Tiberius Sniper Rounds, Info from TK

[cockerpunk]

guys, its all about the boundary layer and how it sheds off the back of the paintball.

[DevilMan]

Pixie Dust FTW!!!

DM

[malJohann]

guys, its all about the boundary layer and how it sheds off the back of the paintball.

Correct. With subsonic speeds an elongated ellipse with a tapered back is the best aerodynamic shape (like the wing of a propeller aircraft), but if that length is not practical for the application an elongated ellipse abruptly chopped in half is the best. The seperation of air is cleaner, causing less contamination of the "clean" air flowing around the object, thus dragging less turbulent air in its wake. Less turbulence = longer retention of its kinetic energy = further range for the same starting speed.

[cockerpunk]

Correct. With subsonic speeds an elongated ellipse with a tapered back is the best aerodynamic shape (like the wing of a propeller aircraft), but if that length is not practical for the application an elongated ellipse abruptly chopped in half is the best. The seperation of air is cleaner, causing less contamination of the "clean" air flowing around the object, thus dragging less turbulent air in its wake. Less turbulence = longer retention of its kinetic energy = further range for the same starting speed.

exactly

the skirt around the back of the ball fundamentally changes the effect of LP pocket shedding we see of the back of a paintball.

and replaces it with a presumably a less turbulent wake, and certainly not a cyclical system like the LP pocket shedding, reducing drag and providing less radial forces and better accuracy.

[pump]

so the straight lines of the FS has less drag than the curve of a ball?


i would think that the rounded back would allow for a smoother release of air

but again im not the aeronautical engineer.


so drag along the sides of the ball or FS affects range more than drag off the back?




does fineness work at all in this situation?

http://en.wikipedia.org/wiki/Fineness_ratio

[brycelarson]

additionally, the orientation of the first strike in the air is going to be controlled in large part by the center of gravity. If you set these guys down they sit up straight. Nearly all of the weight is in the front 1/4 of the length. This means that even without the fins it would travel relatively straight. the fins get the rotation going - which helps with accuracy.

[Spider-TW]

additionally, the orientation of the first strike in the air is going to be controlled in large part by the center of gravity. If you set these guys down they sit up straight. Nearly all of the weight is in the front 1/4 of the length. This means that even without the fins it would travel relatively straight. the fins get the rotation going - which helps with accuracy.

Right. It's just like a model rocket. You want the center of pressure behind the center of mass. The skirt, fins or not, shifts the centers backward and forward respectively. The spin keeps the effects of defects from pushing the round to one side. The fins keep it spinning as long as it flies, instead of the spin becoming too slow to be useful.

It would be cool to get some factory "blanks" or "blems" that didn't have fins but still had the skirt, just to see the difference.

so the straight lines of the FS has less drag than the curve of a ball?


i would think that the rounded back would allow for a smoother release of air

but again im not the aeronautical engineer.


so drag along the sides of the ball or FS affects range more than drag off the back?




does fineness work at all in this situation?
http://en.wikipedia.org/wiki/Fineness_ratio

You're right, all things being equal, a round back is usually better. However, a sphere is not much better in the first place. The 'release of air' on a sphere would normally occur right where you see the skirt start on the first strike, just after the center line. The turbulence you get is not much less than a flat back, it just doesn't have as much room to develop. The skirt lets the air stay attached up to the end, resulting in less friction on the surface.

The fins are kicking the air in a tangential or sideways direction as it leaves the back of the skirt. This throws the air outward and forces it to curl under before it collapses. It makes the collapse more orderly and less dramatic.

Fineness is a geometric parameter that helps you judge a design. Ballistic performance involves many effects and geometry is just one.

A good example of subtle airflow changes is seen in the different vintages of pickups. The old ones were pretty square, and leaving the tailgate down would get you a little better gas mileage. Then they sloped the cab and they were quieter but still could use the tailgate down. Now they slope the sides of the cab and the bed, shorten the distance between the roof edge and the top of the tailgate. I've heard that letting the tailgate down is actually worse for drag now, but the bed has the same foot print.

[hitech]

guys, its all about the boundary layer and how it sheds off the back of the paintball.

Come on now, this isn't deep blue!

Anyone interested can read about it in the spinning paintball thread in deep blue.

BTW, If i remember correctly there is no significant difference in drag with the tailgate up vs down.

added: I guess if/when these become a reality I'll have to change my tag line.

[Miltonyz]

BTW, If i remember correctly there is no significant difference in drag with the tailgate up vs down

Not to hijack the thread further but mythbusters tested this with I believe Ford F-150's. They found that the tailgate being down decreased mileage. My very nontechnical understanding was that with the gate up air gets trapped in the back and forms a "bubble" which redirects the new air away and doesnt let it put a lot of downforce on the bed. With the gate down the air came straight over the cab and straight down into the bed increasing downforce in the bed.

[hitech]

Not to hijack the thread further but mythbusters tested this with I believe Ford F-150's. They found that the tailgate being down decreased mileage. My very nontechnical understanding was that with the gate up air gets trapped in the back and forms a "bubble" which redirects the new air away and doesn't let it put a lot of downforce on the bed. With the gate down the air came straight over the cab and straight down into the bed increasing downforce in the bed.

I remember that one also. I remembered it as not being a significant change, but memory is the second thing to go...

[pump]

ah ok i see thanks guys
i talked to my grandfather he said the only way something with a tapered or pointed back can reduce drag is that it has to be long a drawn out .....like a drop of water but more elongated......duh(i should of thought about that)


now how do a make my mag shoot these from a clip?

[Spider-TW]

I remember that one also. I remembered it as not being a significant change, but memory is the second thing to go...

Drag doesn't matter much when you got a tank full of fuel at 60 mph. 200 mph with no fuel is a different problem. The pickup was just a visualization. Maybe not that many people have spent much time in the back of a pickup on the highway. Bed sheets, leaves and sticks make interesting analysis tools.

Besides firearm ballistics, there are some books of high speed photographs of fluid flow that really help to see what goes on. "Album of Fluid Motion" by Milton Van Dyke is all pictures and has a few that apply here. The rest of the pictures are pretty interesting too.

[pump]

http://www.mathematik.uni-dortmund.de/~featflow/album/vanDyke.html

[Ninjeff]

ah ok i see thanks guys
i talked to my grandfather he said the only way something with a tapered or pointed back can reduce drag is that it has to be long a drawn out .....like a drop of water but more elongated......duh(i should of thought about that)


now how do a make my mag shoot these from a clip?

Easiest way i can figure is with a top magazine feeding downward into the breach. Like the British Bren gun from WW2

[Spider-TW]

http://www.mathematik.uni-dortmund.d...m/vanDyke.html

a whole website of tech tease. That is it though. Should be in engineering libraries for anyone near a campus.