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

 

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CrazyL  (D 17699)

Sep 7, 2007, 7:36 PM
Post #151 of 364 (2226 views)
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Re: [AFFI] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

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In reply to:
the 45 degree deal should be discarded entirely.
Quote:
I know what i do to try to keep others from killing me while skydiving.
Takes me back to an earlier inquire concerning the number of fatalities directly attributable to poor exit separation how many have there been?

Freefall collisions? Canopy collisions? Malfunctions created by close proximity?

Would it be impossible to ascertain such a fact?


Perhaps the salient point that CrazyL is potentially suggesting is that the utilization of the 45 degree method of teaching and obtaining separation is here to stay - like it, believe in it or otherwise. It is in use across the board by very experienced individuals in the skydiving arena. Is that such a bad thing?
Whether it is correct or not, is there evidence that utilization of such a philosophy has created enough if any fatalities to suggest that we should be so concerned about it? Maybe that is the question we should be asking? Maybe not?
Maybe the 45 degree myth is here to stay, i'm a bit afraid of that. Have there been any fatalitues due to jumpers who used the 45 degree myth and/ or the 10 seconds for separation?


CrazyL  (D 17699)

Sep 7, 2007, 7:51 PM
Post #152 of 364 (2222 views)
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Re: [rehmwa] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

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Does Perris really advocate that method?

Knowing so many people there, I really doubt it.

The fact you learned little from the post is due to you. Summary - The 45 has no basis in how people fall and separate in freefall. That's the lesson. That one can still use it to force someone to stop and look and pause for a moment is interesting, and might be better than nothing. But it is no more than just assigning a single delay time that doesn't consider real wind conditions - and, leaving that time arbitrarily up to each jumper.

Look at the winds, check the plane's ground speed on jump run, pick an exit separation that matches. It's not hard to do, it's not hard to learn. SDAZ has the generic rules posted inside the airplane even.

For odd jump run directions and wind conditions, then maybe have someone smarter about it figure it out and get it announced.

The conviction comes from seeing people that use the 45 degree rule falling past me and my friends in freefall because they didn't wait enough on a high uppers wind day. The conviction comes from seeing that happen around my wife and friends. The 45 degree thing would have them exit with the same delay on a low wind day as on a VERY high wind day (relative to the ground winds).

You bet I'm motivated to teach people how to do it right. You bet I'm motivated to eliminate stupid and dangerous old timer 'rules' that don't work.

Get us started on exit order. The 45 degree attitude also leads you wrong on that too.
You know, I think you and I both are after the same thing. Probably using similar techniques. Maybe you feel strongly that I solely believe and use the 45 degree myth, your wrong if thats the case. Sounds like you and/or your wife and friends have nearly been killed by freefallers that should have given you more separation. You know what, me too. Has happened a few times. The worst case was when an 8 way rw went after me and a buddy freeflying. Jumprun into the wind on a high wind day. I opened and travelled crosswind then turned upwind. There was an eerie sound then 8 freefallers one on each and every side of my canopy. They must have broken off and began tracking directly above me, thank god they missed me. Yes I was scared shitless and thought I was about to get hit and die right there. Something changed that day, it was exit order. This 45 degree myth sucks yet seems to work. Is there any other 'easy to understand' concept that 'works really well'. I understand the separation deal. You should not be worried if i'm exiting after you. It's the newbies who count fast who I can tell that the f!@#$cker is going to exit too close to me and my group that I would like to feel comfy with. Call Perris and find out what method they advocate. And know the difference between 'post' and 'thread'. No need to summarize the 'thread' for me but it is nice of you, thanks.


pilotdave  (D License)

Sep 7, 2007, 8:35 PM
Post #153 of 364 (2210 views)
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Re: [CrazyL] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

Quote:
This 45 degree myth sucks yet seems to work. Is there any other 'easy to understand' concept that 'works really well'.

