bmcd308

>> If the winds at opening altitude are from the same direction as the winds at exit altitude, add the two numbers. If not, subtract them.

>>Now I wonder what to do with the BASE experience? Will that make me a terrible skydiver?

You do not get a separate coach number - it's just your license number. USPA does charge an annual renewal fee - I think it is $25. Do not know how many coaches and instructors are out there. ---------------------------------- www.jumpelvis.com

I can't really get out of work until 3:30 or so. Looks like rollout will be from my house at 4:00 or 4:30. Kevin is getting off at 3:30, too, and he'll have all his stuff and head straight to the hizzay. Bring an empty bladder for the drive. ---------------------------------- www.jumpelvis.com

OK. I'll give up trying to explain myself. ---------------------------------- www.jumpelvis.com

You're not dumb. I have watched a former professional pickpocket who had become a professional entertainer / pickpocket. He was the entertainment at a restaurant when my family was on vacation, and he came to the table, talked to us for a while and told us that he was a magician pickpocket, shook everyone's hands, did a disappearing act with my dad's watch that was very impressive, then gave dad's watch back. Then he gave me mine back, and he gave my sister back the lipstick from her purse. I was about 13, and I have no idea how or when he got my watch. My sister was shocked, too. Point is - people can get really good at anything they put their minds to. Brent ---------------------------------- www.jumpelvis.com

Just this weekend, I had a newer jumper ask me for a gear check before boarding - chest strap misrouted. Drakeshelby had a newer jumper ask him for a gear check, and the bridle was routed incorrectly - I had never seen anyone do it this way before. The jumper had the bridle going from the grommet out the bottom left of the container when he closed the bottom and top flaps. I guess this did not look right, so he layed it up on top and closed the left flap, then routed it out the bottom right corner under the right flap. The pin was in the section of bridle that went from the bottom left to the top right and out under the bottom of the right flap, so it was wrapped once around the right flap. While the bridle might have slipped between the deployment bag and the right flap enough to pull the pin, it also might have (and maybe I should say probably would have) resulted in a pc in tow. Interestingly, the jumper had tucked things in carefully so that it looked something close to correct from the outside. It was only because it looked a little odd that Kevin wound up actually untucking it to see how it was routed. Brent ---------------------------------- www.jumpelvis.com

>>So you are willing to bet your life on the reliability of the air at exit altitude and on the ground for landing, but at opening altitude you consider it unreliable. Interesting concept.

Let me run a quote from one of my very first posts on this thread by you again: >>I have never disagreed with the idea that IF we assume that there is some wind at 3,000 feet that wind will have a tendency to force the previous group's canopies downwind. However, if that wind at 3000 feet stops blowing on the way to altitude, our reliance on the wind at 3000 feet to provide separation will have been ill-advised.

>>By the way, I'm not sure who is left on your side.

>>Do you dispute this?

Not necessarily. If that airmass is not moving (winds died at opening altitude), it will not have moved. Agreed. Lower winds that push the skydivers back up the line of flight represent a special case that needs to be understood. This whole most recent "argument" has been the result of my pointing out that the original argument was one that resulted from a difference in the definition of "separation" between the two sides. I do not think I am actually arguing with anyone. Brent ---------------------------------- www.jumpelvis.com

I do understand the physics of separation, and I understand that until my feet touch it, the ground has nothing to do with anything. However, if I were to follow your separation advice and leave half a second behind you, I might go whistling by as you were saddling out and then deploy right under you. I bet the discourse on the ground would not be as civil as the one we are having here in that case, and you'd be telling me that next time I damn well better wait until we were farther apart. If all you're arguing is that identical spaceballs dropped from the plane under almost any circumstances will not collide on the way down, then fine, you're right, too. ---------------------------------- www.jumpelvis.com

We are not worried about whether identical spaceballs pitched out of the plane will collide before they get to the ground. Everyone agrees that even if they land in the same hole, they will arrive there at different times. That does not mean that there is adequate separation between groups. ---------------------------------- www.jumpelvis.com

>>As long as the plane has a positive airspeed, the groups leave at least more than zero seconds of separation in the door, and the uppers and lowers aren't going in opposite directions, there will be no collision. Because the groups will never occupy the same space at the same time RELATIVE TO THE AIRMASS!

