exit order question

[kallend 2,027]

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Yes, but all of your examples have nothing to do with the topic here, and people have taken the "wrong science" and been wrong from both camps.

That's why my point conceded that the answer was correct, but questioned the "goodness" of it because it can lead to some wrong thinking.

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I've heard the theory that a horizontal versus vertical mode of flight will affect drift even when the relative wind is from below.

>Thats true. Its based on time exposed to the winds aloft. A freeflier that has a freefall of 45 >seconds will drift less than a flat flyer that is exposed for 1:20.


In editing that item for brevity I suppose I deleted the "wrong science" part of it. The belief was that drift was affected due to surface presented to the winds aloft - misunderstanding that only presentation to the relative wind matters. I also based my statement on somewhat of an ambiguity about the term drift. Not how far you drift but how fast. The statement I was referencing would have it go the other way. Vertical flyers present a greater surface to the winds aloft and hence drift further.


>It is the best model you have. You can claim that flat fliers will funnel...OK, but freefliers cork.

I said that both happen, both are common, and both increase the complexity of the model.
I'm not arguing for a different exit order, I'm arguing for a better understanding that things may not not always as simple as our models make it seem.


>You take a good freefly group and they penetrate much more into the hill than an expereinced 4way team that almost floats on exit.

fine. but lets be honest. Who is on most of the loads at most of the dropzones? Not kickass freefly groups penetrating with maximum effectiveness into the relative wind, and not flat groups that are launching funnel free.

Who is the rule of thumb for? The experienced guys know how to keep themselves safe in any condition.

Let's change the context.

Consider two passenger trains, A and B. A arrives at the station 10 minutes before B. If the passengers can wander around randomly between compartments on each train, does it prevent you from knowing which group of passengers arrives first?

Skydivers' erratic behavior does not affect the basic principle that faster fallers will drift less and have more forward throw than slow fallers. It simply means that when figuring out how much spacing should be left between groups, you have to have a bit extra as margin of safety.

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

[mnealtx 0]

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Even in no wind a head downer will travel significantly farther along the line of flight than a belly flier (some 400 - 500 ft farther under "typical" conditions).

How so? This element seems to go beyond the basic "faster falling = less time in the relative wind". The theory then becomes far more complex and thus unpredictable. What's the theory behind this? And what controlled observations have actually supported it? Not just computer programs that simulate the theory.


Also head downers RARELY fall straight down unless they are with a ball.
some translation in any direction is possible.

Try throwing a dart and a badminton birdie horizontally with the same initial speed. Which goes farther?

A question on this, if I'm allowed to simplify the problem a bit...

RW jumper exits, belly to the relative wind. FF jumper exits, back to the relative wind... why is there a difference in forward throw? I'm fully cognizant of the fact that the RW jumper will get more drift from winds aloft during the freefall.

Mike
I love you, Shannon and Jim.
POPS 9708 , SCR 14706

[tso-d_chris 0]

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Try throwing a dart and a badminton birdie horizontally with the same initial speed. Which goes farther?
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I knew you could simplify the explanation!

For Great Deals on Gear

[tso-d_chris 0]

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The BC of a dart or a birdie depends on the mass, and your analogy was not so great because they have such a different mass.

Add weight to the badminton birdie so it weighs about the same as the dart. The dart will still travel farther horizontally in the given scenario.

For Great Deals on Gear

[kallend 2,027]

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The BC of a dart or a birdie depends on the mass, and your analogy was not so great because they have such a different mass.

Add weight to the badminton birdie so it weighs about the same as the dart. The dart will still travel farther horizontally in the given scenario.

Doesn't matter. Not all skydivers are the same weight, are they?

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

[kallend 2,027]

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Even in no wind a head downer will travel significantly farther along the line of flight than a belly flier (some 400 - 500 ft farther under "typical" conditions).

How so? This element seems to go beyond the basic "faster falling = less time in the relative wind". The theory then becomes far more complex and thus unpredictable. What's the theory behind this? And what controlled observations have actually supported it? Not just computer programs that simulate the theory.


Also head downers RARELY fall straight down unless they are with a ball.
some translation in any direction is possible.

Try throwing a dart and a badminton birdie horizontally with the same initial speed. Which goes farther?

A question on this, if I'm allowed to simplify the problem a bit...

RW jumper exits, belly to the relative wind. FF jumper exits, back to the relative wind... why is there a difference in forward throw? I'm fully cognizant of the fact that the RW jumper will get more drift from winds aloft during the freefall.

If you set up a scenario where two skydivers have the same terminal velocity, they will have the same drift and the same forward throw. It doesn't matter if they are back or front to the relative wind.

If the back-to-wind guy drifts less, as you state, then he must be spending less time in the upper winds, which implies he's going faster, which implies a higher ballistic coefficient, which implies more forward throw.

