Jan 7, 2002, 10:08 AM
Post #1 of 66
Changing exit order - wind?
OK, I understand that when there are no uppers blowing it is good to put the freeflyers out first (vertical separation). And I understand that when the uppers are blowing it is advisable to put the belly flyers out first (horizontal separation). However when do you make this decision? I know it can't be exact, but roughly at what wind speed would you change the exit order?
Any knowledgeable opinions welcome (although I know I'll get Clay's anyway... )
PS to keep it simple, for my question, assume the load consists only of freeflyers and belly flyers, all opening at the same altitude and the biggest RW formation is a 4-way.
Yes you will!!!! I don't know though...I say if you always put Free Flyers out first you don't have to guess on wind speed. My DZ doesn't see it that way though. We usually put "big groups" out first regardless of wind velocity. It doesn't really matter. If you put good speration times between groups you shouldn't have a problem. We use 5-6 sec on no wind days and I have personally used as much as 15 sec when the winds were around 55-60 knts at altitude. Just tell the people behind you yelling "Go...Go.." to STFU!!!
"I got some beers....Let's Drink em!!!" Clay
billvon (D 16479)
Jan 7, 2002, 10:28 AM
Post #3 of 66
>OK, I understand that when there are no uppers blowing it is good to put the >freeflyers out first (vertical separation).
>And I understand that when the uppers are blowing it is advisable to put the belly > flyers out first (horizontal separation).
-- I'm editing this to avoid giving bad advice here ---
Freeflyers are in freefall for a shorter time, and so get blown back less than belly flyers. The extra time that the belly flyers spend in freefall is time spent being blown _away_ from the freeflyers. Thus if belly flyers get out first, the later-exiting freeflyers will descend and open more quickly, while the belly flyers are still getting pushed away from them.
I got the first version backwards. Late night last night.
(This post was edited by billvon on Jan 7, 2002, 11:11 AM)
One factor that often gets left out is....What is the wind direction relative jump run. I have seen upwind mostly but cros wind jump runs as well......Cross wind is definately the safest but puts more demand on the pilot.
If the jumpers are all pulling at similar altitudes it is much better to try to get horizontal separation. Take this example. Skydivers are exiting a plane from 13000 ft. A free flyer gets out planning to pull at 3000 ft. He actually pulls at 3300. He has a farely quick opening and is open by 2900 ft. His freefall time is approximately 44 sec. 5 seconds later a belly flier leaves the plane planning to pull at 3000 ft. He pulls at 2200 because they broke off a little late. He has a slow opening and is open by 1400 ft. His freefall time is approximately 60 sec. So do you think the freeflier will have descended 1500 ft under canopy in just 16 seconds. Not likely unless he is flying something like an FX loaded at 2.4 and went into a hard dive right away. If they have no horizontal separation, they are going to collide.
One other thing to think about. Assuming the belly and freeflier are both good and don't slide all over the sky, the belly flier will drift more than the free flier. If you put the free flier out first the belly flier can drift right over the top of him, where if you put the belly flier out first they will drift farther apart. Since I believe it is better to get horizontal separation for reasons stated above, i believe in putting belly fliers out first in all but absolute no uppers. We do not see that very often.
One other thing. The times and opening distances I used were just off hand. Just for illustration. I know they might not be exact but should work for this illustration. And as far as people pulling at there assigned altitudes, things don't always go right. Most accidents are caused by a chain of events.
Bill, I don't understand your analogy that belly jumpers will be blown back towards the freefliers if they exit first. Not if like most drop zones, jump run is into the wind. Say if the plane is going north, then the wind is blowing to the south. So the drift will be to the south. If the freeflier gets out second, he will be further to the north as the plane is flying north and the belly flier will be drifting to the south. This will put the farther away.
billvon (D 16479)
Jan 7, 2002, 11:03 AM
Post #7 of 66
>Bill, I don't understand your analogy that belly jumpers will be blown back > towards the freefliers if they exit first. Not if like most drop zones, jump run is > into the wind. Say if the plane is going north, then the wind is blowing to the > south. So the drift will be to the south.
> If the freeflier gets out second, he will be > further to the north as the plane is flying north and the belly flier will be drifting to > the south. This will put the farther away.
Yep, you're right. I just mentally reversed an old example I had printed out.
(This post was edited by billvon on Jan 7, 2002, 11:06 AM)
I can't find it but I remember seeing a site linked form "www.enclave.com" that had quite a study of this subject. To include illustrations and bunches of math for those of you that need it. Anyone else seen it?
I've always been taught you exit slowest to fastest (with a few special case exceptions like skysurfers, high pullers, birdman suits, etc.). So belly fliers go first, biggest-way to smallest. Then freefliers, biggest-way to smallest.
