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# Wind direction during deployment

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skydiverek

Physics professor and skydiver with thousands of jumps, John Kallend, wrote here on DZ.com that you will "become one with the (horizontal) wind" only after 8 seconds in freefall. So, if the horizontal wind is 40 mph, then you will be moving 40 mph (in freefall) against the ground, only after 8 seconds.

I agree. I would add that when the upper level winds are from different directions with different speeds as the altitude changes, you end up drifting this way, and then that.

I collect a lot of GPS data and you can see the drift vary, base on the direction and speed of the uppers. Little acceleration rams this way, and then that way.

On a 22,000 foot jump we when through a layer of strong uppers. it was just a layer maybe a few thousand feet thick but we hit 80 MPH "drift" in an odd direction and then went back to drifting in another direction. Odds are we were never "one" with the air on that 80 MPH zone but we were moving pretty fast.
Instructor quote, “What's weird is that you're older than my dad!”

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SansSuit

How much does the wind direction affect the opening of a canopy? I would think that opening while facing straight into the wind would give the best (on heading) opening. How about 45 or 90 degrees off the wind line? Could that cause twists in a canopy that is susceptible to squirrelly openings?

Seriously?
Chuck Akers
D-10855
Houston, TX

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Quote

Here's how to calculate what to do for your example:
060 x 15 = 900
080 x 10 = 800
060 x 330 = 19800
Total: 900 + 800 +19800 = 21500

According to Theodore Knocke (see pages 340-341), the optimum drag coefficient is at 21500 is: pi / (1.16 ^ 2) = 2.3335

21500 / 2.3335 = 9213.6276

7986.4968 / 090 = 102.3736 kts = 117.7297 mph.

So your best bet is to face 90 degrees to the wind at about 120 mph.

At our drop zone, we used to have a placard by the door to help folks with this, but what we found was that on break-off everybody would track the same direction for optimal openings. Now only one jumper gets the optimal openings and the others are all basically screwed.

We have assigned people grid, magnetic, and true headings to give even more people the opportunity to open on the optimum heading.

You forgot to mention that if you convert from degrees to radians it works in those countries that use the metric system.

Other than that, flawless. Well done!
Shit happens. And it usually happens because of physics.

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flyhi

Quote

Here's how to calculate what to do for your example:
060 x 15 = 900
080 x 10 = 800
060 x 330 = 19800
Total: 900 + 800 +19800 = 21500

According to Theodore Knocke (see pages 340-341), the optimum drag coefficient is at 21500 is: pi / (1.16 ^ 2) = 2.3335

21500 / 2.3335 = 9213.6276

7986.4968 / 090 = 102.3736 kts = 117.7297 mph.

So your best bet is to face 90 degrees to the wind at about 120 mph.

At our drop zone, we used to have a placard by the door to help folks with this, but what we found was that on break-off everybody would track the same direction for optimal openings. Now only one jumper gets the optimal openings and the others are all basically screwed.

We have assigned people grid, magnetic, and true headings to give even more people the opportunity to open on the optimum heading.

You forgot to mention that if you convert from degrees to radians it works in those countries that use the metric system.

Other than that, flawless. Well done!

Not quite ~ it's all reversed in the southern hemisphere.

~ If you choke a Smurf, what color does it turn? ~

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angryelf

Yet you can have horizontal drift in freefall?

Of course. That's what John is talking about. Horizontal drift only occurs relative to the ground. There is no drift relative to the wind because the jumper and the wind move together.

A flag draped from a hot air balloon will hang limp even if the balloon is moving across the ground. This is because the balloon is moving relative to the ground but it's sitting still relative to the air mass it is in.

Ever see a fish swim 100 mph? Put it in s fish bowl, hop in your car, and drive 100 mph. That's the freefall drift you are talking about. The fish's position is changing rapidly relative to the ground, yet its speed relative to the water in the bowl (like the air we fall through) is zero when it sits still.
Chuck Akers
D-10855
Houston, TX

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angryelf

Yet you can have horizontal drift in freefall?

