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Re: [Martini] Opening High for Bad Spots

 

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kallend  (D 23151)

Feb 19, 2004, 4:42 PM
Post #151 of 246 (742 views)
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Re: [Hooknswoop] Opening High for Bad Spots [In reply to] Can't Post

 

You know, I'm not sure why I'm participating here. Everything I believe has been laid out for anyone to see on my web site. I update it as my ideas evolve, so there's nothing I can say here that isn't already there.

If you think I got it wrong, let me know and if I agree I will fix it.


diverdriver  (D 19012)

Feb 19, 2004, 4:58 PM
Post #152 of 246 (738 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
Not if the premature deployment altitude has winds of 80kt too. Say they left 10 seconds apart, AND the premature canopy then flies directly into the wind (up jumprun) at 30kt. It is still going downwind from the path of the next jumper at 80-30 = 50kt, and will cover about 750ft in this time. So the second jumper will pass 750ft upwind of the open canopy even though it's flying towards him.

The bigger problem is the premature deployment at an altitude where the wind is << 80kt.


Yah, I know. And in my later post I talked about real world circumstance and the winds at lower altitudes WERE less than 80 knots. (Actually, the winds aloft at exit were 85 knots and my KTAS was 105).

But I do understand what you are getting at.


johnny1488  (D 25453)

Feb 19, 2004, 5:10 PM
Post #153 of 246 (731 views)
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Re: [mnischalke] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
Separation has to do only with the air between 13.5k(+/-) and 3k (+/-). Why else do you think the pilots post those little predicted wind numbers on the dry-erase board near manifest?

With out the ground, those little numbers are completely meaningless. Actually, without the ground, those numbers dont exhist. I believe that is why the ground is a factor.

I might be totally wrong but I dont think I am stupid. I have been arguing over opening points, not seperation after a canopy has drifted away. For my point, I visualize throwing ballons filled with paint out of an aircraft over a ground that will show the impact points. Winds aloft or airspeed win not change the IMPACT POINTS. Only groundspeed of the aircraft will. Once each balloon leaves the aircraft, they are all affected by the same winds, be they in the same direction, every diferent direction, 100kts or 0 kts.


kallend  (D 23151)

Feb 19, 2004, 6:25 PM
Post #154 of 246 (724 views)
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Re: [Hooknswoop] Opening High for Bad Spots [In reply to] Can't Post

There's a whole lot of talking at cross purposes here. People are talking at each other rather than to each other.

1. Physics. There is absolutely no doubt whatsoever that from the point of view of physics, the ground is completely irrelevant. The factors that control horizontal separation AT ANY ALTITUDE are (a) the difference between airplane speed at exit altitude and the windspeed at the opening altitude and (b) the time between exits. Since it is a DIFFERENCE in windspeeds, adding or substracting any arbitrary number corresponding to groundspeed to each number makes no difference whatsoever to that difference.

EXAMPLE: (all winds assumed headwinds)

Case A. airspeed 80 kt, wind at altitude 40kt, wind at 3000ft = 20kt., groundspeed 80-40 = 40kt, plane speed with respect to 3000ft air: 80 - 40 + 20 = 60kt.


Now reduce winds at both altitudes by 10kt: (same as changing the Earth's rotation rate by 10kt and keeping the airmass exactly the same)

Case B airpseed 80 kt, wind at altitude 30kt, wind at 3000ft = 10kt, groundspeed 80-30 = 50kt, plane speed with respect to 3000 ft = 80 - 30 + 10 = 60kt, same as Case A. So the groundspeeds are different but the speeds over the 3000ft airmass are the same and the horizontal separation at 3000ft will be the same.

Arguing that impact points on the ground have any relevance is only meaningful if you choose to deploy your canopy at zero agl. I for my part do not like that idea.

2. From practical point of view. Will you get in trouble if you use groundspeed as a reference? Probably not. Not because the physics is incorrect (it isn't) but because the windspeed at opening altitude is USUALLY pretty close to the windspeed on the ground. Hence the error created by using groundspeed is USUALLY negligibly small, and USUALLY acts in a direction that increases separation (so it's kind-of "fail safe".

