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Post by Kerr on Jun 23, 2017 17:03:13 GMT
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Post by RiftandRend on Jun 23, 2017 22:54:51 GMT
I don't understand why railguns can't achieve these velocities. If nanomaterials like graphene are used projectile melting and barrel erosion becomes nearly irrelevant. Due to the very small scale of the barrel and projectile atomicly perfect manufacturing is not completely impossible and friction could be minimised. I highly doubt a coilgun could reach these velocities without being massive. Unlike railguns, they can't scale the projectile down and have to scale the energy up. This assumption is based on in game tests and my entry level understanding of physics. Edit: Upon a more thorough reading, are you assuming 99.99% efficiency of these hypothetical coilguns? "A 3100km/s pellet of 2 micrograms can be accelerated with only 10MJ of energy, and it will deliver than 10MJ to the target."
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Post by ross128 on Jun 23, 2017 23:49:50 GMT
Hmm, well once you get into the microgram range, if the projectile carries a charge you could accelerate it in a cyclotron in order to squeeze a very long acceleration track into a compact space.
Though at that point you've basically got a particle cannon.
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Post by matterbeam on Jun 24, 2017 0:50:41 GMT
I don't understand why railguns can't achieve these velocities. If nanomaterials like graphene are used projectile melting and barrel erosion becomes nearly irrelevant. Due to the very small scale of the barrel and projectile atomicly perfect manufacturing is not completely impossible and friction could be minimised. I highly doubt a coilgun could reach these velocities without being massive. Unlike railguns, they can't scale the projectile down and have to scale the energy up. This assumption is based on in game tests and my entry level understanding of physics. Edit: Upon a more thorough reading, are you assuming 99.99% efficiency of these hypothetical coilguns? "A 3100km/s pellet of 2 micrograms can be accelerated with only 10MJ of energy, and it will deliver than 10MJ to the target." The issue, as I understand it, is friction. Two surfaces cannot rub together at such velocities without vaporizing. Halfway methods such as trying to conduct through the plasma that is generated from two surfaces rubbing at several km/s only works at relatively low velocities and carries a significant efficiency penalty, plus massive wear and tear. Graphene and carbon supermaterials do not help when the contact friction generates temperatures in excess of 10000K. Coilguns do not contact the projectile. A coilgun that reaches these velocities will be massive because of the teslas the magnets need to generate. Using a very flat, very wide disk-shaped projectile maximizes the magnetic volume the projectile traverses while accelerating, which means that rather short coilguns can be used. I'm not sure what you're pointing to with that last quote. Electric engines achieve 98% efficiency today. Accelerators with electron recycling achieve 99.9% efficiency or more. A linear motor like a coilgun will have similarly high efficiencies. A 3100km/s 2 ug projectile will contain 9.61MJ of kinetic energy, I was only rounding figures. My point there was that the projectile delivers all its kinetic energy to the target.
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Post by RiftandRend on Jun 24, 2017 0:58:08 GMT
The issue, as I understand it, is friction. Two surfaces cannot rub together at such velocities without vaporizing. Halfway methods such as trying to conduct through the plasma that is generated from two surfaces rubbing at several km/s only works at relatively low velocities and carries a significant efficiency penalty, plus massive wear and tear. Graphene and carbon supermaterials do not help when the contact friction generates temperatures in excess of 10000K. Coilguns do not contact the projectile. Wouldn't making the barrel and projectiles perfectly smooth remove nearly all friction?. The reason I questioned the efficiency is because in game coilguns have difficulty breaking 50% efficiency, let alone 99.
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Post by bigbombr on Jun 24, 2017 3:04:57 GMT
Wouldn't making the barrel and projectiles perfectly smooth remove nearly all friction?. The reason I questioned the efficiency is because in game coilguns have difficulty breaking 50% efficiency, let alone 99. Making barrel and projectile perfectly smooth will reduce, but not remove friction. I suggest you look up video's of IRL railguns and take note of the massive amount of barrel material being ejected every shot. I remember there was once massive hype involving railgun research, they managed to extent barrel life from 3-4 shots to 20+ shots. Coilguns would be a lot more efficient if we could use different capacitors for every stage. They'd probably match or even exceed railguns in muzzle velocity per mass.
