Interesting PBN thread on the HammerHead

[fallout11]

A sphere of the same volume, size, and surface characteristics as a paintball will behave identically to a paintball, as far as fluid mechanics are concerned.

None of the basic fluid dynamic laws care what the actual material is, so long as it has similar surface properties.

[cledford]

Originally posted by fallout11
A sphere of the same volume, size, and surface characteristics as a paintball will behave identically to a paintball, as far as fluid mechanics are concerned.

None of the basic fluid dynamic laws care what the actual material is, so long as it has similar surface properties.

Well that was the point - but now I'm reconsidering my idea. The whole point is to build something that would easily show how a paintball is bobbled around in flight to the average joe.

The reason I came up with the idea is that a paintball flies too fast, too far to illustrate anything to anyone. I was thinking that with a denser medium that things would slow down enough to see what was going on. I'm just not sure that water would be dense enough, especially considering that the speed of the object propelled would have to equal what ever the appropriate rate of travel in the denser fluid would be, and that might be hard to pull off.

-Calvin

[fallout11]

Water actually makes a fairly good medium for demonstrating fluid flow problems, and test tanks are frequently used for such experimentation, often with dye injected to show wakes, vortices, and turbulence.

Well, the more I think about it, the more complex accurately "modelling" it becomes.
That's a whole field of science by itself.
The real question becomes how accurately are we wanting to model it?
75%?
90%?
99%?

11/16" ball bearings dropped in a tank of water is a 75% accurate or better model. You have my word on it as a degreed engineer.

But I'm afraid you could spend days working equations, running perfect tests, and posting detailed explanations and video, only to have the inevitable **** say what you did was wrong, gravity doesn't exist, and red guns shoot further.

[SlartyBartFast]

Originally posted by cledford
I was thinking that with a denser medium that things would slow down enough to see what was going on. I'm just not sure that water would be dense enough, especially considering that the speed of the object propelled would have to equal what ever the appropriate rate of travel in the denser fluid would be, and that might be hard to pull off.

-Calvin

As I hinted at in the deep blue thread, there are so many variables that to try and 'scale' all the interactions is probably folly.

Because to properly do it, you'd have to fire the object horizontally through the new medium and then track the flight somehow. And it would be difficult to fire something through a medium slow enough to observe but at the same time not have gravity be the major effect that overwhelms all others.

Simply dropping something like a submerged marble from a controlled point to a container placed directly below should illustrate the point. Oil may be a better medium than water. But if water works it means you only have to lug the container and marbles around.

After dropping a number of marbles you could see how many fell directly in the container and how many missed. The nubmer that miss would be due to vortex shedding and other hydrodynamic forces.

Then you face the impossible task: Convincing the religious barrel fairy believers that your demonstration applies to paintball.

[RRfireblade]

Originally posted by SlartyBartFast


Then you face the impossible task: Convincing the religious barrel fairy believers that your demonstration applies to paintball.

That's completely true. We all know the effects of a sphere traveling through a fliud.How does re-scaling an easily tested process of firing a ball down a barrel provide any realistic relevance?

[fallout11]

I agree with Slarty, and said so in Deep Blue.

Another point worth considering.
Most paintball targets are 20 yards away from the launcher. That's a long distance to travel though and interact with a fluid medium, lots of opportunity to go "off target".

Even a 1 degree deviation gives you a spread effect of 25" in diameter at 60 feet.
So unless you had an aquarium tank 20 yards deep, you'd be ignoring this very important fact.

[fallout11]

Originally posted by RRfireblade


That's completely true. We all know the effects of a sphere traveling through a fliud.How does re-scaling an easily tested process of firing a ball down a barrel provide any realistic relevance?

That wasn't the point, RRfireblade.
Cledford sought a slow-moving, easily repeatable analogy so you could actually "witness" the physics at work.

Munition manufacturers test fire their weapons and rounds through ballistic jels and clays, using ultra-fast cameras, to test their effectiveness, knock down power, and penetration against people. Because it's easy to see "what happened" that way.

Your arguement is why do they bother, when they could just go out and shoot people with them to see.

[RRfireblade]

Originally posted by fallout11



Your arguement is why do they bother, when they could just go out and shoot people with them to see.

No, my arguement there is 'cause they can't shoot people to see.They used to shoot animals for more accurate results before the obviously ensueing PITA peeps and the like put a stop to it.

As far as paintball,your talking about creating a testing process that's more complicated and difficult at best to corrolate directly to paintball.

It's easier and more effective to use actual paintball equiptment for the testing.It's not like testing bullet ballistics or accuracy at firearm distances.In an open air environment,anything even remotely considered long range is laughable to test with a paintball.

[fallout11]

Point well taken.

I appologize if I sounded argumentative.

[cledford]

Originally posted by RRfireblade

It's easier and more effective to use actual paintball equipment for the testing. It's not like testing bullet ballistics or accuracy at firearm distances.In an open air environment,anything even remotely considered long range is laughable to test with a paintball.

RRfireblade,

Normally, I would completely agree with you - this is not intended to produce data regarding PB ballistics, it is intended to influence PB consumers to *want* to test PB ballistics using the processes you describe.

