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Flatline Theories...

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UV Halo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote UV Halo Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2005 at 12:31am
Okay, based on everything I've seen this is what I think so far:

Lift is the main (if not the only reason) a paintball flies farther.  It allows the ball to stay in the air quite a bit longer (thereby giving it more time to move forward).  This lift is what is caused just by the fact that the ball is backspinning.  The amount of lift (how much it negates the force of gravity is dependent on how fast it spins).  Here is a picture illustrating it:



However, there may be a reduction in drag for a spinning ball.  This woud not be an acceleration as KillerOne, and a few others have stated but, rather the ball not slowing down as much.  The spinning (no matter the direction) would cause a small layer of turbulence around the ball which allow the air to flow more smoothly around the ball. 
  The odd part is, that for every source I have found that mentions spin causing drag reduction, they talk about it only working for a rough sphere or, in the context of it causing the top of the ball to get the drag reduction first, which contributes to the lifting force.  The last line of Monk's referenced paragraph has caused me to look around to see if I can find other references.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Millslane Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2005 at 1:52pm
for those of you who have said this thread is pointless, you are so wrong.

even if nothing it actually settled here, it a great thread to be used as an example on how two people with different opinions are discusisng their opinions in a clear, intellegent, and respectable manner. its very east to respect the other half when they respect you.

this get my vote for the best thread in this place.

well done guys!

beats the heck out of the crappy threads lined withing every section...

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is this a good gun?
the flatline sux big monkey butt
and so on
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Clark Kent Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2005 at 3:46pm

Ok.

I heard back from one of my rocket scientists, and he wasn't sure.

I also had a chat with another friend of mine, however.  Not a rocket scientist, but one of the smartest people I know.  This is all off the top of his head from aerodynamics class a zillion years ago.  This all assumes subsonic travel - supersonic aerodynamics are different.

Drag has two parts - friction and back pressure. 

Friction is ... friction between the traveling body and air molecules. 

A traveling body creates a small vacuum pocket (or at least pocket of thinner air) behind itself, in the space it just vacated.  This vacuum pocket sucks on the body to creates backwards pressure.  This is called back pressure.

As velocity increases, so does friction, and the vacuum pocket gets bigger, so back pressure also increases.

Now - we rotate the sphere.  Rotation along the axis of travel (like a bullet) gives a different result, so we will ignore that case.

Rotation increases friction.  On one side of the sphere (the side that it rotating into the wind, so to speak) friction will increase, and on the other side it will decrease.  The increase is greater than the decrease, however, due to inefficiencies introduced at the point of separation.  So overall, friction is increased with rotation.  As the rotation increases in speed, so does the friction.  More rotation = more friction.  This will reduce velocity faster.

Rotation also increases turbulence - it moves the air around.  Some of this moved air will land in the vacuum pocket behind the sphere.  This will reduce the back pressure.  So initially rotation reduces back pressure.  This allows velocity to be retained longer.  More rotation = greater reduction in back pressure.

But - once the vacuum pocket has been fully filled by turbulence, this effect stops.  The back pressure can only be reduced to zero.  Faster rotation beyond this point will yield no further benefits on drag.

For most bodies, the drag reduction benefit from back pressure reduction far outweighs the drag increase cost from friction increase.  Therefore, rotation tend to have a net reducing effect on drag.

However, when rotation is more than fast enough to max out the back pressure reduction, friction continues to increase, and at some point the friction increase exceeds the back pressure benefit, which leads to a net increase of drag.

Therefore, the short answer is:  Depends.

For a given body, traveling at a given velocity, rotation will reduce drag, unless the body is rotating very fast, in which case it will increase drag.

The intercept - the point at which rotation increases drag - is lower for bodies that create turbulence on their own, like rough bodies.  So a smooth body will gain more from rotation than a rough body.

The intercept is higher for bodies traveling at higher velocities, since the higher velocity creates a larger air pocket and more back pressure.

To get an exact answer to our question, we would have to determine the Reynolds number of a paintball, and use that to determine a drag coefficient.  We would also have to determine the exact rotations per second of a Flatline paintball.

The answer could be faster, slower, or both.  For instance, it might be that a ball leaving a Flatline initially has high enough velocity to take max advantage of the rotation effect on back pressure (allowing it to retain velocity better), but as velocity drops the rotation is causing a net increase in drag, causing faster velocity dropoff. 

Or the rotation could be a benefit the whole time, or a detriment the whole time.  Impossible to determine without knowing more about the aerodynamic qualities of a paintball.

There.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote UV Halo Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2005 at 7:32pm
Millslane-  Thanks for the compliments!  All I wanted was for this to be an intelligent discussion, and most, of the people who have particpated have provided just that.


Clark- Thanks for the awesome feedback!  However, it's all addressed here.

