Paintball Spin Physics - Getting to the final Answer

[AGD]

[AGD]

I appologize, I thought I had posted the tifs when I first put up the pics but I must have forgotten. Please download the tif and look at the pics, they are much clearer than the lousy jpg's in the thread. Sorry about that, you cant get good data from lousy pics. Here is the link and its in the data thread.

AGD


spin data

[Pstan]

Might I propose someone take a look into the varying ballistic coefficients of paintballs as the mysterious "X" force.


Considering what Mr. Kaye posted above on Force "X", let's look at paintballs. Paintballs have a terrible BC. Might we also say that the BC of every paintball fired is different from the next because of their inconsistant nature. So far, unless handloaded, we cant control the orientation of every round that enters and exits the gun. Might not the Force "X" be the minute diffences in the BC of each and every ball fired? And might not the fact that even Nylon paint has bad accuracy be a result of the poor BC of paintballs in general? If you have a really good Paint/Barrel match flyers still occur. Possibly due to the fact that the tip/width/tail of every projectile fired is minutely different from the last or the next? The Flatline would override this as it imparts the hard spin along a verticle line that overcomes the BC and changes trajectory? Fill on the ball would do so also as it induced a spin?

A few sites on BC that might make more sense....

http://www.chuckhawks.com/bc.htm

From Mr. Hawks...
"Ballistic Coefficient (BC) is basically a measure of how streamlined a bullet is; that is, how well it cuts through the air. Mathematically, it is the ratio of a bullet's sectional density to its coefficient of form. Ballistic Coefficient is essentially a measure of air drag. The higher the number the less drag, and the more efficiently the bullet cuts through the air. So for purposes of flying through the air efficiently, the bigger the BC number the better.

BC is what determines trajectory and wind drift, other factors (velocity among them) being equal. BC changes with the shape of the bullet and the speed at which the bullet is traveling, while sectional density does not. Spitzer, which means pointed, is a more efficient shape than a round nose or a flat point. At the other end of the bullet, a boat tail (or tapered heel) reduces drag compared to a flat base. Both increase the BC of a bullet."

http://www.aeroballisticsonline.com/ballistics/bc1.html

http://www.uslink.net/~tom1/calcbc/calcbc.htm

This may be completely off the wall and entirely wrong, but it's the best a feeble mind like mine can come up with. And, I do realize that paintballs and bullets may be an "Apples and Oranges" comparison, but BC is what describes the change in the shape of projectiles over the years in firearms. I think someone did mention that the firearms world solved this problem long ago, or something to that effect.


Respecfully,

Pstan

[AGD]

Pstan,

Good comeback! Yes BC can affect things in flight. Problem is that all spheres have the same drag coefficient with is something like .7 or .8. The nylon balls being perfectly round to better than 1000th of and inch and missing the seam should fly straight and true but they don't. In fact the shot group for nylon balls is hard to differentiate from regular paint.

This would seem to sugest that the seams, drag coefficient differences and small size variations are not a substantial portion of our X force.

AGD

[BlackVCG]

I could sit here and rattle off all of my Fluid Mechanics knowledge, but this explains things pretty well.

http://www.princeton.edu/~asmits/Bicycle_web/blunt.html

Pstan- The difference between the bullet and the paintball is that one is a streamlined body and the other is considered a bluff body, respectively.

Tom- Not for all spheres. Take a look at the graph. It's a function of the Nr (Reynolds Number), but for all paintballs shooting through air you can consider it the same.

I haven't been reading this thread, but when I find the time I'll look it over and see if I can add some input. It seems like an entertaining conversation thus far.

[AGD]

Black,

Yes of course you are right about the DC being different at different R. You all should look at the site Black pointed out. Very informative especially figure #3....


AGD

The trip wire thing is cool too, I will have to look at that more.

[[5x5]]

Larry De La Brandais turned me towards this very interesting discussion thread, and I thank him for it. You may not. Although I haven't done much on the paintball physics subject for awhile, I still remember some of the stuff I put together, and certainly still have an interest in it. (As a reminder: http://home.attbi.com/~dyrgcmn/pball/pballphys1.html

[cledford]

Somewhere along the line (in this thread) I thought I saw it mentioned that just about every ball fired through a paintgun experiences the magnus effect to some varying degree. I think it was further stated that the problem is that there isn't anyway to control which direction the effect causes the ball to travel and is essentially random. A description stated that due to this occurrence that the shot pattern of paintguns would look like a donut - or, if a straight line was run through the exact center of the bore to the impact point, the Magnus effect would cause the ball impacts to hit at varying distances from the desired point in a complete ring around that actual point of aim.

