Re: [Martini] Opening High for Bad Spots

[Hooknswoop 19]

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Something else to consider when looking at comparing zero groundspeed jumpruns to jumping from fixed objects is bridge day. They huck how many jumpers through the same column of air in how many hours with how much separation? Think about it.

They have to wait until the previous jumper(s) are below where the next jumpers will be opening and that when the next jumper opens, there will be separation between the already open canopy and the opening canopy. You can’t have someone take a 1 second delay followed immediately by a 3 second delay from the same exit point. They do not do that a bridge day.

Derek

[Hooknswoop 19]

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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

[Hooknswoop 19]

*Let’s take the high wind example again. Let’s say there is 80 knot uppers and the jump ship has an airspeed of 80 knots and a ground speed of zero knots. Let’s also say these winds taper, linearly, to zero knots at 3,500 feet.

Group 2 exits 10 seconds after group 1. Group 1 pulls at 3,500 feet, group 2 pulls at 3,000 feet. Do see a reason to be concerned here?

*Let’s take it another direction. Let’s say the uppers are 90 knots and the jump ship has an airspeed of 80 knots. The jump ship has a ground speed of –10 knots. Let’s again say these winds taper, linearly, to 10 knots at 3,500 feet.

Group 2 exits 10 seconds after group 1. Group 1 pulls at 3,500 feet, group 2 pulls at 3,000 feet. Do see a reason to be concerned here?

In zero wind, at 80 knots, the jump ship covers 674 feet across the ground. In both of theses examples, airspeed has not changed, only ground speed.

I would like for Kallend to weigh in on what is more important for separation, airspeed or ground speed.

Derek

[velo90 0]

Can we go back to your tower?

13,500 ft high and 60 mph winds at the top. No ground speed cos it is a tower. We are both on top of the tower and I jump first and pull after 3 seconds.

You are also going to pull after three seconds. According to your theory you will have to wait ages before you jump because we have no ground speed.

What do you think is going to happen to me on my canopy in 60 mph winds? I am certainly not going hang around very long. What would be the separation if you wait 5 seconds before jumping assuming my canopy is capable of 30 mph and I try to fly back to the tower?

I know this is extreme but it's explains the principle that ground speed does not matter. In reality we only use ground speed as a good indicator for calculating separation.

[Hooknswoop 19]

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Can we go back to your tower?

Sure, but let's use an example that is not extreme. Let's say the winds are 40 knots at the top and zero at 4,000 feet, my deployment altitude. You plan on deploying at 3,000 feet. How long would you wait after I exited to follow?

Jumping in winds of 60 knots at deployment altitude is not realistic. If you did, yes you wouldn't have to wait very long between groups because of canopy drift. Usually winds at deployment altitudes are a lot less than 60 knots and therefore a lot of time is required to alloy the previous group to drift out of the airspace for a zero ground speed jump run.

If the winds are equal to the canopy's airspeed at deployment altitude and the jumper holds into the wind, they are slowly descending down the same airspace the next group will occupy shortly. IF the first canopy pulled a but high and the second canopy pulls a bit low, there is no separation and risk of collision.

Derek

[johnny1488 1]

Again I dont think derek is arguing that jumpers dont move once under canopy. If you pull after 3 seconds and then hold into the wind, can he exit the tower? WE have been discussing opening points, not what happens after that. WE exit over a point on the ground, we open over a point on the ground, we land at a point on the ground, it is the reference by which we measure everything. You dont say "I opened over that mass of air over there" Yes jumpers move under canopy, but that would mean we would have to wait for there freefall to be over to be sure they would not be in the same point as we were planning to open.

This horse is getting pretty damn tired of being beat. I think it was dead 3 pages ago, but I think we actually agree on most points, we just dont know it.

Johnny
--"This ain't no book club, we're all gonna die!"
Mike Rome

[velo90 0]

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Can we go back to your tower?
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Sure, but let's use an example that is not extreme.

That's the problem, you are always using examples where the speed over ground is not much different to the speed of the aircraft relative to the air mass where you open.

I have already agreed that generally ground speed works. You keep proving to me that ground speed generally works. But it works by chance!

Go back to my tower example, ZERO ground speed, and still separation. Ground speed is irrelevant!

