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Rifled Railgun

Reduce the build accuracy required
  (+2)
(+2)
  [vote for,
against]

Rail guns are very difficult to make as they require all the components to be built to exacting standards to make sure the projectile is in constant contact with the charged sides. Whilst this is possible it does mean that after it has been fired, the walls of the barrel may have been damaged and it may therefore not fire again.

To solve this, have a twisted barrel on the railgun. As the projectile moves forward it is forced to twist by contact with the walls. This contact may reduce the accuracy over time but would increase the contact and therefore increase the usability and production value.

If the railgun were used as a weapon it also increases the accuracy of the shot.

miasere, Jan 25 2006

[link]






       Why not just rifle the barrel like a normal gun?
MikeOxbig, Jan 25 2006
  

       I was thinking about rifling / projectile spin in the context of my Satellite Hunters post, and also in regards to the flying cylinder / safe fan thread. Rifling causes spin, which stabilizes a projectile: important regardless of the type of projectile. Minor asymmetries in a fast moving nonspinning projectile (like a 30.06 bullet) would cause big changes in the flight path. Without rifling, a railgun would be essentially a superpowered musket. This is with an atmosphere I think, although I understand the Pioneer spacecraft revolve for stability as well.   

       The downside: interaction between projectile and barrel rifling increases friction, which must to some degree slow the projectile. This becomes a big deal at extremely high acceleration / velocity. I think most rail damage is from arcing, not friction, but I cannot imagine increasing friction between rails and projectile would help.   

       In "Satellite Hunters", rifling is accomplished in the pre-rail acceleration phase: the projectile emerges from the 30.06 rifle barrel already spinning. In a homogenous projectile (say a lead bullet), I do not think that subsequently engaging the rails would necessarily decrease spin.   

       + because I am enamored of railguns right now.
bungston, Jan 25 2006
  

       I get the feeling that the grooving would get worn down rather quickly. But railguns a fricking sweet nonetheless.
notmarkflynn, Jan 25 2006
  

       //If the railgun were used as a weapon//   

       As opposed to?   

       "On your marks... Set..."
PHTOOM! {{Headshot!}}
friendlyfire, Jan 25 2006
  

       /as opposed to/   

       You could use a railgun to launch things into orbit, or at more distant targets in space. A battery of railguns operating in concert, either in orbit or on the surface, could be used as an antimeteor defense - which I suppose is a weapon of a sort. In my "Darken the Sky" idea, a railgun is used to put reflective particles in the upper atmosphere. It has been proposed that railguns be used for other applications requiring high velocity or extreme pressure: for example, injecting fuel pellets into fusion reactors.
bungston, Jan 25 2006
  

       I'm ignorant in many aspects of the science here, but I've often wondered if you could spin the projectiles prior to introducing them into the propulsion.   

       That's the purpose of rifling, no?. If the projectile enters a six chamber emag spinner prior to being lauched, accuracy need not suffer.   

       Just a dream, though.
Zimmy, Jan 26 2006
  

       I wonder why the object must be between the rails, when it could be placed on top of the rails? A magnetic force could be arranged to keep the object in touch with the rails.   

       Rifling: if the object was cylindrical, then use a rotating magnetic field on the object as it slides up the rails.   

       Imagine the end view of object O sitting astride the two rails []   

          __
 /    \
 \_ _/
[]    []
Ling, Jan 26 2006
  

       [Ling] - I think you can do that. I have seen attempts to fire a penny with such an arrangement.
bungston, Jan 26 2006
  

       First: rifling would be much harder to build than would one with a straight barrel. Nowadays rifled barrels use "progressive twist" too, which is even harder to do right. Due to muzzel velocities I wouldn't be surprised if the first shot down the barrel didn't un-twist the rifling, too! Second: there's no need; railguns are point-and-shoot devices and no leading of the target is required over the short distances (maybe 20 miles max) between gun and target. Even a bad shot that hits its mark will destroy the target due to spalling, etc.
Steamboat, Jan 27 2006
  

       Hm.
bristolz, Jan 27 2006
  

       Mind you, if I was in a space-craft that was fired into space by a rail gun, I wouldn't be very happy to have it rifled!
Ling, Jan 27 2006
  

       [Steamboat], Rifling is hard to put into any gun however does increase accruracy significantly as it stops tumbling of the projectile and centres the aerodynamics.
miasere, Jan 27 2006
  

       //I wouldn't be very happy to have it rifled!// [ling] good point. What would happen if the projectile contained a contrarotating inner pod? Would that affect the overall stabilisation?
Some shaped-charge anti-tank rounds should not be spun, but must be fired from rifled barrels, so they're fitted with loose rings which engage with the rifling, but don't cause the round to spin. I wonder if this affects accuracy.
coprocephalous, Jan 27 2006
  

       [coprocephalous] These rings would affect accuracy as they would act like gyros keeping the projectile level.   

       [21 Quest] The projectile would still be affected by gravity so its not that big a deal.
miasere, Jan 27 2006
  

       /if I was in a space-craft that was fired into space by a rail gun/ - I think you would not mind so much, after experiencing the acceleration.   

       I think railgun launched space crafts will be a robots-only affair.   

       Spinning the exterior: ok - whether done in the railgun or before entering the gun (as in the 30.06 Satellite Hunter). But contact with the rails is a big deal with railguns, and projectile spin introduces another variable. Spinning the interior is a different matter. The interior could be mechanically revved up to high speed before the projectile was launched into the rails - maybe just using a motor and an interface. No modification would need to be done to the railgun. This should provide the same gyroscopic stability function.
bungston, Jan 27 2006
  

       Maybe you could answer this one [bungston]:   

       Since the projectile in a railgun is permeated with a pretty intense magnetic field, would it be possible to apply some sort of external magnetic rifling? Magnetic grooves so to speak? Would this interfere too much with the magnetism in the gun itself?
TIB, Jan 27 2006
  

       I cannot answer, because I have only the vaguest understanding of the "Lorentz forces" that drive the projectile. I do not think that Lorentz forces manifest in everyday situations on a scale we can see.
bungston, Jan 28 2006
  

       The Lorentz force is with you, in every motor that you see (and also the ones that you don't).
[TIB], you are correct: see my earlier anno about rotating magnetic field ( like a 3 phase motor)
Ling, Jan 28 2006
  
      
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