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k_marr08

Does wind speed and gusts affect descent rate?

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That would be nice of him.
Aside from "Created unique real time aerodynamic parachute simulations", he's listed skidiving as one of hobbies but I can't find out if he is member on dz.com



He also lists: Electrical and Computer Engineering, field of Human-Computer Interactions

But he doesn't list PHYSICS or AERODYNAMICS.
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The only sure way to survive a canopy collision is not to have one.

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wolfriverjoe

You are right in that it takes a bit of time for the wind to overcome your inertia. That is easily demonstrated by the "forward throw" you get when you leave the plane. The plane gives you forward velocity that you bleed off as you fall.
But by the time you open (presuming a typical freefall) you are going more or less straight down (relative to the airmass), aren't you?



Correct. Although the approach is asymptotic, for practical purposes you are "at one with the airmass" after 6 - 10 seconds of freefall. Under canopy it will take even less time on account of the larger surface area.
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The only sure way to survive a canopy collision is not to have one.

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unkulunkulu

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Do you think I'm wrong and this truly is a simple problem with a simple solution? Am I over-thinking it?



The relativity principle is very strong and buried deeply in the laws of physics, you can rely on it very confidently. It's way more essential than aerodynamics, lift etc (if you can speak like that). So _my_ opinion is yes, this is simpler in a way, because we only need to know one principle, we don't have no know anything about aerodynamics, because it's dynamics, but the question is about kinematics, i.e. known velocities.



Well, this is true in a steady wind (no change in speed and direction) all the way to the ground.

The original question also mentions gusts. Once gusts and wind shears are included, it DOES become a question of dynamics.
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The only sure way to survive a canopy collision is not to have one.

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Gentlemen, I assure you, maple seed doesn't know about physics or aerodynamics.
Yet it does fly longer (time) in wind.



Go ahead and make a descent arrestor out of maple seeds. Please report your findings.
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The only sure way to survive a canopy collision is not to have one.

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unkulunkulu

I wrote about that in post #15, first page. First, we have to understand basics (steady uniform wind), then move to gusts and shears.



You are STILL late to the party:

From 2003:

www.dropzone.com/cgi-bin/forum/gforum.cgi?do=post_view_flat;post=750328;page=1;sb=post_latest_reply;so=ASC;mh=25;
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The only sure way to survive a canopy collision is not to have one.

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unkulunkulu


The relativity principle is very strong and buried deeply in the laws of physics, you can rely on it very confidently. It's way more essential than aerodynamics, lift etc (if you can speak like that). So _my_ opinion is yes, this is simpler in a way, because we only need to know one principle, we don't have no know anything about aerodynamics, because it's dynamics, but the question is about kinematics, i.e. known velocities.

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A parachute forward speed of 20 knots, combined with a windspeed of 20 knots BEFORE they interact.

What exactly do you mean that parachute forward speed is 20 knots BEFORE interaction?



I'm aware of the reference frame principle. I have a physics degree myself, but not a good understanding of aero and fluids. If everything is constant for the entire skydive, then you're right, it's simple. But reality is messier. We have different winds at different altitudes for example. So what I mean by "before interacting" is that I'm picturing a layer of wind flowing horizontally without any obstruction, measured at a certain velocity. Then a parachute descends into it from above, as it moves through the vertical column, and then you've both altered the speed and direction of the wind as it flows around the canopy, lines and jumper's body. It will also take time after entering that layer for the jumper to approximate the reference frame of the wind.

But yeah, probably over-thinking it, this wasn't the intent of the original question.

"So many fatalities and injuries are caused by decisions jumpers make before even getting into the aircraft. Skydiving can be safe AND fun at the same time...Honest." - Bill Booth

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We have different winds at different altitudes for example.

I'm talking steady and uniform winds and steady condition. Means: no changes in wind speed wrt time and space, so equal winds at different altitudes. Also, after the transitional processes died out (i.e. becoming one with the airmass). Shears do affect the canopy, of course, haven't you been there?

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So what I mean by "before interacting" is that I'm picturing a layer of wind flowing horizontally without any obstruction, measured at a certain velocity. Then a parachute descends into it from above, as it moves through the vertical column, and then you've both altered the speed and direction of the wind as it flows around the canopy, lines and jumper's body.

