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Re: [Martini] Opening High for Bad Spots

 

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freakydiver  (D 26421)

Feb 19, 2004, 10:01 AM
Post #101 of 246 (762 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

That's a pretty balsy assumption - one I sure as hell wouldn't want to make.


freakydiver  (D 26421)

Feb 19, 2004, 10:05 AM
Post #102 of 246 (758 views)
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Re: [pccoder] Opening High for Bad Spots [In reply to] Can't Post

"Basically the rule is something like > 7 secs separation on the Caravan and > 5 secs on the King Air."

People - there is no hard a fast BASIC rule for seperation. Every single year I see more and more close calls because of the 45 degree friggin MYTH and people never adjusting their exits based on uppers. If your DZ told you 5 seconds on the King Air and never ever varied from that 5 seconds, find another DZ with experienced LOs. pccoder, you really should put a great deal of thought into this because it really affects not only you, but the group exiting before you. There really should be an on-board calculator becuase as I've stated, I've seen more and more close calls every single year in this sport due to shitty generalizations on how to achieve proper seperation. THIS IS NOT A TOPIC TO GET LAZY ON.


johnny1488  (D 25453)

Feb 19, 2004, 10:18 AM
Post #103 of 246 (754 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
No, in actuality, your separation would be the same no matter what your ground speed.

Same uppers/ same direction on the same day
Get out of an otter facing into a 70kt headwind 10 seconds after another jumper. Then get out of an otter with a 70kt tailwind 10 seconds after another jumper.(180 degrees from the first jump run) The first you could very well have a close call with. The second you propably will never see.


johnny1488  (D 25453)

Feb 19, 2004, 10:22 AM
Post #104 of 246 (752 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
Just for argument's sake let's say there's a layer of clouds at 200 ft and you can't see the ground at all. You have no idea which way you are flying with respect to the ground (no instruments except your airspeed indicator). Your airspeed remains constant and positive.

If you trust the winds aloft you will know the seperation using the airspeed indicator. All this can be worked out on the ground and the exit seperation time can be worked out knowing the direction of the winds and jumprun.


johnny1488  (D 25453)

Feb 19, 2004, 10:37 AM
Post #105 of 246 (746 views)
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Re: [freakydiver] Opening High for Bad Spots [In reply to] Can't Post

I think Tom Buchanan (tombuch here) wrote a pretty good article about this subject. it can be read here:
http://www.ranchskydive.com/safety/tb_article15.htm

He brings the useable length of the jumprun into the equation.


Premier billvon  (D 16479)
Moderator
Feb 19, 2004, 10:48 AM
Post #106 of 246 (740 views)
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Re: [JFC3] Opening High for Bad Spots [In reply to] Can't Post

> wait until they're at 45 degrees from the door and then jump and have some fun?

Cause colliding with an open canopy is often not that fun, and you risk that if you rely on the 45 degree rule. They never reach 45 degrees, which means you either wait forever or you just guess at what _you_ think 45 degrees is. And everyone has a different opinion on what 45 degrees is.

>Half of one 6 dozen of another how will I end up on top of them

From your point of view:

The upper winds are strong, but they drop off with altitude. You follow a freefly group out. They have a perfect head-down exit, so they get a lot of throw and reach the angle you like quickly. You get out 4 seconds later.

You are now in freefall about 1000 feet above them and about 600 feet from them laterally. Since the winds drop off with altitude, that means they are always in _less_ wind than you are (cause they're 1000 feet lower.) They get less push than you do. Since you are upwind of them, the stronger winds at your altitude pushes you slowly towards them.

At deployment altitude, they have slid almost directly beneath you. One guy deploys a little high, his canopy has a hard opening and surges directly beneath you. Result - you collide with a canopy.

How to avoid that? Leave more time between groups when the plane is flying into strong winds and the winds at opening altitude are lighter (which is usually the case.)