Saw this used not too long ago on a very windy day (uppers). Experienced jumper in my group said to the newbie exiting behind us: "The winds are very strong today... we're barely moving over the ground. Give us 18 seconds before you exit. Yes, 18. Count all the way to 18 after we leave the plane, then exit. 18 seconds. 18...."

That was repeated a few times on the way up. Very simple. And it worked just fine.

Are you arguing that the 45 degree rule isn't a bad idea since freefall collisions are rare even when it's used and it's simple? That's what I'm reading... hopefully I'm wrong.

Dave


(This post was edited by pilotdave on Sep 7, 2007, 8:37 PM)


AFFI  (D 25538)

Sep 7, 2007, 10:57 PM
Post #154 of 364 (2188 views)
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Re: [CrazyL] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

[reply Sounds like you and/or your wife and friends have nearly been killed by freefallers that should have given you more separation.
Nope...

I have had em close enough to see the whites of their eyes, but that is just part of the risk we take and I personally do not consider that too close for my comfort.
Maybe I spent too many years racing high performance bikes but too close is if they leave some skin on my ring sight! Anything else is just a cool moment.

I remember about 6 years ago I was in DeLand and a jumper approached me in the packing tent to apologize, and to thank me for not chewing his ass for blazing past me in freefall. I just chuckled and said it was not close enough to swap spit, no worries - then proceeded to have a talk about stuff, like separation and beer. It was a good time and the video was priceless - whites of his eyes

No need to get worked up, calm is best, at least for me - And it is easier to gain an audience that way...

The only big deal is the one that kills ya and you wont even see that one coming unless your lucky!

A lot of folks (yes I said folks) say "no worries", but how many actually mean it? I don't fuss about the 45 thing because I am not going to change the minds of thousands of skydivers who use it - all I can do is get lucky every now and then and educate someone willing to consider my point of view. I find it comical that people get their panties in a wad over it - so it is not what is isnt, so what?

How many people have been killed by it?
That is the question that the ranters do not seem to have an answer for eh?


(This post was edited by AFFI on Sep 7, 2007, 11:39 PM)


Premier billvon  (D 16479)
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Sep 8, 2007, 1:12 PM
Post #155 of 364 (2141 views)
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Re: [rehmwa] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

> Does Perris really advocate that method?

Yes, some people at Perris still do, and they're influential enough that people listen to them.


Premier billvon  (D 16479)
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Sep 8, 2007, 1:14 PM
Post #156 of 364 (2140 views)
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Re: [CrazyL] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

>Is there any other 'easy to understand' concept that 'works really well'.

"If you get farther forward in the plane it climbs faster." It usually doesn't; indeed, most aircraft climb a bit slower. But it helps with weight and balance on jump run, and in an aircraft emergency it's generally better to have weight a bit too far forward than a bit too far back.


CrazyL  (D 17699)

Sep 9, 2007, 7:00 PM
Post #157 of 364 (2093 views)
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Re: [AFFI] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

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all I can do is get lucky every now and then and educate someone willing to consider my point of view.
You know what, that's what i'm looking forward to reading here. Even from remwa. Not looking for a rant. Looking for another jumpers point of view and opinion. Looking for those real life stories of how close calls due to lack of separation. In the past i've learnes quite a bit sitting around the bonfire sip'n beers and listening to the older jumpers tell black death stories. Some of the stories give the 'reason to'... 'cause someone nearly/or did get injured or killed doing it. And I definately agree about the visit after such an occurence. No need to be ugly and rude. That just pisses most people off and all they hear then is ugly and rude. Being calm and educational seems to work well.


CrazyL  (D 17699)

Sep 9, 2007, 7:12 PM
Post #158 of 364 (2089 views)
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Re: [rehmwa] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

In reply to:
Does Perris really advocate that method?

