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Re: [Martini] Opening High for Bad Spots

 

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velo90

Feb 20, 2004, 1:14 PM
Post #201 of 246 (757 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

Quote:
Eames is saying that it is OK for two people to open at the exact same point over the ground at staggered times because by the time the second group gets to that point, the airmass in which the first group is flying will have moved (i.e. the first group will be over a different point on the ground).

And Eames is correct in that assumption.

Quote:
My point is that I do not want to have to rely on the airmass in which the first group deployed to have moved away from the point over the ground where the second group is deploying to achieve separation.

You don't have to rely on it, the way a number of people work these days they ignore it, in most cases to their advantage. When you understand why it makes a difference, you can save your ass on unusual days.

Quote:
Canopy drift is fine for additional separation

But sometimes it can give reduced separation.

And unless you can see that, you are out of touch with reality. Sorry, but the information has been provided in these forums often enough. Read, study and then you will understand why canopy drift is (sometimes) a factor that should not be ignored.


velo90

Feb 20, 2004, 1:20 PM
Post #202 of 246 (752 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

Quote:
and leave half a second behind you, I might go whistling by as you were saddling out and then deploy right under you.
I doubt that very much. You would never catch him up. You'd be close, that true, but you would not be right under him.

Have you ever done tandem videos?


eames  (D 23844)

Feb 20, 2004, 1:23 PM
Post #203 of 246 (752 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
However, if I were to follow your separation advice and leave half a second behind you, I might go whistling by as you were saddling out and then deploy right under you. I bet the discourse on the ground would not be as civil as the one we are having here in that case, and you'd be telling me that next time I damn well better wait until we were farther apart.

That was not advice, I wrote, "By the way, I don't recommend trying it... I hope you found that obvious." Apparently you didn't.

I also never said "half a second." You said, "0.5 seconds."

Enough with semantics.

Quote:
My argument is that separation between groups does not depend on groundspeed.

Actual separation (in terms of the airmass, which is all that matters) depends on three things: Airspeed of the plane on jumprun, the difference between the velocity of the winds at jumprun altitude and opening altitude, and the time left between groups.

Nowhere does groundspeed factor into separation.

Do you dispute this?

-Jason


bmcd308  (D 27472)

Feb 20, 2004, 1:24 PM
Post #204 of 246 (751 views)
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Re: [velo90] Opening High for Bad Spots [In reply to] Can't Post

Quote:
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Quote
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Eames is saying that it is OK for two people to open at the exact same point over the ground at staggered times because by the time the second group gets to that point, the airmass in which the first group is flying will have moved (i.e. the first group will be over a different point on the ground).

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And Eames is correct in that assumption.

Not necessarily. If that airmass is not moving (winds died at opening altitude), it will not have moved.

Quote:
But sometimes it can give reduced separation.

And unless you can see that, you are out of touch with reality.

Agreed.

Lower winds that push the skydivers back up the line of flight represent a special case that needs to be understood.

This whole most recent "argument" has been the result of my pointing out that the original argument was one that resulted from a difference in the definition of "separation" between the two sides.

I do not think I am actually arguing with anyone.

Brent


bmcd308  (D 27472)

Feb 20, 2004, 1:29 PM
Post #205 of 246 (748 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

>>Do you dispute this? <<

Only to the extent that some were defining separation as the distance between opening points relative to the ground. If separation is defined as the distance between opening points relative to the ground, then groundspeed on jumprun matters rather than airspeed on jumprun.

Brent


velo90

Feb 20, 2004, 1:34 PM
Post #206 of 246 (744 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

Quote:
Not necessarily. If that airmass is not moving (winds died at opening altitude), it will not have moved.

can't argue with you there.
Quote:
This whole most recent "argument" discussion has been the result of my pointing out that the original argument was one that resulted from a difference in the definition of "separation" between the two sides.

Well actually I thought it started due to the idea that ground speed determines separation.
It doesn't.


eames  (D 23844)

Feb 20, 2004, 1:37 PM
Post #207 of 246 (742 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
If separation is defined as the distance between opening points relative to the ground, then groundspeed on jumprun matters rather than airspeed on jumprun.

Are the jumpers on the ground? Then why would you define separation in terms of the ground?

Actual separation (the distance between two groups when the second group opens, with respect to the ground or the airmass) does not change with groundspeed. It only changes with the airspeed of the plane on jumprun, the difference between the velocity of the winds at jumprun altitude and opening altitude, and the time left between groups. That's it. No matter what the groundspeed is.

-Jason


(This post was edited by eames on Feb 20, 2004, 1:42 PM)


eames  (D 23844)

Feb 20, 2004, 1:39 PM
Post #208 of 246 (738 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
...definition of "separation" between the two sides

By the way, I'm not sure who is left on your side. I believe I can safely say that Hook now agrees with what we're saying.

