Hooknswoop

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

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

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? Derek

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

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

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

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

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 doesn’t 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 aircraft’s 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

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

Exactly, more separation as a result of the increased ground speed with no change in the airspeed. OK, call it linear, that doesn’t change anything. It is still ground speed that matters. Derek

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

Because of the 10 knot increase in ground speed. Because there was zero wind and with zero wind ground speed = airspeed. Derek

I think she was think at least one side would release, and maybe both, but it was an unknown. I don't think she thought for sure only one side would have released. Andi- correct me if I am wrong. Derek

Here's 2: Bell 206 BIII Jet ranger, UH-60 Blackhawk. Let’s look at 2 more realistic scenarios: 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. Scenario 2 has a 10-knot increase in airspeed over scenario 1. By your reasoning, less time needs to be left between groups in scenario 2 because of the 10 knot increase in airspeed. Both scenarios have a 10 knot ground speed. I disagree. Derek

I am curious, what canopy are you jumping and opening in 88.6 mph (130 fps) winds? 20 mph (29.3 fps) gives only 440 feet of drift after opening (and excluding the foward speed of the canopy) in 15 seconds, a long space betweeen exits. Derek

Very serious. If jumper one opens with line twists and flies upwind (the canopy’s airspeed minus the 130 fps wind speed gives jumper one’s ground speed) at time t and jumper 2 opens in the exact same airspace (which is the definition of no separation) at t+15 with line twists and flies down wind (for a ground speed of 130 fps plus the canopy’s airspeed). They have very little separation and may have a collision since they are flying towards each other at their combined airspeeds. Canopies should have opening points some distance apart. If canopy speed was sufficient for separation, why track at break off? Why not just turn away and pull and let the canopy’s airspeed provide the separation. Derek

That means they will open in the exact same airspace with only the 15 seconds of canopy speed for separation. If a group of 4 exits first, then another group of 4, then the second group of four will be opening within the first group’s airspace. That is zero separation. We do not rely on a canopy’s airspeed for separation. What if the first jumper has line twists and flies into the wind and the second jumper has line twists and flies downwind? They will have a high chance of eating up that 15 seconds and having a collision. Separation means opening points are separated not the same opening point with canopy speed used for separation. The same opening point means there is zero separation. Derek

Um, no, it will drift down wind, just like the jumpers exiting from the 13,500 foot tower would. If you dropped 2 balls from the tower, 15 seconds apart they would hit the same spot on the ground. I.e. no seperation. Derek

So if the jump ship has zero ground speed (130 fps-130fps), then it might a well be a 13,500 tower. If someone jumps off a 13,500 foot tower and then someone else jumps off the same tower 15 second later, they will open at the same exact point, as they will drift the exact same amount. The only separation will be from the first’s person’s canopy speed as they fly for 15 seconds. And there would be no forward throw, since the jumper has no forward momentum. Derek

But what? It works for any case. If you need 2,000 feet of separation from the group you are following out, do you wait for the aircraft to fly through the air for 2,000 feet or do you wait for the jump ship to fly 2,000 feet over the ground? If you wait for the jump ship to fly through the air for 2,000 feet and it has zero ground speed, you will have zero separation, not 2,000 feet. If a Piper Cub is flying with a 40 knot airspeed into a 45 knot head wind, it has a –5 knot ground speed. If a jump ship is moving with the wind and not into the wind, relative to the ground, it has a negative ground speed. What would you call it if a jump ship was backing up over the ground on jump run? “Going forward in reverse”? Sounds like something the French Army would say. Derek

Wrong, you have a ground speed of -25 kts. Derek

Airspeed for a particular jump ship tends to be constant for each jump run. If the jump ship always flies into the upper winds for jump run, then as the upper wind speed increases, the jump ship’s ground speed decreases and more time must be left between exits in order to achieve the same amount of separation. The pilot could increase the aircraft’s jump run speed equal to the upper winds (if the aircraft had the performance to do so) and the amount of time between exits could remain constant, but this isn’t done. Therefore, exit separation is a function of the aircraft’s ground speed on jump run. In order to ensure separation between groups the following groups must look at the ground and allow sufficient ground distance to be covered before exiting. This is why the 45-degree rule for exit separation does not work. So, as a jump ship’s ground speed decreases, more time must be left between exits to ensure the same amount of separation. This is why I said that separation is a function of ground speed. Ground speed (for a particular jump ship) is the variable, since airspeed is constant. Ground speed is used to adjust the length of time between groups. Derek

Any word from the FAA yet? Derek

*bump*

There was recently a Cypres mis-fire that had not been serviced. It had not been updated witht he shielding and fired on the ground near a radio-wave source. Derek