golol
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Post by golol on Jan 24, 2017 10:34:59 GMT
This idea just came to my mind and I'm wondering if this was considered. Next to a weapon system it could also be used as a propulsion mechanism. but let's see how effectivr it is: With 1 atm of pressure and a barrel radius of about 5.6mm (1 cm2 of area) we would get a total force of 100000N/m2 * 0.0001m2 =10N That's not very impressive and assuming a length of 1 meter for the barrel and no loss of pressure during the acceleration you would get 10 Joules of energy. But with a 1g projecile we do get sqrt(2*10/0.001)= 146 meters per second velocity. This shows that the we are not lacking orders of magnitude. Gas pressure can go up to 1000atm in commercial containers though, which would give us over 4 km/s. What about pressure loss? If the valves ar really fast you would only use the volume of the barrel of gas which means that each shot reduces your power by (volume of Barrel/volume of gas chamber). As a result you have a tradeoff between a small bore radius with a probably insignificant loss or a bigger bore radius with far more power but a considerable power loss per shot. Batteries were requested and gas pressure seems like a highly efficient energy storing system. I well could imagine it used on micro drones. But is it better than a simple combustion weapon? I don't know  . But the material strain could be a lot smaller due to the distribution of the acceleration over the length of the barrel. |
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Post by theholyinquisition on Jan 24, 2017 17:13:16 GMT
This idea just came to my mind and I'm wondering if this was considered. Next to a weapon system it could also be used as a propulsion mechanism. but let's see how effectivr it is: With 1 atm of pressure and a barrel radius of about 5.6mm (1 cm2 of area) we would get a total force of 100000N/m2 * 0.0001m2 =10N That's not very impressive and assuming a length of 1 meter for the barrel and no loss of pressure during the acceleration you would get 10 Joules of energy. But with a 1g projecile we do get sqrt(2*10/0.001)= 146 meters per second velocity. This shows that the we are not lacking orders of magnitude. Gas pressure can go up to 1000atm in commercial containers though, which would give us over 4 km/s. What about pressure loss? If the valves ar really fast you would only use the volume of the barrel of gas which means that each shot reduces your power by (volume of Barrel/volume of gas chamber). As a result you have a tradeoff between a small bore radius with a probably insignificant loss or a bigger bore radius with far more power but a considerable power loss per shot. Batteries were requested and gas pressure seems like a highly efficient energy storing system. I well could imagine it used on micro drones. But is it better than a simple combustion weapon? I don't know . But the material strain could be a lot smaller due to the distribution of the acceleration over the length of the barrel. Pressurized-gas weaponry isn't that much more effective, and tankage tends to be heavy. If you must use gas, use a light-gas gun. |
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golol
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Posts: 25
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Post by golol on Jan 24, 2017 17:55:36 GMT
Yea, I came aound that too while doing some research on the topic. These things could be competitors to railguns but it would probably be pretty complicated to get them to shoot fully automatic at a reasonable rate.
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Post by Easy on Jan 24, 2017 18:34:07 GMT
How would it compare to the conventional cannons we use?
It seems like you're going to trade system mass for higher projectile velocity. I can see it allowing for higher ballistic efficiencies, but I'd have to see the math to be sure.
Then again we can have pretty ridiculous bore sizes for a one gram projectile so the light-gas gun might not do much better than that.
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golol
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Posts: 25
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Post by golol on Jan 24, 2017 18:48:01 GMT
The question is if the gas in this case has a limited expansion velocity or something like that.
I assumed that the pressure on the back of the projectile stays pretty much constant throughout the whole length of the barrel. This is under the assumption that the pressure container has a far far higher volume than the barrel which means that the pressure in the container + whole barrel length is like 99% of the original pressure.
It could, however, be that the gas can't keep up with the rapidly accelerating projectile because it has a limit (like the speed of sound) for it's expansion speed. I just don't knoe the physics here. It surely has some limit but the question is if it is relevant (not many many times the maximum projectile speed). If the pressure decrases along the barrel you're probably not much better off than with a conventional gun.