However, he talks about smooth balls only.  Because the 100% Reynold's number of a paintball will probably never be determined.  Why? Not counting that some balls are a little lopsided, The seam:
  • Perpendicular to the air flow- yes but, certainly not as much as a rough ball.
  • In line with the flow (horizontally, or vertically) not much, if at all.
  • Any other angles, who knows??
  • To compound all this, the seam varies from brand to brand, batch to batch, ball to ball.
So, the simplest explanation is for a smooth ball, since a paintball is mostly smooth, especially for Evil, and maybe a couple other brands.

He explains how the reynolds number is obtained for a non-spinning ball.  However, later in this section, he talks about how he derived the Reynolds number for a spinning paintball for use in his calulator.

Then he goes on to say that one limitation he has with his calculator is that he considers the spin constant throughout the ball's flight, and talks about why this is unrealistic.

All in all, I believe his calculator is the best estimate we have at our disposal. 

It predicts a paintball fired from five feet up, with zero elevation at 280fps, will hit the ground at a speed of 133fps, 113ft downrange, in .601 seconds.

It also predicts that a paintball fired with the same height, elevation and speed but, with 16000RPM will hit the ground at a speed of 102.7fps, 158.8ft downrange, in 1.001 seconds.  I tried multiple RPM settings in 1k increments and found 16000 to be the most beneficial, while the higher up I went, the benefit shrank and at around 29000RPM, the ball actually gets a shorter range.  These range numbers sound close to real life for my flatline.  I don't know what the apex promises so, I dunno.  But, it's pretty clear that the switch controls the amount of spin, while the twist determines the orientation (backspin, topspin, everything else).

Okay so what does it say about the speed of a paintball 75ft down range? (please note that the calculator calculates in time increments):
No spin = 170.2fps @ 75.69'
16KRPM = 168.6fps @ 75.18'

To try this yourself only modify the two right hand bars.  The top one has to be typed in with backspin =90, while topspin= -90.  The Bottom bar has to be set using the scroll bar.


What really needs to be done, is the dual chronograph test.  To compare this mathematic model with the real world.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote daveandchig Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2005 at 6:50am
interesting discussion gentlemen.  With my somewhat ecclectic physics background, i find it extrememly hard to believe that a spinning ball will hit harder at any range than a non spinning ball.  This especially holds true when the ball is spinning at a rate high enough to cause enough friction on its downside to lift it.  Any amount of friction that is great enough to alter the course of an object will also slow it down, hence, less force upon impact.  Very simple principles are at work behind my logic on this one, and I think any of you with a bit of lwits about you will find it near impossible to argue that friction causes loss of speed.  I dont have any sources to list, or links to add, but that doesnt change the fact that course altering friction will cause a more severe decelleration effect.  By the way, i am glad to join the forum and look forward to many more of these thought provoking threads.
you're no daisey.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Clark Kent Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2005 at 1:18pm
Did you read the various points about back pressure?  Nobody is arguing, I don't believe, that friction is reduced.  It's just that friction is not the only force acting on a body traveling through a fluid.

Edited by Clark Kent
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Post Options Post Options   Thanks (0) Thanks(0)   Quote daveandchig Quote  Post ReplyReply Direct Link To This Post Posted: 17 October 2005 at 2:44am

Originally posted by Clark Kent Clark Kent wrote:

Did you read the various points about back pressure?  Nobody is arguing, I don't believe, that friction is reduced.  It's just that friction is not the only force acting on a body traveling through a fluid.
 

I do believe i recall something being mentioned about back pressure...think it was said that as a spherical object travels through a fluid at any velocity, there is a low pressure area created directly opposite the path of travel on the trailing edge of the sphere....seems to me that when there is a low pressure area behind something, it would tend to slow down at an even greater rate.  Am i way off base with that idea?  Look at Bernoulli's theorem and the way a wing works.  Lower pressure on top of the wing, atmospheric pressure on bottom of wing....wing goes up>>>into the area of lower pressure.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Clark Kent Quote  Post ReplyReply Direct Link To This Post Posted: 17 October 2005 at 2:47am

I was referring to my own post half-way up this page, where I discuss back pressure at some length.  Essentially, rotation causes turbulence, which in some circumstances relieves the back pressure, which in turn reduced overall drag.

Bernoulli's principle is of limited utility when applied to a sphere - it's principal implication here is through it's nephew the Magnus effect, which changes the trajectory of a rotating sphere.

Incidentally, I just heard back from another friend, who works in the aerospace division of Honeywell.  He also did not have a specific answer.  The one I posted above is the best I have been able to uncover.  UV's link also provides lots of great information.



Edited by Clark Kent
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bruce A. Frank Quote  Post ReplyReply Direct Link To This Post Posted: 17 October 2005 at 5:00am
You guys are just going to force me to dig out my old chronograph. Haven't used it in 12 years and we moved once since then. I will continue to search.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Monk Quote  Post ReplyReply Direct Link To This Post Posted: 17 October 2005 at 2:43pm
So are we in agreement yet, that a spinning paintball will create lift and reduce drag?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Clark Kent Quote  Post ReplyReply Direct Link To This Post Posted: 17 October 2005 at 2:46pm

Spinning will create lift, yes.  As to reducing drag, it depends on the velocity of the ball, the drag coefficient of the paintball, and the speed of rotation.