Knowing so many people there, I really doubt it.
Summary - The 45 has no basis in how people fall and separate in freefall.
In reply to:
So did you call or visit Perris, did you read any of the latest posts? Do you still doubt. So you don't believe me. who cares. I don't believe you know 'so many people at Perris, if you do you've never dicussed this thing about separation. I'll tell you how the 45 degree myth works. It makes the next group hang out in the door for a period of time and watch the group in front of them fly away. Does it give 'proper' separation. Maybe, maybe not. Have you ever did a BASE jump? 3 second delay? On your first 'freefall ' BASE jump, how fast did you count? I'd bet if you've ever had the balls to do a first 'freefall' BASE jump you counted really fast, and probably went head down. My point is about the 'counting' it works too. Newbie being all excited will count to 10 faster than what 10 seconds is, i'll bet you. So what is a sure fire way to get separation between you and the newbie? For me it's let them go in front of me so I have control of the separation when it's possible for me to let them by.


CrazyL  (D 17699)

Sep 9, 2007, 7:15 PM
Post #159 of 364 (2088 views)
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Re: [billvon] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

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>Is there any other 'easy to understand' concept that 'works really well'.

"If you get farther forward in the plane it climbs faster." It usually doesn't; indeed, most aircraft climb a bit slower. But it helps with weight and balance on jump run, and in an aircraft emergency it's generally better to have weight a bit too far forward than a bit too far back.
I believe it. But in a Cessna 182, leaning forward on take off, what does that do? Does it help with lift in any way. We did that 'lean forward on take off' a whole lot jumping 182's.


Erroll

Sep 10, 2007, 4:04 AM
Post #160 of 364 (2052 views)
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Re: [AFFI] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

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...too close is if they leave some skin on my ring sight!

Priceless!Wink


pilotdave  (D License)

Sep 10, 2007, 5:14 AM
Post #161 of 364 (2060 views)
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Re: [CrazyL] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

Quote:
But in a Cessna 182, leaning forward on take off, what does that do? Does it help with lift in any way.

No, leaning forward hurts lift. That doesn't necessarily mean it's a bad idea to lean forward on takeoff, but it will increase takeoff distance and reduce the climb rate. Probably such a small amount you'd never notice, but it will happen.

Moving the center of gravity forward means the horizontal stabilizer has to produce more "negative lift" to keep the nose up. The total amount of lift the wings need to make in order to get off the ground and climb has to go up to compensate for the higher stabilizer load. It's perfectly equivalent to adding weight to the plane.

The other part of it is that in order to get the nose up, more elevator is needed. That makes more parasite drag. The higher lift from the wings and stabilizer produces more induced drag as well.

But none of that matters if the plane is outside its center of gravity limits. If the center of gravity is too far aft, the plane will be unstable in pitch and stall recovery might become impossible. But if the difference between being inside the limits and outside the limits is the way the jumpers lean, there's something wrong.

Myth Busted.

Dave


(This post was edited by pilotdave on Sep 10, 2007, 5:14 AM)


rehmwa  (D 12816)

Sep 10, 2007, 7:17 AM
Post #162 of 364 (2039 views)
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Re: [CrazyL] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

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So did you call or visit Perris, did you read any of the latest posts? Billvon answered that one, sad enough .......I'll tell you how the 45 degree myth works. It makes the next group hang out in the door for a period of time and watch the group in front of them fly away. that's exactly what I noted on the post where I summarized your position but at that time you took exception to it because I mocked it Have you ever did a BASE jump? just the one, I counted slow, but only took 5 counts instead of the 7-8 the others were, the exit was fine and head up, though another guy did go head down - I still watch the vid once in a while, it's was very fun ....... So what is a sure fire way to get separation between you and the newbie? For me it's let them go in front of me so I have control of the separation when it's possible for me to let them by. you got that right, those that can't/won't learn can just go first, as long as exit order isn't compromised - you noted the problem that can cause

blues - we're on the same side, but I think you can do it without using a negligent and flawed concept.

(AFFI - you must be the most coolest and extreme skydiver on the planet. "skin on the ringsight" LaughLaughCrazy I bet women want you and men want to be like you.)


