Physics behind why a large formation falls slower

[gingergal 0]

Hi All,
Can anybody explain why a large formation falls slower?

Thanks!

[keithbar 1]

Because big way jumpers are a bunch of skinny floaty fuckers.

i have on occasion been accused of pulling low . My response. Naw I wasn't low I'm just such a big guy I look closer than I really am .

[kallend 1,621]

Interference drag.

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The only sure way to survive a canopy collision is not to have one.

[riggerrob 558]

Mostly, they get lazy and forget to arch.

Outer rings pulling also flattens the formation.

[gingergal 0]

Thanks all. I was having a bit of a debate of exactly why they fall slower! Google was not helping

[kallend 1,621]

riggerrob

Mostly, they get lazy and forget to arch.

Outer rings pulling also flattens the formation.

Disagree.

Even big ways consisting of very very good RW skydivers fall more slowly as they grow, and some formation designs (many zippers, densely packed) fall slower than others (open design, with lots of holes). If your "theory" were correct, formation design would be irrelevant. It isn't.

...

The only sure way to survive a canopy collision is not to have one.

[chuckakers 369]

kallend

***Mostly, they get lazy and forget to arch.

Outer rings pulling also flattens the formation.

Disagree.

Even big ways consisting of very very good RW skydivers fall more slowly as they grow, and some formation designs (many zippers, densely packed) fall slower than others (open design, with lots of holes). If your "theory" were correct, formation design would be irrelevant. It isn't.

I agree with John.

My guess is that it's along John's thought of "interference drag". Think of the difference in the drag created by a single, somewhat aerodynamic person vs a large body (made up of multiple individuals) that is extremely flat with small holes in it as the wind sees it.

Also consider the burble, which may be the biggest factor. If I'm getting this right, aerodynamic engineers pay as much or more attention to reducing burble drag behind a moving body as they do on splitting the wind efficiently in the front.

It would be interesting to see what the burble above a big-way looks like relative to a single jumper or small group.

Chuck Akers
D-10855
Houston, TX

[AlanS 1]

chuckakers

It would be interesting to see what the burble above a big-way looks like relative to a single jumper or small group.

So who wants to volunteer to be in that experiment?

I'd like to know if there is any data on the speed of big ways as they grow in size.

And I'm also wondering if anyone it makes sense (when trying out a new suit for example) to just take the suit to a wind tunnel and ask them to slow down the speeds to those ranges and see how the suit flies.

[mjosparky 3]

It takes longer to build large formations, so the jumpers fall slower giving them more time.

My idea of a fair fight is clubbing baby seals

[KoKo 0]

Quote

"interference drag"

You can see this for yourself with a simple experiment. Drive about 70-mph down the highway, roll down the window, and stick your hand out, palm into the wind. With your fingers together, note the amount of wind force pushing on your hand. Next, open your fingers as wide as you can, and note the force of the wind on your hand - it should feel about the same, or less. Lastly, close your fingers a little so that there is still some space between them, but not as much - you will feel MORE drag then when the fingers are wide open. It's the same surface area, but the wind is blowing through your fingers differently.

I used to do this to determine the optimum hand position for making the best wind deflections for fast maneuvers. Cupping the hands with fingers closed seems like the logical choice, but it's not so. Having the fingers open a little bit produces more drag than with the fingers closed.

Probably the same principal with a bunch of skydivers in formation.

[diablopilot 2]

You're correct John. But so is Rob. Both are valid reason, though I suspect your ego chokes on that idea.

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You're not as good as you think you are. Seriously.

[theonlyski 3]

chuckakers

Also consider the burble, which may be the biggest factor. If I'm getting this right, aerodynamic engineers pay as much or more attention to reducing burble drag behind a moving body as they do on splitting the wind efficiently in the front.

I believe that's called 'pressure drag'.

"I may be a dirty pirate hooker...but I'm not about to go stand on the corner." iluvtofly
DPH -7, TDS 578, Muff 5153, SCR 14890
I'm an asshole, and I approve this message

[pchapman 261]

diablopilot

You're correct John. But so is Rob. Both are valid reason, though I suspect your ego chokes on that idea.

I think John got picky because Rob wrote "mostly", probably just using it casually and in a bit of a cynical tone about skydivers. But then John would object that Rob looks like he's suggesting that the factor with the greatest weight was "lazy skydivers" changing their body position.

John probably gets a bit pedantic... because I thought that kinda was his job.
In addition to interference drag (affected by formation design), skydivers not maintaining the desired body position, and stretching of the formation affecting body position, I'll add another small factor: The design and spacing of formations can put some skydivers into positions where they have to stretch to achieve the grips (e.g, people filling the gaps between a 4 way star, when going for leg grips).

[kallend 1,621]

pchapman

***You're correct John. But so is Rob. Both are valid reason, though I suspect your ego chokes on that idea.

I think John got picky because Rob wrote "mostly", probably just using it casually and in a bit of a cynical tone about skydivers. But then John would object that Rob looks like he's suggesting that the factor with the greatest weight was "lazy skydivers" changing their body position.

John probably gets a bit pedantic... because I thought that kinda was his job.
In addition to interference drag (affected by formation design), skydivers not maintaining the desired body position, and stretching of the formation affecting body position, I'll add another small factor: The design and spacing of formations can put some skydivers into positions where they have to stretch to achieve the grips (e.g, people filling the gaps between a 4 way star, when going for leg grips).

Why would the same skydivers get lazy on, say, a 120 way but not on a 12 way? Why would they get lazy in formations with lots of zippers and not ones with an open structure? That argument makes no sense.

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The only sure way to survive a canopy collision is not to have one.