-Jason


(This post was edited by eames on Feb 20, 2004, 1:49 PM)


bmcd308  (D 27472)

Feb 20, 2004, 1:50 PM
Post #209 of 246 (728 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

>>By the way, I'm not sure who is left on your side. <<

I don't have a side. But if I did, Isaac Newton would be on it.


velo90

Feb 20, 2004, 1:57 PM
Post #210 of 246 (724 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

Quote:
I don't have a side. But if I did, Isaac Newton would be on it.

Errr , Kallend is as near as we get to Isaac Newton here, trust him.


eames  (D 23844)

Feb 20, 2004, 1:57 PM
Post #211 of 246 (724 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
I don't have a side. But if I did, Isaac Newton would be on it.

I award you zero points, we are all dumber for reading that, and may god have mercy on your soul. Wink

[That was a joke.]

I think we're done here.

-Jason


bmcd308  (D 27472)

Feb 20, 2004, 2:02 PM
Post #212 of 246 (721 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

Let me run a quote from one of my very first posts on this thread by you again:

>>I have never disagreed with the idea that IF we assume that there is some wind at 3,000 feet that wind will have a tendency to force the previous group's canopies downwind. However, if that wind at 3000 feet stops blowing on the way to altitude, our reliance on the wind at 3000 feet to provide separation will have been ill-advised. <<

I think you will see that I have not been specifically arguing with your choice of inputs into your separation model.

I will admit that as a practical matter I very much like the idea of opening at a different point over the ground than the one at which the group before me opened five seconds earlier in every case except the one where their airmass is moving toward my different point over the ground. And in that case, I would want a different jump run.

Brent


eames  (D 23844)

Feb 20, 2004, 2:08 PM
Post #213 of 246 (717 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
I have never disagreed with the idea that IF we assume that there is some wind at 3,000 feet that wind will have a tendency to force the previous group's canopies downwind. However, if that wind at 3000 feet stops blowing on the way to altitude, our reliance on the wind at 3000 feet to provide separation will have been ill-advised.

Depends on the windspeed at altitude (difference between the velocity of wind at jumprun altitude and opening altitude). If the difference is a large, yes, there is something to worry about. This all fits perfectly into the model that has been described.

In reply to:
I will admit that as a practical matter I very much like the idea of opening at a different point over the ground than the one at which the group before me opened five seconds earlier in every case except the one where their airmass is moving toward my different point over the ground. And in that case, I would want a different jump run.

That's fine, I'm not trying to tell you what to do.

-Jason


(This post was edited by eames on Feb 20, 2004, 2:24 PM)


kallend  (D 23151)

Feb 20, 2004, 3:21 PM
Post #214 of 246 (696 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
>>Correct, but generally this is not included in the calculations for separtion. The result is we get even more separation than we bargained for in most cases.
But unless you understand why that is, you will not understand why in some cases you end up with less separation. Such conditions occur where I jump. <<

This is exactly my point.

Eames is saying that it is OK for two people to open at the exact same point over the ground at staggered times because by the time the second group gets to that point, the airmass in which the first group is flying will have moved (i.e. the first group will be over a different point on the ground).

My point is that I do not want to have to rely on the airmass in which the first group deployed to have moved away from the point over the ground where the second group is deploying to achieve separation. Because if it does not, the two airmasses will be one and the same.

Canopy drift is fine for additional separation that is not counted in the time between groups. And as you point out, when jump run is opposite the opening altitude winds, the opportunity for skydivers from different groups to occupy the same space (no matter how it is defined) is increased.

Brent

Brent

So you are willing to bet your life on the reliability of the air at exit altitude and on the ground for landing, but at opening altitude you consider it unreliable. Interesting concept.


kallend  (D 23151)

Feb 20, 2004, 3:24 PM
Post #215 of 246 (694 views)
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Re: [velo90] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
Quote:
I don't have a side. But if I did, Isaac Newton would be on it.

Errr , Kallend is as near as we get to Isaac Newton here, trust him.

I was in college with Isaac Newton. About 300 years later than him.


kallend  (D 23151)

Feb 20, 2004, 4:03 PM
Post #216 of 246 (690 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

Quiz time.

1 kt is very close to 1.5 ft/sec, and using ft/sec is easier.

A balloonist and his girlfriend are floating along at 2500ft agl. He looks at his chart and sees there is a DZ below. Not that he can do anything about it. The DZ is near the ocean and an easterly wind is blowing him due west at 40ft/sec. He looks down and sees the DZ drift by below him. He feels not a breath of wind, because he is the wind. He lights a cigar.

He looks up and sees an Otter way above him, going west. He recalls the weather briefing, that at altitude the winds are prevailing westerlies, but down low the ocean effect has them in the opposite direction. He gets out his laser rangefinder and determines that the Otter is moving at 50 ft/sec relative to his balloon. A quick calculation tells him that the Otter's groundspeed is 50+40 = 90ft/sec. He knows an Otter flies jumprun at 140ft/sec, so he deduces the uppers are 50ft/sec from the west.

