Fluid Dynamics... Your input?

[BoReDFaST]

[FatMan]

Well, I'm not convinced

So, there are lots of holes in your theory. Not sure where to start.

First off, you have assumed lots of things are constant that aren't. I understand why you've done that, but what you have NOT done is shown that the variations in these things and the resulting effects do not completely overshadow the effects you are discussing.

You make huge leaps of logic in the main text where you suggest that issues such as operating pressure and bolt operation result in particular effects. You have no data to support those conclusions.

Even if some of these effects DO exist (and I believe some of them do - though they might not be the ones you claim) you have not shown that they affect the flight of the ball enough to alter the primary characteristic (range).

It is highly unlikely that the conditions surrounding a recently fired ball are significantly different - but they may be a bit different. The thing is, you haven't really shown anything - you've just theorized that these different effects are taking place.

Personnally, I'd like to see a more rigorous treatment of these things. I'm not sure if they would change paintball, but they'd be cool none the less.

FatMan

[BoReDFaST]

I didn't actually come up with this theory, I just need your guys' input.

[bjjb99]

Visualizing gas dispersion patterns with Schlieren photography.

The theory you present is a very interesting one. I'm not sure how valid it is, but I do know of a way to test it using high speed Schlieren photography. I'm sure many of the folks reading this forum have seen the pictures of the shockwave coming off a bullet, or the air patterns around a person's sneeze? That's Schlieren photography. Basically it's a way of detecting slight variations in the air (or other medium, such as water) resulting from pressure and temperature fluctuations.

For an example of some Schlieren systems, here's a couple of URLs:

1. http://www.grc.nasa.gov/WWW/OptInstr/schl.html
2. http://www.rit.edu/~andpph/text-schlieren-focus.html

If you use the setup in URL number 2 above, use a photographic studio stobe light as your light source, and trigger the strobe when the paintball is within the field of view of the camera, you should get images somewhat similar to the one in this URL (minus the shockwaves):

http://courses.ncssm.edu/hsi/ss/schlieren/pages/803_19.htm

Using this imaging technique, you could determine whether a paintball has the trailing "teardrop of gas" you theorize at various distances from the muzzle of the paintgun being tested. All in all, it would be a fascinating experiment to perform.

BJJB

[BoReDFaST]

Great, thanks for your input!

[ShinyGuy]

It is an interesting theory. You seem to assume alot of things regarding how long effects last. I'm not saying you're wrong, I'd just like to see some of these things tested.

First you assume that the shocker's low pressure/high volume flow is less turbulent by the time the gas gets to the muzzel than the high pressure/low volume burst from the bushmaster. That 4.4 inch^3 room of expansion space (in a 12 inch barrel) could reduce the turbulance quite a bit (this is the same thing a muffler on an engine does; useing volume to reduce sound/turbulence). It's likely that barrel porting has as large an effect on turbulence as the initial burst of gas. (either to disipate the turbulence to introduce it as the air flows over the ports. Again testing would be needed to see what effect this really has.)

You also mention that less turbulent gas resists flow seperation better than more turbulent gas. (We all agree that turbulence at the muzzel is bad) This effect diffinately exists (if there is any difference by the time the air is at the muzzel). The question is how long does this effect last.

It sound like you have a good basis for some very interesting experiments.

[Miscue]

Confuscious say: High speed video shows that the ball leaves the barrel before the air does. The ball does not ride with the air blast.

Turbulence from the marker is a non-issue.

You also did not mention anything about barrel pressure. Operating pressure and barrel pressure are two different things. The ball sees barrel pressure, not operating pressure. But makes no difference, just making a point.

Any gun, using any barrel... with the ball leaving at 300fps... will result in same distance.

I think the answer to why different guns vary in range in the real world can be found in a psychology book.

[ShinyGuy]

Originally posted by Miscue
Confuscious say: High speed video shows that the ball leaves the barrel before the air does. The ball does not ride with the air blast.

As the ball leaves the barrel the pressurised air behind it sees the low pressure air in front of the ball and as the air is less massive than the paintball some of the air should accelerate past the ball as both are leaving the barrel. How much air stays ahead of the ball and for how long are the big questions here. If you have evidence that show that no air passes the ball I'd like to see it (and I'd like to know why the air doesn't accelerate past the ball). If what you're saying is that the air that passes the ball is too small a quantity, or gets striped away too fast, to have any measurable effect then I suspect you're probably right.

Turbulence from the marker is a non-issue.

You also did not mention anything about barrel pressure. Operating pressure and barrel pressure are two different things. The ball sees barrel pressure, not operating pressure. But makes no difference, just making a point.

Right. The pressure and turbulence as the ball leaves the barrel are what matter, not the pressure as it starts its acceleration. While it is possible that there are differences between different guns and different barrels here it is definately not as simple as low pressure=long range.

Any gun, using any barrel... with the ball leaving at 300fps... will result in same distance.

Since we measure velocity about a foot away from the end of the barrel this is true. If the effects we are talking about are measurable they are gone by the time the ball passes the chrono. Still I would like to see if there are any differences in acceleration for the first 2 or 3 inches after the ball leaves the barrel.

I think the answer to why different guns vary in range in the real world can be found in a psychology book.