[velo90 0]

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WE exit over a point on the ground, we open over a point on the ground, we land at a point on the ground, it is the reference by which we measure everything. You dont say "I opened over that mass of air over there"

And that is the problem, because we are in an air mass.
You need the separation in that air mass. We are not on the ground until we land. That means we have to study what happens to objects that move through the air mass. The ground does not matter.

This horse has been beaten many times on DZ.com and it will continue to be flogged as long as people say ground speed is what matters for exit seperation.

Oh, BTW the way, I don't think we agree at all.

[Hooknswoop 19]

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That's the problem, you are always using examples where the speed over ground is not much different to the speed of the aircraft relative to the air mass where you open.

Isn't that usually the case, or do you usually jump in winds where the uppers are 80 knots and 80 knots at 2,000 feet?

You are relying on canopy drift for separation, but there isn't much wind at deployment altitude to give you that drift/separation. Hence the longer amount of time required to wait for that drift to provide separation.

With a low ground speed, more time must be left between groups than with a high ground speed.

I didn't get a straight answer before, so I'll ask you;

Do you think that for a ground spped that provides 2,000 feet of separation between opening points for 10 seconds between groups provides that same 2,000 feet with 10 seconds between groups as the ground speed decreases from increased upper winds?

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Go back to my tower example, ZERO ground speed, and still separation. Ground speed is irrelevant!

Go back to my tower example, zero ground speed and zero separation because of zero wind at deployment altitude.

Now change it to 80 knots of ground speed and zero knots at deployment altitude with time left between groups, you get separation.

What is the difference between my tower example and this one? Ground speed providing separation. You cannot rely on canopy drift to provide separation.

Derek

[SkymonkeyONE 3]

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If you shoot a bullet from a rifle in to 100 mph headwind, wait 5 minutes and shoot another bullet from that rifle, providing that the wind hasn't changed and that you are standing in the same place, aiming the same and from the same height, both bullets will land in the exact same place.

That is a brilliant analogy. I must admit that what few working brain cells I have left have been scrambled by this back and forth banter, but I will now conclude that both people can be/are right (assuming their positions on their respective arguments).


I am going to try my best to split this thread in two and move this part of the discussion over to Safety and Training. Any mixing of the "chuck/alan/brian" part is simply a product of my inability to unscramble the thread to that degree.

Chuck

[velo90 0]

Please read this

Actually read the whole thread.

I done.

[Hooknswoop 19]

I read the thread and it seems that the majority agree that referencing groundspeed to ensure separation is the way to go........

Derek

[mnischalke 0]

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If you pull after 3 seconds and then hold into the wind, can he exit the tower?

Simply, yes. If we are basing this on the 60 mph model, if one canopy opens at 3 seconds, he's facing wind which is 60 mph, relative to the ground. Even facing into the wind, there is no canopy that I know of--which someone will actually land--that will go 60+ mph and therefore cannot get into the airspace of the next jumper.

The danger of hitting a canopy which was out before you comes into play only when the differential between windspeed at jump altitude and the windspeed at deployment altitude differs greatly. If it's 100kts at jump altitude, and 0 at deployment altitude, the canopys can be open in the same airspace, if the second group delays deployment for a distance equal to the first group's opening altitude plus the descent rate of the open canopy of the first group. Still, this is all based on speed in relation to the ground, but irrelevant to the ground because you're not on the ground.

Do we agree that the canopy arrests the descent of a jumper and prolongs the exposure to the wind? Then--and this is the important part--if we use the sliding rule of windspeed reduction with altitude loss, a canopy will move even more quickly away from the next group's path (column of air) the higher the deployment (since the winds only decrease with loss of altitude in this model).

mike

Girls only want boyfriends who have great skills--You know, like nunchuk skills, bow-hunting skills, computer-hacking skills.

[velo90 0]

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I read the thread and it seems that the majority agree that referencing groundspeed to ensure separation is the way to go........

Also from that thread.....

Kallend - Strictly speaking, you want to cover distance relative to the air at opening altitude. Usually this is pretty much the same as distance over the ground, but if the uppers are in the opposite direction to the lowers then you can find yourself with reduced separation.

Winsor - If you wish to pick a critical speed, it is that of the aircraft with regard to the airmass at opening altitude.


Winsor - the ground winds and ground speed are entirely immaterial, and have no effect whatsoever on the path of bodies THROUGH THE AIR.

Kallend - and the ground is irrelevant until you get there. It does serve as an approximate guide to what is happening at opening altitude, which is why groundspeed based methods usually work OK.

Winsor - Groundspeed is related only by coincidence.