All this happens in the no wind situation as well and this is accounted for when we say that the "canopy airspeed is 20knots".

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unkulunkulu

All this happens in the no wind situation as well and this is accounted for when we say that the "canopy airspeed is 20knots".



Ah yes, of course, it's already accounted for. So I was overthinking. Thanks for the conversation, I concede.

"So many fatalities and injuries are caused by decisions jumpers make before even getting into the aircraft. Skydiving can be safe AND fun at the same time...Honest." - Bill Booth

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JeffCa

***
The relativity principle is very strong and buried deeply in the laws of physics, you can rely on it very confidently. It's way more essential than aerodynamics, lift etc (if you can speak like that). So _my_ opinion is yes, this is simpler in a way, because we only need to know one principle, we don't have no know anything about aerodynamics, because it's dynamics, but the question is about kinematics, i.e. known velocities.

Quote

A parachute forward speed of 20 knots, combined with a windspeed of 20 knots BEFORE they interact.

What exactly do you mean that parachute forward speed is 20 knots BEFORE interaction?



I'm aware of the reference frame principle. I have a physics degree myself, but not a good understanding of aero and fluids. If everything is constant for the entire skydive, then you're right, it's simple. But reality is messier. We have different winds at different altitudes for example. So what I mean by "before interacting" is that I'm picturing a layer of wind flowing horizontally without any obstruction, measured at a certain velocity. Then a parachute descends into it from above, as it moves through the vertical column, and then you've both altered the speed and direction of the wind as it flows around the canopy, lines and jumper's body. It will also take time after entering that layer for the jumper to approximate the reference frame of the wind.

But yeah, probably over-thinking it, this wasn't the intent of the original question.

This has all been analysed at length in the "canopy" forum a decade ago. Look it up.
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The only sure way to survive a canopy collision is not to have one.

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I am the developer of the skydiving simulator for static line interactive. I am away from good Internet access right now. I will read the thread once I am back early next week.

Alexander
Regards, Alexander. http://staticlineinteractive.com

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kallend

This has all been analysed at length in the "canopy" forum a decade ago. Look it up.


Now, what's wrong with checking it up all over again?
What are you afraid, that you've spent all your life in wrong conclusions?
I don't think so.
Muffle up and enjoy the ride.
What goes around, comes later.

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***This has all been analysed at length in the "canopy" forum a decade ago. Look it up.


Now, what's wrong with checking it up all over again?
What are you afraid, that you've spent all your life in wrong conclusions?
I don't think so.
Muffle up and enjoy the ride.

I am not aware of any changes in the laws of fluid dynamics in the past decade. Please tell us which changes would lead to different conclusions.
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The only sure way to survive a canopy collision is not to have one.

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kallend

I am not aware of any changes in the laws of fluid dynamics in the past decade...


Me neither but I am very interested in reading fresh thinking, which you are regularly shutting down with "I am a physics professor... and You can do a search" attitude.
I have no reputation to lose so I can afford dumb questions. I'd expect better of authority like yourself, encouragement even.

I understand that if I drop a steel ball into lake, it will hit bottom in exactly the same time as if dropped in fast river's same depth bottom. That's what I get from this lenghty thread so far.

It doesn't explain though, how some German pine seeds flies 700 kilometres in high wind (when in no wind - it just drops down).
What goes around, comes later.

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***I am not aware of any changes in the laws of fluid dynamics in the past decade...


Me neither but I am very interested in reading fresh thinking, which you are regularly shutting down with "I am a physics professor...



Regularly? I suggest you look that word up in a dictionary since you are not using it correctly.

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and You can do a search" attitude.
I have no reputation to lose so I can afford dumb questions. I'd expect better of authority like yourself, encouragement even.



I told you where to look, gave a link even. Why do you want to rehash old arguments long since settled?

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I understand that if I drop a steel ball into lake, it will hit bottom in exactly the same time as if dropped in fast river's same depth bottom. That's what I get from this lenghty thread so far.