"Why can't I just jump and have fun?" is a foolish thing to say. It's a bad excuse no matter what you're neglecting, whether it's gear checks, dirt dives or exit separation.


kallend  (D 23151)

Feb 19, 2004, 12:10 PM
Post #107 of 246 (708 views)
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Re: [JFC3] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
What caused me to read this incredibly long thread is the very first post I see which states that the 45 degree rule does not work. Yet no one has shown me why it doesn't.

Whether I'm supposed to peak into the cockpit and calculate airspeed vs. wind speed or look 3 miles down at the ground and determine how fast I'm moving is it just not easier and much more reliable to look out at the last group, wait until they're at 45 degrees from the door and then jump and have some fun? Please tell me how that does not work. They're on a different column of air. They have an appropriate time-relationship distance. Half of one 6 dozen of another how will I end up on top of them (unless you back slide like an SOB like me).Crazy

Do a forum search on the 45 degree rule, and you'll find so many explanations about why it doesn't work you'll be up til midnight reading them. It doesn't work. It is dangerous to rely on it.


kallend  (D 23151)

Feb 19, 2004, 12:12 PM
Post #108 of 246 (707 views)
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Re: [JFC3] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
I went to it when it was mentioned in the thread. But if it's going to tell me the group before me never reaches 45 degrees it's wrong. It's time vertical and more importantly horizontal. 45 degrees from where I am when I exit. Granted in different conditions that time to get to 45 is longer and they're much smaller but they will get there.

Edit to say: I am no genius at this and I won't present any calculations to prove my point I'd rather have someone else (and there seems to be a bunch out there) who has got their minds wrapped around this better show me plainly why common sense just doesn't work in this situation.

I always find it amusing when people argue physics with physicists after claiming no talent for the subject.


kallend  (D 23151)

Feb 19, 2004, 12:18 PM
Post #109 of 246 (706 views)
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Re: [Hooknswoop] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
Quote:
Have you read Kallend's power point presentation yet?

All your thoughts about separation are correct IF you would forget about the ground and think about where you deploy the parachute. We are not interested in the ground, we are interested in the air mass where the parachutes open.

If you have a 15 kts wind at 3000 ft and jumper a deploys at a point A above the ground. Then 10 seconds later the second jumper deploys into the first jumper. They have deployed at different points above the ground, but unfortunately they have no seperation.


If the wind speed lower to the ground is blowing in the same direction as the uppers then .....
Your method (using ground speed) to calculate the time between exits for good separation at pull time will give a time that is (most often) longer than necessary. Not a bad thing, more separation is better, but on big planes you might need a go around more often.

Now if we have wind shear and the lowers are blowing 180 to the uppers, your method (ground speed) will give you a time that is too short. This problem may not be of interest to you, but for me it is very important. At my dropzone we have this situation occasionally.

I don't think anyone here is ever going to convince you that ground speed is irrelevant. Most of the time the way you think about this problem is not going to cause any harm. BUT, if we do have wind shear, and the lower's are 180 to the uppers, then please do what you put in your sig line , THINK.

Ground speed is the only way to determine distance between opening points.

*With 5 seconds between exits and 80 knots of airspeed and 80 knots of uppers for zero grounds speed, the groups will open at the same point in space, 5 seconds apart. The only thing that will prevent a collision is the first group drifting downwind once they open.

*With 5 seconds between exits and 80 knots of airspeed and 0 knots of uppers for 80 knots grounds speed, the groups will have opening points 674 feet apart. Same airspeed, different ground speed, increased separation of opening points.

No one has contradicted this.

Same airspeed, change in ground speed caused change in separation between opening points.

*With 5 seconds between exits and 180 knots of airspeed and 180 knots of uppers for zero grounds speed, the groups will open at the same point in space, 5 seconds apart.

100-knot increase in airspeed, no increase in separation between opening points. Again, the only thing that will prevent a collision is the first group drifting downwind once they open.