Not to be confused with vertical drift, which is the actual freefall...

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My thoughts exactly. It seems the newer gen. "X" sky divers are coming up with some crazy theories. It makes me wonder if the quality of our instructional personal and facilities. This question from this OP reminds me of the "High riser pressure" thread.

Best
Richard

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rwieder

My thoughts exactly. It seems the newer gen. "X" sky divers are coming up with some crazy theories. It makes me wonder if the quality of our instructional personal and facilities. This question from this OP reminds me of the "High riser pressure" thread.

Best
Richard

You do realize the OP is closer to your generation than ours. According to his profile he has been in this sport for 19 years. He is obviously trolling.

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Hi Sans,

I have read every posting in this thread.

Please copy each & every posting then paste it all into the JOKE OF THE DAY CLUB thread in the Bonfire.

And is your question only about jumping in daylight or have you considered the differences when the sun goes down?

JerryBaumchen

PS) Sheesh, some people just do not know where they should be.

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wolfriverjoe

***After reading through this thread I understand why people have such a problem with the airplane on the treadmill problem.

Yeah...

Seriously, unless there is a very strong wind shear, right at or before opening (8 sec ~ 1500ft) there will be zero horizontal component to the relative wind (unless induced by the jumper through tracking or similar).

Indeed if you cross through a severe gradient / wind shear line that's, say, 90 degrees off heading from the direction you are facing right when you deploy then it would be similar to making a base jump with a steady cross wind. Assuming your canopy is stable in yaw, it will turn into the crosswind. It's similar if you're on final and your canopy is in full flight and there is a cross-wind gust, your canopy will yaw a bit into the gust.

That's all just to say, "Yes, qualitatively that can happen." Quantitatively, on the other hand...

When you're making a base jump with very little airspeed, the effect of a crosswind on heading performance can be dramatic. When your skydiving canopy is in full flight you have a fair amount of airspeed, so even strong gusts aren't likely to turn your canopy more than a small amount. During deployment at terminal you'd have to have one hell of a wind gradient to swamp out the other dominant factors of heading performance like differential loading you were putting on the sides of the canopy by not being perfectly level.

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Wolfriverjoe is correct

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OK, obviously I deserve all of the ridicule so far inflicted. I'm having problems with a basic concept and I'm trying to wrap my head around it.

Let me try this from a different direction (pun intended).

Are there any side-to-side differences in canopy that is flying straight and level but pointed 90° from the air mass around it? If a canopy is being pushed through the sky from one side, are the internal pressures (or whatever measurements used) still the same left-to right?
Peace,
-Dawson.
http://www.SansSuit.com
The Society for the Advancement of Naked Skydiving

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angryelf

If you have multiple currents (relative wind of 112 kts and, say a horizontal breeze of 40 kts) and you "stick a paddle in it"-it has to affect you to some degree.

For the boat analogy I offer this: a boat in a consistent current will move with that current-I agree. But, float that same boat in a big river going 6 kts downstream/midstream and let it roll past a small tributary pumping out a 1/4 of the main river's volume at 3 kts and I guarantee it will affect the boat in the main current! Where it hits the boat, mass of the boat, amount of water the boat is drawing, how much initial and secondary stability the boat has, whether the boat is sideways (broached) in the current, etc will add to the variables. Sticking a paddle into the 3 kt side current adds an infinite new layer of variables...

What if you have wind velocities varying in the 200-800 vertical feet it takes your canopy to open, while you decelerate? Hypothetically, lets say at pitch we have 20kts from 270, but as the canopy's outer cells are inflating winds are 10 kts at 250. This will have to impact the opening to a small degree!

"wind" is 3 dimensional in skydiving. It has to have some (minor, yes) impact on the whole deployment sequence. It affects how planes and canopies fly, it affects us in freefall, why would it suddenly stop affecting us because we dumped a PC?

