velo90

Quite right, but your happy cone is rather big. An aircraft flies in straight lines (or maybe there is a hook turn in there). This means that in reality the jump run cannot use all of that cone. If the pilot knows there are swamps and crocs to the left of the cone he can fly the aircraft more to the right of the cone. A good spot can turn into a bad one if the jumper has a mal.

I thought I said that about 50 odd posts ago But there again, I am not a physics professor so who is going to believe me

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. 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?

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.

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

hmmmm... before I answer can someone give me the dictionary definition of scared? Don't want to start an arguement on the basis of what a word means. Take the word safe for instance...... Oh, that's another thread.

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.

Please read this Actually read the whole thread. I done.

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.

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!

Seems like he has a split personality

They had enough time to fix the problem. Jan 1998 Sleeve

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.

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.

At last, a voice of reason

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

When I think about exit seperation on a jump run I am not normally thinking about the problems of congestion when landing the canopy. I am mainly concerned that each jumper has his own column of air to use.

And now we know where you surf

Try to think about the canopy speed as the speed of the canopy due to wind drift and not it's own speed. After I got put down by Ron & Kallend I invested a lot of time reading the stuff Kallend put on the web. I believe at least for some people (me included) there are some ways in which we think that are fundamentally wrong. I finally figured out what was going on after I stopped thinking about the ground. The ground is irrelevant!

Thankfully we are parachutists and we don't hit the ground That is why ground speed is irrelevant. We need to look at what the plane/tower is doing relevant to point (air mass) where we open our canopies.

That's right! With the wind blowing at 130 ft/sec that's some distance they will cover before the next jumper arrives and opens. The 15 second delay allows the 1st jumper to be blown horizonataly away before the next jumper exits. They both follow the same trajectory but are still in their own vertical column of air.

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? I do neither 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. You will not have zero seperation at opening time! I am assuming the upper winds at at ~80kts, the same speed as the aircraft 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 As I said, it's all been done before and although the resources are out there, some people just don't seem to use them.

That would work great in court.... Sorry judge I was not speeding, you see I was in reverse gear which means I was doing -40mph. BTW If you do a jump run with the wind do you then have a negative ground speed?

Hooknswoop, what you have just said roughly works for the normal case but.... Why do we keep having to redo the problem? What's even worse is there are a number people taking part in this thread that took part in all the other threads about exit seperation and they have not learned anything! It's obvious numerous people never even bothered to look at Kallend's web site, or if they did, they never understood what was presented there. Ground speed is irrelevent for exit seperation, but in most cases it is a useable indicator to work out exit seperation.

Yes it did have HMA lines. The two A lines in the middle broke.