Fluid Dynamics... Your input?

[Hamster Huey]

paintball dimples

Shooter/Boredfast/whoever-wants-to-read,

I don't know if you've come across this in your research or have done any calculations to the effect, but I remember reading some papers in the last couple months that pointed out that the height of the surface asperities required in order to generate a turbulent boundary layer is a lot smaller than one would imagine - certainly smaller in scale than golf ball dimples. Have you run across anything like this? I think I need to go back and review when I have some time.

[ShooterJM]

Re: paintball dimples

Originally posted by Hamster Huey
Shooter/Boredfast/whoever-wants-to-read,

I don't know if you've come across this in your research or have done any calculations to the effect, but I remember reading some papers in the last couple months that pointed out that the height of the surface asperities required in order to generate a turbulent boundary layer is a lot smaller than one would imagine - certainly smaller in scale than golf ball dimples. Have you run across anything like this? I think I need to go back and review when I have some time.

Yeah I did read that actually. Tried to calculate it out and I have what I think are decent starting sizes. Of course theoretical and practical are two entirely different things.

I still think the toughest part is coming up with a viable manufacturing process.

[DJSOLID]

When does the Bernoulli effect become evident? Isn't it when low pressure behind the sphere matches the coefficent of drag created by high pressure in front of the sphere? Or something to that effect? Does it really apply to this at all?

Two things would be fantastic tools to use in an experiment like this.

1. A tank fill with some kind of gaseous dye, smoke or particle that can be seen or flourecses under UV so that the gases that exit the barrel can be seen with high speed photography. - maybe this has been done - I dunno.

2. A "perfect paintball" possibly made of solid plastic or some other material that could be used as a control group. As near as I can figure it - all testing results can be compromised by low paintball quality. - also may exist - dunno.

[bjjb99]

Great Balls of Nylon!

Don't know whether the first test you mentioned has been done, DJSOLID, but I do know that AGD often uses solid nylon balls during some of their paintgun tests.

Perhaps the Schlieren photography described earlier in this thread could be combined with AGD's nylon paintballs to get an idea of how the gases are behaving behind the paintball.

BJJB

[PBchopR]

Vacuum velocity increase

So theoretically, couldn't one use a vacuum in front of a fired paintball to reduce the inevitable compression of the barrel air that is generated when a paintball is forced through it? This probably wouldn't amount to much more velocity, but it might allow for higher speeds with less ball breakage. In fact, a paintball gun could be made to fire using vacuum instead of pressure... A simple valving system could be made utilizizing a port near the muzzle, combined with a valve.

[PBchopR]

And Viola.. A boltless paintball gun..

Should I patent this or what?

[ShooterJM]

Re: And Viola.. A boltless paintball gun..

Originally posted by PBchopR
Should I patent this or what?

Sure, why not? Figure out the valve timing and an efficient way to get the needed vacuum and you could be good to go.

[Redkey]

vacuum to lauch a ball?

If my memory in working with RTM molding serves me correctly... the max force that can be pulled with a vacuum is about 14 psi. Not really enough to get a ball moving with much velocity.

Also... you'd have to close off the muzzle of the barrel otherwise you would just be sucking air down the barrel while the paintball just sat there. Plus the breach behind the ball would have to be open otherwise as the ball moved forward you would generate a vacuum behind it that would counter act the vacuum pulling the ball down the barrel.

A vacuum can be generated by passing high velocity air over a series of small openings... not a very efficient process though.

The idea of shooting into a vacuum is an interesting one, although not too practical.

[PBchopR]

Vacuum, revisited

I think you were referring to Bernoulli's principle.. But if yo took a paintball gun barrel, open at both ends. Put a paintball at the breach end, closed off the muzzle end, and pulled vacuum at the muzzle while opening the muzzle blocking valve.... It does seem impractical but possible. But perhaps utilizing the venturi effect elswhere to evacuate some air from the barrel? I could almost do that one myself, I just don't know if there would be an advantage. Really, if that were to increase the paintball velocity, you would have to turn down the gun to stay at 300 fps anyway! You might gain efficiency, however...

[BlackVCG]

From what I know about Bernoulli's Equation, it's based on the assumption of conservation of energy. I do know that it only works for incompressible fluids because you're assuming that the specific weight at point A and the SW at point B are the same.

[Butterfingers]

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 would never think my gun is better just because I paid more for it. My gun if better because it is shiny [/B][/QUOTE]

Thats impossible. There is no force accelrating the ball when it leaves the barrel. The net positive acceleration away from the barrel the second it leaves the barrel is ZERO no matter what gun you use. All a ball carries once it leaves the gun is its momentum which is its Velocity times its Mass.

