velo90 0 #201 February 20, 2004 QuoteEames is saying that it is OK for two people to open at the exact same point over the ground at staggered times because by the time the second group gets to that point, the airmass in which the first group is flying will have moved (i.e. the first group will be over a different point on the ground). And Eames is correct in that assumption. QuoteMy point is that I do not want to have to rely on the airmass in which the first group deployed to have moved away from the point over the ground where the second group is deploying to achieve separation. You don't have to rely on it, the way a number of people work these days they ignore it, in most cases to their advantage. When you understand why it makes a difference, you can save your ass on unusual days. QuoteCanopy drift is fine for additional separation But sometimes it can give reduced separation. And unless you can see that, you are out of touch with reality. Sorry, but the information has been provided in these forums often enough. Read, study and then you will understand why canopy drift is (sometimes) a factor that should not be ignored. Quote Share this post Link to post Share on other sites
velo90 0 #202 February 20, 2004 Quoteand leave half a second behind you, I might go whistling by as you were saddling out and then deploy right under you. I doubt that very much. You would never catch him up. You'd be close, that true, but you would not be right under him. Have you ever done tandem videos? Quote Share this post Link to post Share on other sites
eames 0 #203 February 20, 2004 QuoteHowever, 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. That was not advice, I wrote, "By the way, I don't recommend trying it... I hope you found that obvious." Apparently you didn't. I also never said "half a second." You said, "0.5 seconds." Enough with semantics. QuoteMy argument is that separation between groups does not depend on groundspeed. Actual separation (in terms of the airmass, which is all that matters) depends on three things: Airspeed of the plane on jumprun, the difference between the velocity of the winds at jumprun altitude and opening altitude, and the time left between groups. Nowhere does groundspeed factor into separation. Do you dispute this? -Jason Quote Share this post Link to post Share on other sites
bmcd308 0 #204 February 20, 2004 Quote -------------------------------------------------------------------------------- Quote -------------------------------------------------------------------------------- Eames is saying that it is OK for two people to open at the exact same point over the ground at staggered times because by the time the second group gets to that point, the airmass in which the first group is flying will have moved (i.e. the first group will be over a different point on the ground). -------------------------------------------------------------------------------- And Eames is correct in that assumption. Not necessarily. If that airmass is not moving (winds died at opening altitude), it will not have moved. QuoteBut sometimes it can give reduced separation. And unless you can see that, you are out of touch with reality. 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 Quote Share this post Link to post Share on other sites
bmcd308 0 #205 February 20, 2004 >>Do you dispute this? << Only to the extent that some were defining separation as the distance between opening points relative to the ground. If separation is defined as the distance between opening points relative to the ground, then groundspeed on jumprun matters rather than airspeed on jumprun. Brent ---------------------------------- www.jumpelvis.com Quote Share this post Link to post Share on other sites
velo90 0 #206 February 20, 2004 QuoteNot necessarily. If that airmass is not moving (winds died at opening altitude), it will not have moved. can't argue with you there. QuoteThis whole most recent "argument" discussion 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. Well actually I thought it started due to the idea that ground speed determines separation. It doesn't. Quote Share this post Link to post Share on other sites
eames 0 #207 February 20, 2004 QuoteIf separation is defined as the distance between opening points relative to the ground, then groundspeed on jumprun matters rather than airspeed on jumprun. Are the jumpers on the ground? Then why would you define separation in terms of the ground? Actual separation (the distance between two groups when the second group opens, with respect to the ground or the airmass) does not change with groundspeed. It only changes with the airspeed of the plane on jumprun, the difference between the velocity of the winds at jumprun altitude and opening altitude, and the time left between groups. That's it. No matter what the groundspeed is. -Jason Quote Share this post Link to post Share on other sites
eames 0 #208 February 20, 2004 Quote...definition of "separation" between the two sides By the way, I'm not sure who is left on your side. I believe I can safely say that Hook now agrees with what we're saying. -Jason Quote Share this post Link to post Share on other sites
