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Re: [Martini] Opening High for Bad Spots

 

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eames  (D 23844)

Feb 18, 2004, 2:40 PM
Post #51 of 246 (894 views)
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Re: [cliffharris] Opening High for Bad Spots [In reply to] Can't Post

What? But, I have no merit Colonel!


johnny1488  (D 25453)

Feb 18, 2004, 2:44 PM
Post #52 of 246 (887 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
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?

Never, except at the end of the tube/impact point of the ground/opening point if the canopies dont move.


Hooknswoop  (D License)

Feb 18, 2004, 2:44 PM
Post #53 of 246 (885 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

The alternative is not unthinkable. I caught that before you edited it.

You agree that the objects should hit the same point, and the aircraft should not be moving, but the program doesnt show that, so there must be something wrong with it. Do you agree?

I agree that after opening, the first group will drift and eventually if the second group waits until they drift far enough away, they can exit and use the same airspace safely. They will share the exact same opening point because the aircraft has zero ground speed.

As the aircrafts ground speed increases, for a constant airspeed, less time needs to left between groups.

As I already said:

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.

The bottom line is that separation of opening points is a function of ground speed and time between exits. This is the reason the free fall drift program requires the airspeed of the jump ship and the wind speed it is flying in. It then calculates the ground speed of the jump ship and uses that number in the calculation of the separation of opening points. Increase airspeed and wind speed 10 knots each and there is no change in the separation between opening points.

For your diagram, there is zero separation between opening points. The marbles pass through the same points in space. The only reason they do not collide is that the first marble is out of the way by the time the second marble comes by. For someone tracking up the line of flight, then holding, they may be in that way if only 15 seconds are left between the exits. The first group must clear the airspace in order for the second group to use the same airspace.

Your marbke example demonstrates that there is something wrong with the free-fall simulator program.

Derek


(This post was edited by Hooknswoop on Feb 18, 2004, 2:48 PM)


eames  (D 23844)

Feb 18, 2004, 2:50 PM
Post #54 of 246 (877 views)
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Re: [johnny1488] Opening High for Bad Spots [In reply to] Can't Post

Yeah, I'll admit: You can still collide with someone if you try really hard.

-Jason


Hooknswoop  (D License)

Feb 18, 2004, 2:50 PM
Post #55 of 246 (875 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

Do you leave more time between the group in front of you if the upper winds increase, but the jump ship's airspeed is the same?

Derek


eames  (D 23844)

Feb 18, 2004, 2:56 PM
Post #56 of 246 (871 views)
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Re: [Hooknswoop] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
The alternative is not unthinkable.

My bad on that point, I got a little too excited.... I hope you understand. I'm very cynical.

In reply to:
You agree that the objects should hit the same point, and the aircraft should not be moving, but the program doesnt show that, so there must be something wrong with it. Do you agree?

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.

-Jason


Hooknswoop  (D License)

Feb 18, 2004, 2:57 PM
Post #57 of 246 (869 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

Just to clarify, you do not agree that to identical objects tossed of a tower and subjected to identical winds will hit the same point on the ground?

Derek


eames  (D 23844)

Feb 18, 2004, 3:01 PM
Post #58 of 246 (865 views)
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Re: [Hooknswoop] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
Do you leave more time between the group in front of you if the upper winds increase, but the jump ship's airspeed is the same?

Yes, and I've explained why in this thread. Higher wind speeds promote canopy traffic congestion (assuming an upwind opening point), because it takes less time to get to the landing area going downwind. Ground speed comes into play after opening, when everyone is aiming for the same spot on the ground.

-Jason


Hooknswoop  (D License)

Feb 18, 2004, 3:02 PM
Post #59 of 246 (864 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

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


Hooknswoop  (D License)

Feb 18, 2004, 3:05 PM
Post #60 of 246 (861 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

So you think that regardless of ground speed, for a constant airspeed, 15 seconds between groups will result in the same amout of separation between opening points?

Derek


eames  (D 23844)

Feb 18, 2004, 3:05 PM
Post #61 of 246 (859 views)
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Re: [Hooknswoop] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
Just to clarify, you do not agree that to identical objects tossed of a tower and subjected to identical winds will hit the same point on the ground?

They would, if they were not subject to canopy opening (sudden shallow descent-rate) followed by controlled canopy flight.

-Jason


Hooknswoop  (D License)

Feb 18, 2004, 3:08 PM
Post #62 of 246 (945 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

Quote:
They would, if they were not subject to canopy opening (sudden shallow descent-rate) followed by controlled canopy flight.

Then you agree that, for zero ground speed, group 1 and group2 will share the same exact opening point and that for a true airspeed of 80 instead of indicated, the separation would be zero for your example and not 484 feet?

Quote:
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!!!

Derek


eames  (D 23844)

Feb 18, 2004, 3:09 PM
Post #63 of 246 (944 views)
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Re: [Hooknswoop] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
So you think that regardless of ground speed, for a constant airspeed, 15 seconds between groups will result in the same amout of separation between opening points?