[eames 0]

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I read the thread and it seems that the majority agree that referencing groundspeed to ensure separation is the way to go........

Dude, don't pull some kind of dz.com rank here. It's split pretty evenly.

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.

So according to you, PhreeZone, johnny1488, Nullified, and the rest of the "majority," you wouldn't be able to tell how far each group would be separated? So you're saying that depending on which cardinal direction you're facing your separation would change?

Hook, give me a relationship, give me a set of equations, that relates ground position and separation in that scenario, or in any scenario for that matter (ground speed is a function of ground position). I know that kallend could give us one that relates airspeed and separation.

If you can, you should be give the Nobel prize for proving that relativity as we know it is inconsistent.

-Jason

[Hooknswoop 19]

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Dude, don't pull some kind of dz.com rank here.

Rank? Me? Ha!

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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.

So according to you, PhreeZone, johnny1488, Nullified, and the rest of the "majority," you wouldn't be able to tell how far each group would be separated? So you're saying that depending on which cardinal direction you're facing your separation would change?

Hook, give me a relationship, give me an equation, that relates ground position and separation in that scenario (ground speed is a function of ground position).

If you can, you should be give the Nobel prize for proving that relativity as we know it is inconsistent.

Correct, if you did not know your ground speed, you couldn't know your separation.

Again the tower analogy;

*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.

*Same tower except the winds taper off to 10 knots, linearly. The second jumper will miss the first jumper as the first jumper drifts for 5 seconds at 10 knots. They won't miss by much.

No one seems willingy to answer my question:

Do you believe that at a given ground speed, 10 seconds delay produces 1,000 feet of separation. As the uppers increase, and the airspeed remains constant, does the same 10 second delay produce the same 1,000 foot separation between opening points? The only change being ground speed.

Derek

[velo90 0]

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Do you believe that at a given ground speed, 10 seconds delay produces 1,000 feet of separation. As the uppers increase, and the airspeed remains constant, does the same 10 second delay produce the same 1,000 foot separation between opening points? The only change being ground speed.

NO, there I have answered.

The only change being ground speed
I'll give you a tip here, the ground speed is not the only thing that has been changed

[velo90 0]

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Do you believe that at a given ground speed, 10 seconds delay produces 1,000 feet of separation. As the uppers increase, and the airspeed remains constant, does the same 10 second delay produce the same 1,000 foot separation between opening points? The only change being ground speed.

YES, there I have answered (again)

I am assuming that the wind speed from exit height all the way to the ground has increased by the same amount and the wind is blowing in the same direction from top to bottom.

[winsor 186]

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I read the thread and it seems that the majority agree that referencing groundspeed to ensure separation is the way to go........

Derek

Yeah, and if you polled one population or another you could support any number of demonstrably incorrect conclusions.

This is a definitive case of the classical fallacy of relevance "Argumentum ad Populum ."

Physics is not amenable to solution by quorum.


Blue skies,

Winsor

[JFC3 0]

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).

"Five days? But I'm angry now!"

[eames 0]

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Correct, if you did not know your ground speed, you couldn't know your separation.

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

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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.

No, he wouldn't. The first jumper would have drifted downwind of the opening point (with very little vertical speed because he's under a parachute) for 5 seconds at 40 knots. Did you not catch my cylinder/marble analogy. Should I draw you another diagram?

This is silly anyway, because most jump planes travel 80+ knots, and that is what determines separation. The only time I've agreed that the speed of the uppers has anything to do with separation is in the special case that the speed of the wind equals the speed of the plane. The airspeed of the plane is all that matters... until after opening.

I'm quite happy to just disagree with you at this point.

-Jason

[pccoder 0]

I hear ya.
My DZ has two planes, a Grand Caravan and a King Air.

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

I guess there will be the time where the winds, etc. can cause that to be a problem. But, I don't see myself busting out the scientific calculator at the door to compute all that.

PcCoder.net

[PhreeZone 15]

Go to Kallends calculator and see when the groups hit 45 degrees. Hint, they never will. Kallends entire website with the powerpoint will teach you about why the 45 degree thing is wrong.

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[JFC3 0]

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.

"Five days? But I'm angry now!"

[Hooknswoop 19]

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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.

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No, he wouldn't. The first jumper would have drifted downwind of the opening point (with very little vertical speed because he's under a parachute) for 5 seconds at 40 knots.

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

Derek