Fluid Mechanics in Paintball

[ShooterJM]

Originally posted by AGD
The Magnus effect as you are describing affects spinning spheres. Most paintballs fired from markers have little spin and when they do it is usually not enough to distort the airflow enough in a particular direction. The testing we have done shows that the small induced spin on paintballs does not correlate with where it hits the target when the spin is below 6000 rpm.

AGD

Out of curiosity was there no correlation whatsoever, or just no positive correlation? Did you find that there was a constant or exponential type of drop off in RPMs during flight? If it's trade information or something like that don't worry about it. Just trying to figure out if my calculations are wrong.

[CRySyS]

Tom's talking about spinning the ball along the axis it is traveling down. Like what the Armson Stealth tries to do with rifleing or what AGD did when they spun(sp?) a barrel at high rpm and then fired the ball out of it. But spinning the ball along the perpendicular horizontal axis, like slice on a tennis ball as you said, can and does create lift altering the trajectory of the ball. Backspin will give the ball upward lift that fights gravity; forespin will aid gravity and driv ethe ball down.

The Tippmann flatline works and it works well but to answer your initial question, of all the flatlines I've put together and shot I don't remember ever seeing any balls just drop down. I have seen odd shots rise higher so I propose that the reverse magnus effect is present most of the time but is not strong enough to reverse the backspin lift, and odd shots that do not experience the reverse effect would then go flying higher than normal. I can neither proove nor deny that statement, It's only my little theory I came up with to explain and corolate what I see with what you said. I'm on my way to S. Padre Island for PACS so I'm not going to proove it but I can't wait to get back and see where this thread goes.

[Croix71]

The testing we have done shows that the small induced spin on paintballs does not correlate with where it hits the target when the spin is below 6000 rpm.

hehe thanks TK, I was curious how many rpms it would take to effect a paintball.

forespin will aid gravity and driv ethe ball down

I agree with ya there CRySyS. If the paintball is spinning forward fast enough (not sure how many rpms it would take)it could generate enough lift to rise but after reaching it highest point it will drive the ball down sacrificing distance.

Sooooo, we need to find a way to get a paintball to spin more than 6000 rpms, with a back spi, and make it safe and affordable.

[eskimo]

? if you could make paintballs shaped like golf balls i.e. dimpled, then could you control the ball? What about just altering the casing/shell? If it's a gelitain layer with fluid inside, then why not just make balls with dimples? Patent anyone?

[ThePatriot]

If i recall correctly, paintballs in severe cold get dimples on them. This dimpling normally causes the paint to shoot HORRIBLY, so i do not think dimpling a paintball would show any advantage what so ever.

[eskimo]

I think the big difference is the regularity of the dimples, if it's more structured, like a golf ball, as apposed to one large dimple, then I would guess that you could model the flight of a paintball like a golf ball?? The other factor mentioned is cold, and when the ball gets colder you introduce a solid, or more solid. I think that's a whole different post. I still have the question, "Does the paint inside the ball act independant of the shell? or do the shell and fill act as one mass?" I have seen sides that support both.

[Croix71]

I would think that doing a comparison between the two will yield such a minute difference it would considered negligible.

[ShooterJM]

Originally posted by eskimo
I think the big difference is the regularity of the dimples, if it's more structured, like a golf ball, as apposed to one large dimple, then I would guess that you could model the flight of a paintball like a golf ball?? The other factor mentioned is cold, and when the ball gets colder you introduce a solid, or more solid. I think that's a whole different post. I still have the question, "Does the paint inside the ball act independant of the shell? or do the shell and fill act as one mass?" I have seen sides that support both.

Yes regularity is key in dimpleing. Basically the dimples cause the laminar layer of air to disrupt slightly making it turbulant. This delays boundry layer seperation at the rear of the golf ball and gives increased range. Size of the dimples is a big factor too. The smaller the dimples, the less unused turbulance there is and therefore the more efficient the design. However, if the dimples are too small their effect is negligable because there isn't enough disturbance in directional flow to make it non-laminar. One process has been patented, but as far as I can tell it didn't work. Too expensive with bad shooting paint. It would seem gel doesn't have the structural integrity to retain shape during the drying process.

[CRySyS]

I think you misunderstood me. When I said forespin will create lift I meant lift toward the ground. Anti-lift you could call it. Forespin will not lift away from the ground unless the whole reverse magnus effect thing did something. Because the lower pressure side is facing down that is direction the ball will pull. With backspin the low pressure side is up, opposite of gravity, which counteracts gravities pulling effect making a flat straight trajectory. This is what you see comming out of a flatline. I don't know how fast a flatline spins the ball but I think its as much as 6000 rpm. Keep in mind I have absolutely no clue, I may be wrong, the thing may fling them out at 50000 rpm and I wouldn't know. The Mk I eyeball can see what it want to see. I tried to simulate the flatline barrels effect on the paintball calculator but it doesn't work properly. A flatline will actually lift up at higher velocities before comming back down. Thats why flatline Tippmann are chronoed in at 260 or less, to prevent the ball from flying up up and away. If anyone knows of a better calculator to use I'd love to hear of it. Didn't NASA have one on their kids site?

[CRySyS]

Ooo, look what I just found...

physics of paintball

I havn't read the page yet but the last graph shows the wave effect I described where the ball rises and then falls.

[ShooterJM]

Originally posted by CRySyS
Ooo, look what I just found...

physics of paintball

I havn't read the page yet but the last graph shows the wave effect I described where the ball rises and then falls.

Excellent web page! I'm going to have to read all that when I get a chance!

[AGD]

The paintball physics page is pretty good and very factual. He is working from theory and our test results show a few slightly different things but it's 95% right on. Someone try and get him here to deep blue.

The fluid inside the paintball acts independently of the shell (at first). If the barrel induces a spin on the shell of the ball the fluid does not spin with it instantaneously. We have photographed the spinning ball slowing down after leaving the barrel in flight. The shell slows down while the fill speeds up and at some point they match.

Dimpled paintballs don't fly any better than regular ones. We made them and shot them. I'll try and find the pic.

AGD

[BlackVCG]

Here's an interesting discussion from awhile back that correlates with this discussion.

Theroretical Paintball Physics

[ShooterJM]

Originally posted by AGD
The paintball physics page is pretty good and very factual. He is working from theory and our test results show a few slightly different things but it's 95% right on. Someone try and get him here to deep blue.

Dimpled paintballs don't fly any better than regular ones. We made them and shot them. I'll try and find the pic.

AGD

It's that 95% part that's bothering me. I checked and the last update to the page was in 2000. I did email him and extend an invitation to him though, it'd be nice to hear his theories, especially if they've changed.

I'm not sure how much information you'd care to give out on the dimpled paintballs experiment, Tom, but I'm very interested in the details. I've been trying to calculate the perfect pattern, size, frequency and volume of paintball dimples for the last 3 months. In addition to shell material changes, manufacturing process differences and fill. Did you refrence existing patants? Ah, the suspense is killing me.

[eskimo]

Does the fluid's properties inside the paintball have different effects? Do more dense fills "fly" better than less dense?