exit separation please help

[Newbie 0]

after having read that post on it in Talk Back i wanted to clarify the situation. Normally i count, or wait for the jump master, but i want to actually know how to LOOK for separation. Im trying to get into the habit of watching someone go and seeing where they are after my count, but what angle should they be at to my view to have adequate separation? WHat i mean is if straight down out the door is 0 degrees, and looking at the horizon via the planes tail is 90 degrees, what angle should the group/person be at for adequate separation, and how should that be altered, if at all to groups of different numbers/disciplines.

Please note im new to this so explanations in the most basic terms would be appreciated.

Thanks

"Skydiving is a door"
Happythoughts

[TALONSKY 0]

Well it seems in this matter my opinion was totally wrong so I have deleted it.
Sorry
Kirk

[bobsoutar 0]

Rule of thumb it's 45 degrees but situations change depending on wind speed, group size etc.

Try to get a proper briefing for spotting and jumpmastering as this stuff is much better learnt face to face.

[quade 4]

Unfortunately, waiting for a 45 degree angle to occur isn't really based in science and is at best wishful thinking.

quade -
The World's Most Boring Skydiver

[nacmacfeegle 0]

Bob the 45 degree thing has been poo pooed, try a search on the forums, this has been chatted about in great depth...

--------------------

He who receives an idea from me, receives instruction himself without lessening mine; as he who lights his taper at mine, receives light without darkening me. Thomas Jefferson

[grega 0]

huh if i'd wait for group before me to be at 45degrees, when jumping from casa 212 with that speedy pilot, it would of been more than 30 seconds of separation with plane flying at speed well above terminal

"George just lucky i guess!"

[billvon 3,109]

>WHat i mean is if straight down out the door is 0 degrees, and
> looking at the horizon via the planes tail is 90 degrees, what angle
> should the group/person be at for adequate separation . . .

That doesn't work. It's like trying to figure out your speed in a car by the angle you see the edge of the road at. It doesn't change with your speed, and the angle out the aircraft door doesn't change with winds (which are the primary issue in terms of changing your separation.)

The simplest way is to cheat and look at the GPS. Leave .2 miles between groups and you'll be fine, even with pretty large groups. That's 1000 feet between groups.

The next simplest way (and actually a much safer way) is to look at the ground. Look at the ground when the group ahead of you gets out, wait until the plane covers 1000 feet, then go. Alternatively, wait until the plane covers 500 feet, then set up your exit and go. This gives the added benefit of being able to check for traffic.

Another way is to wait, say, 5 seconds between groups (5 seconds is pretty good for a King Air or an Otter with a minimal cut) and then add time for upper winds, if you're flying into them (which you usually are.) 10 seconds with 40kt uppers would be a good separation; if the uppers are 80kts you can't get good separation because the plane simply doesn't fly much faster than that. (Of course, you wouldn't generally be jumping on such a day.)

The final way is, of course, just to ask someone on the load. We used to spend the first 2-3 loads at Brown asking each other what the uppers were doing, what the separation should be, where the spot was. Once we had that dialed in we'd generally be good for the rest of the day.

[kallend 2,146]

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At my dropzone we were never taught to count but simply what for the jumpers before us to be at a 45° angle.
Blue skies
Kirk

There is no basis in math or physics for this method, and most planes don't have a protractor on board anyway.

You might want to take a look at

www.iit.edu/~kallend/skydive/separation.pdf

[pilotdave 0]

check out /wingsuit/WingsuitMovie.wmv on my server (50 megs) if you have a chance. These guys literally go UP after exiting the C-130. How cool is that?? Forget 45 degrees, wait till they hit 110 degrees!
Dave

[LouDiamond 1]

Truth be told, most people can't eye ball 1000 ft or 500ft from altitude even if they have two easy to identify land marks and ploted the distance between the two on the ground using a map. Throw into that equation the possibility that your not looking straight down at your land mark. So really, two different people could have two different interpetations of what 1000 or 500 ft look like from altitude. But that goes more into spotting and that takes lots of practice hanging out of an A/C with someone who knows what they are doing behind you.