Of course, real skydivers don't hold a constant attitude throughout the skydive so there will always be some deviation from the ideal cases. However, a strategy for exiting safely can't depend on knowing exactly how people will be thrashing around - you just have to add an extra margin to allow for this.

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

[mnealtx 0]

Hello John, hope you had a great New's Years!

I'm sorry, I should have been more precise with my question.

I know that the total drift over the course of the skydive will be less for the freeflyer vice the bellyflyer.

My question was (assuming back or belly to wind), how does the freeflyer get "more forward throw" than the belly flyer?

Mike
I love you, Shannon and Jim.
POPS 9708 , SCR 14706

[tso-d_chris 0]

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Doesn't matter. Not all skydivers are the same weight, are they?

I agree.

For Great Deals on Gear

[Scrumpot 1]

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Yes, but the BC depends on mass, so the shape would also have to change for your statement to be true.

But their "shape" (ie: presentation into the resisting force, ie: relative wind) is different. -No?

Therefore, the prof's considerations seem (at least to this non-physics professor) to be applied correctly and perfectly valid. Or is there something else in my observation of your 2's debate over this that I am still missing??

-Grant

coitus non circum - Moab Stone

[sundevil777 102]

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My question was (assuming back or belly to wind), how does the freeflyer get "more forward throw" than the belly flyer?

Do you mean 'back' or 'head' into the wind for the freeflyer?

The head into the wind (head down) freeflyer will get more forward throw, everything else being equal, because they present less drag in a head down orientation - the forward speed from the plane will take longer to bleed off.

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[sundevil777 102]

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Yes, but the BC depends on mass, so the shape would also have to change for your statement to be true.

But their "shape" (ie: presentation into the resisting force, ie: relative wind) is different. -No?

Therefore, the prof's considerations seem (at least to this non-physics professor) to be applied correctly and perfectly valid. Or is there something else in my observation of your 2's debate over this that I am still missing??

-Grant

Of course the shape is different. But because the BC depends on the mass of an object, as you change the mass, the shape would have to change from the original state in order for the BC to remain the same (as mass changes).

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[sundevil777 102]

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The BC of a dart or a birdie depends on the mass, and your analogy was not so great because they have such a different mass.

Add weight to the badminton birdie so it weighs about the same as the dart. The dart will still travel farther horizontally in the given scenario.

Doesn't matter. Not all skydivers are the same weight, are they?

Wrong, it does matter, in that if the birdie is heavy enough, or the dart light enough, the birdie will go farther than the dart.

Are you this stubborn with your students?

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[tso-d_chris 0]

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Wrong, it does matter, in that if the birdie is heavy enough, or the dart light enough, the birdie will go farther than the dart.

Wouldn't the birdie have to be significantly (several times) heavier than the dart before it would have the same BC? There is rarely that much variance in the weight of skydivers, especially considering that a person's surface area tends to increase with body weight.

For Great Deals on Gear

[kallend 2,027]

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The BC of a dart or a birdie depends on the mass, and your analogy was not so great because they have such a different mass.

Add weight to the badminton birdie so it weighs about the same as the dart. The dart will still travel farther horizontally in the given scenario.

Doesn't matter. Not all skydivers are the same weight, are they?

Wrong, it does matter, in that if the birdie is heavy enough, or the dart light enough, the birdie will go farther than the dart.

Are you this stubborn with your students?

Shuttlecock - Official name for the object that badminton players hit. Also known as "birdie." Weight: 0.17-0.l9 ounces.

My competition darts weigh 26g (0.92 oz), around 5 times as heavy as a birdie.

If you can find a competion dart that goes less far than a competition legal birdie when thrown at the same speed, I'll buy a set.

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

[sundevil777 102]

The birdie and dart analogy is lousy because both the weight and Cd are very different - very different. I realize you won't find a birdie that is heavier than a dart, but there is nothing special about that analogy, and because it includes the 2 variables that define the BC as changing, it is less instructive than an analogy where only 1 variable changes.

So the effectiveness of the analogy is lost when someone asks, "Is it the mass or drag that causes the change?" The answer to the question is yes, both. Why not just use an analogy where the drag changes, with mass constant. Same jumper, exiting in a different orientation.

Why is a lesson on ballistic coefficient needed? The important variable being changed is drag, not mass. The mass of jumpers is not constant, but is less of a variable than the drag from exiting in different orientations.

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[Ron 10]

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The birdie and dart analogy is lousy because both the weight and Cd are very different - very different

The analogy was good since 99% of the people would have been satisfied given it.

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Why is a lesson on ballistic coefficient needed?

Because if a person asked which it was Mass or Drag that caused the change? You would have to explain BC. Which takes into account both mass and drag.

Since most skydivers are close to the same weight all you really need to answer is drag. And the shuttle cock vs dart did that quite well.