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Post by omnipotentvoid on Jun 27, 2017 7:10:34 GMT
It might be relevant to point out that, as projectile mass approaches zero, railguns will approach lasers in their effect (if not their function). There is probably a sweet spot where the properties of bothe are mixed ideally. If it is possible to find this sweet spot, the question becomes whether or not it is possible to build railguns that can fire projectiles of the size needed at the rate required.
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Post by bigbombr on Jun 27, 2017 12:07:44 GMT
It might be relevant to point out that, as projectile mass approaches zero, railguns will approach lasers in their effect (if not their function). There is probably a sweet spot where the properties of bothe are mixed ideally. If it is possible to find this sweet spot, the question becomes whether or not it is possible to build railguns that can fire projectiles of the size needed at the rate required. But wouldn't smaller projectiles lose proportionally more mass to ablation? At some point, you're firing nothing but gas. I'm personally more interested in coilguns and ion cannons (firing ions one by one to prevent electrostatic dispersion of your beam).
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Post by omnipotentvoid on Jun 27, 2017 13:05:25 GMT
One of the main problems with coilguns, is that the accelerating force is reliant on incredibly strong magnetic fields. For the purposes of this thread, the main disadvantage is saturating small projectiles. Railguns do not face this problem, as the accelerating force has nothing to do with the projectile, rather with the charge flowing through it. In addition to this, it is easier to form railgun projectiles to minimize internal acceleration stress allowing faster acceleration (currently not simulated in game). Furthermore, railguns allow for long rod shaped projectiles. These have better armor penetrating properties and even if they don't penetrate, they concentrate their energy in a smaller area, making them more effective against heavy targets. Further more, as projectiles decrease in mass and thus size, building the firing coils becomes more difficult. As the bore radius approaches or even dips below the wire radius, the magnetic field becomes less homogeneous, reducing efficiency and increasing projectile stress in the best case scenario or outright dashing the projectile against the coil in the worst case scenario. That's not to mention the width of the isolation between winding causing issues. The in homogeneous field also makes it impossible to simulate in game.
To point out another drawback of coilguns irl. One reason for weapons designers to go for railguns over coilguns, is that the intense magnetic field in coilguns makes it almost impossible to launch electrically controlled munitions. Railguns, capable of achieving similar acceleration with comparably tiny fields and thus allow for such munitions.
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Post by bigbombr on Jun 27, 2017 13:29:09 GMT
One of the main problems with coilguns, is that the accelerating force is reliant on incredibly strong magnetic fields. For the purposes of this thread, the main disadvantage is saturating small projectiles. Railguns do not face this problem, as the accelerating force has nothing to do with the projectile, rather with the charge flowing through it. In addition to this, it is easier to form railgun projectiles to minimize internal acceleration stress allowing faster acceleration (currently not simulated in game). Furthermore, railguns allow for long rod shaped projectiles. These have better armor penetrating properties and even if they don't penetrate, they concentrate their energy in a smaller area, making them more effective against heavy targets. Further more, as projectiles decrease in mass and thus size, building the firing coils becomes more difficult. As the bore radius approaches or even dips below the wire radius, the magnetic field becomes less homogeneous, reducing efficiency and increasing projectile stress in the best case scenario or outright dashing the projectile against the coil in the worst case scenario. That's not to mention the width of the isolation between winding causing issues. The in homogeneous field also makes it impossible to simulate in game. To point out another drawback of coilguns irl. One reason for weapons designers to go for railguns over coilguns, is that the intense magnetic field in coilguns makes it almost impossible to launch electrically controlled munitions. Railguns, capable of achieving similar acceleration with comparably tiny fields and thus allow for such munitions. You haven't addressed my criticism on railguns and projectile ablation. Does this mean both coilguns and railguns have fundamental minimum projectile sizes? For coilguns, saturation isn't an issue, the projectile has to survive the acceleration in the first place (magnetic susceptibility is not the reason I use magnetic metal glass, it's high strength is). And weren't there coilgun types that used eddy currents (which is less efficient but doesn't have saturation issues)? Either way, I suspect coilguns would be superior CIWS (no barrel ablation, can have efficiencies in excess of 99%), which would probably be the main role of kinetic weapons (aside from orbital bombardement of fortified positions).
