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Post by RiftandRend on May 16, 2018 0:56:53 GMT
An issue with very high velocity railguns is barrel and projectile overheating due to friction. I may have a solution in the form of a new type of projectile. A core of high melting point material (eg. tungsten) encased in low melting point, conductive material (eg. lead or conductive polymer). As the projectile contacts the barrel, the outer layer will melt, preventing them temperature from far exceeding its melting point. As this layer melts and boils away, the projectiles diameter will shrink, necessitating a tapering barrel to maintain contact. The layer of material sublimating off of the outer layer should protect the system from overheating, and may reduce friction by acting as a lubricant. This should allow railguns to achieve a higher velocity before overheating destroys the projectile, but suffers inherent inefficiencies. This naturally has some issues, notably the energy inefficiency of accelerating material that will not be aimed at the target. Another potential issue is residue buildup on the inside of the barrel. Any thoughts?
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Post by Fgdfgfthgr on May 16, 2018 5:50:22 GMT
Won't that super-heated plasma damage the barrel?
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Post by RiftandRend on May 16, 2018 8:11:13 GMT
Won't that super-heated plasma damage the barrel? Ideally the temperatures wouldn't far exceed the boiling point of the ablator jacket, but yes.
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Post by AtomHeartDragon on May 16, 2018 21:28:07 GMT
Your conducting polymer is unlikely to keep conducting while melted. Alloy or ionic fluid should work better, but I'm not sure if meaningful lubrication at typical railgun velocities is even a thing and any energy losses will be turned into massive amounts of heat.
Coilguns or plasma armatures anyone?
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Post by jtyotjotjipaefvj on May 16, 2018 23:12:25 GMT
You might also run into issues with the conductor leaving the barrel and leaving the heavier core behind. It doesn't sound like there's any mechanic to prevent this from happening.
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Post by AdmiralObvious on May 17, 2018 6:00:32 GMT
I can sort of see this working with single use rails. It won't matter much if the weapon can fire again if the rails are designed to be disposable.
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Post by AtomHeartDragon on May 17, 2018 16:57:57 GMT
I can sort of see this working with single use rails. It won't matter much if the weapon can fire again if the rails are designed to be disposable. But then there isn't much point trying to lubricate them and if there is, you can put your melty layer on the rails instead of projectile, without having to get creative with their geometry.
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Post by Pttg on May 17, 2018 17:25:40 GMT
Maybe make the projectile a hollow cone with a rocket nozzle. Point the thing down range, fill it with a dense propellant -- perhaps UHMD plastic, or ice. Then the waste heat is put to good use accelerating the projectile, but the barrel doesn't need to be strong enough to contain the exhaust gasses.
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Post by RiftandRend on May 18, 2018 0:15:49 GMT
You might also run into issues with the conductor leaving the barrel and leaving the heavier core behind. It doesn't sound like there's any mechanic to prevent this from happening. The core doesn't necessarily have to be denser, it's just what I had in mind when I came up with this.
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Post by RiftandRend on May 18, 2018 0:18:36 GMT
Your conducting polymer is unlikely to keep conducting while melted. Alloy or ionic fluid should work better, but I'm not sure if meaningful lubrication at typical railgun velocities is even a thing and any energy losses will be turned into massive amounts of heat. Coilguns or plasma armatures anyone? Its irrelevant whether the polymer conducts when melted, as it should be left behind by the projectile as it moves down the barrel. Lubrication is not the main focus of this idea, only a possible side benefit.
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Post by AtomHeartDragon on May 18, 2018 16:36:10 GMT
Your conducting polymer is unlikely to keep conducting while melted. Alloy or ionic fluid should work better, but I'm not sure if meaningful lubrication at typical railgun velocities is even a thing and any energy losses will be turned into massive amounts of heat. Coilguns or plasma armatures anyone? Its irrelevant whether the polymer conducts when melted, as it should be left behind by the projectile as it moves down the barrel. Lubrication is not the main focus of this idea, only a possible side benefit. If it's going to lubricate, it'll also have to conduct. If it's not going to lubricate you'll be dumping a lot of energy into dragging around and heating a layer of liquid bogging your projectile down. OTOH dealing with core getting left behind shouldn't be that hard - make the core highly conductive. I wonder if it would be possible to quickly (and blindly) re-coat the rails with ablative metallic lubricant. A revolving, multibarrel assembly could then be a workable solution for heavy hitting railguns.
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Post by RiftandRend on May 19, 2018 23:35:37 GMT
Its irrelevant whether the polymer conducts when melted, as it should be left behind by the projectile as it moves down the barrel. Lubrication is not the main focus of this idea, only a possible side benefit. If it's going to lubricate, it'll also have to conduct. If it's not going to lubricate you'll be dumping a lot of energy into dragging around and heating a layer of liquid bogging your projectile down. OTOH dealing with core getting left behind shouldn't be that hard - make the core highly conductive. I wonder if it would be possible to quickly (and blindly) re-coat the rails with ablative metallic lubricant. A revolving, multibarrel assembly could then be a workable solution for heavy hitting railguns. I never said the core would not be conductive. If you read the post, I mentioned tungsten would make an acceptable candidate. The barrel of the proposed weapon tapers, which is intended to force sublimated jacket material off of the sides of the projectile.
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Post by AtomHeartDragon on May 20, 2018 0:11:09 GMT
The barrel of the proposed weapon tapers, which is intended to force sublimated jacket material off of the sides of the projectile. Why? If you have gone through trouble of accelerating something, you might as well hit the enemy with it.
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Post by RiftandRend on May 20, 2018 0:32:50 GMT
I added a Simple illustration.
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Post by AtomHeartDragon on May 20, 2018 15:23:24 GMT
First thing first - you probably don't want to scrape your lubricant off the projectile. Railgun fouling sounds orders of magnitude worse than chemgun fouling. That's yet another reason for using something that will stay conductive when molten.
If this might work at all I would go with lithium. Imagine a lithium sabot - either continuous or more likely as pairs of lithium slugs set into more conventional armature. Lithium has number of traits going for it here: it's soft, melty (453K), not a bad conductor (11 MS/m, contrary to what CoADE says), has very low density, high thermal capacity and high thermal expansion (which should help it fill the gaps as it travels down the rails, no narrowing down necessary). Additionally, it's very reactive which might allow some way of getting rid of residue by flushing the barrel chemically (although lithium oxide is a solid and I don't know how clingy it would be).
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