Six to Eight seconds might not be enough

[skHIjunky 0]

Just this last weekend I ended a most beautiful 5-way sit with a normal pull at 3,000, and as always my Stiletto sniveled me down to about 2,100-2,200. Imediately after recieving a most beautiful fully open canopy another jumper that was not on our dive, still in freefall and no more than twenty feet away, nearly took me out. So, needless to say I was just a little pissed off. As pissed as I was, I approached this jumper in a calm manner and asked, "what was that"? Well when in the presence of a descent human being you expect to hear an appology, instead this SKYGOD proceeded to question how many jumps I have (405), and then he had the odasity to weasel his way into denying any fault in the matter. FAULT.....Giving the the group ahead (us) four seconds out the door, and just to make sure he almost killed someone, this moron deploys at 2,000 feet. At some point probably 130 jumps ago I was in a similar situation to this except for coming close to a open canopy scared the crap out of me. As soon as my feet hit the ground I was already on my way to spew out an overly appolagetic appologie.
MY POINT.... My point is this. The day this happened to me was the day that I learned to watch the group that exited in front of me. Watch I do, and after almost killing one of my now good friends I was told by her, and everyone who saw the video tape of me sniveling away fourty feet infront of her.....WATCH THE GROUP, OR PERSON EXITING BEFORE YOU UNTIL THEY ARE AT A FOURTY FIVE DEGREE ANGLE FROM THE PLANE. Seven seconds can be more than enough seperation, and also can be just enough to exit about 800 ft. directly above fellow skydivers. I have given twenty five seconds inbetween exits and proceeded to climb out about one half a mile north of the dropzone and deployed a half of a mile south of the dropzone. The question that enters my head is this. As a new jumper I had accumulated about 275 jumps and was not once told to watch for the 45 degree angle, why didn't anyone tell me this? My plea is this..... Please fellow jumpers, please, tell everyone that you can about watching for the fourty five degree angle. Going out of your way and spending twenty seconds telling that new jumper this, and other safety tips may save their life, or even yours.
You must be dead to be a God, don't be a Skygod

[billvon 3,120]

> The question that enters my head is this. As a new jumper I had accumulated about 275 jumps and was not
> once told to watch for the 45 degree angle, why didn't anyone tell me this?
Because it doesn't work. The 45 degree angle tells you how quickly a group comes off the hill, how much throw the plane gives you, and how fast the plane is going through the air. It does not tell you how much separation you will get from the previous group. On a day with 15mph uppers, you will see the previous group hit that 45 degree angle in exactly the same amount of time as on a day with 60mph uppers. If you rely on it on the day with the 60mph uppers, you will not get enough separation.
Calculating the exit separation works - a minimum of 1000 feet for 4 way sized groups should be used. As an alternative, just look out the door at the ground. Wait until you see the plane cover 1000 feet and get out (or wait until it covers 700 feet, assuming you will take a few seconds to give the count and go.)
-bill von

[AggieDave 6]

Bill, besides experience, is there a sort of generic scale to work this off of? In other words, is there a chart that says if the uppers are X give a X count between groups? I know personally, I find out what the uppers are and base the count off of my limited experience and by talking to members of the group before me. Although, I know that I'm probably off from ideal more then I should be. I also watch the group leave, watching for the 45degs from the aircraft also.
"Wait...are you selling Penis Mighters?"

[skHIjunky 0]

Bill, are you searching for ways to slam what people have to say (RE: First words BECAUSE IT DOESN'T WORK). I hear what you are saying and I was simply trying share the news that would have prevented me from ever comming close to hitting my friend at 120mph. There has to be a little common since used in the factoring of course, and if the winds are in fact blowing at 60mph at alltitude, you could wait all day and never see the 45 degree angle. Also, a person with very low jump numbers may not even be able to tell when they are over the dropzone, and most likely wouldn't even be able to tell that a thousand ground feet has passed. My reasoning is simply this, if the people or person who exited before you are at a fourty five degree angle, then your sure not going to be on top of them at any point.......
You must be dead to be a God, don't be a Skygod

[quade 4]

Quote

My reasoning is simply this, if the people or person who exited before you are at a fourty five degree angle, then your sure not going to be on top of them at any point....

Although that may sound like a good plan, it's not really based in the physics of freefall and it doesn't really work all the time.
This particular topic has been gone over with a fine tooth comb by a number of folks and you can get a lot of information at;
http://www.omniskore.com/freefall_drift2.html
http://www.iit.edu/~kallend/skydive/
quade
http://futurecam.com

[quade 4]

Quote

Bill, besides experience, is there a sort of generic scale to work this off of?

