Forums: Skydiving: Safety and Training:
Novice question on line of flight

VOT  (Student)

May 9, 2011, 5:06 PM
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 Novice question on line of flight Can't Post
I have been reading a good bit on exit order and different theories on placement of RW and FF divers and have come across a question on the regular line of flight patterns for most DZ's. Do most DZ's make their line of flight perpendicular to the wind? or do they make it parallel? i ask this because im pretty sure on the majority of my jumps we have gone perpendicular to the wind, making wind drift negligent in the placement of RW and FF divers?

May 9, 2011, 5:43 PM
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 Re: [VOT] Novice question on line of flight [In reply to] Can't Post
I have been reading a good bit on exit order and different theories on placement of RW and FF divers and have come across a question on the regular line of flight patterns for most DZ's. Do most DZ's make their line of flight perpendicular to the wind? or do they make it parallel? i ask this because im pretty sure on the majority of my jumps we have gone perpendicular to the wind, making wind drift negligent in the placement of RW and FF divers?

It depends. It depends on the DZ, what they typically do, how many aircraft are in the air and a handful of other factors.

It also depends on the winds aloft. Although the winds aloft are often times similar to the ground winds, they aren't always.

Are you basing your observation on the ground winds or the winds aloft? I'm not saying that you were incorrect in your observation that the jump runs were perpendicular to the winds aloft, I'm just curious if you looked at the winds aloft to make the observation.

VOT  (Student)

May 9, 2011, 8:04 PM
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The DZ had a print of the wind direction and temp on a wall, it had the wind direction at canopy altitude the same as the direction but not velocity as in free fall n the DZ only had my aircraft flying at the time

(This post was edited by VOT on May 9, 2011, 8:43 PM)

dragon2  (D 101989)

May 9, 2011, 11:24 PM
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As an example, at my DZ we generally fly into the wind. However, if there's little wind or a LOT of wind and especially if the upper winds are from the south, we fly perpendicular. This gives everyone a chance to reach the DZ, and in the case of wind from the south, gives everyone a chance on clearing the runway and the glider runway at 2000/1500 ft.

We still have the same exit order in place. It makes sense to keep it the same allways, to avoid confusion and to make last minute changes in jumprun possible without the "airplane shuffle" you might get otherwise.

JohnMitchell  (D 6462)

May 9, 2011, 11:46 PM
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ask this because im pretty sure on the majority of my jumps we have gone perpendicular to the wind, making wind drift negligent in the placement of RW and FF divers?
I think you meant "negligible".

Although we talk about wind drift a lot it's only one factor in why the slow fallers jump first. Even with no winds at all, aloft or on the ground, the belly fliers should leave first. Why? Because the slower a group's fall rate, the less forward throw they get after exit. In other words, they'll coast forward less distance along the jump run line than a faster falling group. So upwind, crosswind, no wind, stick with the system.

Belly fliers, then freeflyers = more separation = good thing

Free flyers, then belly = less separation = bad thing

May 10, 2011, 12:01 AM
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Belly fliers, then freeflyers = more separation = good thing

Free flyers, then belly = less separation = bad thing

Only when jumprun is into the wind.

Hellis

May 10, 2011, 12:08 AM
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Belly fliers, then freeflyers = more separation = good thing

Free flyers, then belly = less separation = bad thing

Only when jumprun is into the wind.

If your quoting would have been a little higher you would have got this part:

Quote:
So upwind, crosswind, no wind, stick with the system.

Belly fliers, then freeflyers = more separation = good thing

Free flyers, then belly = less separation = bad thing

Meaing all but downwind use that system

VOT  (Student)

May 10, 2011, 8:52 AM
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 Re: [JohnMitchell] Novice question on line of flight [In reply to] Can't Post
"Because the slower a group's fall rate, the less forward throw they get after exit."

Aw of course! So I guess my real question then is when would a line of flight with a head wind be appropriate/necessary?

(This post was edited by VOT on May 10, 2011, 8:59 AM)

JohnMitchell  (D 6462)

May 10, 2011, 8:56 AM
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Belly fliers, then freeflyers = more separation = good thing

Free flyers, then belly = less separation = bad thing

Only when jumprun is into the wind.
No, you're wrong. It works in no wind and cross wind. The forward throw effect is independent of any winds.