Derek

Scenario: 80kt true airspeed into 80kt headwind at 13k. Groundspeed = 0. Headwind at 12k also 80kt.

Jumper 1 exits.

Jumper 2 waits 10 seconds and exits. Follows exactly same path down as jumper 1 relative to the ground (agree?).

Unfortunately, 0.001 second after jumper 2 commits, jumper 1 has a premature deployment. He is at 12k in 80kt winds. Jumper 1 is looking the other way and does not see.

Do they collide?


velo90

Feb 19, 2004, 12:19 PM
Post #110 of 246 (706 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

Quote:
The airspeed of the plane is all that matters... until after opening.

No eames Crazy The air speed is not all that matters. The speed of the aircraft relative to the air mass where you open is what matters.

By the way, you would reach 45 if the aircraft is flying fast enough. But we don't generally exit at those sort of speeds.

I feel sorry for Kallend. He's put so much effort in trying to educate people and has not really changed much. Or is it just in these forums?


kallend  (D 23151)

Feb 19, 2004, 12:20 PM
Post #111 of 246 (706 views)
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Re: [Hooknswoop] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
Quote:
Not necessarily. The program might be shifting the visual so that the trajectories can be seen more easily. True, the reference points don't move, but it may have been easier to program it with them fixed in place. Maybe we should ask kallend.

I think the error we are seeing is the difference between indicated airspeed and true airspeed. The opening separation should be zero.

Derek

Depends which version you use. The online (java) version does it differently from the downloadable version. You are likely to see the true/indicated problem on one of them (forget which right now).


kallend  (D 23151)

Feb 19, 2004, 12:25 PM
Post #112 of 246 (699 views)
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Re: [velo90] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
Quote:
The airspeed of the plane is all that matters... until after opening.

No eames Crazy The air speed is not all that matters. The speed of the aircraft relative to the air mass where you open is what matters.

By the way, you would reach 45 if the aircraft is flying fast enough. But we don't generally exit at those sort of speeds.

I feel sorry for Kallend. He's put so much effort in trying to educate people and has not really changed much. Or is it just in these forums?

Anyone that wants to use my Powerpoint presentation and calculator for Safety Day is very welcome so to do.


JFC3  (C 31790)

Feb 19, 2004, 12:35 PM
Post #113 of 246 (693 views)
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Re: [billvon] Opening High for Bad Spots [In reply to] Can't Post

Thanks billvon and I think I see what you're saying but to the situation you propose:

If a group gets out and hits a perfect head down in high winds they're not going to get to my "45 degree rule" (which I have no stronger basis for other than hearing it from people I trust and seeing good results from it so please don't think it's my bible I just want to understand this as it's always been a concern of mine) not in 4 seconds at all. In fact while they will become very small before they are there they would get there. So no matter if I caught the same gust they did leaving the plane so much time has gone by that we've all but eliminated the possability of collision. They would have been sitting in that gust for the last 15 seconds + (please don't say you'd have left in 4 - although I've been to DZ's that insisted on it - I don't go to there anymore) No? Hell, they'll be packing up before I open!Sly

To the point that 45 degrees is different to everyone I just gotta say, huh? I mean my 45 may be your 46 but I think any simpleton could identify 45 degrees. Right???

And I am not foolisd (a foolish thing to accuse me of). If I were I doubt this subject would interest me enough to ask. And you had me believing in the value of what you had to say until then. Thanks anyway.

Anyone who can make a point without making an insult?Unsure


JFC3  (C 31790)

Feb 19, 2004, 12:42 PM
Post #114 of 246 (692 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

Geez. Touchy much?

I wasn't saying it was faulty and I've been given some interesting leads to read up on the faulty-ness of the 45 degree rule. And will. But please relax. I'm asking only because with such a discussion on this subject and no discussion on the claim the 45 degree doesn't work I just wanted to ask. And still while being insulted no one has shown my why it does not work.