Relative to the moving airmass, yes.

-Jason


Hooknswoop  (D License)

Feb 18, 2004, 3:16 PM
Post #64 of 246 (939 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

Quote:
So you think that regardless of ground speed, for a constant airspeed, 15 seconds between groups will result in the same amout of separation between opening points?

--------------------------------------------------------------------------------


Relative to the moving airmass, yes.

Let me clarify the question.

You think that regardless of ground speed, and assuming that 15 seconds will leave 2,000 feet of separation between opening points in zero wind, as the upper winds increase and the ground speed of the jump ship decreases, 15 seconds delay between groups will still create 2,000 feet of separation between groups?

Derek


Hooknswoop  (D License)

Feb 18, 2004, 3:32 PM
Post #65 of 246 (928 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

Quote:
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!!!

Actually there is a 18.5 knot ground speed.

The program is set up for stand ICAO atmosphere. The standard temperature at 15,000 ft MSL is 5.51 degree F. The program uses 14,000 ft MSL for the exit altitude. Allowing the 1,000 foot error, that gives a true airpseed of 98.5 knots.

65 knots indicated is equal to 80.1 knots true airspeed at 15,000 feet. Try these numbers to get zero (or almost zero ground speed):

Indicated Airspeed (kts) 65
Upper winds (kts) 80 Headwind
Lower winds (kts) 15 Headwind
Altitude of wind change 6000
Exit delay (sec) 15

Both slow fallers

Derek


(This post was edited by Hooknswoop on Feb 18, 2004, 3:36 PM)


eames  (D 23844)

Feb 18, 2004, 4:05 PM
Post #66 of 246 (920 views)
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Re: [Hooknswoop] Opening High for Bad Spots [In reply to] Can't Post

In reply to:
Then you agree that, for zero ground speed, group 1 and group2 will share the same exact opening point and that for a true airspeed of 80 instead of indicated, the separation would be zero for your example and not 484 feet?

The opening point would be the same point in space, with respect to the ground, but by the time the second group got there, the first group would have continued downwind with an arrested descent rate at a velocity equal in magnitude and opposite in direction to that of the aircraft (aircraft speed = -windspeed here) for the same amount of time that the second group gave them in the door.

-Jason


johnny1488  (D 25453)

Feb 18, 2004, 5:46 PM
Post #67 of 246 (909 views)
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Re: [eames] Opening High for Bad Spots [In reply to] Can't Post

So the first jumper who opens facing up wind and colapses their slider and fumbles with their chest strap sees the second jumper scream past them when they pull 5 seconds late after they have a hard pull.

Thats why I believe horizontal seperation is the only thing that matters. I look out of the plane to see how much distance the plane has made since the last group exited.

I just think jumpers need to know the ralationship between the ground speed of the plane and the amount of time needed to be given between groups.


(This post was edited by johnny1488 on Feb 18, 2004, 5:57 PM)


Hooknswoop  (D License)

Feb 18, 2004, 5:52 PM
Post #68 of 246 (905 views)
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Re: [johnny1488] Opening High for Bad Spots [In reply to] Can't Post

Quote:
So the first jumper who opens facing up wind and colapses their slider and fumles with their chest strap sees the second jumper scream past them when they pull 5 seconds late after they have a hard pull.

Or the second group funnels and falls fast while the first, and larger group builds a slow, tight formation. The second group catches up to the first group and eats up the separation they would have had from canopy drift.

Derek


mnischalke  (D 26290)

Feb 18, 2004, 8:36 PM
Post #69 of 246 (880 views)
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Re: [johnny1488] Opening High for Bad Spots [In reply to] Can't Post

I think what some folks may not be realizing is that the aircraft, even traveling 100 kts in 100 kts headwind (thereby negating groundspeed), is still traveling through the air at 100kts. The first group may exit the aircraft at exactly the same spot above the ground as the second group, but the first group will be in a totally separate column of air than the second group, given a reasonable delay between exits. Therefore, the space in which the first group will deploy will be continuing to move downwind, and the position the second group's deployment will be further upwind (even though it may be over the same place on the ground). The reason to increase time between groups on jumpruns with high winds at altitude is because generally, the winds decrease by opening altitudes and thereby causing a stacking effect. Nonetheless, the groups will be opening in different columns of air, no matter their position over the ground. The only case in which this whole thing is negated is when the wind at 3000 is zero or 180 degrees from the winds at altitude.

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.

I guess the thing is with groups falling through columns of air (irrespective of position over the ground), if groups are falling faster or slower, with columns which are straight down, or askew from sliding, the closer to the ground you get, the higher the likelyhood of converging columns of air. If you leave an aircraft after me with a reasonable delay and you have a backslide which is causing you to directly intersect my column of air at some point, if I dump at 6k, you have a lesser chance of hitting my canopy than you do if I open at 3k. That chance increases further by 2k (unless your backsliding so hard you bisect my column at 3k and get past me. got me?