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Post by matterbeam on Jun 27, 2017 14:02:51 GMT
omnipotentvoid, bigbombr: Induction coilguns. The upper limit is the material strength of the projectile. Downside is higher currents. @bigbomr: Ablation is due to friction heating. Small projectiles would have to problem of rubbing/melting away their contact points and cutting the electric loop, thus ending acceleration. Big projectiles have more surface area to work with.
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Post by omnipotentvoid on Jun 27, 2017 14:25:41 GMT
bigbombr true, projectile ablation is a big problem. There are potential work around though. Using non solid armatures is a solution, if you can reduce projectile friction. This is the main reason I didn't bring it up. Coilguns have friction problems too, unless you levitate the projectile in the coil. If that is possible, you can do the same in railguns and use non solid armatures. I sort of mentioned this when I talked about the coilguns slug being dashed against the coils: in micro coilguns, in homogeneities in the magnetic fields will cause the levitation effect to fail in in coils with bore diameters less than the wire diameter, forcing you to use solid guides which will cause the friction you wish to avoid. Beyond that, I find that the ability to essentially negate internal stresses due to acceleration in railguns are far to advantageous to opt for coilguns for reasons of ablation.
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Post by bigbombr on Jun 27, 2017 16:20:43 GMT
omnipotentvoid , bigbombr : Induction coilguns. The upper limit is the material strength of the projectile. Downside is higher currents. @bigbomr: Ablation is due to friction heating. Small projectiles would have to problem of rubbing/melting away their contact points and cutting the electric loop, thus ending acceleration. Big projectiles have more surface area to work with. Do the projectiles have to have magnetic properties or are these unnecessary for induction coilguns? If magnetic properties are unneeded, you could use graphene as ammunition.
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Post by AdmiralObvious on Jun 27, 2017 17:23:51 GMT
Do the projectiles have to have magnetic properties or are these unnecessary for induction coilguns? If magnetic properties are unneeded, you could use graphene as ammunition. They probably should (also graphene does have some magnetic properties, same as rubber). You ideally want the projectile to be resistive to the magnetic field so you can propell it faster, but not so much so that the shot melts.
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utilitas
Junior Member
I can do this all day.
Posts: 59
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Post by utilitas on Jun 28, 2017 5:57:01 GMT
Wouldn't a high vacuum effectively act as an unpolarized dielectric material?
Ablation could be solved by not making it a vacuum. You could make a hybrid coil/railgun, where the coils are used only to keep an asymmetric projectile (a combination of a paramagnetic or antiferromagnetic material and a diamagnetic) oriented in line with the axis of the barrel. Then you'd just fill the barrel with a suitable atmosphere prior to firing (no need for an end seal) and propel the projectile through the conductive atmosphere. Ablation would still exist, but be severely diminished due to all the plasma being guided by the coils as well.
But there comes one major issue when approaching significant fractions of c. Coil switching. A railgun has no active components except for the flux wave down its rails, but a coilgun has to switch its coils on and off. You would need to use progressively smaller and smaller, thinner and thinner coils as the projectile speeds up, otherwise you risk losing quite a lot of efficiency to residual inductive flux - in the best case scenario. Worst comes, the projectile will spin out as the coils are unable to switch back off in time and misalign. Those coils could get extremely small, and therefore extremely fragile.
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