I would never think my gun is better just because I paid more for it. My gun if better because it is shiny

[bjjb99]

Multiple chronographs

Another means of determining whether paintguns yield different ranges would be to measure the average paintball velocity for a given paintgun as a function of distance from the barrel.

To perform this test, you would have to set up a series of chronographs at various distances from the paintgun (say, 2 feet, 5 feet, 10 feet, 20 feet, and 50 feet). You would want to arrange the chronographs so that a single shot could pass over (or through, for "light curtain" designs) all the chronographs. Fire around a hundred shots, record the paintball velocity from each chronograph for each firing, average the results from each distance, and you've got an idea how the paintball decelerates in flight. Perform this test on several paintguns which all possess the same muzzle velocity, and see whether paint fired from some guns retains its velocity more than others.

BJJB

[ShooterJM]

Originally posted by ShinyGuy
It's likely that barrel porting has as large an effect on turbulence as the initial burst of gas. (either to disipate the turbulence to introduce it as the air flows over the ports. Again testing would be needed to see what effect this really has.)

You also mention that less turbulent gas resists flow seperation better than more turbulent gas.

I suspect that the volume and pressure scavenged by barrel porting will reduce any backpressure to negligable. Barrel length is also key.

As for less turbulent gas resisting flow seperation better then more. Not sure I understand exactly how this is being applied. Using the golf ball example, laminar flow is turned into turbulent flow to help delay boundry layer seperation.

BoReDFaST: You might be interested in this thread as well

http://www.automags.org/forums/showthread.php?s=&threadid=28150

[BoReDFaST]

OOOohh that helps. Thanks a lot guys for your support.

[BlackVCG]

Re: Multiple chronographs

Originally posted by bjjb99
Another means of determining whether paintguns yield different ranges would be to measure the average paintball velocity for a given paintgun as a function of distance from the barrel.

To perform this test, you would have to set up a series of chronographs at various distances from the paintgun (say, 2 feet, 5 feet, 10 feet, 20 feet, and 50 feet). You would want to arrange the chronographs so that a single shot could pass over (or through, for "light curtain" designs) all the chronographs. Fire around a hundred shots, record the paintball velocity from each chronograph for each firing, average the results from each distance, and you've got an idea how the paintball decelerates in flight. Perform this test on several paintguns which all possess the same muzzle velocity, and see whether paint fired from some guns retains its velocity more than others.

BJJB

You can do this and get a general idea by averaging the results, but the main problem with this is that chronographs have a margin of error of +/- 3%

This test was conducted a long time ago and in one of the tests the second chronograph in the series was showing a higher velocity than the second chronograph. Thus leading to the myth that barrels affect range.

[ShinyGuy]

Originally posted by ShooterJM
Using the golf ball example, laminar flow is turned into turbulent flow to help delay boundry layer seperation.

The difference between a golf ball and what we are talking about is that the golf ball is traveling through still air. By generating turbulence the golf ball reduces parasite drag. All the rules that apply to golf balls apply to paintballs equally once they are clear of the initial burst of air from the barrel. If the paintball is surounded by a pocket of air traveling at near the same speed the paintball does not experience any drag for a while as it would have a relative velocity of 0 to the air in contact with it. That pocket of moving air would be striped away by drag from the still air that it is moving through and after the moving air has been striped away the paintball will start to decelerate. I would guess that that air pocket is striped away within the first inch or 2 after the paintball leaves the barrel and thus all balls are equal by the time they pass the chrono. But I would love to see some good old experimental research on this.

[ShooterJM]

Originally posted by ShinyGuy


The difference between a golf ball and what we are talking about is that the golf ball is traveling through still air. By generating turbulence the golf ball reduces parasite drag. All the rules that apply to golf balls apply to paintballs equally once they are clear of the initial burst of air from the barrel. If the paintball is surounded by a pocket of air traveling at near the same speed the paintball does not experience any drag for a while as it would have a relative velocity of 0 to the air in contact with it. That pocket of moving air would be striped away by drag from the still air that it is moving through and after the moving air has been striped away the paintball will start to decelerate. I would guess that that air pocket is striped away within the first inch or 2 after the paintball leaves the barrel and thus all balls are equal by the time they pass the chrono. But I would love to see some good old experimental research on this.

Gotcha, (note to self: read entire thread before commenting). Yeah that would be an interesting experiment. I'd even just be interested to know what the pressure is in the barrel just as the paintball exits. Ported and non-ported.

[bjjb99]

Re: Multiple Chronographs

BlackVCG,

I remember reading about the test you described. If I recall, none of the chronographs used were calibrated prior to the actual test. Calibration with a known velocity (preferably a series of known velocities spanning the expected velocities to be measured) would have detected the high readings of the second chronograph.

For the experiment I described above, the experimenter cannot just go out, get a half-dozen chrony-type chronographs, set them up, and expect to get good results. Each chronograph used in testing requires a series of calibration procedures prior to use. As demonstrated in the test you described, it's difficult to get good measurements if the ruler's length is not accurately known.

The environmental conditions during calibration and the actual test would have to remain resonably constant. I'm guessing that the test would have to be performed indoors to eliminate wind, lighting variations, and significant temperature fluctuations. An indoor shooting range might do the trick, or perhaps AGD's long hallway with the dented door at the end... :)

BJJB