Effect of different forces acting on small sphere.

CrazyRabbit

In the sport of airsoft, a device is used to propel a small 0.2g spherical pellet down a non-rifled barrel. To increase range, a 'hop up' device is used to place a backspin on the pellet. This counteracts the force of gravity (Bernoulli principle) allowing the pellet to travel further.

The questions I have are; what effect would rifling the barrel have on the pellet that is already affected by the backspin? Would the rifling further increase the range, or would it affect the path of the pellet in a way that would reduce accuracy? (causing the pellet to move horizonatally left or right)

Definition of rifling for anyone unsure about what it means:
rifling
n : the cutting of spiral grooves on the inside of the barrel of
a firearm designed to cause the bullet to spin around it's own axis [syn: grooving]

Thanks for your help on this. Physics is not my strong point.

humbert

rifling a barrel wouldn't help a spherical bullet travel because the purpose of rifling is to keep an arrow or cylindrical shaped projectile pointing in the direction of motion which improves aerodynamics and accuracy. For a spherical projectile it's orientation wont matter.

It would probably have a detrimental affect on the accuracy for the reasons you mentioned.

CrazyRabbit

Thanks humbert for you reply.

Thomas_S_Hunterson

Just as a matter of interest, are the Airsoft guns in Ireland constrained to a 1 Joule muzzle energy? (giving them a legal classification as toys?)

planck2

humbert wrote:

rifling a barrel wouldn't help a spherical bullet travel because the purpose of rifling is to keep an arrow or cylindrical shaped projectile pointing in the direction of motion which improves aerodynamics and accuracy. For a spherical projectile it's orientation wont matter.

It would probably have a detrimental affect on the accuracy for the reasons you mentioned.

i don't understand

ApeXaviour

i don't understand

The rifling would impart a spin to cylindrical-like projectile, keeping its orientation gyroscopically stable.

I don't see how this would necessarily be detrimental on a spherical projectile. It'd be completely superfluous though.

Edit: actually, if the spherical projectile was spinning, collision with this "hop-up device" would likely influence its direction.

sean_keevey wrote:

Just as a matter of interest, are the Airsoft guns in Ireland constrained to a 1 Joule muzzle energy? (giving them a legal classification as toys?)

Your question might better be answered here:
http://www.boards.ie/vbulletin/forumdisplay.php?f=466

planck2

ApeXaviour wrote:

The rifling would impart a spin to cylindrical-like projectile, keeping its orientation gyroscopically stable.

I don't see how this would necessarily be detrimental on a spherical projectile. It'd be completely superfluous though.

Edit: actually, if the spherical projectile was spinning, collision with this "hop-up device" would likely influence its direction.

Your question might better be answered here:
http://www.boards.ie/vbulletin/forumdisplay.php?f=466

This is what I meant by "I don't understand", the ball's spin will effect it's trajectory because don't forget that you have to include drag effects and the spin will have some influence on the amount of drag. this could be tested by having the spherical bullet move through a viscous fluid.

Professor_Fink

Actually there is another point that I think might be missed here. The ball can only spin about one axis at a time. To get maximum loft, it should be spinning about an axis normal to both the direction of motion and to the direction in which gravity is acting.

Rifling the barrel will change the orientation of this axis, giving it non-maximum lift, with the additional force contributing to a curve to either the right or left of the trajectory. In the worst case, rifling could actually cause the ball to be propelled into the ground.

ApeXaviour

planck2 wrote:

This is what I meant by "I don't understand", the ball's spin will effect it's trajectory because don't forget that you have to include drag effects and the spin will have some influence on the amount of drag. this could be tested by having the spherical bullet move through a viscous fluid.

If it's spinning about the same axis of its direction of motion then how would the drag be an issue? It'd surely all cancel in this case. At least the only thing it will affect is the ball's own angular velocity.

Professor_Fink wrote:

The ball can only spin about one axis at a time. To get maximum loft, it should be spinning about an axis normal to both the direction of motion and to the direction in which gravity is acting.

Sooo... backspin. Yeah that's intuitive. How would one achieve that. Have the upper side of the barrel made more rough of a surface? I'd worry about over doing it though. Bullets by their nature being rather fast, it might cause the ball to curl upwards.

Professor_Fink wrote:

Rifling the barrel will change the orientation of this axis, giving it non-maximum lift, with the additional force contributing to a curve to either the right or left of the trajectory. In the worst case, rifling could actually cause the ball to be propelled into the ground.

As I understand rifling, it will specifically induce spin about the axis of motion. So I don't believe it should have an effect on trajectory at least (given a smooth exit from the barrel, ie no collision with some "hop-up" mechanism)

Professor_Fink

ApeXaviour wrote:

I'd worry about over doing it though. Bullets by their nature being rather fast, it might cause the ball to curl upwards.

That can certainly happen. I assume the device is set up to give just the right amount of backspin.

ApeXaviour wrote:

As I understand rifling, it will specifically induce spin about the axis of motion. So I don't believe it should have an effect on trajectory at least (given a smooth exit from the barrel, ie no collision with some "hop-up" mechanism)

I was assuming the presence of a hop-up mechanism.