The only time that using groundspeed is likely to give less than desirable separation is when the low altitude winds are in the opposite direction to the uppers, and wind drift blows the canopies of the first group in the direction of the next group instead of away from it.


If you took college physics, it's all about Galilean relativity.


Can we go home now?


(This post was edited by kallend on Feb 19, 2004, 6:31 PM)


Hooknswoop  (D License)

Feb 19, 2004, 8:17 PM
Post #155 of 246 (710 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

Quote:
Can we go home now?

Yes, I was wrongBlush. Thank you for explaining it to me and for everyone else's patience with me.

Derek


velo90

Feb 20, 2004, 1:11 AM
Post #156 of 246 (697 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

I thought I said that about 50 odd posts ago Wink
But there again, I am not a physics professor so who is going to believe me Frown


kallend  (D 23151)

Feb 20, 2004, 7:40 AM
Post #157 of 246 (686 views)
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Re: [velo90] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
I thought I said that about 50 odd posts ago Wink
But there again, I am not a physics professor so who is going to believe me Frown

I'm just more persuasive. It must be something to do with your hat (in the avatar).Cool


bmcd308  (D 27472)

Feb 20, 2004, 8:09 AM
Post #158 of 246 (675 views)
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Re: [Hooknswoop] Opening High for Bad Spots [In reply to] Can't Post

>>Yes, I was wrong<<

No, you weren't. Here is the quote that ties it all together.

>>Separation means opening points are separated not the same opening point with canopy speed used for separation. The same opening point means there is zero separation. <<


You think about separation the way I do - I do not want to open in the same x,y,z coordinates over the ground as the previous group.

Velo90, Eames et. al. point out that while you are freefalling into the x,y,z coordinates of the previous group, the previous group is under canopy, being moved in the x and y axes.

You (and I) define that as zero separation. They do not. A million posts will not resolve that.

Brent


velo90

Feb 20, 2004, 9:19 AM
Post #159 of 246 (664 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

Firstly, I am not sure what x, y, and z are.
Secondly, Idefine separation as the horizontal distance between myself and other jumpers. I would like this separation when I deploy my parachute. Also I would like this separation if my parachute prematurely deploys or I have a mal and need to deploy my reserve.
Of course there are cases where I won't have this seperation, like if my parachute prematurely deploys while in the middle of a relative jump Unsure By default there are people next to me. However, I do not want people on top of me, from the following group for instance.

Your example (and maybe mine, I forget) of people deploying at the same point above the ground and then making space due to wind drift for the next person is something that does not happen in reality. The lower winds would have to be so strong that no sane person would be jumping.


velo90

Feb 20, 2004, 9:20 AM
Post #160 of 246 (662 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

Quote:
I'm just more persuasive. It must be something to do with your hat (in the avatar). Cool
Ok, I have changed my avatar (you might need to refresh your browser). Do you think I will be taken seriously now? Wink


kallend  (D 23151)

Feb 20, 2004, 9:25 AM
Post #161 of 246 (666 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
>>Yes, I was wrong<<

No, you weren't. Here is the quote that ties it all together.

>>Separation means opening points are separated not the same opening point with canopy speed used for separation. The same opening point means there is zero separation. <<


You think about separation the way I do - I do not want to open in the same x,y,z coordinates over the ground as the previous group.

And with respect to WHAT ORIGIN are you measuring x, y, z? Then justify your choice.

And what if the previous group has already landed? Would that make a difference?


mnischalke  (D 26290)

Feb 20, 2004, 9:37 AM
Post #162 of 246 (660 views)
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Re: [velo90] Opening High for Bad Spots [In reply to] Can't Post

Quote:
However, I do not want people on top of me, from the following group for instance.

If they are above you at, say 7k, they're still gonna be above you at 3k.


bmcd308  (D 27472)

Feb 20, 2004, 9:38 AM
Post #163 of 246 (658 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

>>And with respect to WHAT ORIGIN are you measuring x, y, z? Then justify your choice. <<

The origin could be any point on the ground. Let's say it's the center of the peas.

