rehmwa 2 #301 June 10, 2011 http://www.omniskore.com/freefall_drift2.html this is great for everybody to look at - Thanks John and Winsor for reminding me of it ... Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants Quote Share this post Link to post Share on other sites
GreenLight 5 #302 June 10, 2011 Quotehttp://www.omniskore.com/freefall_drift2.html this is great for everybody to look at - Thanks John and Winsor for reminding me of it Never would have believed it without this motion chart. They have been telling me for years now that "all the computer models tell us that the FF must exit after the SF."Green Light "Harry, why did you land all the way out there? Nobody else landed out there." "Your statement answered your question." Quote Share this post Link to post Share on other sites
LouDiamond 1 #303 June 10, 2011 Quote Since we are not calculating orbital mechanics requiring precision to the 20th decimal place, then instead of complicating it for newbies to make ourselves feel smart, we should keep it basic. So the simplified chart is great - and yes, lot of 'standard' assumptions. I have issues with it only in the case when the assumptions are off. Example - lowers and uppers are in completely different directions. Cross wind or downwind jumpruns, high openings, etc etc etc. Mixed up exit orders (like FF before belly, etc). Thank you, you beat me to saying it. It's not 100% written in concrete double your money back (minus shipping and handling) guaranteed, nothing in skydiving or life is. There are instances where it may not work as you pointed out. However, given the nature of how DZ operations typically work, this is the 99% solution for most DZs on most given days. It is not a replacement for common sense or good sense I should say and there might be some DZs where it is not the right answer based on how they have to operate (cross wind, etc). Most people know how to turn their TV on but have no clue why the mans face appears in the magic black box( or care why), they simply want to watch TV. The chart is like a remote control, if you don't use it correctly, ie: point it in the wrong direction, hold it backwards, use the wrong remote,etc, it will not work as intended and or as efficiently. But when you do use it correctly, your TV comes on and life is good again. The chart works when used correctly and in the right circumstances. The other issue it presents that we've discussed in the past, is that each person counts different from another, some count fast, some slow. Does the count start right as the persons body leaves the plane or the last person in the group leaves the plane? Should we put an electronic timer by the door in conjunction with the chart, yada yada yada? So yes, there is and isn't a simple answer to this question but people seem to love to over think or over complicate it. Which is why this thread will still be alive a decade from now repeating everything that has already been said, only the names will have changed (like the Bon Jovi song). "It's just skydiving..additional drama is not required" Some people dream about flying, I live my dream SKYMONKEY PUBLISHING Quote Share this post Link to post Share on other sites
rehmwa 2 #304 June 10, 2011 Quotebut people seem to love to over think or over complicate it. I like the discussions and appreciate the deep dives. As long as we don't lose those that don't get the basic bits in the first place. Those that really dig into the details "get it" already. I'm not worried about Kallend or Winsor opening on top of me. But because of this type of thread, I now have a bunch of other people that I'm not worried as much about much as I would have been - that's a win. ... Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants Quote Share this post Link to post Share on other sites
billvon 2,394 #305 June 10, 2011 >Maybe you could give examples, including the math, of why it doesn't work for other conditions? Separation = (aircraft ground speed + wind speed at opening) * time between groups. All speeds in feet per second, all directions normal (i.e. flying into the wind, winds at opening the same direction as jump run winds.) This neglects throw and intentional tracking. If winds at opening are light, then equation reduces to (aircraft ground speed * time.) If upper winds are high, then groundspeed decreases and separation decreases. If lower winds are high, then that only helps you. You can use groundspeed and be fine - better than fine, since you get even more separation. But if the winds at opening altitude are opposite direction (i.e. are negative) now you can get in trouble. Now you might think that ground speed is fine, that 150 feet per second times 6 seconds would give you 900 feet. But if the winds at opening altitude are 50 feet per second from the _other_ direction (as happens here during Santa Ana winds) then that would reduce your separation to 600 feet. Quote Share this post Link to post Share on other sites
pchapman 261 #306 June 10, 2011 I'd like to clarify that in billvon's example of opposite direction lower winds, the equation itself isn't failing. Nothing wrong with the math, as long as one allows winds to be positive or negative in magnitude. But in practice, it may be easy to miss that the lowers are from a different direction or have shifted, giving lower separation than typical for a given ground speed seen from the aircraft. (Naturally if the winds are not all in line, then one gets into vectors and components of the winds along the jump run. The simple form of the equation is no longer sufficient.) Quote Share this post Link to post Share on other sites
Divalent 89 #307 June 10, 2011 QuoteBasically, if I exit with 1000 ft separation from the previous group, how is it that I won't be 1000ft away at opening? (Assume same discipline, same fall rate, same opening altitude) My head is starting to hurt given all the complications and factoring and parameters that people are throwing in here, when it seems to me that it is just as simple as you stated: Assuming same fall rate and opening altitude (and no tracking), then the only thing you need to do is use the ground speed to calculate the time need to go 1000 ft (or 500ft, or whatever you want). If the plane has GPS, the pilot should be albe to tell you ground speed in real time. If he doesn't, then you have to estimate it based on upper winds speed and direction, and a/c speed into the relative wind. Quote Share this post Link to post Share on other sites
