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CIWS-Safe

Intentionally Poor Aerodynamics for Aerial Gunfire
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With the increase in rocket and missile attacks on civillian populations, countries are investigating putting in C-RAM (Counter Rocket Artillery and Mortar) systems. One of the preferred implementations is the same as the Naval Close in Weapons System (hence the title). This is essentially one or more automatic gatling guns that track and shoot down the incoming munitions.

One problem with this approach is that in dense civillian populations, all of these thousands of bullets are going to come back down, potentially doing severe (or even lethal) damage to anything under them, including the civillian populations you are trying to protect.

I suggest, therefore, that these bullets be equipped with small spring loaded flaps along one side. These flaps are designed to be held aerodynamically closed as long as the bullet is moving along its axis above a certain speed (and are held closed inside the barrel). This allows the bullet to travel normally along the path to its intended target.

Once the bullet slows sufficiently near the peak of it's travel, the flap pops open. Once open, they push the bullet off-axis, preventing it from remaining spin stabilized and increasing it's tumble. This slows the bullet during it's return to earth, minimizing harm to anyone who finds themselves in the wrong place at the wrong time.

There obviously would be significant design challenges to work out (eliminating bullet imbalance and tumbling from the effects of holding the flaps closed), and there would be a minimum effective angle (if enough of the starting velocity isn't upwards, it won't slow enough before turning back down). I'm pretty sure all of that could be dealt with, however, and the end result should be something that could be placed in/near heavily populated areas without nearly as much fear of collateral damage.

MechE, Nov 16 2012

Folding wing glider http://makeprojects...Glides+Down!/1934/1
I had one of these when I were wee! [pocmloc, Nov 17 2012]

[link]






       The PHALANX automated gatling cannons are only one part of CIWS, albeit a totally badass part.
Alterother, Nov 16 2012
  

       CIWS rounds are often set to explode after a certain amount of air time to prevent collateral damage.
Voice, Nov 16 2012
  

       Okay, the naval appear to be mixed. You're right, the only (current) land version uses explosive shells, apparently specifically for this purpose. So the idea may be less necessary, but I think it would still work.
MechE, Nov 16 2012
  

       When I was a kid building rocket kits, one of the methods used to return a rocket to the ground was throwing its center of balance behind it's center of pressure at apogee. It did this by blasting the solid rocket motor into a little cradle below the rocket. Kind of hard to explain but basically it made the rocket unstable and it would tumble back to earth in a very un-aerodynamic configuration.   

       You could have something like this where a timed charge went off in the bullet at the end of its flight reshaping it so it would tumble or spin on it's way down decreasing it's terminal velocity to something safer for the people underneath it.   

       But I suppose at that point you'd just want to blow the whole bullet up and get some possible fragmentation to do some damage to your target as well while it's up there.
doctorremulac3, Nov 17 2012
  

       [21] That was my first thought, but that takes some of the range and punch out of the weapon. That's why I tried to come up with something that allows the bullets to reach the limit of their effective range before it introduces the extra drag.
MechE, Nov 17 2012
  
      
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