So x,y, and z define an opening point. In this thread, at least a portion of the argument (when there is an actual argument) concerns whether it is acceptable for two groups to share the same opening point. By postulating unrealistic winds at opening altitude, there are those who can demonstrate that separation can be achieved as a result of canopy drift by the first group before the second group reaches that same opening point over the ground. Using their vocabulary, the first group will be in a different airmass than the second. Using mine, the first group will have moved away from the opening point, so the values of x, y, and z will have changed.



>>And what if the previous group has already landed? Would that make a difference? <<

Of course. The goals of exit separation are to avoid freefall collisions and to minimize the opportunity for canopy collisions at pulltime between members of different groups. If the first group has landed, then by definition there will not be a freefall collision or a collision at pulltime.


velo90

Feb 20, 2004, 9:42 AM
Post #164 of 246 (653 views)
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Re: [mnischalke] Opening High for Bad Spots [In reply to] Can't Post

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If they are above you at, say 7k, they're still gonna be above you at 3k.

Maybe, but I don't want people on top of during any portion of the dive. I am not sure what you are trying say.


kallend  (D 23151)

Feb 20, 2004, 9:43 AM
Post #165 of 246 (652 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
>>And with respect to WHAT ORIGIN are you measuring x, y, z? Then justify your choice. <<

The origin could be any point on the ground. Let's say it's the center of the peas.

So x,y, and z define an opening point. In this thread, at least a portion of the argument (when there is an actual argument) concerns whether it is acceptable for two groups to share the same opening point. By postulating unrealistic winds at opening altitude, there are those who can demonstrate that separation can be achieved as a result of canopy drift by the first group before the second group reaches that same opening point over the ground. Using their vocabulary, the first group will be in a different airmass than the second. Using mine, the first group will have moved away from the opening point, so the values of x, y, and z will have changed.



>>And what if the previous group has already landed? Would that make a difference? <<

Of course. The goals of exit separation are to avoid freefall collisions and to minimize the opportunity for canopy collisions at pulltime between members of different groups. If the first group has landed, then by definition there will not be a freefall collision or a collision at pulltime.

Well, I disagree with you. The only origin that makes sense is an origin in the airmass you are in. Canopies aren't drifting in that airmass, the ground is, but the people you are trying to avoid aren't on the ground.


bmcd308  (D 27472)

Feb 20, 2004, 9:49 AM
Post #166 of 246 (646 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

>>Well, I disagree with you. The only origin that makes sense is an origin in the airmass you are in. Canopies aren't drifting in that airmass, the ground is, but the people you are trying to avoid aren't on the ground. <<

I'm not sure where we have room to disagree. If we choose a different origin, one of the two of us will simply have to transalate into the other's coordinate system. At any time, t, neither of us wants to have the same x,y, and z coordinates as the other. At any time, t, it is possible to translate one system of defining a point in space to the other. We could just as easily translate it to polar coordinates with an origin in the peas, or polar coordinates with an origin that stays with the plane.

Brent


mnischalke  (D 26290)

Feb 20, 2004, 9:52 AM
Post #167 of 246 (645 views)
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Re: [velo90] Opening High for Bad Spots [In reply to] Can't Post

What I am saying is that if they converged on your column of air and end up above you at any time during the jump, they're gonna be there when you deploy too. I just tried to explain the same thing in this thread.


kallend  (D 23151)

Feb 20, 2004, 9:55 AM
Post #168 of 246 (643 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
>>Well, I disagree with you. The only origin that makes sense is an origin in the airmass you are in. Canopies aren't drifting in that airmass, the ground is, but the people you are trying to avoid aren't on the ground. <<

I'm not sure where we have room to disagree. If we choose a different origin, one of the two of us will simply have to transalate into the other's coordinate system. At any time, t, neither of us wants to have the same x,y, and z coordinates as the other. At any time, t, it is possible to translate one system of defining a point in space to the other. We could just as easily translate it to polar coordinates with an origin in the peas, or polar coordinates with an origin that stays with the plane.