Jumping in here . . .
Well, I guess it depends on a number of things like the layout of your DZ, but for me at Perris a really easy "scale" is the paved runway.
Since the runway is parallel to the landing area and the landing area is just about the middle of the distance between the ends of the paved section AND the paved section is just a little over 3,000 feet long . . . On a "no wind" day -if- the first group exits at the beginning of the runway, then the next group could exit about 1/3 of the way down. The next group about 2/3 the way down and the last group at the far end. This is assuming 4 4-way groups. Larger groups would require MORE distance.
Obviously, winds at altitude will offset this quite a bit, but it's not too difficult to judge the distances by just sort of looking at the runway length.
Definately helps if you know the layout of the DZ you're jumping at.
quade
http://futurecam.com

[weid14 0]

Bill isn't trying to slam you. I have never known him to do that to anyone. He is simply trying to save you or someone else's life. the 45 degree thing won't work. Do a search on exit separation, you'll find a wealth of info....

[diverdriver 7]

Ok, I know I've posted this chart before but I'll put it up again. It is all based on groundspeed. This groundspeed is easily read from a GPS. Ok, let's not argue about using GPS for spotting. But you have to admit that getting the current and exact groundspeed from a GPS is a handy tool in the subject of this thread.
Groundspeed:
100+ knots = 5 seconds between exits NOT 5 seconds then start climbing out.
90 - 100 = 8 seconds between exits.
80 - 90 = 12 - 15 seconds
70 - 80 = 15 - 20 seconds
less than 70 = 20 seconds +
20 - 30 knots = 45 seconds
The lowest groundspeed I've seen in the Otter is 17 knots. 50 SECONDS between exits. Man that was crazy.
Now, this is a chart that I use between small groups to medium (4-8 ways). If you change the diciplines or group sizes then adjustments need to be made to the times. Use your heads. Flats first largest to smallest, Freaks largest to smallest, high pullers, students, then tandems. I have never had a problem with this order and it works in all wind conditions except when you start with a downwind jump run.
Anything else?
www.DiverDriver.com the jump pilot resource
Chris Schindler
ATP/CFII
D-19012
www.DiverDriver.com

[SkyDekker 1,465]

Quote

Flats first largest to smallest, Freaks largest to smallest, high pullers, students, then tandems.

Just because I am a complete newbie.....I am trying to figure out what the reasoning is behind this exit order. That way I would probably understand it a bit better.
Thanks,
SkyDekker
"We cannot do great things, only small things with great love" Mother Theresa

[PhreeZone 20]

Check out the freefall drift pages that are listed above. Basically the flats get more drift in the wind then the freaks do. This drift can push flats over the top of the freaks if the winds are high enough.
Cause I don't wanna come back down from this cloud... ~ Bush

[skHIjunky 0]

Thank you for this chart. If all dropzones had this chart posted on a board with the winds at alltitude, maybe this wouldn't be an issue. I know I was not being slammed, and obviously safety is on everyones mind or else we would be chatting in the low pullers forum. Thanks for the input, web pages and most of all the better methods.

[SkyDekker 1,465]

Thanks Phree, that makes sense. I was thinking fall rate, but I see how it has more to do with drift rate than fall rate, or at least more so a combination of the two...
SkyDekker
"We cannot do great things, only small things with great love" Mother Theresa

[billvon 3,120]

>Bill, are you searching for ways to slam what people have to say . . .
I am not trying to slam anyone. However, if someone posts advice on a board I moderate that could get someone injured or killed, don't expect me to mince words in my reply. The 45 degree angle thing does not work.
>There has to be a little common since used in the factoring of course, and if the winds are in fact blowing at 60mph at alltitude, you could wait all day and never see the 45 degree angle.
That's not true. The plane, and the people who exit from it, see only the plane's airspeed when they exit. It isn't until they pass through some shear (i.e. when they start seeing less and less wind) that exit separation changes become apparent.
>Also, a person with very low jump numbers may not even be able to tell when they are over the dropzone, and
>most likely wouldn't even be able to tell that a thousand ground feet has passed.
If someone can't tell what they are over before they get out, there's something very wrong there. The ability to spot, at least well enough to know what general area you're getting out over, is an ability that should be learned before a student ever graduates. As in this case, lack of that ability can be dangerous both to the jumper and the other people in the plane.
-bill von