A 4-way team leaves the Otter (they saw the balloon but mistook it for a water tower). They turn 22 points. At 4000ft they are directly above the balloon, breakoff and track. Each tracks 300 ft before deploying. They are all open at 2500ft. One has line twists and is in a slow turn, another opened off heading, a third is stowing his slider while the other is messing with his booties. Each skydiver is 300ft from the balloon, in various directions. It is a cool sight.

The balloon pilot sees a second 4-way team leave the Otter after 11 seconds, (they figured 990ft should be ample separation from the first group based on the 90ft/sec groundspeed; that leaves 300ft for their tracks, 300ft for the other teams' tracks, and 330 ft as a buffer between the groups). They turn 26 points.

He sees the second team also break and track at 4000ft, each tracking 300ft. in equally spaced directions.

The girlfriend coughs because the cigar smoke is hanging around, there is no wind to disperse it.

How far from the balloon is the center of the second group, and is there a risk of collision between groups?

Note - It is not at all uncommon for upper and lower winds to be in opposite directions if you are near the Great Lakes, the ocean, or mountains.


(This post was edited by kallend on Feb 20, 2004, 6:15 PM)


mnischalke  (D 26290)

Feb 20, 2004, 4:12 PM
Post #217 of 246 (686 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

Damn,

That was awesome! I especially liked the bit about the girlfriend coughing from the cigar smoke!

Very illustrative...Laugh


eames  (D 23844)

Feb 20, 2004, 4:46 PM
Post #218 of 246 (680 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
How far from the balloon is the center of the second group, and is there a risk of collision between groups?

I figure the center of the second group will be about 1100 ft from the balloon. And No, there's no chance of collision because even if a member of each group tracked right at each other there would still be 500 ft between them. How'd I do?

Edit: They may have less than 500' between them if the member of the first group that was heading toward a member of the second group while tracking continued toward him under canopy. But, he couldn't travel 500' in 11 seconds under canopy in brakes, so there's still no change of a collision.

-Jason


(This post was edited by eames on Feb 20, 2004, 5:06 PM)


johnny1488  (D 25453)

Feb 20, 2004, 4:49 PM
Post #219 of 246 (677 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

Damn I was gonna say 110 feet. My brain hurts, but I like itCool

And as for collision If they didnt already they are lucky because the second group overtook the first.


(This post was edited by johnny1488 on Feb 20, 2004, 4:51 PM)


kallend  (D 23151)

Feb 20, 2004, 6:18 PM
Post #220 of 246 (645 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
In reply to:
How far from the balloon is the center of the second group, and is there a risk of collision between groups?

I figure the center of the second group will be about 1100 ft from the balloon. And No, there's no chance of collision because even if a member of each group tracked right at each other there would still be 500 ft between them. How'd I do?

Edit: They may have less than 500' between them if the member of the first group that was heading toward a member of the second group while tracking continued toward him under canopy. But, he couldn't travel 500' in 11 seconds under canopy in brakes, so there's still no change of a collision.

-Jason

No.


eames  (D 23844)

Feb 20, 2004, 6:43 PM
Post #221 of 246 (642 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
No.

Okay, I think I see where I went wrong. The center of the second group is only 110 ft from the balloon and yes, there is a risk of collision between groups (and the balloon).

I think johnny1488 would have been right.

-Jason


mnischalke  (D 26290)

Feb 20, 2004, 7:47 PM
Post #222 of 246 (625 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

horizontally, 550 ft. yes, if the closest jumpers on each group went directly along the line of flight.

(edit, I am an idiot. I reversed the groups in my first try. oops)


(This post was edited by mnischalke on Feb 20, 2004, 8:11 PM)


kallend  (D 23151)

Feb 20, 2004, 8:37 PM
Post #223 of 246 (615 views)
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Re: [mnischalke] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
horizontally, 550 ft. yes, if the closest jumpers on each group went directly along the line of flight.

(edit, I am an idiot. I reversed the groups in my first try. oops)

You win.Smile

And the collision hazard doesn't depend on the presence of an observer in the balloon. He just provided a convenient origin.

The ground is irrelevant except as an approximate indicator of what is going on at opening altitude. All you need to know is that the plane is going 50ft/sec faster than the balloon, and multiply that by the exit delay 50 x 11 = 550ft. The groundspeed doesn't enter the equation, and it never does.

And real circumstances exist where blindly relying on groundspeed might kill you.


johnny1488  (D 25453)

Feb 20, 2004, 8:59 PM
Post #224 of 246 (611 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

I see where I made my mistake also. This is starting to make a lot more sense to me now. Thanks for puttin up with me and others like me Blush


eames  (D 23844)

Feb 20, 2004, 9:04 PM
Post #225 of 246 (609 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
50 x 11 = 550ft.

Don't you have to subtract the 40 x 11 = 440 ft that group one drifts while under canopy since the uppers and the lowers are heading in opposite directions?

-Jason


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