>>Correct, but generally this is not included in the calculations for separtion. The result is we get even more separation than we bargained for in most cases. But unless you understand why that is, you will not understand why in some cases you end up with less separation. Such conditions occur where I jump.

>>Look at a point in the sky relative to the ground. Now look at that same point in the sky five seconds later. Assuming there's wind, the same air does not occupy that space

>>Can you see that we don't open our parachutes at ground level? And can you see that when you open your parachute your vertical descent rate will decrease significantly? And can you see that you will then travel horizontally away from your opening point?

>>However, I dispute his thesis that you can't rely on "canopy drift" for separation, but have to ensure separation relative to some fixed point on the ground.> If I place the origin at the point most important to ME, then I am not drifting. The ground is drifting, and I'm not worried (within a few seconds of opening) about colliding with anything on the ground. >The only thing I can possibly collide with is something at the same altitude I am.

>>But my origin is moving with respect to yours. And my origin is where I am and close to where the potential collision hazard is. Your origin is 3000ft below and moving. I don't care a hoot what is going on down there. >What if a layer of light industrial haze obscured the ground? Whast relevance does your origin have now?

>>Well, I disagree with you. The only origin that makes sense is an origin in the airmass you are in. Canopies aren't drifting in that airmass, the ground is, but the people you are trying to avoid aren't on the ground.

>>And with respect to WHAT ORIGIN are you measuring x, y, z? Then justify your choice. >And what if the previous group has already landed? Would that make a difference?

>>Yes, I was wrong

Neither ---------------------------------- www.jumpelvis.com

Think of an airspeed indicator as a device that measures how hard the air is pushing against it. When you stick your head out to spot, your smiling mug is an airspeed indicator. The amount of wind you "feel" is what determines your indicated airspeed. If you held a child's windmill out the door and counted how fast it was spinning, you would have made a primitive airspeed indicator. As each molecule of air moved past the windmill, it would push it some. True airspeed is the rate that individual molecules of air move past a specific point. This is a little harder to feel on your face, since you are not good at detecting changes at the molecular level. So TAS winds up getting calculated based on IAS and the density of the air, which is a function of altitude and temperature. TAS is the speed you are actually moving through the air - or the speed at which individual molecules of air are moving past a specific point. Why not just talk about TAS? Because IAS ("felt" speed) is what generates lift. Think about the windmill out the door in a plane that will fly a constant true airspeed. As the plane goes higher, the less dense air pushes less and less on the windmill as the air moves past the blades, because there are fewer molecules to actually do the pushing. So the windmill turns more slowly, even though the speed of the plane through the air (its TAS) remains the same. In order to figure out how fast the individual molecules of air are moving through the windmill, we have to take into account the fact that there are fewer molecules pushing on the windmill blades. Now take the plane up higher still. Eventually, you will notice that the thinner air is pushing less and less on the windmill, until it is hardly turning at all. At this point, you will hear a funny buzzing noise and a bunch of profanity from the cockpit. The buzzing was the stall warning. The profanity was the pilot. The pilot will do some cool pilot stuff, and pretty soon, your windmill will be spinning along quickly again. For purposes of being a "cool" skydiver, it is important to recognize the distinction between IAS and TAS, but to act as if it does not exist when talking to pilots. This is because they understand this on an instinctive, gut level, and they do not even have to think about it. Arguing with them about it will only make you look silly. And they are used to dealing with people who do not understand it, so they won't really judge you for appearing not to have a clue. It is only when you try to appear to have complete command of the concept but do not that you look like an azz. Brent ---------------------------------- www.jumpelvis.com