I think people agree that order should be conducted in a way that maximizes separation between groups. There are a lot of factors that weigh into that decision, but the main one is going to be how jump run is conducted relative to the uppers. If jumprun is with the wind (downwind/tailwind), you'll want to exit fastest to slowest. If jumprun is against the wind (upwind/headwind) you'll want slowest to fastest. Crosswind seems to be pretty much a wash.
"Zero Tolerance: the politically correct term for zero thought, zero common sense."
(This post was edited by Zennie on Jan 7, 2002, 11:47 AM)
billvon (D 16479)
Jan 7, 2002, 11:25 AM
Post #10 of 66
>Not to be argumentative, but this is the exact opposite of what I've been taught, >what I've been told by people and what I've seen at both local (turbine) dropzones.
You are correct; I just reversed my favorite example above. It, of course, became clear to me seconds after I hit the post button. I agree that belly flyers first when flying into the wind makes more sense, and had I thought about it for more than about five seconds (since that's what we do at Otay) I would have realized that my example was exactly backwards.
I have a freefall drift simulator on my website. YOU get to enter the windspeed and the exit count. You will see a graphical display of seperation vertically and horizontally. The simulator is courtesy of Professor John Kallend of IIT.
The dz I used to call home (Delmarva) ALWAYS put flat fliers out first citing that they will blow much further back and away from the freefliers coming straight down. My new home dz (ZHills) puts freefliers out first because they get down much quicker so will always be out of the way of the flat fliers. I can see arguments for both sides and this topic always confuses the crap out of me. The main downside of putting freefliers out first though is what if I am freeflying and have a premature opening at, say, 7,000. Then I am right in the path of the flat fliers! At least I think I am. I just wish there was one standard rule (yeah, right!) so I wouldn't have to think so much about it with every new dz! It gets very confusing! Not to mention inconvenient when you think you're out last but you're out first and you have to crawl over the flat fliers to get to the door!
it's not an issue as long as there is enough separation (horizontal), it's achieving that separation that causes issues how long to wait and will the DZ do a go around. most major Dz's freefliers get to load the plane first. play with the simulators, you'll see what happens.
And it is that concern that I will never allow free fliers out first without a huge, and I mean 20 second or greater, seperation between the last free flier and first flat group. Also, I try to do crosswind jumpruns mostly to also help the horizontal seperation when possible. Free fliers think they are the only ones flying little canopies and it isn't true. I see a lot of free fliers dumping at 3,000 or much higher because of the potential crazy mal they can get into with them. Flat fliers I see are still going to the old altitudes of 2,000 or above and now we have the potential for disaster. Just because we haven't had the collisions happening really up to this point doesn't mean it isn't a problem. Either you miss and you survive or you hit and you're dead. There's no "small" mistake on this issue.
Flats first, freaks last, unless you plan on pulling above 5,000 then the freaks go before you.
Assuming an upwind jumprun, the freaks should always go out last (or as the guy at Lake Whales called us, 'the devil worshippers) If for some strange reason, you're doing a down-wind jump run, they should go out first. Cross-wind I think you could still debate the freefliers go first. Another thing to keep in mind is where in relation to the DZ will everyone be getting out. If the free fliers get out first, and let's say they get 15 seconds less freefall time, and the flat fliers gave an 8 second delay, they could be under canopy a good 20-30 seconds before others start opening - is there a chance you're going to fly under the next group? Just something to think about. And numbers aren't absolute - you can't say "take 8 seconds between groups" and hope that works all the time. Winds change, jump-run speed may change, size of groups change... when in doubt, ask someone who knows. If you don't know, and someone asks you, don't be too proud to say "I'm not sure, ask someone else"
I ain't happy, I'm feeling glad I got sunshine, in a bag
Thanks for all the input guys! I don't have any say over exit orders, pretty much just go along with whatever the JM says, but it is still good to be informed. I did a bit of searching and found the following on Tamara Koyn's site - the paragraph on exit orders is quite good.
What would you experienced jumpers do if you found yourself in Dove's position? Say for example you went to a DZ where they always put freefliers out first regardless of uppers - what would you do?
Thanks for the links, that simulator was really interesting.
Not much you can do in my situation unfortunately. At least not as far as changing policy is concerned. You just have to pray the flat fliers give you good separation. Sadly I have seen a lot of them come too close to me for comfort. I make sure to do a complete 360 barrel roll before dumping - even on solos.
Nothing you can do? Complain! Complain to the load master, manifestor, pilot or DZO and if that doesn't work then leave! If the almighty dollar is all they care about and are ignoring PHYSICS then they really don't understand shit about aviation. I have spent my entire adult life involved with aviation safety and you don't want to hang around people who stick their head in the sand on safety issues. Please don't accept the status quo. That's why I ended up creating my website because I was frustrated with people dieing and had to try and do something about aircraft safety. Your money is not worth as much as your life. Take it from someone who has too many friends barried in the ground. Vertical seperation is not enough to keep these groups seperated. Horizontal seperation is the only thing that will keep you safe in skydiving.