Brent

But my origin is moving with respect to yours. And my origin is where I am and close to where the potential collision hazard is. Your origin is 3000ft below and moving. I don't care a hoot what is going on down there.

What if a layer of light industrial haze obscured the ground? Whast relevance does your origin have now?


Premier billvon  (D 16479)
Moderator
Feb 20, 2004, 10:01 AM
Post #169 of 246 (641 views)
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Re: [mnischalke] Opening High for Bad Spots [In reply to] Can't Post

>What I am saying is that if they converged on your column of air and
> end up above you at any time during the jump, they're gonna be
> there when you deploy too.

No. Winds change with altitude. If the winds drop 10kts for every 1000 feet, and you are 1000 feet directly above another group, they will move away from you at a speed of 10kts (17 feet per second.) After a 60 second freefall they would be 1020 feet from you. (Again, you wouldn't be jumping in wind conditions that bad, but it is still a factor to consider in moderate winds.)


eames  (D 23844)

Feb 20, 2004, 10:02 AM
Post #170 of 246 (641 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
What if a layer of light industrial haze obscured the ground? Whast relevance does your origin have now?

Exacly.... I asked this same question earlier in the thread. He just hasn't thought it out enough....

-Jason


mnischalke  (D 26290)

Feb 20, 2004, 10:11 AM
Post #171 of 246 (638 views)
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Re: [billvon] Opening High for Bad Spots [In reply to] Can't Post

Your model assumes falling straight down the column of air. Mine (the only way someone could get above you given any real separation between groups) is considering sliding of either group. The farther through space the two groups get, considering a slide, the closer they get until the converge. The angle of the sliding group decides the point of convergance. So, the higher you open, the less the likelyhood of convergance.


eames  (D 23844)

Feb 20, 2004, 10:14 AM
Post #172 of 246 (634 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
At any time, t, it is possible to translate one system of defining a point in space to the other.

Prove it. Show me a change of basis for these two systems. It's impossible because there is no relationship between the two systems. Q.E.D.


kallend  (D 23151)

Feb 20, 2004, 10:26 AM
Post #173 of 246 (629 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
In reply to:
At any time, t, it is possible to translate one system of defining a point in space to the other.

Prove it. Show me a change of basis for these two systems. It's impossible because there is no relationship between the two systems. Q.E.D.

Of course there's a relationship.

However, I dispute his thesis that you can't rely on "canopy drift" for separation, but have to ensure separation relative to some fixed point on the ground. If I place the origin at the point most important to ME, then I am not drifting. The ground is drifting, and I'm not worried (within a few seconds of opening) about colliding with anything on the ground.

The only thing I can possibly collide with is something at the same altitude I am.


velo90

Feb 20, 2004, 10:28 AM
Post #174 of 246 (628 views)
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Re: [mnischalke] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
What I am saying is that if they converged on your column of air and end up above you at any time during the jump, they're gonna be there when you deploy too. I just tried to explain the same thing in this thread.

I presume you are refering to your idea that pulling higher can give more seperation than going lower.
If this is the case, during normal wind conditions I would entirely agree. I am of the opinion, and I think you are, if the exit timing is right, there is no harm in pulling high. Pulling low may make thing worse.

Pulling low is bad news anyway, I have an AAD.


eames  (D 23844)

Feb 20, 2004, 10:35 AM
Post #175 of 246 (626 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
Of course there's a relationship.

Once again, I've oversimplified. Yes, there's a relationship that depends on the characteristics of the airmass (velocity of the airmass relative to the ground and the velocity of the airmass relative to itself, and the change in velocity of the airmass between altitude and opening). But to describe those characteristics in terms of the airmass itself requires simple subtraction. To describe those characteristics in terms of the ground requires the addition of a variable, that variable being the velocity and direction of the airmass. So separation must be described in terms of the airmass. Is that correct?

-Jason


(This post was edited by eames on Feb 20, 2004, 11:07 AM)


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