And I tell people skydivers are the best nicest people aroung.Crazy


diverdriver  (D 19012)

Feb 19, 2004, 1:13 PM
Post #115 of 246 (684 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

Ok, I'm coming into this thread late here. Man did it take me a long time to read through all that AGAIN. Anyhow, I realise that we always have new people here and they must be educated. This education will continue until the day we no longer skydive.

I don't know if I'm going to add anything to this thread or just muddy the waters. When I talk to people about exit seperation I talk about indicated grounspeed. And you will have the physicists like Kallend, and Winsor roll their eyes at me. And yes, guys, I know that it is the differential between exit winds and deployment winds that will get you the seperation. But I think you will agree that during normal operations that looking at the groundspeed will give you a basic idea of what that differential will be? You certainly won't have 80 knots winds at 3K will you? So, we do know there is some differential and grounspeed is an indirect indicator (read easier to understand) way of looking at seperation.

John knows I'm a hell of a spotter with my GPS and he lets me roll on with my grounspeed explanations like a loving pappa who knows his kid is still wrong but close enough.

The things we need to remember when choosing exit seperation is:

1. As the upper winds increase we DO need to give more time in the door for proper seperation.
2. The 45 degree rule DOES NOT WORK and can get you killed potentially.
3. Running jumprun when the winds are in OPPOSITE directions requires special care be given to seperation.

People need to stop arguing who's physics is better. I've seen a lot of useless bantering on this thread. The work has already been done by some very bright minds. There are some highly educated (on the subject) people trying to teach something here and the newer jumpers might be mindful of listening to them a bit.


mnischalke  (D 26290)

Feb 19, 2004, 1:15 PM
Post #116 of 246 (683 views)
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Re: [kallend] Opening High for Bad Spots [In reply to] Can't Post

Quote:
Do they collide?

no, not even close.


eames  (D 23844)

Feb 19, 2004, 1:33 PM
Post #117 of 246 (677 views)
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Re: [velo90] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
No eames The air speed is not all that matters. The speed of the aircraft relative to the air mass where you open is what matters.

Okay, there are other factors, and my explanation is by no means comprehensive, but I will maintain that the only thing the ground has to do with exit separation is that it adds a bit of dynamics to the fluid flowing over it.

-Jason


eames  (D 23844)

Feb 19, 2004, 1:37 PM
Post #118 of 246 (674 views)
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Re: [Hooknswoop] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
Why would he drift at 40 knots from the opening point, when there is zero wind at the deployment altitude of 3,000 feet?

Okay, I understand what you're saying, but this would only happen in the very special case that the speed of the uppers matches the airspeed of the plane and there is no wind at opening altitude. Do you ever see this happening?

-Jason


eames  (D 23844)

Feb 19, 2004, 1:48 PM
Post #119 of 246 (664 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
14,000 tower. Winds are 40 knots at the top, tapering to zero, linearly, at 3,000 feet, the deployment altitude. Two jumpers, jumping rounds, exit 5 seconds apart. The second jumper pulls a little late. He will hit the first jumper.

I totally see where you're coming from with this now. But the only time that skydiving is analogous to being on a 14,000 ft tower is when the uppers match the AIRSPEED OF THE PLANE. Separation is mostly due to the airspeed of the plane.

Yes, if the change in velocity of the mass of air is so drastic that it goes from a magnitude equal to the airspeed of the plane at 14,000 ft all the way down to zero at 3000 ft, there is a very high collision possibility. But I can't say I remember a single day when this condition existed.

-Jason


(This post was edited by eames on Feb 19, 2004, 1:49 PM)


Hooknswoop  (D License)

Feb 19, 2004, 1:57 PM
Post #120 of 246 (654 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

Quote:
Okay, I understand what you're saying, but this would only happen in the very special case that the speed of the uppers matches the airspeed of the plane and there is no wind at opening altitude. Do you ever see this happening?

Not any more likely than exiting with 80 knot winds from exit to opening.