It doesn't explain though, how some German pine seeds flies 700 kilometres in high wind (when in no wind - it just drops down).

I suggest you take a physics class. I also suggest you learn the difference between a steady wind and a turbulent, gusty wind.

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

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It doesn't explain though, how some German pine seeds flies 700 kilometres in high wind



Because zey are better zan uzzer pine seeds!

Surely you've heard of thermals. A dandelion seed or pine seed can easily get caught up in them, including ones in storms. A heavier object with a greater descent rate like a glider takes some skill to go far with thermals. A steel ball, well, that's not going to go anywhere except in a tornado.

[I have some German heritage so I can make the joke even under the rules of political correctness.]

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If I am to make a maple seed out of aluminium or other material and/or size to match density to water in proportion, as it does have proportion in air...

and it emulates behavior in water exactly like real one in the air...

You are positive that it will hit bottom of, say 2 feet deep pool at the same time as in another pool, same depth, with artificial steady water current (of any speed)?

Give me a "yes" and I quit and thank you for your patience.
What goes around, comes later.

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If I am to make a maple seed out of aluminium or other material and/or size to match density to water in proportion, as it does have proportion in air...

and it emulates behavior in water exactly like real one in the air...

You are positive that it will hit bottom of, say 2 feet deep pool at the same time as in another pool, same depth, with artificial steady water current (of any speed)?

Give me a "yes" and I quit and thank you for your patience.



Since you can't make a 2' deep pool with steady current of a viscous fluid that has the same speed all the way to the bottom, your thought experiment is rather meaningless because there's no way to test it.

Rather like all the statements on canopy flight that ignore turbulence and wind shear.

And these effects have been exhaustively discussed a decade ago. Quit being lazy, look it up and stop wasting everyone's time.
...

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

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If I am to make a maple seed out of aluminium or other material and/or size to match density to water in proportion, as it does have proportion in air...

and it emulates behavior in water exactly like real one in the air...

You are positive that it will hit bottom of, say 2 feet deep pool at the same time as in another pool, same depth, with artificial steady water current (of any speed)?

Give me a "yes" and I quit and thank you for your patience.



the answer is "no"

i vagely remember the episode of mythbusters where they proved that a bullet shot horizontally falls slower than just dropped

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kallend


And these effects have been exhaustively discussed a decade ago. Quit being lazy, look it up and stop wasting everyone's time.



From one (very recently retired) teacher to another, I question your professional attitude as a physics professor if you have these kinds of comments towards people trying to think out the concepts for themselves, instead of just being lazy and going to the back of the book for the answer. Yes, looking up the answer is the lazy solution here, contrary to what you might think. Seriously, we're trying to consider it for ourselves, there's no harm in it, and you keep coming here telling us to stop and check an old thread. I would never tell my students to stop thinking for themselves and just look it up. They can look it up after they've thought about it themselves. I am aware of the old thread, but have liked the way this new thread forced me to think. If you think we're wasting your time, don't read it.

"No class, we won't be doing the tickertape cart experiment this year, we'll just be looking up what should happen. It would be wasting our time to do or discuss anything that has already been done. Read the lab report from last year's students. No, no, don't try to think about what might happen if a wave passes through a double-slit, that would be lazy and it has already been done. Look it up."

"So many fatalities and injuries are caused by decisions jumpers make before even getting into the aircraft. Skydiving can be safe AND fun at the same time...Honest." - Bill Booth

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>Since you can't make a 2' deep pool with steady current of a viscous fluid that has the same speed all the way to the bottom

sure u can
just move the entire pool (with still water in it)
boom! for the object dropped from above in it its tye perfectly steady current of viscous fluid
or just drop the object in nonmoving still pool with same horizontal speed
its relativity
e = mc2

maybe u should take physics 101 mr "physics professor" :P

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sky12345

I vagely remember the episode of mythbusters where they proved that a bullet shot horizontally falls slower than just dropped

Ahh, the problem here is that a canopy's airpseed stays the same regardless of windspeed. The bullet analogy is more suited to a skydiver exiting a moving aeroplane compared to a balloon or a helicopter. In this case, the airspeeds are different, so descent rate is affected.

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