bmcd308 0 #209 February 20, 2004 >>By the way, I'm not sure who is left on your side. << I don't have a side. But if I did, Isaac Newton would be on it. ---------------------------------- www.jumpelvis.com Quote Share this post Link to post Share on other sites
velo90 0 #210 February 20, 2004 QuoteI don't have a side. But if I did, Isaac Newton would be on it. Errr , Kallend is as near as we get to Isaac Newton here, trust him. Quote Share this post Link to post Share on other sites
eames 0 #211 February 20, 2004 QuoteI don't have a side. But if I did, Isaac Newton would be on it. I award you zero points, we are all dumber for reading that, and may god have mercy on your soul. [That was a joke.] I think we're done here. -Jason Quote Share this post Link to post Share on other sites
bmcd308 0 #212 February 20, 2004 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. << I think you will see that I have not been specifically arguing with your choice of inputs into your separation model. I will admit that as a practical matter I very much like the idea of opening at a different point over the ground than the one at which the group before me opened five seconds earlier in every case except the one where their airmass is moving toward my different point over the ground. And in that case, I would want a different jump run. Brent ---------------------------------- www.jumpelvis.com Quote Share this post Link to post Share on other sites
eames 0 #213 February 20, 2004 QuoteI 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. Depends on the windspeed at altitude (difference between the velocity of wind at jumprun altitude and opening altitude). If the difference is a large, yes, there is something to worry about. This all fits perfectly into the model that has been described. QuoteI will admit that as a practical matter I very much like the idea of opening at a different point over the ground than the one at which the group before me opened five seconds earlier in every case except the one where their airmass is moving toward my different point over the ground. And in that case, I would want a different jump run. That's fine, I'm not trying to tell you what to do. -Jason Quote Share this post Link to post Share on other sites
kallend 2,148 #214 February 20, 2004 Quote>>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. << This is exactly my point. Eames is saying that it is OK for two people to open at the exact same point over the ground at staggered times because by the time the second group gets to that point, the airmass in which the first group is flying will have moved (i.e. the first group will be over a different point on the ground). My point is that I do not want to have to rely on the airmass in which the first group deployed to have moved away from the point over the ground where the second group is deploying to achieve separation. Because if it does not, the two airmasses will be one and the same. Canopy drift is fine for additional separation that is not counted in the time between groups. And as you point out, when jump run is opposite the opening altitude winds, the opportunity for skydivers from different groups to occupy the same space (no matter how it is defined) is increased. Brent Brent 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.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
kallend 2,148 #215 February 20, 2004 QuoteQuoteI don't have a side. But if I did, Isaac Newton would be on it. Errr , Kallend is as near as we get to Isaac Newton here, trust him. I was in college with Isaac Newton. About 300 years later than him.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
kallend 2,148 #216 February 21, 2004 Quiz time. 1 kt is very close to 1.5 ft/sec, and using ft/sec is easier. A balloonist and his girlfriend are floating along at 2500ft agl. He looks at his chart and sees there is a DZ below. Not that he can do anything about it. The DZ is near the ocean and an easterly wind is blowing him due west at 40ft/sec. He looks down and sees the DZ drift by below him. He feels not a breath of wind, because he is the wind. He lights a cigar. He looks up and sees an Otter way above him, going west. He recalls the weather briefing, that at altitude the winds are prevailing westerlies, but down low the ocean effect has them in the opposite direction. He gets out his laser rangefinder and determines that the Otter is moving at 50 ft/sec relative to his balloon. A quick calculation tells him that the Otter's groundspeed is 50+40 = 90ft/sec. He knows an Otter flies jumprun at 140ft/sec, so he deduces the uppers are 50ft/sec from the west. A 4-way team leaves the Otter (they saw the balloon but mistook it for a water tower). They turn 22 points. At 4000ft they are directly above the balloon, breakoff and track. Each tracks 300 ft before deploying. They are all open at 2500ft. One has line twists and is in a slow turn, another opened off heading, a third is stowing his slider while the other is messing with his booties. Each skydiver