Re: [Martini] Opening High for Bad Spots

[johnny1488 1]

99% of the time at my dz we use an unpwind jumprun. If I needed to, without knowing the windsaloft, I could simply look at the ground speed and tell what kind of seperation I needed to give. The ground is the only thing that matters when giving seperation. Winds aloft really has no bearing because we are all subject to the same wind after we exit the plane. throw from the plane means nothing (with the exception of presentation to the relative wind, in which the effect is minimal). Look at Kallends simulator again. You could be going 500 mph through the air. If your groundspeed is zero, you will have zero seperation at pull time, period.

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

[eames 0]

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Here's 2: Bell 206 BIII Jet ranger, UH-60 Blackhawk.

Right, in that case you'd need to take more time between exits.... because there would be less (or no) airspeed for separation.

Unless you have a function that describes the significant decrease in horizontal airspeed between the winds at altitude and 3000 ft for your scenarios, your scenarios are not objective. But I'll comment anyway:

Yes, if the airspeed is greater, less time is required between groups to achieve the same separation.

Okay, we disagree.

One more try: Let's say there's is NO wind. You throw a toy paratrooper (nearly strait-down trajectory) out of an otter flying at 80 knots (airspeed), and you keep flying strait until the paratrooper hits the ground. Once the paratrooper hits the ground you've covered a certain distance across the ground. Now perform the same experiment at 90 knots (airspeed)... let the paratrooper go at the exact same spot. When the paratrooper hits the ground this time the plane has traveled farther along the ground away from the paratrooper, right? Was this due to a change in groundspeed or airspeed?

I know, groundspeed.... Then how would you explain the fact that the difference in distance that the plane traveled away from the impact point of the paratrooper would remain constant regardless of the direction of flight, windspeed, or wind direction?

-Jason

[johnny1488 1]

If groundspeed were irrelevent, then on a jump run into 70mph headwind with 70mph airspeed, you would give the same amount of time as you would if the pilot then turned 180 degrees and did another jump run at 70 mph airspeed. The entire first pass would open on top of one another and the second pass would be miles apart. It is groundspeed that determines the amount of time left in between groups.

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

[velo90 0]

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Let’s look at 2 more realistic scenarios:

I think that is the problem. I say ground speed is irrelevant, you say it is not.
I can provide a good example where ground speed is irrelevant but it does not fit into your real world of skydiving. Hence the minus 25 kts problem.

So, if you can accept what is more important than ground speed, is the speed of the aircraft relative to the air mass where the parachutes will be opened, we have made a 1st step.

Of course things get far more complicated when you have wind shear, but for the moment we will leave that aside.

Try reading the stuff from Kallend

[johnny1488 1]

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Then how would you explain the fact that the difference in distance that the plane traveled away from the impact point of the paratrooper would remain constant regardless of the direction of flight, windspeed, or wind direction?

I dont think he is trying to say that. He is saying that it is ground speed that determines how long a group has to wait in order to have a predetermined distance between groups at opening. once you leave the plane, where it is when when you open is irrelevent. After you leave the plane, the plane now only matters to those still in it.

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

[Hooknswoop 19]

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One more try: Let's say there's is NO wind. You throw a toy paratrooper (nearly strait-down trajectory) out of an otter flying at 80 knots (airspeed), and you keep flying strait until the paratrooper hits the ground. Once the paratrooper hits the ground you've covered a certain distance across the ground. Now perform the same experiment at 90 knots (airspeed)... let the paratrooper go at the exact same spot. When the paratrooper hits the ground this time the plane has traveled farther along the ground away from the paratrooper, right? Was this due to a change in groundspeed or airspeed?

Because of the 10 knot increase in ground speed.

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I know, groundspeed.... Then how would you explain the fact that the difference in distance that the plane traveled away from the impact point of the paratrooper would remain constant regardless of the direction of flight, windspeed, or wind direction?

Because there was zero wind and with zero wind ground speed = airspeed.

Derek

[Hooknswoop 19]

If airspeed is all that matters, why doesn't the 10 knot increase in airspeed create more separation in my examples below?;

1) 70 knots of wind at altitude. 80 knot airspeed on jump run. 15 knots of wind speed at 3,000 feet, the opening altitude (I have jumped in these winds).