Rotation could either reduce or increase drag, depending on those variables.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote daveandchig Quote  Post ReplyReply Direct Link To This Post Posted: 17 October 2005 at 4:50pm
what an incredible collection of paintball physics at play here!  I am impressed by the desire of you gentlemen to understand the key elements at play when paintballing.  Clark Kent, i went back and read the post you mentioned, and it all makes much more sense to me now.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 13entley Quote  Post ReplyReply Direct Link To This Post Posted: 17 October 2005 at 5:06pm

im sorry but the flatline
OWNS

nuff said

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Monk Quote  Post ReplyReply Direct Link To This Post Posted: 17 October 2005 at 5:51pm
Ok, let me refrase that.

The spin on a paintball causes lift.

It will also cause less drag going fast, and more going slow.

So the debate is now, what speed is fast and when does that turn into slow.

Is 300fps fast enough to cause a spinning ball to decrease drag?


Edited by Monk
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Clark Kent Quote  Post ReplyReply Direct Link To This Post Posted: 17 October 2005 at 6:02pm

Originally posted by Monk Monk wrote:


Is 300fps fast enough to cause a spinning ball to decrease drag?

I don't think we know enough about the aerodynamic qualities of a paintball to know that.  We would also have to know the rotational speed.

And, of course, we have the further problem that velocity is constantly reducing - so even if 300fps is fast enough for spin to help, 200 fps might not be (which would be the velocity after a short while).

Ugh - complicated.  The flight calculator that UV posted is impressive, but I'm not man enough to know how accurate it is.

We definitely need some science.  If somebody develops a data set, I would be happy to crunch the numbers.  (I could also help with experimental design, I just don't have the wherewithall to perform the actual study).

Come to think of it, if we did a proper study with a good write-up, I bet we could get it published someplace...  (Most likely WARPIG, but hey - published is published)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Monk Quote  Post ReplyReply Direct Link To This Post Posted: 17 October 2005 at 10:15pm
Does anyone have a highspeed camera?

Or does anyone have a force/pressure sensor?

I have a feeling that the math of it is going to be way over any of our heads.

So if we can experiment, its just as good as a formula.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bango Quote  Post ReplyReply Direct Link To This Post Posted: 17 October 2005 at 11:00pm
Where's KillerOne?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Clark Kent Quote  Post ReplyReply Direct Link To This Post Posted: 17 October 2005 at 11:53pm

Any formula is based on theory, and theory is what we are trying to test.

The only way to conclusively determine the answer to our question is to run a couple of experiment.

I have method in mind that would involve a gun bench w/clamps, an A-5 with a Flatline and other smoothbore barrel, two chronographs, and a couple hundred paintballs.

The resulting statistical analysis won't be that complicated.  I can handle that, as can a number of folks here, I suspect.

All we need is some volunteers.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote LordJovian Quote  Post ReplyReply Direct Link To This Post Posted: 18 October 2005 at 2:09pm

Wow. You guys need to go back and read this. It's pretty much the same statements repeated over and over again.

It is relatively easy to explain-

1. Distance- apparently everyone has accepted this, because it's true.

2. Ball hitting harder- I'm guessing this is the main arguement here? Hard to tell since every post is the same. Basically, this comment is too broad. What does "hitting harder" mean? Did the ball dry up and harden into a rock? Is it gaining speed? Does it break different?

Easy answer here- the ball is slowing down (decelerating) slower than a normal ball- so yes, it "feels" like it's hitting harder compared to a ball without backspin. BUT, at longer range here's the tricky part. Most players that have been playing a while know a ball that doesn't break hits harder and hurts more than one that does. Why? When it breaks, the paint and shell is shot off in different directions. The force of your skin pushing back has reached a point to push the ball into pieces. We'll give this a number- say it takes 10 "hit force" from your body to break a normal ball at normal speed (say 130 fps). If the ball slows down more than 130 fps, it would drop. However, the flatline keeps shots up in the air that shouldn't be up in the air. So, if a ball from the Flatline hits you at 95 fps, we'll say the ball won't break until 25 "hit force" from your body. Unfortunately, your body reaches only 20 "hit force" and doesn't break the ball, and sends it bouncing. 20 HF is twice as much as 10, so it hurt twice as much, thus making it seem it "hit harder."

Simple.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Clark Kent Quote  Post ReplyReply Direct Link To This Post Posted: 18 October 2005 at 2:59pm

Not so simple, Jovian, if I am understanding your post correctly.

Most of us read "harder" to mean "retains velocity better".  And whether a rotating sphere retains velocity better or worse than a non-rotating sphere traveling through a fluid is not simple at all.  As discussed, there are a number of variables that impact this issue.

Now, you do raise a good point about perceived "hard-ness" based on whether the ball breaks or not, but that is really not what this discussion has been about.

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