I'm not a scientist, and without investing a fortune in doing hundreds of jumps, charting heading, freefall delays, exact weather readings, perfectly consistent deployment altitudes/barometric pressures/etc and then plugging it all into a computer to get some abstract numbers that really won't affect my openings (skydiving, that is) a great deal-I don't have a way to "prove" the above "hypothesis".

At the end of the day-I'm making it up as I go and maybe I'm dead wrong... I learned why bigger Sabre 1's had secondary brake lines a few years ago by stubbornly hammering at what I thought was the right answer-so maybe this will be another one of those learning experiences. Or maybe it will be another fun internet discussion that gets people thinking.

-Harry

Hey! You're right - You're not over-thinking this in the least.

Every fight is a food fight if you're a cannibal

Goodness is something to be chosen. When a man cannot choose, he ceases to be a man. - Anthony Burgess

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The only time it would have noticable effect, is if you have a change in horizontal air speed, as you deploy through it. Lets say 10kts with bag extraction, but 35kts(noticable) with cells inflating.

Yet, I cannot see that you will have "twists" of any nature, more an effect of wing trying to fly into wind, or away, depending on the angle of wind to the canopy, and in which stage of deployment you move from 10 to 35.
You have the right to your opinion, and I have the right to tell you how Fu***** stupid it is.
Davelepka - "This isn't an x-box, or a Chevy truck forum"
Whatever you do, don't listen to ChrisD.

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SansSuit

Are there any side-to-side differences in canopy that is flying straight and level but pointed 90° from the air mass around it? If a canopy is being pushed through the sky from one side, are the internal pressures (or whatever measurements used) still the same left-to right?

The thing that we're trying to make clear is that if the object (canopy & skydiver) is in equilibrium with the surrounding fluid (the air), there is no "pushing" involved. Just as when one is flying back to the DZ with a tailwind, there is no pushing on the back of the canopy.

Like a balloon that's been flying, or a boat in the river current (ignoring air drag from the part above water), there's no push needed because there's no drag. The object and the surrounding fluid are moving together with no pushing and pulling involved.

As others point out, when there's a change in the fluid flow, it takes time for the object to adapt to the fluid's flow. A dandelion seed dropped from a bridge will almost instantly conform to the movement of a 10 mph wind, while a base jumper (if there were altitude) would take many seconds to have the wind accelerate the jumper to pretty much the same horizontal speed as the wind. The same applies to a skydiver exiting at 90 mph horizontally in an air mass.

Even when there is a sudden change in the fluid flow, like a wind gust, one has to consider the direction in airflow as a whole, using vectors to figure out the actual direction.

Say a skydiver is flying 30 mph forwards, and hits a gust that's 10 mph from the side. Maybe it just happened, or maybe he was flying between the tall buildings in Dubai, was in wind shadow behind one, and then came out in the open. The canopy wouldn't feel a 10 mph push from the side. It would feel the vector sum of 30 mph forwards and 10 from the side -- so the wind the canopy feels would be from 18.4 degrees away from straight ahead (if I did the trig right). (For simplicity, we're ignoring descent angle here. Also, gusts usually aren't perfectly 'instant', so there may be some transition time from the one situation to the next.)

Only once one understands basics like that, THEN one can get into the questions about how wind from different angles actually affects the flight of a canopy -- such as how easily a gust from the side might tend to roll a wingtip under, or what the directional stability of the canopy is and so how quickly it would tend to turn into the direction of the wind, etc.

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SansSuit

Are there any side-to-side differences in canopy that is flying straight and level but pointed 90° from the air mass around it? If a canopy is being pushed through the sky from one side, are the internal pressures (or whatever measurements used) still the same left-to right?

Think of it this way - you swim through a pool of water at 20mph. That's your canopy flying through the air. The pool is still. The air is still. You move through the water at 20mph. You move through the air at 20mph. You move past objects outside the pool at 20mph. You fly across the ground at 20mph.

