Paintball Spin Physics - Getting to the final Answer

[hitech]

Originally posted by bjjb99
...the spatial separation...with a uniform distribution in azimuth about the paintball's axis...

Show off!

[m-98]

I haven't read all the posts here, I read the first. The paintball's liquid fill may not spin when a ball is shot, so if you could get the fill to spin with the shell wouldn't that help improve accuracy? Couldn't you make a paintball with a shell inside that is connected to each end of the paintball so that when the ball started spinning it would force the fill to move also. I really can't explain it well so look at the picture. I don't know if this would work and I know that it has flaws but it's just a general idea.

[hitech]

Originally posted by m-98
...so if you could get the fill to spin with the shell wouldn't that help improve accuracy?

Nope. Why do you think it would improve accuracy?

BTW, Tom did try it and it did not improve the accuracy.

[m-98]

Thanks, sorry for wasting everybody's time.

[hitech]

Originally posted by m-98
Thanks, sorry for wasting everybody's time.

No problem. BTW, your not wasting anyones time. Posting is what it's all about.

[osiris]

Originally posted by hitech


I'm thinking that very periodic could easily mean significantly more vortices are shed from one area of the sphere that the other. It would follow that the sphere would then change course. This would alter the angle of attack and maybe that could further alter things. As you have probably guessed, I don't know. However, it sure seems feasible to me.

Very interesting. Something has to be causing the vibrations that cause that noise.

[bjjb99]

Greetings, Osiris, and welcome to Deep Blue. If you're who I think you are, then you're speaking of me when you talk about the someone over at rec.sport.paintball. I look forward to your contributions to this forum.

BJJB

[nerobro]

*blinks a few times* Rec.Sport\.Paintball has something OTHER than iditos screaming the praise of smart part? My god. If you are from R.S.P. Welcome. :-) I have a whole bunch of interstesting stuff on RSP from the late 90's if you're intersted.. just search for Nerobro on groups,google.com

People have tried oblong, and finned paintballs. the real issue with them is feeding them. AGD makes a series of VERY VERY VERY VERY accurate paintballs with a skirt on them and riffling on the skirt. The balls (shells more like it) spin up after the leave the barrel and have 90% hit on a human target at 100 yards. Though I may be off on my numbers. And this is also with a paintball that weighs 3x what a normal ball weighs.

Now, how could we get wasp waisted paintballs to feed? AGD's solution was a rotary clip. seems reasonable.... but 10-12 shots at a time... you better hit what you're aiming at.

For rotational oscillations, very high oscillation frequencies and amplitudes can nearly eliminate vortex shedding and can result in significant reductions in drag, by as much as a factor of six [15, 16].

Application of a sound field producing induced velocities greater than the turbulence velocities has been found to supress free stream turbulence levels, and "substantially increases the coherence of the vortex shedding along the span of the cylinder as is usually found when a cylinder is oscillated" [12, 17].

this in particular interests me... if we could MAKE the ball shake faster would it be more accurate? maybe that's the benifit that comes from flying in the wake of the previous ball. it might shake more......

[osiris]

Please check and correct my comments here:

http://groups.google.com/groups?dq=&hl=en&lr=&ie=UTF-8&threadm=3EB3DD4C.4BD2%40nowhere.antispam.com&prev=/groups%3Fhl%3Den%26lr%3D%26ie%3DUTF-8%26group%3Drec.sport.paintball

as necessary.

-m-

[hitech]

[Bloencustoms]

I am very impressed by all of this, and want to thank everyone who has contributed to this discussion. It's the most fascinating thing I have read in a very, very long time. The math is completely beyond me, but I think I have at least a superficial grasp of the forces acting on a paintball in flight now. This has changed the way I look at paintball, and the way I listen to them fly over my head as well.

I also thought that if the barrel was imparting some kind of effect on the accuracy of paint (or nylon) balls, why not test them using some other means of acceleration? At first, I though that some kind of sled could be devised to launch them, gradually accelerating them over a long distance to reduce the deformation that rapid acceleration would cause. Still, with nylon balls exhibiting similar inaccuracy, deformation wouldn't be that big a factor. So, why not test them using a sabot of some kind that would be pulled away from the ball by wind resistance similar to a shotgun wad? It still could impart some kind of friction. Then you're right back to using a barrel.