(This post was edited by rehmwa on Sep 10, 2007, 7:17 AM)


CrazyL  (D 17699)

Sep 10, 2007, 5:27 PM
Post #163 of 364 (1991 views)
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Re: [pilotdave] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

In reply to:
Quote:
But in a Cessna 182, leaning forward on take off, what does that do? Does it help with lift in any way.

No, leaning forward hurts lift. That doesn't necessarily mean it's a bad idea to lean forward on takeoff, but it will increase takeoff distance and reduce the climb rate. Probably such a small amount you'd never notice, but it will happen.

Moving the center of gravity forward means the horizontal stabilizer has to produce more "negative lift" to keep the nose up. The total amount of lift the wings need to make in order to get off the ground and climb has to go up to compensate for the higher stabilizer load. It's perfectly equivalent to adding weight to the plane.

The other part of it is that in order to get the nose up, more elevator is needed. That makes more parasite drag. The higher lift from the wings and stabilizer produces more induced drag as well.

But none of that matters if the plane is outside its center of gravity limits. If the center of gravity is too far aft, the plane will be unstable in pitch and stall recovery might become impossible. But if the difference between being inside the limits and outside the limits is the way the jumpers lean, there's something wrong.

Myth Busted.

Dave
Thanks for busting the myth Dave. So does leaning forward help stall recovery if the a/c were to possibly stall on take off?


CrazyL  (D 17699)

Sep 10, 2007, 5:34 PM
Post #164 of 364 (1990 views)
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Re: [rehmwa] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

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In reply to:
So did you call or visit Perris, did you read any of the latest posts? Billvon answered that one, sad enough .......I'll tell you how the 45 degree myth works. It makes the next group hang out in the door for a period of time and watch the group in front of them fly away. that's exactly what I noted on the post where I summarized your position but at that time you took exception to it because I mocked it Have you ever did a BASE jump? just the one, I counted slow, but only took 5 counts instead of the 7-8 the others were, the exit was fine and head up, though another guy did go head down - I still watch the vid once in a while, it's was very fun ....... So what is a sure fire way to get separation between you and the newbie? For me it's let them go in front of me so I have control of the separation when it's possible for me to let them by. you got that right, those that can't/won't learn can just go first, as long as exit order isn't compromised - you noted the problem that can cause

blues - we're on the same side, but I think you can do it without using a negligent and flawed concept.

(AFFI - you must be the most coolest and extreme skydiver on the planet. "skin on the ringsight" LaughLaughCrazy I bet women want you and men want to be like you.)
I'm with you man. AFFI must be.... Ya, i'd like the concept of separation to be taught well and true, similar to EP's. I did'nt check but are you an instructor, i'm not. Reason i ask is that is there anything on the A license proficiency requirements card that has to do with exit separation and exit order? I'm thinking about sitting through a first jump course and check out how jumpers are being trained these days.


pilotdave  (D License)

Sep 10, 2007, 7:27 PM
Post #165 of 364 (1973 views)
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Re: [CrazyL] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

Quote:
Thanks for busting the myth Dave. So does leaning forward help stall recovery if the a/c were to possibly stall on take off?

Well, if the CG was within limits, leaning forward probably wouldn't be necessary. If the CG was so far aft of limits that it caused a stall, leaning probably wouldn't help. Wouldn't hurt either, I guess. I don't know how much you could possibly shift the CG (in a 182) by leaning one way or the other. I'd guess (and hope) not very much.

Dave


winsor  (D 13715)

Sep 11, 2007, 5:24 PM
Post #166 of 364 (1888 views)
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Re: [LouDiamond] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

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The conviction comes from seeing people that use the 45 degree rule falling past me and my friends in freefall because they didn't wait enough on a high uppers wind day. The conviction comes from seeing that happen around my wife and friends. The 45 degree thing would have them exit with the same delay on a low wind day as on a VERY high wind day (relative to the ground winds).