"No free man shall ever be debarred the use of arms." -- Thomas Jefferson, Thomas Jefferson Papers, 334

[kallend 2,027]

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Why is a lesson on ballistic coefficient needed? The important variable being changed is drag, not mass. The mass of jumpers is not constant, but is less of a variable than the drag from exiting in different orientations.

It was needed because you made such a fuss about darts and birdies having to have the same mass to form a good analogy. I know skydivers whose exit weights vary over a range of > 2:1, so your nitpicking was ill placed, irrelevant and a total distraction.

Physics test#2

An object is dropped from 13,000ft altitude in a standard atmosphere and achieves a terminal velocity of 135mph.

Which of the following quantities can be calculated from the data given?

(a) its mass
(b) its drag coefficient
(c) its frontal area
(d) its ballistic coefficient

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

[sundevil777 102]

Answer is the BC only.

So what, the issue is why do people go farther forward in the direction of travel when they exit head down (head into relative wind). The important thing changing is the drag, not mass.

You put forth an analogy that added in a different mass, which was not relevant to a person knowing why their own trajectory will be different depending on how they exit.

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[mnealtx 0]

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My question was (assuming back or belly to wind), how does the freeflyer get "more forward throw" than the belly flyer?

Do you mean 'back' or 'head' into the wind for the freeflyer?

The head into the wind (head down) freeflyer will get more forward throw, everything else being equal, because they present less drag in a head down orientation - the forward speed from the plane will take longer to bleed off.

I'm talking *ONLY* about the exit and forward throw - unless the freeflyer is presenting the side of their body to the relative wind, I don't see any possible way for them to get more forward throw. I don't see how head up (RW) or head down (FF) would make any difference in the exit and forward throw, assuming that they exit with the broadest axis of their body (belly/back) presented to the relative wind.

Mike
I love you, Shannon and Jim.
POPS 9708 , SCR 14706

[speedy 0]

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The birdie and dart analogy is lousy because both the weight and Cd are very different - very different

The analogy was good since 99% of the people would have been satisfied given it.

I found the anaolgy bad because I thought about the difference in weight as well.

While you may make assumptions about the knowledge and intelligence of students in your physics class, you cannot do the same with the people in this forum. A number of them think that a birdie is one under par for a hole in golf.

Dave

Fallschirmsport Marl

[sundevil777 102]

FFers like to exit with their head into the wind. RWs like their chest into the wind.

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[kallend 2,027]

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The birdie and dart analogy is lousy because both the weight and Cd are very different - very different

The analogy was good since 99% of the people would have been satisfied given it.

I found the anaolgy bad because I thought about the difference in weight as well.

While you may make assumptions about the knowledge and intelligence of students in your physics class, you cannot do the same with the people in this forum. A number of them think that a birdie is one under par for a hole in golf.

Another person who thinks all skydivers weigh the same.

...

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

[mnealtx 0]

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FFers like to exit with their head into the wind. RWs like their chest into the wind.

Aha... *now* the light bulb comes on... thanks for clearing that up for me.

Mike
I love you, Shannon and Jim.
POPS 9708 , SCR 14706

[Ron 10]

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I found the anaolgy bad because I thought about the difference in weight as well.

With weights the same the result would still be the same. It's drag that matters, not weight.

If you jump out of a plane and stay flat, dumb, and happy, you wil reach a speed of about 120 MPH correct?

If you jump out of the same plane wearing the same jump suit, but go head down you will fall faster correct?

So the only thing that changed was your amount of drag or BC.

Take a big ballon suit from the 70's and go flat...Will you fall faster in it, or a tight comp RW suit?

Again only the BC changes, your weight didn't.

Most skydivers are around the same weight, and since these "experiments" have show that DRAG is the major factor weight is not important.

The analogy is good. Its only people who do not understand how drag is the important factor that think weight matters.

Do you think that a dart and a birdy of the same weight will change the outcome? It would take a VERY heavy shuttlecock to go the same distance with the same amount of input....A difference that would nto relate to skydivers. It would be like a 1,000 pound RW jumper vs a normal weight VRW guy.

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A number of them think that a birdie is one under par for a hole in golf.

The terms birdy and shuttle cock have been used plenty in this discussion. If people want to understand the concepts, they can google the term if they don't know it.

"No free man shall ever be debarred the use of arms." -- Thomas Jefferson, Thomas Jefferson Papers, 334

[billvon 2,991]

>It's drag that matters, not weight.

Well, it's a combination of both. (To be exact, it's ballistic coefficient.)

Take a guy who exits belly to earth to do a 10 second delay. Watch his exit path. Now load the same guy up with 70lbs of weight and try the same experiment; from the perspective of the door he will not get 'blown back' as much, since he has more inertia for drag to act against. From the ground, the heavier guy will be seen to have more 'throw.'

But as many people have pointed out, this is not predictable; exits funnel and jumpers have different weights/jumpsuits. Which is why throw is not a reliable way to get exit separation.