billvon 2,394 #308 June 10, 2011 >then the only thing you need to do is use the ground speed to calculate >the time need to go 1000 ft (or 500ft, or whatever you want). Agreed. 95% of the time, that's all you need to estimate separation. Quote Share this post Link to post Share on other sites
rehmwa 2 #309 June 10, 2011 Quote >then the only thing you need to do is use the ground speed to calculate >the time need to go 1000 ft (or 500ft, or whatever you want). Agreed. 95% of the time, that's all you need to estimate separation. which is pretty much what we've all been saying. we just want to sound smart while saying it ... Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants Quote Share this post Link to post Share on other sites
Divalent 89 #310 June 10, 2011 Quote>then the only thing you need to do is use the ground speed to calculate >the time need to go 1000 ft (or 500ft, or whatever you want). Agreed. 95% of the time, that's all you need to estimate separation. Assuming you are considering separation of otherwise equivalent jumpers (e.g., belly fliers with the same fall rate and opening altitude), doesn't this cover 100% of the time? Quote Share this post Link to post Share on other sites
Remster 24 #311 June 10, 2011 QuoteAssuming you are considering separation of otherwise equivalent jumpers (e.g., belly fliers with the same fall rate and opening altitude), doesn't this cover 100% of the time? That's why, normally, you want belly jumper out 1st, followed by freeflyers. This adds to the separation, as opposed to taking away from it if you went FFer, then RW.Remster Quote Share this post Link to post Share on other sites
billvon 2,394 #312 June 10, 2011 >Assuming you are considering separation of otherwise equivalent jumpers (e.g., belly >fliers with the same fall rate and opening altitude), doesn't this cover 100% of the >time? No. The one case it does not cover (i.e. might not allow enough separation) is flying into the wind with winds at opening altitude from the OPPOSITE direction (i.e. uppers 40 out of the north, lowers 15 out of the south.) However, that's an unusual case; the only place I've ever seen that happen with any regularity is in Socal just as a Santa Ana starts. Sometimes the uppers will switch to out of the east while the lower winds are still out of the west/northwest as normal. It's not too much of an issue usually because Santa Anas generally mean "too windy for jumping." And honestly even at Perris, where the above might be a factor, the system used most often is "always wait 7 seconds" along with "wait longer if the uppers are strong" combined with "and leave even more time if you find yourself opening too close to other groups." Quote Share this post Link to post Share on other sites
Divalent 89 #313 June 11, 2011 QuoteQuote>Assuming you are considering separation of otherwise equivalent jumpers (e.g., belly fliers with the same fall rate and opening altitude), doesn't this cover 100% of the time? No. The one case it does not cover (i.e. might not allow enough separation) is flying into the wind with winds at opening altitude from the OPPOSITE direction (i.e. uppers 40 out of the north, lowers 15 out of the south.) Okay, then I ain't seeing it with respect to this exception. Seems to me that if we assume there are 4 jumper each doing a straight downward belly solo (no drift, fall rates the same), and opening at the same altitude, then if you string the exits out every 1000ft (relative to the ground) along the jump run, then you will have a string of openings all separated by 1000ft. Upper winds push the jumpers south some distance, then the lower winds push them north a bit, but the relative north/south movement will be exactly the same for all 4 of them. (Imagine if there were 4 planes 1000 ft apart that dropped them simultaneously. Wouldn't they always remaind 1000 ft apart?) I do understand that if you have different fall rates and/or groups that will drift and/or track, etc, that you may need to take more things into consideration. And I understand that assuming everyone falls exactly the same and open at the same altitude is an unlikely scenario in the real world. But I still don't see how ground speed alone in this narrow hypothetical situation is not sufficient 100% of the time. Quote Share this post Link to post Share on other sites
GreenLight 5 #314 June 11, 2011 OK guys I think I get it and if I read any more my head is going to start hurting again. We are going to go over this info on the ground in a few hours and the chart is what we are going with. If we tried to absorb all that has been said in this thread it could become very confusing. But the basics are there and we really appreciate the depth that the thread has gone to in order to illistrate what is actually happening in most cases. The most dramatic thing I think I saw here was the computer model showing the difference between fast fallers and slow fallers. I have argued that point with the higher ups at our DZ for years and not once did any of them show me this model. Thanks again. You won't see us opening up around your group in the future. By the way, we always count out load before we climb out. We get some pretty goofy looks from the other people in the plane every time we do it. I have not heard anyone else counting since my early days in DC-3s. Green Light "Harry, why did you land all the way out there? Nobody else landed out there." "Your statement answered your question." Quote Share this post Link to post Share on other sites
kallend 1,623 #315 June 12, 2011 Why are we still discussing this? Newtonian physics hasn't changed in the last few years.... 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