Nullified  (C 32259)

Feb 18, 2004, 9:35 PM
Post #70 of 246 (874 views)
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Re: [mnischalke] Opening High for Bad Spots [In reply to] Can't Post

Quote:
I think what some folks may not be realizing is that the aircraft, even traveling 100 kts in 100 kts headwind (thereby negating groundspeed), is still traveling through the air at 100kts. The first group may exit the aircraft at exactly the same spot above the ground as the second group, but the first group will be in a totally separate column of air than the second group, given a reasonable delay between exits. Therefore, the space in which the first group will deploy will be continuing to move downwind, and the position the second group's deployment will be further upwind (even though it may be over the same place on the ground). The reason to increase time between groups on jumpruns with high winds at altitude is because generally, the winds decrease by opening altitudes and thereby causing a stacking effect. Nonetheless, the groups will be opening in different columns of air, no matter their position over the ground. The only case in which this whole thing is negated is when the wind at 3000 is zero or 180 degrees from the winds at altitude.
Given a ground speed of 0mph at exit, and assuming that 1st and 2nd exiting groups fall at the same rate and experience the same winds at various altitudes and open at the same altitude, groups 1 and 2 will have opened at the exact same place.
With 0 groundspeed, the aircraft becomes a fixed object. Assuming all variables remain equal for both groups, they will open in the identical position, whether the 2nd group gave 3 seconds of separation or 125 years.


mnischalke  (D 26290)

Feb 18, 2004, 9:48 PM
Post #71 of 246 (869 views)
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Re: [Nullified] Opening High for Bad Spots [In reply to] Can't Post

It remains a fixed object relative to the ground.

The ground doesn't matter until you land.

The aircraft is still traveling through the air. The air is moving, thus causing separation horizontally and vertically based upon delay between groups. No matter where above the ground the groups open, the air continues to move the first group away from the spot of deployment. Each group has it's own column of air and unless the second group is sliding, the two groups will never share the same air.


Nullified  (C 32259)

Feb 18, 2004, 10:38 PM
Post #72 of 246 (863 views)
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Re: [mnischalke] Opening High for Bad Spots [In reply to] Can't Post

Quote:
It remains a fixed object relative to the ground.

The ground doesn't matter until you land.

The aircraft is still traveling through the air. The air is moving, thus causing separation horizontally and vertically based upon delay between groups. No matter where above the ground the groups open, the air continues to move the first group away from the spot of deployment. Each group has it's own column of air and unless the second group is sliding, the two groups will never share the same air.

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.

Exiting a plane is no different. At 0mph groundspeed, both groups will exit at the exact same point over the Earth. 2 seconds or 20 minutes makes no difference...again, providing that all other variables remain equal.

The aircraft is the gun, the skydivers are the bullets and the ground awaits.

Another...
If at 1000' I'm under canopy at point A, and I fly with no input until I land, I will land at point B. If the next person is under the same canopy and loading and at the same point A at 1000' that I was at 1000', given the same winds, flying without input will put that person exactly at my landing point B.

The ground DOES matter before you land. You're using it as a fixed reference point to spot your exit. Given the same fixed reference point and fixed variables, 50,000 skydivers exiting at the same point over the course of the life of our universe will open at the exact same point.

As for sharing the same air, you're right...providing that all variables remain equal, they will not occupy the same space/time. But, the opening coordinates will be identical with regards to space.

Stay safe,
Mike


mnischalke  (D 26290)

Feb 18, 2004, 10:48 PM
Post #73 of 246 (860 views)
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Re: [Nullified] Opening High for Bad Spots [In reply to] Can't Post

I understand your analogy, but it's inconsistent with this discussion. Bullets are affected by wind, but they don't have parachutes.

Nonetheless, no matter how fast you fire your gun, those bullets will not run into each other in flight.

Remember, it's what happens at the deployment altitude that matters. The ground has nothing to do with this situation other than it's where you're going.


Nullified  (C 32259)

Feb 18, 2004, 11:27 PM
Post #74 of 246 (854 views)
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Re: [mnischalke] Opening High for Bad Spots [In reply to] Can't Post

Quote:
Nonetheless, no matter how fast you fire your gun, those bullets will not run into each other in flight.
If this is the point that you've been trying to make, then I agree with you.
It's possible that we've been on not exactly the same page during this discussion.
I'm not arguing that the two groups will deploy at the same time and position...just at the same position.

If this clears it up between us, then either I have misinterpreted your earlier posts or you weren't quite clear...or a combination of both.

Stay safe,
Mike


velo90

Feb 19, 2004, 12:50 AM
Post #75 of 246 (847 views)
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Re: [Hooknswoop] Opening High for Bad Spots [In reply to] Can't Post

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.


(This post was edited by velo90 on Feb 19, 2004, 12:50 AM)


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