<snip>

I have included a excel spreadsheet that breaks what time to use down based on aircraft ground speed, <snip>

Though it is better than the "45 degree rule" from the standpoint of exit separation, the dependence upon ground speed to achieve separation is only marginally so.

A rigorous treatment includes ground speed minus winds at opening altitude, which gives the speed of the aircraft with regard to the air mass at opening altitude. In this calculation ground speed cancels out, and is thus not a factor either way.

Using the straight "ground speed" approach with stiff uppers out of a very slow aircraft (say a Chinook making just a few knots of airspeed) on a downwind jump run, you could put out successive groups over a long stretch of real estate, but they would be right on top of each other in the air.

The point is not what piece of ground you're over - that's spotting. Where you are with regard to other groups in the air is separation, and it is a function of airmass only. Quite what you are or are not doing with regard to the ground is immaterial to the issue of staying apart in the air.

Having taught Physics I am quite used to how people do not grasp why the "45 degree rule" does not work. I am also used to how people do not comprehend how ground speed is irrelevant to separation in the air.

From a practical standpoint, I am just as happy with someone who achieves sufficient separation with 45 degrees or ground speed as I am with someone who understands the physics involved.

On the other hand, if you claim that 45 degrees or groundspeed has anything directly to do with why, I am more than happy to point out exactly how and why you are quite wrong.


Blue skies,

Winsor


Premier LouDiamond  (D 25931)
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Sep 11, 2007, 7:56 PM
Post #167 of 364 (1869 views)
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Re: [winsor] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

I have a strange sense of deja vu.

So are you saying that you disagree that factoring for winds at opening altitude, aircraft ground speed and time do nothing to help determine seperation between groups?


Since most people won't do the math while on jump run, know what 1000 feet over the ground from altitude looks like or find out what the wind speeds are, it is easier for most people to understand a simple time hack before leaving based off the method used in the excel chart I attached to post #9 of this thread back in 2005. Is it perfect? No, but as BillVon said, it's a 90% solution that even beginners can easily grasp and it is much more effective than the 45 rule. People counting at the right cadence is another issue which has also been covered in the earlier posts of this thread, but I think we have already come full circle.

If you have an easier way of establishing the right amount of seperation between groups that the average skydiver can understand and utilize while in the door of the aircraft please do tell.


winsor  (D 13715)

Sep 11, 2007, 8:25 PM
Post #168 of 364 (1865 views)
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Re: [LouDiamond] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

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I have a strange sense of deja vu.

So are you saying that you disagree that factoring for winds at opening altitude, aircraft ground speed and time do nothing to help determine seperation between groups?


Since most people won't do the math while on jump run, know what 1000 feet over the ground from altitude looks like or find out what the wind speeds are, it is easier for most people to understand a simple time hack before leaving based off the method used in the excel chart I attached to post #9 of this thread back in 2005. Is it perfect? No, but as BillVon said, it's a 90% solution that even beginners can easily grasp and it is much more effective than the 45 rule. People counting at the right cadence is another issue which has also been covered in the earlier posts of this thread, but I think we have already come full circle.

If you have an easier way of establishing the right amount of seperation between groups that the average skydiver can understand and utilize while in the door of the aircraft please do tell.

Yup.

Ask the pilot.

You only need to have one person at a DZ who is intimately familiar with how to maintain separation in the air. The pilot, who has a lot at stake regarding the safe execution of jump operations, and is the one person with all the instruments in front of him all the way up, might as well be the person who lays down the law regarding delay between groups.

The "90% solution" works to the extent that you're flying into the wind and the velocity profile with altituude is typical. If those two conditions are not met, all bets are off.

In the same sense that working on Carnot cycle equipment does not qualify one as a thermodynamicist, making a bunch of skydives does not make one a specialist in continuum mechanics theory.

If you threw in a disclaimer that your approach was a rule of thumb that could be used safely most of the time, I'd buy it. However, to start with a diatribe about peoples' lack of understanding and then put forth that spreadsheet as a "solution" is a bit more than I can stomach.