So, I'm not sure where this thread is going from here. It hasn't seen much activity. But I am sure that people want a way to increase the accuracy of their markers. So, what can be done to counteract the vortex shedding? If that's the most significant factor affecting a sphere in flight (beyond gravity), then why not devise a way to negate it?

I worked as a car stereo installer for a few years, and observed the effect that occurs when two subwoofers are played out of phase. They cancel each other out, and the volume is greatly reduced. (Again, I'm no rocket scientist. I can't claim to know to what degree the cancellation has any effect.) But there are some real world applications for this effect. Some military helicopters use out of phase sound to cancel the noise from the rotors, making them much quieter. I have even heard of this technology being used experimentally to quiet the exhaust from automobiles.

After two hours of reading, and one hour of tense nail biting, I find myself somewhat disappointed. Almost a year ago, Osiris mentioned something I had been thinking about for a good part of the read. I was wondering if anyone had recorded the sound made by a paintball in flight, then played it back out of phase during a subsequent shot to see if it had any effect. What if it was that simple? Force the paintball, or the air surrounding it, to oscillate at the same frequency (which decreases with velocity if I read this correctly) only out of phase.

Obviously, it would be impossible to expect people to play paintball with 900-1000 khz tones playing in the background. Still, it might be something to look into.

AGD mentioned a few pages back that players might not care about this discussion. A few of us do. Thanks again gentlemen, this thread is a jewel to be treasured.

[hitech]

Playing a sound 180* out of phase with the sound created by the shedding vortices would indeed cancel it out. The "it", however, is the sound. Trying to pulse air, in the correct direction and at the correct time to "cancel" the shedding of a vortex seems like a monumental task, if not impossible with today's technology.

[Rowdie]

The barrel can make your shot more accurate by keeping the velocity more consistant with the proper paint/barrel match.....

As far as I can tell that's not correct.

Everyone's familure with the blow test? The proper ball to barrel fit means the ball won't roll out but you can blow it out. Well near as I can tell barrels that are too tight according to the blow test actually have the most consistant speed. However, barrels that are of the correct fit, while varying more widely speed wise end up being more accurate.

....

This thread is incredible! I've been reading/studying/contemplating it for two days now.

[Lurker27]

Guess I'll throw my hat in.

I believe that this thread is part of the search for the most accurate shot. Accuracy, of course, means going where you shoot it. Consistency is also important, and not only with regard to velocity

Lets review a few things I believe about paintballs.

They vary in size.

Seam position varies from shot to shot and is effectively random.

Seams are a constant and vary in size.

They expand around .001-.002 due to acceleration (Palmer found similar results)

At least a significant portion of their fill (boundary layer adhering to the shell, perhaps) spins when spin is imparted via the shell.

The only thing that the gun has yet to control with regard to paintball accuracy is spin.

The problem with accuracy comes in the last one.in general the tight barrel match eliminates spin, which only gets us to a certain level of accuracy. A non spinning imperfect sphere...this sounds familiar...it's a knuckle ball. The seams will create vortices behind the m, which will pull the ball in random directions (the original orientation of the spin was random)

So, it's fair to say that paintballs have a built in inaccuracy as long as we use this kind of barrel.

The solution wold seem to be rifling, but a rifled barrel reall should only be able to effectively shoot balls in the range of expansion, .001-.002 within the spec of the barrel.


Rifling would een out all of the vortices, would it not? IIRC the English Baker rifle used spherical bullets in a rifle.

[hitech]

Rifling would even out all of the vortices, would it not?

No, I do not think that it would. The vortices are not due to the seams, but due to the shape of the paintball (sphere). Because of the huge affect the shedding vortices have everything else is not statistically significant. Since this is all based on velocity, the one exception is consistency. The more consistent the more "accurate". However, small variations in velocity are overshadowed by vortex shedding. It boils down to paintball markers are about as accurate they are going to get, given the current projectile and speed limits.