So if this is the effect of uncontrolled Magnus, why not try to control it? The flatline does (in an unintended fashion - they aren't trying to "control" anything - just to induce the effect to utilize the result) but is not "adjustable" and is severe. The Z-Body for the 'mag was designed to produce a similar effect as the flatline - but differs in how it accomplishes this. The Zbody uses a "friction plate" that is adjustable from zero to maximum (I guess where it would crush a ball) and I think most people turn it up to a high degree attempting to reproduce the Tippmann result.

What if a similar system was used to put just the slightest amount on magnus on every ball fired from a gun? Instead of going to far and putting a "major" amount on - why not just apply enough to be certain that effect was always consistent? That should theoretically reduce the group size which is another way of saying "increase accuracy."

This might not be the holy grail - but I'm wondering if the line of thought is reasonable. I guess my thought is, "if paintball guns are inherently inaccurate due to variances (inconsistencies) in the shape/size/form of the projectile, and those variances in the projectile are unchangeable and must be accepted - why not try to control how the projectiles behave by forcing their behavior to be more consistent?" This is based on the huge assumption that the varying magnus I described above is caused by the imperfections in the balls themselves.

-Calvin

[ezrunner]

from precision shooting:

When fired by a human, all shot groups are a donut. The shooter
with the smallest donut wins.

Observationally, paint behaves the same, this is due to the
natural mechanics of the body.

Question: AGD/Tom.. or Glenn,

"Does a paintball marker, when held in a fixed mechanism, exhibit
this same tendency, or is there a pattern grouping that is somewhat
uniform over a reasonably large sample set?"

-rob

[[5x5]]

I believe that the Magnus effect would only produce a well defined donut target pattern if the spin velocities were locked into a small non zero range. I also suspect at least one of the angles defining the spin axis would have to be constant as well. If we set up a coordinate system centered on the ball with x axis being the direction of ball motion, y being in and out of the plane of the page, and z being the vertical axis, then the angle that must be locked is that in the xz plane.

With respect to improving the accuracy by placing a small controlled spin on the ball,I am not sure. You still need only a little friction, or a little asymmetric leakage of gas around the ball to alter its spin axis. If the alteration happened to be along the same axis as the controlled spin the result would be to either speed up the spin, or reduce it. This still leads to dispersion in the trajectory, and a broader shot pattern. Despite this, the controlled spin has momentum, and I think a ball with a controlled spin might therefore resist a change in its spin axis to some extent. On the other hand, many times I have read complaints from people that the accuracy of a flatline barrel is worse than a good straight barrel. At face value, this field observation would tend to negate the hypothesis. However, the preception of inaccuracy could be related to not holding the gun perfectly vertical as has been discussed here. Another possibility is that people can just notice a wayward spin much easier because of the extra distance.

[Redkey]

Hey Gary

I stumbled across your website a couple months ago... was meaning to shoot you an email to say hi and comment on your page.. never got around to it though.

so...

Hi

I like your web page. I had a good laugh at your paintball weight studies... I wonder how many people know the difference between mean and median, not to mention the 95% (three sigma?) confidence level. Any plans for future testing?

Later
Geo

[bryan]

I dont know much about the magnus effect, but i do know that a knuckleball goes crazy in flight. Assuming that a nylon ball was not spinning at all, would it not act in the same way as a knuckleball? How much did the nylon ball spin while in flight compared to a regular paintball. If the spin is comparable then i may be way off but i would think that a nylon ball with no seam would not have as much spin as a paintball with dimples/flatspots/seams.

[[5x5]]

Redkey,
I needed the data on paintball dimensions and weights for my calculations. Once I started measuring and really saw how non round a paintball could be, I realized that a portion of our problems with accuracy must be tied to those odd shapes and seams. It was also one of the few times we had more than one type of paintball around. You obviously can image how boring it was sitting there with a micrometer trying to measure the diameters. Another reason for actually putting the study on the web was that I realized that not a lot of people have balances with 10 microgram accuracy available to them. No plans to do any more studies.

[Redkey]

Ball Weights

Here are some measurements I made. Min of 20 balls were weighed for each paint type. Yes, I know, 0.1 mg resolution is overkill. I also have some seam and pole crush load data around here somewhere.

[hitech]

Welcome [5x5]. Glad to see you are still interested in things like this. Interesting discussion, isn't it? Hopefully Tom will release more data and you can contribute more. Thanks for checking us out.

Larry (Hitech) De La Briandais