times - you don't have to integrate if you just track a couple layers (exit and opening (ground-another assumption)) or more - it doesn't take a masters degree to determine distance traveled at a constant velocity. throw has a deceleration term, I guess if you want to be retentive, but for people just wanting to jump that can't really count at an even pace that take 10 seconds to climb out but think they take 3? seriously


John Kallend did a marvelous job of addressing the subject, so I did not develop it further.absolutely, and the Omniscore application showed his stuff explicitly


3) What the ground is doing is, in and of itself, irrelevant to what objects are doing in freefall. Groundspeed may be used on a "rule of thumb" basis, but its physical relationship to maintaining separation is incidental. but what the ground is doing relative to airplane gives a great indication of the delta between the lowers and the uppers - which absolutely does relate to separation at opening time - it's the entire basis of the discussion - we aren't concerned about separation in freefall, we are concerned about separation at opening time - I agree, this is still in the air - but saying 'groundspeed is not important' is misleading because we are implying that groundspeed is closer to winds at opening altitude

Since we are not calculating orbital mechanics requiring precision to the 20th decimal place, then instead of complicating it for newbies to make ourselves feel smart, we should keep it basic.

So the simplified chart is great - and yes, lot of 'standard' assumptions. I have issues with it only in the case when the assumptions are off. Example - lowers and uppers are in completely different directions. Cross wind or downwind jumpruns, high openings, etc etc etc. Mixed up exit orders (like FF before belly, etc).

...
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