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ZzaphodD
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Joined: 28 Nov 2009
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 Posted: Tue Apr 10, 2012 3:46 am Post subject: |
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| Fallon Kell wrote: | | Grimace wrote: | Fallon, while I don't doubt your desire to dispel physics myths and promote math and science, I also know a thing or two about recoil and firearms and explosives. I know that a cannon firing a 40 pound projectile (as shown in that video clip) would have a fair bit more recoil than was demonstrated in the firing of that non-explosive projectile fired by the rail gun in the video.
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As I understand it, that was actually a 7 lb projectile, and the recoil may have been mitigated by the enourmous weight of the gun and the fact that it was attached to the building. Regardless, I'm just saying that Newton's third (?) law of motion dictates that total recoil be the same for any two projectiles of identical weight and velocity.
In game mechanics, recoil would be the same between firearms and railguns of the same damage rating. Whether you choose to represent recoil as a penalty to successive shots, or just tell your players how much it hurt to fire that .458 Lott with a broken rib, an observant GM will almost certainly consider recoil. |
Im all for the 'if you want recoil, then go for recoil. If not, invent technobabble' arguement here.
I even lost track of the arguement.
Is the main question wether the (supposedly) extended time of acceleration will lower the (experienced) recoil or not?
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atgxtg
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| Posted: Tue Apr 10, 2012 10:09 am Post subject: |
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| ZzaphodD wrote: |
Is the main question wether the (supposedly) extended time of acceleration will lower the (experienced) recoil or not? |
No, since that is proven fact.
I believe the original suggestion was that railguns would have NO recoil, and that assumption is false. Anything that propels and object will generate a force and thus have recoil. But there are plenty of ways to reduce the recoil, and that is without resorting to technobabble.One very simple way to ofset the effect of recoil is to simply make the firing weapon more massive.
Firearms have such high recoil because they accelerate the round th high speed over a very short peroid of time. And the round does such a great amount of damage, relative to it's mass, because when it hits something it comes to a stop over a very shot period of time. Incrweaseing those times will reduce the forces generated. That's scientific fact, and has been proven long ago.
Where I see the idea coming into play would be with vehicle mounted weapons. For example, imagine an ISD spinal mounted railgun. THe ISD is about 1600m long, and could have 150m long rail an accelerate a round over a large fraction of a second. Although, based on the incredible high acceleration stats for fighters and the farily limited effectiveness fighters have when ramming captial ships, I doubt railguns would be all that great. |
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CRMcNeill
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Location: Redding System, California Sector, on the I-5 Hyperspace Route.
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| Posted: Tue Apr 10, 2012 10:57 am Post subject: |
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Actually, game mechanics in a sci-fi realm mean whatever the storyteller / GM wants them to mean. Discussing the physics of recoil and how that translates into game rules is fine, but it can just as easily be sidestepped via techno-babble. For example, a GM could ignore recoil in firearms by saying that the weapon is equipped with a repulsor-based recoil absorption system that allows the gunner to fire the super-powerful railgun while only absorbing a mild kick.
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atgxtg
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| Posted: Tue Apr 10, 2012 11:46 am Post subject: |
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True, and in some cases, it would be logical to assume so.
For example, the starfighters are all capable of thousands of Gs of acceleration, yet the pilots don't get squashed into jam. So it makes sense to assume that whatever technology that prevents TIE fighters (and pilots) from going spalt from 4100Gs of acceleration would also be used for any high powered railgun. |
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Grimace
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Location: Montana; Big Sky Country
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| Posted: Wed Apr 11, 2012 12:26 am Post subject: |
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| Fallon Kell wrote: | | As I understand it, that was actually a 7 lb projectile, and the recoil may have been mitigated by the enourmous weight of the gun and the fact that it was attached to the building. |
The text on the page with the video says the projectile was 40 pounds. That's what I was going by.
And yes, the weight of the gun certainly had an effect on the recoil of the weapon. |
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ZzaphodD
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| Posted: Wed Apr 11, 2012 2:40 pm Post subject: |
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| atgxtg wrote: | True, and in some cases, it would be logical to assume so.
For example, the starfighters are all capable of thousands of Gs of acceleration, yet the pilots don't get squashed into jam. So it makes sense to assume that whatever technology that prevents TIE fighters (and pilots) from going spalt from 4100Gs of acceleration would also be used for any high powered railgun. |
Never mind the pilot, the whole starfighter should go up in atoms... 
I still cant take those figures seriously... 
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atgxtg
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| Posted: Wed Apr 11, 2012 3:16 pm Post subject: |
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| ZzaphodD wrote: |
Never mind the pilot, the whole starfighter should go up in atoms... |
Yup, and anything capable of taking that sort of acceleration is going to take a really nasty laser gun to damage it.,
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I still cant take those figures seriously... |
Who takes Star Wars seriously? It's just a bunch of movies. Oh, and a few TV series, a dozen or so computer games, a bunch of novels, comics, tons of toys, and other unassorted collectibles.
The high G ratings do have some merit. They explain how those fighters can turn on a dime they way to do. Since G forces in a turn increase with the sqaure of the velocity a fighter would need to be able to pull a few thousand Gs to make 90 degree turns at the speeds those ships are supposedly moving at. |
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Fallon Kell
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| Posted: Wed Apr 11, 2012 5:11 pm Post subject: |
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| Grimace wrote: | | The text on the page with the video says the projectile was 40 pounds. That's what I was going by. |
That's entirely reasonable, but I've done further research and believe the news story got the figure wrong. After all, that's a solid aluminum slug, about the size of a large can of soup. It would have to be much larger to weigh 40 lbs.
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atgxtg
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| Posted: Thu Apr 12, 2012 10:58 am Post subject: |
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| Fallon Kell wrote: | | That's entirely reasonable, but I've done further research and believe the news story got the figure wrong. After all, that's a solid aluminum slug, about the size of a large can of soup. It would have to be much larger to weigh 40 lbs. |
I think I have to back you up on this one. Other sources claim a 3.2kg slug. This can be backed up by the math. Apparently, on January 31, 2008, the weapon in question fired a round at a velocity of 2520m/s with a energy of 10.64MJ.
Since E=0.5kgV^2, then kg=2E/V^2
kg=21.28MJ/(2520^2), or 3.35kg.(about 7.4 pounds). A 40 pound (18kg) round fired at 2520m/s would have over 57MJ of energy!
But I doubt the round is aluminum. I suspect it would be tungsten, titanium or some other dense ferrous metal..Aluminum would be a lousy choice for a railgun. It is non-ferrous, susceptible to heat, and has a low density-all detrimental for a railgun. |
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Fallon Kell
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| Posted: Sat Apr 14, 2012 2:53 pm Post subject: |
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| atgxtg wrote: | | I doubt the round is aluminum. I suspect it would be tungsten, titanium or some other dense ferrous metal..Aluminum would be a lousy choice for a railgun. It is non-ferrous, susceptible to heat, and has a low density-all detrimental for a railgun. |
Aluminum is inexpensive, easy to form and, crucially, extremely conductive, which are all beneficial to a railgun research program.
This story explains That they use aluminum projectiles, and also describes a 23 lb projectile, implying that they use differing slug weights.
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