2) 80 knots of wind at altitude. 90 knot airspeed on jump run. 15 knots of wind speed at 3,000 feet, again, the opening altitude.

The ground speed is constant and so is the amount of separation for the same delay between groups in both examples. An increase in airspeed didn’t result in an increase in separation with the same delay between groups.

3) 70 knots of wind at altitude. 90 knot airspeed on jump run. 15 knots of wind speed at 3,000 feet, again, the opening altitude.

With #3, and a 10 knot increase in ground speed, and no increase in airspeed, there would be more separation between groups for the same delay between groups.

Derek

[eames 0]

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If airspeed is all that matters, why doesn't the 10 knot increase in airspeed create more separation in my examples below?

There would be more separation, but your examples are useless anyway because you're not specifying what's happening with wind velocity between altitude and 3000 ft.... as I said above. In your examples, is the change between jumprun wind speed and 15 knots at 3000 ft linear, or what? Put numbers in there and show me that there would be no more separation....

-Jason

[PhreeZone 15]

Here is one, a plane flies into a head wind, its Indicated air speed is 90 knots (Otter exit speed) the wind is 30 knots. Its effective ground speed is 60 knots. But if the same plane was flying the other way with the wind pushing it its airspeed would still be 90 knots but its ground speed would now be 120 knots.

Airspeed has not changed at all, but its ground speed has changed a lot. With the higher ground speed you could allow for a shorter delay between groups.

This is almost like the "Canopies will always open downwind" argument

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[eames 0]

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This is almost like the "Canopies will always open downwind" argument

Really, how is that exactly?

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Airspeed has not changed at all, but its ground speed has changed a lot. With the higher ground speed you could allow for a shorter delay between groups.

Relative to the moving airmass, the separation will be exactly the same. Of course it won't be the same across the ground, you're going a different speed with respect to the ground! Why is that hard to understand?

-Jason

[kallend 1,623]

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If airspeed is all that matters, why doesn't the 10 knot increase in airspeed create more separation in my examples below?

There would be more separation, but your examples are useless anyway because you're not specifying what's happening with wind velocity between altitude and 3000 ft.... as I said above. In your examples, is the change between jumprun wind speed and 15 knots at 3000 ft linear, or what? Put numbers in there and show me that there would be no more separation....

-Jason

You put the numbers in. I have a computer program that saves your doing any arithmetic at www.iit.edu/~kallend/skydive/

For separation at opening altitude, what the wind does in between exit and opening altitude doesn't matter at all as long as it doesn't change between one group and the next.

...

The only sure way to survive a canopy collision is not to have one.

[Hooknswoop 19]

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There would be more separation

Exactly, more separation as a result of the increased ground speed with no change in the airspeed.

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but your examples are useless anyway because you're not specifying what's happening with wind velocity between altitude and 3000 ft.... as I said above. In your examples, is the change between jumprun wind speed and 15 knots at 3000 ft linear, or what? Put numbers in there and show me that there would be no more separation....

OK, call it linear, that doesn’t change anything. It is still ground speed that matters.

Derek

[eames 0]

Go check your math on kallend's website... your second example yields more separation than the first... and the third even more than the second... just as it should.

Check out the website, put your examples in there yourself, and then tell me you still disagree.

-Jason

[velo90 0]

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You put the numbers in. I have a computer program that saves your doing any arithmetic at http://www.iit.edu/~kallend/skydive/

At last, a voice of reason
Not that I can do the arithmetic, or that I will blindly believe a computer program. However, after reading your power point presentation (and notes to the presentation) I finally understood

I just wish that more people would take the time to try and understand. It was not easy for me, not being the brightest spark in the firework display, but if I can understand it, then I am sure other people will.

I think the biggest problem for most skydiver's is to remove the ground from the equation. After all that is their main reference point, that is where they are going to land. Here we are not talking about landing, we are talking about opening a parachute in an air mass, that may or may not be moving relative to the aircraft.

Thanks for the education John

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[PhreeZone 15]

On Kallends program with both groups belly speed:

80 kias
20 k headwind
0 knot lowers
6000 feet wind change
5 second delay results in:

669 feet seperation.

80 kias
20 k tailwind
0 knot lowers
6000 feet wind change
5 second delay results in:

1007 feet seperation.

Air speed of the plane never changed, but its ground speed did.

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[eames 0]

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If your groundspeed is zero, you will have zero seperation at pull time, period.