You're a pimped out gangsta however and your pool is on the back of a motherfucking limo heading down the main drag in Vegas. That's just how you roll. The limo is going 20mph

You now swim up the pool - the same way as the limo is going. You pass through the water at 20mph. You pass bitches and hoes on the street at 40mph however as it's your swimming speed plus the speed of the limo. Turn around when you see one of those honeys and swim the other way at 20mph. You're still going through the water at 20mph. The limo though is going 20mph in the other direction though so relative to the sweet ass honey on the side of the street you're staying still - 0mph - and can now find out it's \$200 a roll baby and you gotta bring your own blow.

Stop swimming and still in the water and you'll carry on up the street at 20mph. The water in the pool around you though ain't doing shit - you're travelling at 0mph through the water. You're not being pushed one way or the other, your just stood their in your sweet ass pool heading the fuck up to the Luxor in nice still water - time to get into your bitch-ass Elvis suit though because you're still doing 20mph up the street!

Capiche?

And seriously, edit the profile back to how it was.

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I'll throw my two cents in with another ultra-simplistic take on it...

Within seconds after leaving an aircraft (other than a balloon) one will find oneself in a "lateral" zero wind environment whether the mode is free fall, under canopy, or whatever.

If the jump is from a balloon, one will be in a zero lateral wind mode before exit.

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JohnSherman

Quote

How much does the wind direction affect the opening of a canopy? I would think that opening while facing straight into the wind would give the best (on heading) opening. How about 45 or 90 degrees off the wind line? Could that cause twists in a canopy that is susceptible to squirrelly openings?

None!
You are moving within an air mass which is called the wind if you are on the ground. It is only going to have an effect if you are not in the air mass and the air mass hits you. The relative wind you experience is from your movement within the air mass.
Think about the boat in the water analogy

So far the ONLY sensible response in this thread.
----------------------------------------------
You're not as good as you think you are. Seriously.

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diablopilot

So far the ONLY sensible response in this thread.

I don't know, I thought the swimming pool in the limo was pretty good...

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Quote

I don't know, I thought the swimming pool in the limo was pretty good... Wink

But it completely ignored the relativistic effects when the limousine approaches the speed of light. (1 / sqrt( 1 - (v/c)^2))
For the same reason I jump off a perfectly good diving board.

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DiverMike

Quote

I don't know, I thought the swimming pool in the limo was pretty good... Wink

But it completely ignored the relativistic effects when the limousine approaches the speed of light. (1 / sqrt( 1 - (v/c)^2))

I'm sure that's because it was travelling on Las Vegas Blvd. and traffic is terrible.
"I fly because it releases my mind from the tyranny of petty things." - Antoine de Saint-Exupery

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mrubin

***

Quote

I don't know, I thought the swimming pool in the limo was pretty good... Wink

But it completely ignored the relativistic effects when the limousine approaches the speed of light. (1 / sqrt( 1 - (v/c)^2))

I'm sure that's because it was travelling on Las Vegas Blvd. and traffic is terrible.

Not in the limo only lane!

~ If you choke a Smurf, what color does it turn? ~

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You open into the wind line for quicker opening and you face away from the wind for the slower ones.
Bernie Sanders for President 2016

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>Are there any side-to-side differences in canopy that is flying straight and level but
>pointed 90° from the air mass around it?

No. The only time you notice anything at all is when:

1) you suddenly transition to a different-speed air mass. We call this "turbulence."
2) you land, and thus have to care about the speed you are moving relative to the earth. That's why landing into the wind is usually a good idea.

> If a canopy is being pushed through the sky from one side, are the internal pressures
>(or whatever measurements used) still the same left-to right?

Yes.

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flaperon

I'll throw my two cents in with another ultra-simplistic take on it...

Here's my donut (from yesterday)

Couple of times I've jumped in ~10m/s (20kts) ground wind, up to a deployment altitude.

I believe that deployment direction matters in this case
What goes around, comes later.

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