is 300ft from the balloon, in various directions. It is a cool sight. The balloon pilot sees a second 4-way team leave the Otter after 11 seconds, (they figured 990ft should be ample separation from the first group based on the 90ft/sec groundspeed; that leaves 300ft for their tracks, 300ft for the other teams' tracks, and 330 ft as a buffer between the groups). They turn 26 points. He sees the second team also break and track at 4000ft, each tracking 300ft. in equally spaced directions. The girlfriend coughs because the cigar smoke is hanging around, there is no wind to disperse it. How far from the balloon is the center of the second group, and is there a risk of collision between groups? Note - It is not at all uncommon for upper and lower winds to be in opposite directions if you are near the Great Lakes, the ocean, or mountains.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
mnischalke 0 #217 February 21, 2004 Damn, That was awesome! I especially liked the bit about the girlfriend coughing from the cigar smoke! Very illustrative... mike Girls only want boyfriends who have great skills--You know, like nunchuk skills, bow-hunting skills, computer-hacking skills. Quote Share this post Link to post Share on other sites
eames 0 #218 February 21, 2004 QuoteHow far from the balloon is the center of the second group, and is there a risk of collision between groups? I figure the center of the second group will be about 1100 ft from the balloon. And No, there's no chance of collision because even if a member of each group tracked right at each other there would still be 500 ft between them. How'd I do? Edit: They may have less than 500' between them if the member of the first group that was heading toward a member of the second group while tracking continued toward him under canopy. But, he couldn't travel 500' in 11 seconds under canopy in brakes, so there's still no change of a collision. -Jason Quote Share this post Link to post Share on other sites
johnny1488 1 #219 February 21, 2004 Damn I was gonna say 110 feet. My brain hurts, but I like it And as for collision If they didnt already they are lucky because the second group overtook the first. Johnny --"This ain't no book club, we're all gonna die!" Mike Rome Quote Share this post Link to post Share on other sites
kallend 2,148 #220 February 21, 2004 QuoteQuoteHow far from the balloon is the center of the second group, and is there a risk of collision between groups? I figure the center of the second group will be about 1100 ft from the balloon. And No, there's no chance of collision because even if a member of each group tracked right at each other there would still be 500 ft between them. How'd I do? Edit: They may have less than 500' between them if the member of the first group that was heading toward a member of the second group while tracking continued toward him under canopy. But, he couldn't travel 500' in 11 seconds under canopy in brakes, so there's still no change of a collision. -Jason No.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
eames 0 #221 February 21, 2004 QuoteNo. Okay, I think I see where I went wrong. The center of the second group is only 110 ft from the balloon and yes, there is a risk of collision between groups (and the balloon). I think johnny1488 would have been right. -Jason Quote Share this post Link to post Share on other sites
mnischalke 0 #222 February 21, 2004 horizontally, 550 ft. yes, if the closest jumpers on each group went directly along the line of flight. (edit, I am an idiot. I reversed the groups in my first try. oops) mike Girls only want boyfriends who have great skills--You know, like nunchuk skills, bow-hunting skills, computer-hacking skills. Quote Share this post Link to post Share on other sites
kallend 2,148 #223 February 21, 2004 Quotehorizontally, 550 ft. yes, if the closest jumpers on each group went directly along the line of flight. (edit, I am an idiot. I reversed the groups in my first try. oops) You win.And the collision hazard doesn't depend on the presence of an observer in the balloon. He just provided a convenient origin. The ground is irrelevant except as an approximate indicator of what is going on at opening altitude. All you need to know is that the plane is going 50ft/sec faster than the balloon, and multiply that by the exit delay 50 x 11 = 550ft. The groundspeed doesn't enter the equation, and it never does. And real circumstances exist where blindly relying on groundspeed might kill you.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
johnny1488 1 #224 February 21, 2004 I see where I made my mistake also. This is starting to make a lot more sense to me now. Thanks for puttin up with me and others like me Johnny --"This ain't no book club, we're all gonna die!" Mike Rome Quote Share this post Link to post Share on other sites
eames 0 #225 February 21, 2004 Quote50 x 11 = 550ft. Don't you have to subtract the 40 x 11 = 440 ft that group one drifts while under canopy since the uppers and the lowers are heading in opposite directions? -Jason Quote Share this post Link to post Share on other sites
