4 ms·

> The projectiles would only have the force of gravity/terminal velocity Horizontal velocity will, presumably, be reduced by drag. But it won't be zero for a l

> The projectiles would only have the force of gravity/terminal velocity Horizontal velocity will, presumably, be reduced by drag. But it won't be zero for a long, long ways over the horizon.

UnoriginalGuy 13y ago
Not sure I follow. You point the projectile too low and it just hits the ocean (due to the curvature of the earth), you point it higher than the horizon then the projectile will continue to travel upwards indefinitely until it runs out of energy and then will fall back to earth with the force of gravity. The only way what you're saying works is on a flat planet or against a target within your horizon.
- Filligree 13y ago
  It will still be travelling sideways when it hits the target, and unless your target is a long, long way off it'll be travelling sideways with significant speed. Railgun projectiles, like cannon shells, travel on a parabolic curve - not a half-circle.
  - UnoriginalGuy 13y ago
    Cannon shells cannot be fired over the horizon either. Firing over the horizon will convert the projectile's forward momentum into height, it will reach whatever its apex is, run out of momentum and then fall due to gravity. The angle is just too steep. The only way to make this an effective weapon is to fill it with explosives (since then you've just created a mortar). But firing explosives from a railgun has its own issues. Most weapons which depend on a steep parabolic curve to hit their targets also have explosives in them, like artillery, mortars, ICBMs, etc. You can use a less steep curve to deliver blunt force to a target (catapult, cannon, gun, etc) but these weapons have a finite range as the earth is curved, therefore you'd have to tilt them too far back to overcome that, which will cause all that lovely forward force you're depending on to do damage going up into the sky as it flies higher and higher.
    - Filligree 13y ago
      I'm going to assume that the designers have considered this, and that even though it's over-the-horizon the projectiles will still have significant momentum when they hit.
    - vilhelm_s 13y ago
      You seem to be saying that in order to fire a projectile farther, one needs to make launch angle closer to vertical. But that is not the case, unless the distances get very large you always achieve the longest distance by firing at a 45 degree angle, so half the velocity is in the horizontal direction. Making it more vertical than that will make the range shorter. For extremely large distances (probably not relevant for naval railguns), the curvature of the earth becomes significant. But the correction goes in the other direction, it is optimal to fire at an angle more horizontal than 45 degrees. In the limiting case, the optimal angle for an ICBM is 22 degrees [1], and they will re-enter the atmosphere more horizontal than veritical [2]. [1] http://www.fas.org/rlg/garwin-aps.htm http://www.fas.org/rlg/garwin-aps.htm [2] http://www.fas.org/nuke/guide/usa/icbm/Slide92.JPG http://www.fas.org/nuke/guide/usa/icbm/Slide92.JPG
      - UnoriginalGuy 13y ago
        > You seem to be saying that in order to fire a projectile farther, one needs to make launch angle closer to vertical. I didn't say anything even close to that. Not even ballpark. I said that if you fire at a high angle you won't have much kinetic energy when the projectile finds its target. This topic is about firing non-self-propelled projectiles (cannon balls, railgun pellets, etc) from a ship or some other platform near sea level, several people are claiming that you can fire at a high enough angle to escape the horizon while still maintaining enough forward momentum to do significant damage, I am saying that at those angles the forward momentum is largely consumed as height. The projectile will travel away and up, and then after it reaches its apex where it has consumed a lot of its forward momentum to elevate itself it will fall back to earth only at the speed gravity carries it at (minus wind resistance). So while, yes, you can likely hit a ship or other target beyond the horizon, you cannot do so with more kinetic force than the projectile's weight being carried down by gravity (which is typically not very much relative to the kind of speeds we're talking about when initially fired).

> The projectiles would only have the force of gravity/terminal velocity Horizontal velocity will, presumably, be reduced by drag. But it won't be zero for a long, long ways over the horizon.

UnoriginalGuy 13y ago

Not sure I follow. You point the projectile too low and it just hits the ocean (due to the curvature of the earth), you point it higher than the horizon then the projectile will continue to travel upwards indefinitely until it runs out of energy and then will fall back to earth with the force of gravity. The only way what you're saying works is on a flat planet or against a target within your horizon.

Filligree 13y ago
It will still be travelling sideways when it hits the target, and unless your target is a long, long way off it'll be travelling sideways with significant speed. Railgun projectiles, like cannon shells, travel on a parabolic curve - not a half-circle.
- UnoriginalGuy 13y ago
  Cannon shells cannot be fired over the horizon either. Firing over the horizon will convert the projectile's forward momentum into height, it will reach whatever its apex is, run out of momentum and then fall due to gravity. The angle is just too steep. The only way to make this an effective weapon is to fill it with explosives (since then you've just created a mortar). But firing explosives from a railgun has its own issues. Most weapons which depend on a steep parabolic curve to hit their targets also have explosives in them, like artillery, mortars, ICBMs, etc. You can use a less steep curve to deliver blunt force to a target (catapult, cannon, gun, etc) but these weapons have a finite range as the earth is curved, therefore you'd have to tilt them too far back to overcome that, which will cause all that lovely forward force you're depending on to do damage going up into the sky as it flies higher and higher.
  - Filligree 13y ago
    I'm going to assume that the designers have considered this, and that even though it's over-the-horizon the projectiles will still have significant momentum when they hit.
  - vilhelm_s 13y ago
    You seem to be saying that in order to fire a projectile farther, one needs to make launch angle closer to vertical. But that is not the case, unless the distances get very large you always achieve the longest distance by firing at a 45 degree angle, so half the velocity is in the horizontal direction. Making it more vertical than that will make the range shorter. For extremely large distances (probably not relevant for naval railguns), the curvature of the earth becomes significant. But the correction goes in the other direction, it is optimal to fire at an angle more horizontal than 45 degrees. In the limiting case, the optimal angle for an ICBM is 22 degrees [1], and they will re-enter the atmosphere more horizontal than veritical [2]. [1] http://www.fas.org/rlg/garwin-aps.htm http://www.fas.org/rlg/garwin-aps.htm [2] http://www.fas.org/nuke/guide/usa/icbm/Slide92.JPG http://www.fas.org/nuke/guide/usa/icbm/Slide92.JPG
    - UnoriginalGuy 13y ago
      > You seem to be saying that in order to fire a projectile farther, one needs to make launch angle closer to vertical. I didn't say anything even close to that. Not even ballpark. I said that if you fire at a high angle you won't have much kinetic energy when the projectile finds its target. This topic is about firing non-self-propelled projectiles (cannon balls, railgun pellets, etc) from a ship or some other platform near sea level, several people are claiming that you can fire at a high enough angle to escape the horizon while still maintaining enough forward momentum to do significant damage, I am saying that at those angles the forward momentum is largely consumed as height. The projectile will travel away and up, and then after it reaches its apex where it has consumed a lot of its forward momentum to elevate itself it will fall back to earth only at the speed gravity carries it at (minus wind resistance). So while, yes, you can likely hit a ship or other target beyond the horizon, you cannot do so with more kinetic force than the projectile's weight being carried down by gravity (which is typically not very much relative to the kind of speeds we're talking about when initially fired).