What I envision is pulling up to an event, dropping a ball of something into a clear tube of water, and watching the ball bounce around on it's decent. It is kinda hard to deny what you see and I hope such an illustration would get people thinking. When the wise-alec of the group stands up and cries foul in defense of the barrel of the week - you stick a sheet of paper in his hands with the calculations of the weight ratios and ask him what his "guru" can provide. You then pass out the paper to everyone else and they can take it home and try it themselves. Over time a movement gets started where people expect to see the snake oil salesman pull up to the same event with *something* to help support them in fighting the good cause. We know that the support never comes and PB takes a step forward evolution.

I unfortunately never applied myself at math or the sciences - so figuring some of this stuff out would take me a while - where it's easier to rely on the help of other AO members with the proper education to get pointed in to right direction.

-Calvin

[RRfireblade]

Calvin,

I understand your efforts and do agree with that intent.If it can be done and some one actually does it,that would be wonderful.I often try to be realistic in these types of matters however.It's much like the "cheater" discussion,tons of "if's","coulds" and "justs" but no one actually does anything.To add to that,much of these "ideas" get more and more complicated,expensive and time consuming to realise while at the same time,it's nearly impossible to get even the most basics of things accurately tested and proven.People still argue closed bolts,longer barrels,tragectories,etc, and refuse to see the most basic concepts of physics or any science for that matter.
I'm just saying,start with the basics.In this case for instance,if you set up a marker in a gun vice,targets at range and a hand full of barrels,that display will have as much impact or more,as any other display with having to prove how it relates to real life on top of that.

That's all,KISS was my only real point.

Jay.

[Sir_Brass]

How about instead of trying to model it in the real world, how about a computer-generated model?

I've taken enough programming classes in college to know that it's perfectly possible to write a program that will model and show how a paintball is affected in flight, with all of the real world physics involved.

It can show a 3D model, and the simulation can slow down to show the effects and graph the trajectory of the paintball along the 3 planes in the 3 axis space with respect to time (xy axis, yz axis, and the zx axis).

[cledford]

Originally posted by RRfireblade
I often try to be realistic in these types of matters however.It's much like the "cheater" discussion,tons of "if's","coulds" and "justs" but no one actually does anything.To add to that,much of these "ideas" get more and more complicated,expensive and time consuming to realise while at the same time,it's nearly impossible to get even the most basics of things accurately tested and proven.People still argue closed bolts,longer barrels,tragectories,etc, and refuse to see the most basic concepts of physics or any science for that matter.

[bjjb99]

Originally posted by Sir_Brass
How about instead of trying to model it in the real world, how about a computer-generated model?

I've taken enough programming classes in college to know that it's perfectly possible to write a program that will model and show how a paintball is affected in flight, with all of the real world physics involved.

It can show a 3D model, and the simulation can slow down to show the effects and graph the trajectory of the paintball along the 3 planes in the 3 axis space with respect to time (xy axis, yz axis, and the zx axis).

I've done some basic modeling of paintball flight using table lookups for lateral and drag forces, vortex shedding frequencies, and so forth. It's a reasonable first cut at the problem, but it has never been correlated with any sort of experimental results. I would be very hesitant to state that it accurately represents reality.

In order to really model what's going on, you're talking about a fairly large-scale computational fluid dynamics model showing the effects of a rotating nonuniform spherical object moving through a fluid (air) at a nonconstant velocity in three axes. While I do not doubt that such a model could be constructed in theory, I don't think that you're going to like the computational load such a model imposes on your hardware. To do this right, I think you're talking about microsecond to sub-microsecond time increments. You're also probably talking about 0.001 cubic millimeter voxels near the paintball's surface, with progressively larger volume elements as you get further and further away from the paintball.

Keep in mind that some of the real-world physics you're wanting to include is only partially understood. Take a look at how many papers have been written on air flow over spheres (not cylinders, spheres) at high Re values and you'll see that the physics are only partially understood.

But hey, if it was easy someone would have done it already.

BJJB

[demonguy8]

Alright some food for thought on this accuracy thing....

Can somone figure out the effects of velocity consistancy on a paintball in flight? Im talking very basic projectile motion stuff here (I would be more than happy to have done myself, but its been about 2 years since I had a physics class and I cant remember any of those equations for the life of me) The hypothesis here is that simple fluctuations in velocity are probably causing such a noticible difference in accuracy that the rest is basically negligable by comparison.

I figured the basics would include

Velocity of 300 FPS
distance of say 30 feet (just to make computation easier)
Fired parrallel to the ground with the obvious 9.8m/s grav pull downward
Assume marker is fixed
Assume no wind

Then figure with a velocity of 299 or a deviation of +-5, +-10

Edit: I found the equations I needed and came out with a very CRUDE (I was VERY LAZY on decimals).14in deviation per 1fps meaning that a gun on on a bad day (+-10) has a vertical deviation of 2.8in at 30ft just from the velocity.

So while my hypothesis was SOMEWHAT correct (this is also going off my very lazy math)it would appear that this isnt quite as significant as I was hoping it would be, but IS STILL QUITE NOTICABLE