The second jumper would hit the first jumper, even though there was 40 knots of wind at the exit point. No ground speed resulted in zero separation of opening points.

It illustrates my point though. As you increase the wind speed at the opening altitude in my example, separation is created by canopy drift. Say the wind is 15 knots at opening altitude and 10 seconds is left between groups. That means the canopy of jumper 1 will drift 253 feet down wind in 10 seconds. This is not enough room between jumpers, as that distance can be easily tracked and flown under canopy, eating up the separation created by the drift at opening altitude.

Now lets make the tower an aircraft and give it a ground speed of 15 knots instead of the zero for the tower. Same 10 seconds between exits. The aircraft will cover 253 feet over he ground in that 10 seconds and jumper 1s canopy will drift for another 253 feet. More separation due to the increased ground speed of the aircraft.

More room must between exits as the upper winds increase in speed.

Some examples from Kallends simulator (the only variable I changed for each simulation is the upper winds):

Indicated airspeed: 80
Upper winds: 20
Lower winds: 0
Altitude of wind change: 3000
Exit delay: 10
Both slow fallers

Separation: 1337


Upper winds: 30
Separation: 1168

Upper winds: 40
Separation: 999

Upper winds: 50
Separation: 830

Upper winds: 60
Separation: 661

Upper winds: 70
Separation: 492

Upper winds: 80
Separation: 323

Upper winds: 90
Separation: 154

Upper winds: 100
Separation: 15

As the upper winds increase, the separation between opening points decreases.

What am I missing? (Honestly, if I am wrong, and that is a real possiblility, I will admit itSmile I am either correct or not seeing something)

Derek


eames  (D 23844)

Feb 19, 2004, 1:59 PM
Post #121 of 246 (651 views)
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Re: [Hooknswoop] Opening High for Bad Spots [In reply to] Can't Post

Here's the conclusion I've come to: Separation is due to the airspeed of the plane and the changes in velocity of the airmass relative to itself.

The changes in velocity of the airmass relative to itself are inevitably due to the interaction of the fluid with the ground.

But separation in skydiving has more to do with the airmass itself, and very little to do with the ground (and only very indirectly at that).

-Jason


bmcd308  (D 27472)

Feb 19, 2004, 2:06 PM
Post #122 of 246 (646 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

>>I've jumped out of several Cessnas with zero groundspeed before and I definitely didn't have to wait infinitely to exit after the person in front of me. No tracking, no high pulling, and we weren't even close at pull time. How would you explain that? Was it a miracle? <<

One of you backslides.


eames  (D 23844)

Feb 19, 2004, 2:06 PM
Post #123 of 246 (646 views)
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Re: [Hooknswoop] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
Not any more likely than exiting with 80 knot winds from exit to opening.

This is true, but anywhere in between there will still be separation, will there not?

In reply to:
It illustrates my point though. As you increase the wind speed at the opening altitude in my example, separation is created by canopy drift.

It's not due to canopy drift, it's due to a greater difference between upper and lower winds (like I said before, the airmass with respect to itself). Try increasing the lower winds proportionally.

In reply to:
What am I missing? (Honestly, if I am wrong, and that is a real possiblility, I will admit it I am either correct or not seeing something)

Same here.

-Jason


eames  (D 23844)

Feb 19, 2004, 2:07 PM
Post #124 of 246 (644 views)
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Re: [bmcd308] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
One of you backslides.

Yeah, that's funny.

-Jason


bmcd308  (D 27472)

Feb 19, 2004, 2:09 PM
Post #125 of 246 (642 views)
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Re: [johnny1488] Opening High for Bad Spots [In reply to] Can't Post

>>Also on days where the otter would have zero airspeed on jumprun, we would usually wait a considerable amount of distance past the dz, a usual "there is no too long" day. <<

Were you able to turn points inside the otter that had zero airspeed on jumprun, or did you all just hug each other and wait for the pilot to to sort it out?


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