Separation can best be estimated by knowing the ground speed prior to exit. Most DZ A/C have the little ground speed/seperation secs cheat sheet by the door for reference. Anything else is really a SWAG.

In a perfect world a streamer would be thrown out at the release point and observed to verify winds at descending altitudes and confirm the spot. Combine that with ground speed and the seperation table for estimated times between groups. Even with all that knowledge the person in the door should be watching the group in front of them while they count and observe where that group is going(or not going) just because you get to your count doesn't mean it's cool to get out. If that group before you isn't moving away from you,for what ever reason, then you need to wait a little longer until a percieved amount of seperation is obtained.

Rule of thumb that works with either a tailgate or door. If your in the door and your watching the group they will continue to move down and away from the direction of flight,which will require you to lean out a little bit more in order to maintian a visual on them. For a tail gate the same applies except the group will not only move down but will seem to move higher on the horizon as the plane continues to fly away from the group. You will have a visual indicator (reference) on the ground in relation to the group and to the A/C to make your SWAG.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[billvon 3,109]

>Separation can best be estimated by knowing the ground speed prior to exit.

This is one of the best ways, and you don't even need a cheat sheet. At 13,000 feet, 100 knots is 200 feet per second. Groundspeed of 100 knots? Leave 5 seconds and you'll have 1000 feet of separation, which is plenty for even medium-sized groups. Groundspeed of only 40 knots? 5 seconds would only give you 400 feet of separation, not even enough for 4-way groups.

The above assumes you're flying into the wind and that winds at opening altitude are the same direction but much slower, which is usually the case.

>Even with all that knowledge the person in the door should be
> watching the group in front of them . . .

And looking down to ensure that they are clear of traffic.

>If that group before you isn't moving away from you,for what ever
> reason, then you need to wait a little longer until a percieved
> amount of seperation is obtained.

Again, this just doesn't work. Whether you are flying in a King Air in a 10kt headwind, a 80kt headwind, or a 40kt tailwind, you will see the group that exits ahead of you do _exactly_the_same_thing._ If you decide what a safe visual distance is for an exit in a 10kt headwind, you may end up with a freefall collision if you try to use the same 'sight picture' for an exit in an 80kt headwind.

Watching the group in front of you after they exit simply doesn't work.

[LouDiamond 1]

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>Separation can best be estimated by knowing the ground speed prior to exit.

"This is one of the best ways, and you don't even need a cheat sheet. At 13,000 feet, 100 knots is 200 feet per second. Groundspeed of 100 knots? Leave 5 seconds and you'll have 1000 feet of separation, which is plenty for even medium-sized groups. Groundspeed of only 40 knots? 5 seconds would only give you 400 feet of separation, not even enough for 4-way groups.

Agreed but having the cheat sheet helps settle any bitching and is a good check list item for those days you're not feeling as sharp.

Quote

"The above assumes you're flying into the wind and that winds at opening altitude are the same direction but much slower, which is usually the case.

Agreed

>Even with all that knowledge the person in the door should be
> watching the group in front of them . . .

Quote

"And looking down to ensure that they are clear of traffic.

It goes without saying but good to mention regardless

>If that group before you isn't moving away from you,for what ever
> reason, then you need to wait a little longer until a percieved
> amount of seperation is obtained.

Quote

"Again, this just doesn't work. Whether you are flying in a King Air in a 10kt headwind, a 80kt headwind, or a 40kt tailwind, you will see the group that exits ahead of you do _exactly_the_same_thing._ If you decide what a safe visual distance is for an exit in a 10kt headwind, you may end up with a freefall collision if you try to use the same 'sight picture' for an exit in an 80kt headwind.

That is only employed if AFTER having used the known ground speed/seperation calculation and found it less than ideal. To solely base your seperation on a visual que is as wrong as two boys screwing. But common sense has also taught you that an 80 kt headwind will make the group look as if it is dropping down the pipe(straight down) instead of down and away from the direction of flight.