I agree that your procedure is better than nothing most of the time. Other times it is on a par with trying to gauge 45 degrees.


Blue skies,

Winsor


Premier LouDiamond  (D 25931)
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Sep 11, 2007, 9:11 PM
Post #169 of 364 (1856 views)
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Re: [winsor] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

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Ask the pilot.

Having spent a considerable amount of time in the right seat with pilots in my wingsuit, of those who do give a time delay to the jumpers, all have based it off of the ground speed indicated on their instrumentation which goes back to why the chart is easy to not only use but understand.When I asked about the time delay the pilot(s) passed back and how they obtained them most have confessed to the SWAG method so I don't buy "ask the pilot" as a legit end all,be all solution to the issue.


Quote:
However, to start with a diatribe about peoples' lack of understanding and then put forth that spreadsheet as a "solution" is a bit more than I can stomach.

I never claimed to be a physics teacher but I did stay in a Holiday Inn express once. So instead of just making an obtuse statement about how physics can be used to obtain separation without providing anything of value the reader can apply in the real world, I provided a simple to understand and use chart. I and several large DZs, choose to apply this KISS method ( I don't claim to be the originator of the chart by any means) which only requires jumpers to ask the pilot for the aircraft's ground speed to find the appropriate delay between groups. Not only can it be explained mathematically using simple arithmetic,the average skydiver can grasp, as well as stomach it.

Quote:
I agree that your procedure is better than nothing most of the time. Other times it is on a par with trying to gauge 45 degrees.

If you are refering to doglegs or incompatable winds then I agree. I have delt with both before as well as jumped out of many a chinook.While not common ,they do happen on occassion. So again, if you don't agree with the chart what is your solution to this issue?


winsor  (D 13715)

Sep 12, 2007, 7:26 AM
Post #170 of 364 (1813 views)
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Re: [LouDiamond] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

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Ask the pilot.

FWIW, my point here is that the pilot should be tasked to:

A) Learn the fundamentals of separation and spotting

and

B) Include the evaluation of minimum separation in their scope of work. The pilot should then annouce the minimum delay between groups before takeoff on each load.

I did not mean to imply that simply holding a Commercial ticket guaranteed comprehension of the four-dimensional problem that freefall separation entails. A pilot, however, may be expected to grasp the subject after appropriate instruction, and is in an ideal postition to do a more detailed evaluation than could any of the jumpers.

Trust me, there is more to it than you appear to have considered.

Quote:
I agree that your procedure is better than nothing most of the time. Other times it is on a par with trying to gauge 45 degrees.

If you are refering to doglegs or incompatable winds then I agree. I have delt with both before as well as jumped out of many a chinook.While not common ,they do happen on occassion. So again, if you don't agree with the chart what is your solution to this issue?
Quit relying on comic book physics, for one.

Though we all agree that, if someone waits long enough because they are counting fleas on their dog, using their protractor to estimate 45 degrees, or trying to relate ground speed to how far apart they will be at opening altitude, the goal of achieving sufficient separation is met.

However, to say that one has a good conceptual grasp of the subject because they have an accurate flea tally, 45 degrees nailed, or their relationship to real estate nailed is rubbish.

The chart is bullshit. Somewhat useful bullshit, but bullshit nonetheless.

I recommend that the fundamentals of spotting and separation should be a requisite for S&TA as well as jump pilot qualification. There should be SOMEBODY on hand that has a clue; it just is not that hard.


Blue skies,

Winsor


popsjumper  (D 999999999)

Sep 12, 2007, 7:43 AM
Post #171 of 364 (1808 views)
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Re: [winsor] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

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...B) ...The pilot should then annouce the minimum delay between groups before takeoff on each load.

I would prefer that he announce just prior to exit...that would catch the potentially changing conditions after take-off.


In reply to:
Though we all agree that, if someone waits long enough ...the goal of achieving sufficient separation is met.