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?

-Jason

[eames 0]

Indicated Airspeed (kts) 80
Upper winds (kts) 80 Headwind
Lower winds (kts) 15 Headwind
Altitude of wind change 6000
Exit delay (sec) 15

Both slow fallers

Separation between deployment points: 484 ft.

BUT WAIT A MINUTE, THERE'S NO GROUND SPEED!!!

-Jason

[johnny1488 1]

Someone had to move out of the air. If you dont move you are basically a wind drift indicator. If you throw a wind drift indicator off a bridge (or plane in the air that doesnt move across the ground) and wait 2 minutes and throw another one, unless the winds have changed, they will follow the same path. I have exited an otter with almost zero airspeed after waiting 45 seconds (counted on video) and opened almost right were the group before me opened (the exact same space they occupied only a few seconds earlier). The distance the plane covers over the ground between groups is the distance the groups will have on opening barring differences in drift (rw, freefly, tracking ect)

edited to add: and I am sure its me, but I dont see a way to make both fallers on Kallends program slow, only to put the faster faller out 1st or 2nd.

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

[eames 0]

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I have exited an otter with almost zero airspeed after waiting 45 seconds (counted on video) and opened almost right were the group before me opened (the exact same space they occupied only a few seconds earlier).

The space they occupied only a few seconds earlier? I don't understand... why don't you explain it to me with your bridge analogy. So you throw a wind drift indicator off a bridge, wait 45 seconds, then throw another one, the second one will land within a few seconds of the first? That's quite a riddle....

-Jason

[johnny1488 1]

no it will land 45 seconds later in the same spot

edited to change my time cause i misread your post.

If someone has a slow moving canopy or turns back up the line of flight or opens off heading, its pretty damn close, especially when drift isnt static and things change in the air.

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

[eames 0]

Have you considered that maybe you were just barely upwind of the dropzone and the people that went in front of you were holding into the wind under canopy for 30 seconds of your skydive?

-Jason

[Hooknswoop 19]

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BUT WAIT A MINUTE, THERE'S NO GROUND SPEED!!!

If there is no ground speed, then they should have the same exit point on the graph and the little red block that represents the aircraft shouldn't move. According to the graph, they 2 groups do not have the same exit point and the little red block is moving to the right.

I think something is wrong with the program.

Two bodies that fall at the same rate are tossed off a 13,500 tower and subject to the same winds. They will impact the ground at the same place. If you imagine ground impact as the opening point, then there is zero separation between opening points.

For canopy drift in the above scenario, I calculate 380 feet (6076*15/60/60*15). This is not enough separation. Imagine an 8-way followed by a 4-way. The groups would over-lap on deployment as the 8-way drifted away from the opening point.

For zero ground speed, you would have to wait for the previous group to clear the airspace that you will be in when you open. 45 seconds would have the 8-way drift 1139 feet, still not enough wait time. You are no longer relying on separation between opening points for clearance from other jumpers, you are sharing the same opening point and waiting for them to clear the airspace so you can use it.

For opening point separation, airspeed doesn’t matter, ground speed determines the amount of time that must be left between groups in order to have, for example, a constant 2,000 feet between opening points. Increasing airspeed does not increase the distance between opening points, increasing ground speed does (for a constant time between groups).

Airspeed for a particular jump ship is usually the same from jump run to jump run. As the upper winds increase, a longer time must be left between groups to account for the decreased ground speed.

If only airspeed mattered for separation, we wouldn’t have to increase the time between groups as the upper winds increased, since the airspeed of the jump ship hasn’t changed.

Derek

[johnny1488 1]

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Have you considered that maybe you were just barely upwind of the dropzone and the people that went in front of you were holding into the wind under canopy for 30 seconds of your skydive?

And if they were that would still give us the same amount of freefall drift and no (or not enough) opening separation.

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.

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

[cliffharris 0]

I don't think I like your tone mister. Two demerits!

[eames 0]

I've made a diagram. I just want you to see what I see, even if you don't agree.

On the diagram, just for argument's sake, the thick black line represents a freefall trajectory and canopy flight. Just say for instance that it's a cylinder instead... and you can roll a marble down it. No tricks, only one tube, not to be moved. Can you see that if you roll one marble down it, then another in 10 seconds, they will still never be at the same place at the same time?

-Jason