What I also thought of earlier was using a hydrogen oxygen mixture as the gas and detonating it at some point along the barrel.
It was an interesting math problem and I don't know if the physics were correct but the results were that you could get 4x the energy.
What I did was assume that the barrel is seperated from the container when the gas is detonated. It theb increases in pressure by a factor of roughly 10 (found that in some paper) and undergpes an adiabatuc expansion (the pressure drops in a hyperbola with distance). There is an optimal projectile position along the barrel when the load is exploafed where the "linear" pressure and explosive pressure together result in the highest energy and that was 4x the energy. But light gas guns are probably far more reasonable than pneumatic weapons or this weird mix I described where you have to be suicidal enough to carry huge hydrogen oxygen tannks aroubd haha.
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Post by theholyinquisition on Jan 24, 2017 23:15:32 GMT
The question is if the gas in this case has a limited expansion velocity or something like that. I assumed that the pressure on the back of the projectile stays pretty much constant throughout the whole length of the barrel. This is under the assumption that the pressure container has a far far higher volume than the barrel which means that the pressure in the container + whole barrel length is like 99% of the original pressure. It could, however, be that the gas can't keep up with the rapidly accelerating projectile because it has a limit (like the speed of sound) for it's expansion speed. I just don't knoe the physics here. It surely has some limit but the question is if it is relevant (not many many times the maximum projectile speed). If the pressure decrases along the barrel you're probably not much better off than with a conventional gun. What I also thought of earlier was using a hydrogen oxygen mixture as the gas and detonating it at some point along the barrel. It was an interesting math problem and I don't know if the physics were correct but the results were that you could get 4x the energy. What I did was assume that the barrel is seperated from the container when the gas is detonated. It theb increases in pressure by a factor of roughly 10 (found that in some paper) and undergpes an adiabatuc expansion (the pressure drops in a hyperbola with distance). There is an optimal projectile position along the barrel when the load is exploafed where the "linear" pressure and explosive pressure together result in the highest energy and that was 4x the energy. But light gas guns are probably far more reasonable than pneumatic weapons or this weird mix I described where you have to be suicidal enough to carry huge hydrogen oxygen tannks aroubd haha. |
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Post by bdcarrillo on Jan 25, 2017 1:44:16 GMT
Perhaps a squirt of hypergolic fuel behind the projectile?
A gas combustion gun or ram accelerator may have to contend with propellant escaping to space before the projectile gets to it. Current designs seem to use a rupture disk or frangible diaphragms for gas sealing. That would have to be changed out each time the gun fires and before it's filled with gas.
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Post by Enderminion on Jan 27, 2017 12:14:22 GMT
thats what we have, a mass of explodies (tecnical term) gets burned into a gas that vastly increases in volume and propells a shot (or shell) towards the enemy
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Post by n2maniac on Jan 28, 2017 18:15:30 GMT
Pneumatic weapons are quickly limited by the low speed of sound of the expanding air (which, by the way, ends up getting cold as it expands). It will be outperformed by a conventional gun. theholyinquisition has it right: if you must use a gas gun, use a light gas (where they generally have a scheme that also heats it up). That being said, qswitched has a decent argument against light gas guns in the game. |
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Post by ross128 on Jan 29, 2017 16:12:33 GMT
As mentioned, technically the reason pneumatic weapons never took off is that explosives do the same thing better. All gunpowder really does is store a whole bunch of gasses in a solid form, and then violently convert them back to gasses. Hence why nitro groups are so important in developing explosive compounds, they turn into nitrogen and NOx when they explode. It's a much denser and easier to manage way of storing them than even the best pressurized tank, even if the conversion process does foul up the firing chamber with annoying-to-clean soot.
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Post by bigbombr on Jan 29, 2017 16:30:46 GMT
There is one advantage to (pure) gasguns whose pressure is purely from pre-pressurized tanks: it's the only weapon system with a negative heat output. I wonder, would the expanding gas suck away enough heat to help cool down systems?
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. But the material strain could be a lot smaller due to the distribution of the acceleration over the length of the barrel.