A blanket statement. In that case, the methodology is moot.

Put me solidly in the camp of time, not degrees.


AFFI  (D 25538)

Sep 12, 2007, 7:46 AM
Post #172 of 364 (1806 views)
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Re: [winsor] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

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There should be SOMEBODY on hand that has a clue; it just is not that hard.
Do you have that clue?
If so, could you get a dum-dum like me to understand it so I can teach it in a simplified manner?

Is it really important to understand it like Einstein or can an uneducated half-breed South Texas beaner like me be able to grasp it?


Premier LouDiamond  (D 25931)
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Sep 12, 2007, 8:24 AM
Post #173 of 364 (1795 views)
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Re: [winsor] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

Quote:
the pilot should be tasked to:

A) Learn the fundamentals of separation and spotting

and

B) Include the evaluation of minimum separation in their scope of work. The pilot should then annouce the minimum delay between groups before takeoff on each load.


OK, a valid point and I know there are few pilots who have a grasp on (A). However, in the REAL WORLD it is more common to not encounter (B) and I have even met pilots who clearly had no concept of (A) when it came to dropping skydivers.



Quote:
A pilot, however, may be expected to grasp the subject after appropriate instruction, and is in an ideal postition to do a more detailed evaluation than could any of the jumpers.


Trust me, there is more to it than you appear to have considered.



Thats a blatent assumption on the part of a pilots ability or concern. I know far more skydivers who spend time figuring the winds, exit order and seperation issues out than most (not all)pilots do. This thread and the others in the forum serve as good examples. I would be surprised if you could even find one thread on an aviation forum that discusses this topic as much as skydivers do. I and others fully understand there is more to it and have considered it quite extensively. I have yet to met anyone who can explain the issue in laymans terms and or under 3 hours so that an average skydiver would "get it" and be able to apply it in the real world.




Quote:
Quit relying on comic book physics, for one.



Call them what you like but they work in the real world. It's not I who is relying on them, it's the people from the DoD, Rockwell, Northrop Grumman, etc that also use these so called "comic book physics" quite sucessfully.




Quote:
However, to say that one has a good conceptual grasp of the subject because they have an accurate flea tally, 45 degrees nailed, or their relationship to real estate nailed is rubbish.



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.




Quote:
The chart is bullshit. Somewhat useful bullshit, but bullshit nonetheless.




Ok, your opinion is noted. However, I will ask you for a third time, if you do not agree with the methods described in this thread WHAT IS YOUR SOLUTION? We can go on and on dancing around this but I have yet to see you post anything that provides a solution better than the chart. So please share some of your "conceptual grasp" with the rest of us and show us how to do it right.





Quote:
I recommend that the fundamentals of spotting and separation should be a requisite for S&TA as well as jump pilot qualification. There should be SOMEBODY on hand that has a clue; it just is not that hard


I think these fundamentals should be emphasized better to ALL skydivers. Like you said it's not that hard so it shouldn't be put solely on S&TAs or jump pilots.


Fast  (D 28237)

Sep 12, 2007, 9:18 AM
Post #174 of 364 (1781 views)
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Re: [winsor] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

Is the point that you are trying to get at this?

If the winds are consistent from opening altitude to jump altitude, ground speed is irrelevant to the time needed between groups. What if the winds at altitude were 80 knots (not a likely condition that most of us jump in, but bear with me here) The plane on jumprun would be doing 80 knots airspeed and not moving at all relative to the ground. It would seem that, we would have to wait an infinite amount of time because there is no ground speed. That just isn't true. It is this way because the plane is moving forward relative to the air, which the jumpers will become part of once they get out of the plane. The plane will keep on moving forward in the air and the jumpers will be carried backwards relative to the plane. Everyone got out at the same point over the ground, but there is plenty of separation.