strop45 0 #316 June 12, 2011 Quote Why are we still discussing this? Newtonian physics hasn't changed in the last few years.Because most people don't have a clue who Newton was, let alone what Newtonian physics is. The 45 degree rule still lives and being right, logical, provable, etc is no use against blind faith and 'years of experience'. Boy did I get laughed down and told what I didn't know when I suggested RW should exit before free fliers..."but they're falling faster"...It took your calculator and a session with the DZO to get this changed and enforced.. The 45 degree rule lives on, probably because the time it takes to look gives some separationThe difference between stupidity and genius is that genius has its limits." -- Albert Einstein Quote Share this post Link to post Share on other sites
kmg365 0 #317 June 12, 2011 Quote The other issue it presents that we've discussed in the past, is that each person counts different from another, some count fast, some slow. Does the count start right as the persons body leaves the plane or the last person in the group leaves the plane? Should we put an electronic timer by the door in conjunction with the chart, yada yada yada? My Neptune's clock suffices for that. Simply note the time the previous group leaves and add the required delay. And, NO, I don't stare at it for the entire time. Every responsible skydiver knows that time is better dedicated to giving a few last minute winks at the cute tandem students. Quote Share this post Link to post Share on other sites
rehmwa 2 #318 June 13, 2011 Quote Why are we still discussing this? Newtonian physics hasn't changed in the last few years. why do you keep teaching the same class every year? I mean, YOU already taught it last year ... Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants Quote Share this post Link to post Share on other sites
mjosparky 3 #319 June 13, 2011 Quote Quote Why are we still discussing this? Newtonian physics hasn't changed in the last few years. why do you keep teaching the same class every year? I mean, YOU already taught it last year Sometimes you get tired of teaching the same material to the same people year after year. SparkyMy idea of a fair fight is clubbing baby seals Quote Share this post Link to post Share on other sites
popsjumper 2 #320 June 14, 2011 Quote why do you keep teaching the same class every year? I mean, YOU already taught it last year He didn't pass so he has to re-do....year after year after year...... My reality and yours are quite different. I think we're all Bozos on this bus. Falcon5232, SCS8170, SCSA353, POPS9398, DS239 Quote Share this post Link to post Share on other sites
rehmwa 2 #321 June 22, 2011 So on Saturday, I had a jumper (a little over a year, great progress and current) mention that not only did they count to 6 on the last load, but he also looked out and waited until we were 'about that angle' (held his arm out to about 45) - he noted "that's what a lot of the Eloy crowd told me this winter's trip" sigh so that's why we keep rehashing this thread - it resulted in a good conversation about drift and wind layers, and how a view 'angle' from the door is only good to give an idea of relative throw only, and has nothing to do with opening separation. ... Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants Quote Share this post Link to post Share on other sites
Remster 24 #322 June 22, 2011 Quote he noted "that's what a lot of the Eloy crowd told me this Not to take this into dz bashing (Im pretty sure it's not your intent) but what freaking lot at Eloy told him that?????? We've been using time based delays based on ground speeds and group sizes for a few years, with posted guidelines in the planes and the hangar.... Sigh in deed...Remster Quote Share this post Link to post Share on other sites
rehmwa 2 #323 June 22, 2011 I know, that's what blew my mind. That's a very updated crowd and a highly regarded DZ (absolutely not intended to bash one of my favorite operations - I've known L&L&S since they ran it in Coolidge). It's why it stood out in my mind. ... Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants Quote Share this post Link to post Share on other sites
LouDiamond 1 #324 June 23, 2011 QuoteQuote he noted "that's what a lot of the Eloy crowd told me this Not to take this into dz bashing (Im pretty sure it's not your intent) but what freaking lot at Eloy told him that?????? We've been using time based delays based on ground speeds and group sizes for a few years, with posted guidelines in the planes and the hangar.... Sigh in deed... Indeed. I can guarantee you that was not said by anyone who is a Eloy local unless you are talking about the time delay. You will not hear the 45 degree myth perpetuated in Eloy unless they are themselves a visitor."It's just skydiving..additional drama is not required" Some people dream about flying, I live my dream SKYMONKEY PUBLISHING Quote Share this post Link to post Share on other sites
rehmwa 2 #325 June 24, 2011 QuoteI can guarantee you that was not said by anyone who is a Eloy local Remster already made the point - no need to pile on. I really don't need you guys going into defensive mode, this was individuals telling my newbies, not a DZ practice. they could have been other visitors for all I know. that said - this is about any dz of any size - I doubt you or anyone can "guarantee" what's in the minds of all the jumpers local to most any dz with more than half a dozen regulars. I recognize that your point is about the culture, training, and the high expectations of the DZ and speaking in general. This is learning here, not defense. I mentioned Eloy specifically to point out that there is NOWHERE that's safe from this old myth - if the (IMO) best of the DZs has these outdated practices stealth mode in some attendees, then all DZs probably do. It's why we keep this thread going - continuous training to everyone about opening separation. (If I find out the individuals and they were local, I'll send the info so he can retrain them) ... Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants Quote Share this post Link to post Share on other sites