Quote

"Watching the group in front of you after they exit simply doesn't work.

"

As a sole method of determination, yes, you are correct. As a second method to backstop the calculated seperation between groups is correct.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[billvon 3,109]

>To solely base your seperation on a visual que is as wrong as two
> boys screwing.

Don't tell Keith or Narc that!

>But common sense has also taught you that an 80 kt headwind will
> make the group look as if it is dropping down the pipe(straight
> down) instead of down and away from the direction of flight.

This is a common misconception. If your _airspeed_ slows down due to the headwind you'd be right on - if the headwinds were 80kts and a plane that normally flew at 80kts had to fly at zero airspeed, then you'd see just that. In fact, that's what you _do_ see in a hovering helicopter - everyone just falls straight down.

But the plane can't slow down like that. It will stall. In fact, its airspeed during jump run doesn't change due to the winds aloft, even if it's flying into an 80 kt wind. It may not have any _groundspeed_ but it sure as heck has _airspeed_ - sticking your hand out the door will verify this.

When a person exits, all their body sees is the airspeed. If it's 80 knots, then they'll fall away at a given perceived angle. It doesn't matter what the winds aloft are doing. In fact, even if you're not moving over the ground at all, that airspeed will blow the person back exactly the same as it always does. No 'falling down the pipe.' And no matter how long you wait you will not get sufficient separation, even though it looks exactly the same as it does when there are no winds aloft, and 5 seconds is OK.

>As a sole method of determination, yes, you are correct. As a second
> method to backstop the calculated seperation between groups is
> correct.

Well, I'm not saying it's not that accurate, I'm saying it doesn't work _at_all_. It gives you the wrong information.

[diverdriver 7]

Quote

But common sense has also taught you that an 80 kt headwind will make the group look as if it is dropping down the pipe(straight down) instead of down and away from the direction of flight.

No. You will not drop straight down. What everyone is forgetting is that once you are out the door you are in two completely seperate mediums. One, the plane, you have power and are moving through the air. The other, freefall, you are decelerating your forward throw of the aircraft and beginning to be acted apon by the upper winds. If you have ZERO ground speed you will NOT fall straight down according to the observer unless you are in a balloon or helicopter in hover. You will ALWAYS see the group ahead of you move back towards the tail. THE ANGLE METHOD DOES NOT WORK IN ANY FORM OR FASHION EVER! Please, everyone, stop saying that it partly works or is a good backup. No it is not!

Also, a Twin Otter indicating 80 knots on the airspeed indicator at 13K will NOT be doing 80 knots over the ground in no wind conditions. It will actually be going about 105 knots. SURPRISE PEOPLE! So if you actually do have 80 knot upper winds does not mean you will have no ground speed. I personally have seen 17 knots on the groundspeed during jumprun. We were giving 45-50 seconds PER GROUP! It took 7 minutes to make one pass and everyone landed on and didn't have to make a second pass. If you had looked out the door as the first group left they would have gone back towards the tail just like on every other jump run you've looked out the door. The difference is that you have not gone anywhere in 10 seconds. Be sure you are checking ground speed.

I've posted a chart of ground speed and seperation times many times on this forum. You can run a search and will probably bring it up. Right now I don't have it handy to post.

Chris Schindler
www.diverdriver.com
ATP/D-19012
FB #4125

[quade 4]

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. . . I personally have seen 17 knots on the groundspeed during jumprun. We were giving 45-50 seconds PER GROUP! It took 7 minutes to make one pass and . . .

Somethin' ain't right here . . .

Let's see.

17 knots * 1.15 = 19.55 mph
19.55 mph * 5280 = 103224 fph
103224 fph / 60 = 1720.4 fpm
1720.4 fpm / 60 = 28.67333... fps
28.68 * 45 = 1290 feet of exit separation
28.68 * 50 = 1434 feet of exit sep
1290 * 6 = 7741.7994 total jump run or about 1.47 miles
1434 * 6 = 8604 tjr or about 1.62 miles

NOTE: rounding errors -- rounding errors.