Now, in the real world most of the time the winds are not consistent from opening point to jump point. They vary some by speed and heading. "90% of the time" if you just plan for exit separation based on airspeed at exit, things are going to work just fine. It should, for the most part, always be the same amount of time between groups of a similar discipline. They all have similar "profiles" in the air and will all be affected by the moving mass in a similar manner. The problem results when subsequent groups have wildly different "profiles" in the air. This would be the difference between freefliers and belly fliers, or like students who may be opening their canopy in a different wind condition than everyone else.

Separation over the ground is going to happen on its own as long as you have similar "profiles" in the air.

At least that is how I have always understood the physics to work.


(This post was edited by Fast on Sep 12, 2007, 9:22 AM)


winsor  (D 13715)

Sep 12, 2007, 10:03 AM
Post #175 of 364 (1773 views)
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Re: [AFFI] The "45 degree rule" for exit separation DOES NOT WORK [In reply to] Can't Post

In reply to:
In reply to:
There should be SOMEBODY on hand that has a clue; it just is not that hard.
Do you have that clue?
If so, could you get a dum-dum like me to understand it so I can teach it in a simplified manner?

Is it really important to understand it like Einstein or can an uneducated half-breed South Texas beaner like me be able to grasp it?

First off, it is airspeed and exit interval that establishes distance between groups.

Second, the distance between groups can become less by the time you open if there is a significant difference between winds at altitude and winds at opening altitude.

Third, ground speed, in and of itself, has precisely nothing to do with separation in the air.

Thus, you can use air speed on jumprun to gauge the delay that gives you the desired separation between groups at altitude. Multiply knots by 1.66 to get feet per second.

Separation = airspeed * delay

Example: 8 seconds delay at 90 knots TAS gives around 1,200 some-odd feet between group centers. (8 seconds) * (90 knots) * (1.66 feet/second-knot)= (1195.2 feet)

If the winds at altitude are significant, you can subtract most or all of the headwind from the airspeed in your calculation. This is the part that has ground speed adherents convinced that they have "the solution."

Use a multiplier to account for the difference between airspeed and speed with regard to air at opening altitude.

Note: The delay that gives you your minimum desired separation at exit (airspeed * delay = separation) is the minimum delay you should take.

Example: 90 knots airspeed, 50 knots effective headwind.

Multiplier: 90/(90-50) = 90/40 = 2.25

2.25 * 8 seconds = 18 seconds

So the 8 second minimum delay from our first example becomes an 18 second delay if you have a 50 knot difference between winds at exit altitude and winds at opening altitude.

Since separation is achieved by canopy flight once the parachute opens, we are only concerned with separation between groups between exit and opening.

For people on the ground, the simplest approximation is to use airspeed minus the headwind at altitude, so long as the result is not less than the minimum delay. This value is, of course, groundspeed.

Here I stress that this is an inaccurate approximation, that is valuable only so long as it does not result in an exit separation less than the minimum - a circumstance that can happen all too often if one does not recognize the limitations of this approximation.

If the pilot is watching the GPS, he can come up with the difference between headwinds at opening altitude and headwinds at exit altitude, and use this value for the delay he announces before exit. Thus, it is ideal if the pilot determines the exit delay for each load, and each group knows how much of a delay they need before boarding.

The steps are as follows:

1) Pick a minimum distance between groups with which you can live. 1,000 feet is a good start, and more is better than less in general.

2) Find out the jumprun true airspeed of the airplane. This can vary greatly from airplane to airplane, and from pilot to pilot.

3) Figure out your minimum (no wind) delay.
(true airspeed in knots)*(1.66) = (feet per second)
(minimum distance in feet)/(feet per second) = (minimum delay in seconds)

4) Throw in a multiplier for headwind. The minimum multiplier should be 1.
(true airspeed)/(true airspeed-headwind) = (multiplier)

(minimum delay in seconds)*(multiplier) = (delay in seconds)

This is a fast an dirty treatment, but it keeps you out of the problems one encounters when using ground speed as a basis if air speed is less than ground speed.


Blue skies,

Winsor


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