There is only a net negative acceleration in the direction opposite to a paintballs plane of motion due to air resistance and of course downward due to gravity.

[JRSJKD]

Well, my first post in here...hope I don't dissapoint.
First, I have to agree with Butterfingers.
"There is only a net negative acceleration in the direction opposite to a paintballs plane of motion due to air resistance and of course downward due to gravity."

While a lot of the stuff you guys are talking about I'm not real familiar with I do have some practical knowlege of working with aerodynamics.....at the dragstrip. My single bigest enemy when racing my bike is wind resistance. Even reducing the coeficient of drag by .6% is good for a couple mph on top, not to mention getting there quicker. This includes things as small as removing the mirrors and turn signals. What we are looking for is a smooth elongated shape that lets us slice through the wind with as small of a frontal area as we can get. A pointy shape isn't necassarily better. What is important is a tear drop shape with a small frontal signature. Too big a front area and too much pressure builds up creating more drag. You also want the flow to travel along the bike to reduce dead areas. This is where spheres(like paintballs) are weak.

I think that we are looking to hard at the problem. Other than the already stated foces(gravity, wind resistance), the inate nature of the sphere is probably its worst opponent. As a sphere travels throught the air, there is the initial pressure build up in front and then the air travels over the surface. Because of its shape, it creates a dead spot imediately behind itself creating more drag. You'll notice the more and more "racing" bicycles have gone to oval fraome components to help further reduce co-efficients of drag in order to eliminate the dead spots. To illustrate how much influence drag can have on an object in the 1950's the "dustbin" shaped motorcycle racers were able to reach speeds of around a 155mph, about the top speed of my 2000 yamaha. What's really interesting about this is that they did it with around 40hp as compared to my 95hp. Superior aerodynamics( they were outlwed )

What I would be really interested in finding out is how much even a 1 mph headwind would affect a paitball, and conversley help it in a downwind. We know that aerodynamic forces(dynamic pressure)are proportional to the square of the speed. That means you quadruple the drag or lift when you double the speed. With all of that in mind, I would be really curious to see how different velocities affect paintball distances. Are there instances where a marker shooting at a slower velocity will have better range because of a lower frontal dynamic pressure? What about in a headwind? I've seen tests done where they have shown accuracy to decrease at higher velocities, why not distance?

just a couple of thoughts....

Junior

[JRSJKD]

another thought or two

Just another thought or two.....

In the first post it talks about the phenomena where we have all noticed one gun outshooting another. So we start looking for reasons why this DOES happen. We eventually get into long debates over really complicated physics and concepts. What if it really comes down to only one thing....the individual marker...BUT, not the way it was stated in the first post. IMHO, what makes a marker is its valve system. Accuracy is often(and rightly so), measured by its consitency over the chrono. However, just like the way most people calculate how many BPS they shoot, it's flawed. Instead of measuring one shot, wait ...read, 2nd shot....wait....read, etc, we should be measuring in more real world terms. That is consistency during rapid fire or bursts. It will always be accuracy by volume(due to the inherent in-accuracy of a round projectile), and I don't know about you but in my personal experience people usually shoot at least in short bursts. How well a particular gun's valve system can keep up with rapid fire consistency should be the real measure of it's accuracy/range. In addition to the variable nature of different valve syatems theres the individual flow rate of different air systems. I wonder if we spend to much theorizing about laminar flow rates only to end back up at shootdown All other things aside, all guns shooting at 300fps will have the same range.....as long as its still shooting at 300fps.

All guns are not created equal........I've got my ReTro.....do u????? :P

Junior

[FatMan]

Well said

JRSJKD,

Well said. I think that hits the nail on the head - if the ball exits at(in) the same velocity/trajectory/environmental conditions, it will have the same basic range. But not all guns have the same consistency. Valving and shoot down are big important factors. Paint-to-barrel match is another. Air system can be another.

The physics is complicated - and interesting - but the critical factors have been identifed, and the marketing hype is often just that - hype.

FatMan

[PBchopR]

What makes a gun...?

As far as I can tell, guns that react less during the firing/reloading cycle are capable of shooting farther accurately. I think that's where the perception of better distance comes from; Angel users can shoot far accurately, because of the minimal reciprocating mass involved in their operating cycle. I believe that the "ideal" gun would have a barrel that fits the paint exactly, a propellant that is exactly consistant with every shot, and minimal reciprocating mass(just enough to offset the ball being ejected.) The Holy Grail of guns....