JohnMitchell  (D 6462)

May 10, 2011, 8:59 AM
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 Re: [Hellis] Novice question on line of flight [In reply to] Can't Post
Meaing all but downwind use that system
Downwind does complicate things. The forward throw effect adds separation, but the increased time in the tail wind decreases the separation between belly and freefly. Exactly how much could be calculated by someone with higher math skills than I.

Are downwind jumpruns common where you jump? I've only done a handful of them under unusual circumstances.

JohnMitchell  (D 6462)

May 10, 2011, 9:10 AM
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 Re: [VOT] Novice question on line of flight [In reply to] Can't Post
So I guess my real question then is when would a line of flight with a head wind be appropriate/necessary?
Is your question "Why make the jumprun into the wind?" It's usually done to minimize ground speed on jumprun, but it's not a hard and fast rule. Spotting used to be from smaller planes with typically one group. So jump run was like a bomb run, with accuracy over the target being the goal, the "perfect spot."

Now, with many separate groups exiting on jumprun, only the middle group gets the perfect spot. Everyone else's spot is a compromise. When there are many groups getting out, upwind jumpruns give them more time to get in the door and get ready. However, they have to remember to give enough time (which equals distance) between groups. If you fly downwind, the time between groups to achieve safe separation would be much less.

Or jumping out of a fast plane. I've been in a 20+ way following a 20+ way from the ramp of a C-130. We had maybe 5-6 seconds between the groups, almost as fast as we could assemble and get out. It was plenty of separation at those speeds.

It's sounds as if your DZ uses crosswind jumpruns. Fine. I'm sure it's a good system that works for them. One of the instructors there could tell you more about why.

VOT  (Student)

May 10, 2011, 9:35 AM
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"It's sounds as if your DZ uses crosswind jumpruns. Fine. I'm sure it's a good system that works for them."

Would that mean a crosswind jumprun is irregular for most DZ's?

JohnMitchell  (D 6462)

May 10, 2011, 9:41 AM
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 Re: [VOT] Novice question on line of flight [In reply to] Can't Post
I don't think it's as common as into the wind, but I'm no expert.

billvon  (D 16479)
Moderator
May 10, 2011, 10:12 AM
Post #14 of 19 (1690 views)
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 Re: [VOT] Novice question on line of flight [In reply to] Can't Post
>Do most DZ's make their line of flight perpendicular to the wind? or do
>they make it parallel?

Most fly _roughly_ into the wind.

>i ask this because im pretty sure on the majority of my jumps we have
>gone perpendicular to the wind, making wind drift negligent in the
>placement of RW and FF divers?

If you are truly perpendicular - yes. Unfortunately that is hard to guarantee.

kallend  (D 23151)

May 10, 2011, 12:43 PM
Post #15 of 19 (1648 views)
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Meaing all but downwind use that system
Downwind does complicate things. The forward throw effect adds separation, but the increased time in the tail wind decreases the separation between belly and freefly. Exactly how much could be calculated by someone with higher math skills than I.

Are downwind jumpruns common where you jump? I've only done a handful of them under unusual circumstances.

My freefall simulation can handle downwind jump runs.
http://mypages.iit.edu/~kallend/#skydive

JohnMitchell  (D 6462)

May 10, 2011, 12:47 PM
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Thanks a million, Doc. I was thinking of you when I mentioned math skills earlier.

May 10, 2011, 12:57 PM
Post #17 of 19 (1633 views)
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Only when jumprun is into the wind.
No, you're wrong. It works in no wind and cross wind. The forward throw effect is independent of any winds.
Sorry, had a brainfart. Wanted to say that this rule was not correct when jumprun was with the wind in the back. Did not notice that you already said that. I missed that part.

Empuriabrava regulary has a downwind jumprun. They prefer not to put out jumpers above the sea or the town (with no outs in the town except canals).

May 10, 2011, 1:16 PM
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Quote:
They prefer not to put out jumpers above the sea or the town (with no outs in the town except canals).

Understandable... Although I had the bestest visuals while tracking over the town there...

May 11, 2011, 4:58 AM
Post #19 of 19 (1542 views)
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 Re: [kallend] Novice question on line of flight [In reply to] Can't Post
...
My freefall simulation can handle downwind jump runs.
http://mypages.iit.edu/~kallend/#skydive

That's a real good one to play some!

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