(why *6? because the first group would be zero time)

Ok, that checks out - but dayum that's a mightly long jump run!

45 sec * 6 = 270 sec or 4.5 minutes
50 sec * 6 = 300 sec or 5 mintues

Ahhh, I knew something was fishy.

Never give a bored man a calculator.

quade -
The World's Most Boring Skydiver

[LouDiamond 1]

Quote

This is a common misconception. If your _airspeed_ slows down due to the headwind you'd be right on - if the headwinds were 80kts and a plane that normally flew at 80kts had to fly at zero airspeed, then you'd see just that. In fact, that's what you _do_ see in a hovering helicopter - everyone just falls straight down.

My bad, That is what I thought you were saying in the previous post



>As a sole method of determination, yes, you are correct. As a second
> method to backstop the calculated seperation between groups is
> correct.

Well, I'm not saying it's not that accurate, I'm saying it doesn't work _at_all_. It gives you the wrong information.

[RichM 0]

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Also, a Twin Otter indicating 80 knots on the airspeed indicator at 13K will NOT be doing 80 knots over the ground in no wind conditions. It will actually be going about 105 knots.

I'm not a pilot, please can you explain this to me? (Thinner air?)

Rich M

[kallend 2,146]

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No. You will not drop straight down. What everyone is forgetting is that once you are out the door you are in two completely seperate mediums.

Not everyone, Chris.

[diverdriver 7]

Curses you Riddler! But did you add in 2 minutes for the 2 minute call prior to first drop? That's not part of jumprun? Ok, I'm arguing semantics.

Oh yah.....and

Chris

[diverdriver 7]

Quote

Quote

Also, a Twin Otter indicating 80 knots on the airspeed indicator at 13K will NOT be doing 80 knots over the ground in no wind conditions. It will actually be going about 105 knots.

I'm not a pilot, please can you explain this to me? (Thinner air?)

Yes, thinner air. It is called True AirSpeed or TAS. To calculate TAS you have to correct for nonstandard pressure and temperature. That said, typically with no wind and at altitude, your groundspeed will be about 105 knots when indicating 80-85 knots.

Chris Schindler
www.diverdriver.com
ATP/D-19012
FB #4125

[diverdriver 7]

Nerds don't count in "everyone". >

[billvon 3,109]

>Also, a Twin Otter indicating 80 knots on the airspeed indicator at
>13K will NOT be doing 80 knots over the ground . . .

>I'm not a pilot, please can you explain this to me? (Thinner air?)

Yep. First correction is IAS (indicated airspeed, or what the pilot sees on his airspeed indicator) to TAS (true airspeed, or what your groundspeed would be with no wind). A good rule of thumb is add 2% per 1000 feet, so at 13,000 feet your actual speed is 100 kts if you're going 80 kts.

The next two steps I do is convert to MPH and then FPS. Multiply by 1.15 to get MPH, then 1.46 to get FPS. 80kts IAS becomes 165 fps.

An easier way to do this is to just multiply your (airspeed in knots - windspeed) at 13,000 feet by 2, and that's approximately the number of feet you cover per second. So if your aircraft is flying 80kts, and the winds are 30kts, you cover 100 feet every second. Want to be 500 feet from the previous group? Wait 5 seconds.

[RichM 0]

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An easier way to do this is to just multiply your (airspeed in knots - windspeed) at 13,000 feet by 2, and that's approximately the number of feet you cover per second. So if your aircraft is flying 80kts, and the winds are 30kts, you cover 100 feet every second. Want to be 500 feet from the previous group? Wait 5 seconds.

Sweet, I can do that on run-in, and stash the rest for rainy days. Thanks Bill.

Rich M

[kallend 2,146]

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Want to be 500 feet from the previous group? Wait 5 seconds.

I can't imagine wanting to be that close.

[RichM 0]

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Quote

Want to be 500 feet from the previous group? Wait 5 seconds.

I can't imagine wanting to be that close.

If it's a solo following a solo wouldn't 500ft be plenty?

Rich M