Any ballistics experts out there? I have been wrestling with a thought experiment for some while without success.
The purpose of rifling is to impart spin to a projectile, which gives it gyroscopic stability. My interpretation of that is that as soon as it leaves the barrel it will carry on pointing in the same direction. Hence a small bore rifle bullet will arrive at its target point first. Smooth bore weapons are less accurate because the ammo wavers and tumbles, unless it's stabilised some other way(eg by aerodynamic fins on a sabot round).
That's all fine and dandy for an infantry rifle with a very shallow trajectory, but what about an artillery piece? To take an extreme case, let's consider a howitzer firing at 45 degrees to horizontal. Well that's not really extreme judging by WW1 footage I've seen. Anyway, off goes the shell at 45 degrees. At the top of the parabolic trajectory it's travelling horizontally, as it transitions from going up to going down. But if the gyroscopic forces are still working, it's still pointing 45 degrees upwards. That's the whole point of a gyroscope, as the rotational inertia resists changes in orientation of the axis.
The shell now goes down the other half of the parabola, all the time still pointing up 45 degrees. Ignoring air resistance for the moment, you can see where I am going - the shell hits the target going sideways.
Cartoons usually portray shells orientating themselves along the trajectory, so they hit the target nose first. If they do, what forces act on them to affect the gyroscopic stability? I can't find any articles online that explain this, or even consider what actually happens to projectile orientation. I have the feeling that I have missed something fundamental. If I have, what is it?
The purpose of rifling is to impart spin to a projectile, which gives it gyroscopic stability. My interpretation of that is that as soon as it leaves the barrel it will carry on pointing in the same direction. Hence a small bore rifle bullet will arrive at its target point first. Smooth bore weapons are less accurate because the ammo wavers and tumbles, unless it's stabilised some other way(eg by aerodynamic fins on a sabot round).
That's all fine and dandy for an infantry rifle with a very shallow trajectory, but what about an artillery piece? To take an extreme case, let's consider a howitzer firing at 45 degrees to horizontal. Well that's not really extreme judging by WW1 footage I've seen. Anyway, off goes the shell at 45 degrees. At the top of the parabolic trajectory it's travelling horizontally, as it transitions from going up to going down. But if the gyroscopic forces are still working, it's still pointing 45 degrees upwards. That's the whole point of a gyroscope, as the rotational inertia resists changes in orientation of the axis.
The shell now goes down the other half of the parabola, all the time still pointing up 45 degrees. Ignoring air resistance for the moment, you can see where I am going - the shell hits the target going sideways.
Cartoons usually portray shells orientating themselves along the trajectory, so they hit the target nose first. If they do, what forces act on them to affect the gyroscopic stability? I can't find any articles online that explain this, or even consider what actually happens to projectile orientation. I have the feeling that I have missed something fundamental. If I have, what is it?
via JREF Forum http://ift.tt/1lNQX1v
Aucun commentaire:
Enregistrer un commentaire