[billvon 3,120]

>Bill, besides experience, is there a sort of generic scale to work this off of?
For the most common case - winds approximately the same direction at altitude and opening, winds stronger at altitude, jump run into the wind - you can use either time or ground-based distance as your deciding factor. The easiest way to calculate it is, as Chris pointed out, to look at the GPS, convert that to feet, and figure it out from there. For example, a groundspeed of 100kts is equal to about 160 feet per second, so ten seconds at that groundspeed would give you 1600 feet of separation - enough for all but big formations. Even 5-6 seconds should be sufficient, giving you a separation of 1000 feet which is a good minimum.
Of course, using a "cheat sheet" such as the one Chris provided above is a lot easier.
The other way to do it is the ground. We used to have dirt roads on fields near our DZ that were about 1000 feet apart. That made it easy - wait until you crossed another road, then get out. (Of course, you probably want to wait until just before you cross the road so your climbout puts you over the road.)
-bill von

[diverdriver 7]

Now, not suggesting that this is the way it needs to be done but when all of this freefall drift stuff was figured out there was a "minimum" seperation between groups at opening that had to be attained for "minimum" safety. That distance was 300 feet. This is considering two jumpers opening facing directly at each other and in full flight. From a studying on human reaction in flying, it was figured that three (3) seconds was the minimum time required to recognize there was a collision threat, decide how you were going to avoid that collision, and then do the maneuver to avoid the collision. Using a chart like mine should give you much more than 3 seconds or 300 feet of seperation.
ALSO REMEMBER, it's the groundspeed that's important. Knowing the winds aloft is nice but unless you know what True Airspeed (and it's affected by altitude, temperature, and pressure) the plane is flying it's hard to do the mental math to figure the estimated ground speed on your own. Using a GPS is the easiest, most accurate way to get that groundspeed reading.
I've been on the receiving end of a flat flyer floating over me and opening on the other side of me in freefall. It is very scary.
Cool jumpsuit = 300 bucks
Rig = 4,500 bucks
Good GPS = 500 bucks
Situational Awareness = PRICELESS

[billvon 3,120]

Quote

Now, not suggesting that this is the way it needs to be done but when all of this freefall drift stuff was figured out there was a "minimum" seperation between groups at opening that had to be attained for "minimum" safety. That distance was 300 feet. This is considering two jumpers opening facing directly at each other and in full flight. From a studying on human reaction in flying, it was figured that three (3) seconds was the minimum time required to recognize there was a collision threat, decide how you were going to avoid that collision, and then do the maneuver to avoid the collision. Using a chart like mine should give you much more than 3 seconds or 300 feet of seperation.

I agree, but anything larger than a solo involves tracking for separation, and I generally assume people track around 300 feet from 3-4 ways. If you put two four-ways 1000 feet from each other, and one person in each group tracks towards the other for 300 feet, you then have 400 feet between them - a good minimum, I think.
-bill von

[diverdriver 7]

Yes, exactly. Just letting people know that there was a scientific approach to all this stuff.
Chris

[kallend 2,150]

Check out my web site
http://www.iit.edu/~kallend/skydive/
There's a freefall simulation program you can use to play "what if", and a powerpoint presentation on this exact topic.
You can even get the "angle" plotted out for you if you set both jumpers to the same fall rate and zero exit delay. You will see that the 45 degree angle method is bogus - no basis in physics or in reality.
If you will be at Skydive Chicago's winter expo this weekend, I'm giving a talk on freefall separation.
jk

[kallend 2,150]

See
http://www.iit.edu/~kallend/skydive/ for a Powerpoint presentation that addresses this issue, with graphics and a chart for different group sizes from solo to 10-way.
There's also a downloadable .exe file (no viruses - straight from the compiler and never executed) that lets you play "what if" with various exit scenarios. You can even check the "angle" method out (it doesn't work - no basis in physics).
<<track around 300 feet from 3-4 ways. If you put two four-ways 1000 feet from each other, and one person in each group tracks towards the other for 300 feet, you then have 400 feet between them - a good minimum, I think.
-bill von>>>

[Hooknswoop 19]

Chris-
Nice work. It would be nice to add "Add X seconds for an 8 way, add X seconds for a 9 way", etc to your chart and post it in the back of jump ships. The pilot can pass back the jump run ground speed and then people can refer to the chart as people exit to determine the time between exits. A little digital clock would be pretty cool too.
What do you think?
Hook