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Post by demetrious on May 2, 2017 3:35:22 GMT
I think that conventional cannons are slightly over-modeled at the moment. Consider, if you will, the stock 22mm Turreted Cannon. Note the reload speed, there - 25 milliseconds. That's 0.025 seconds, or 40 times in one second. Now consider the M249 Squad Automatic Weapon: it has a full cyclic rate (it's maximum fire rate, going all-out) of 800 rounds per minute, or about 13.3 rounds fired per second. The fire rate of 40 rounds a second isn't the problem, strictly speaking - it's more than possible with technologies such as electrically-detonated primers and caseless ammunition - but this does not address the heat. Note the Wikipedia page also lists a "sustained" rate of fire, and a "rapid" rate of fire. While the cyclic rate describes how fast the mechanical action can actually complete operation cycles (i.e. shoot,) these figures tell you the practical rate of fire an infantryman can sustain with the weapon. If he wants to keep shooting without pause, he must fire in short bursts, putting no more than 100 rounds per minute downrange, because of the heat buildup. Heat is a familiar problem with machine guns - heavier ones usually come with quick-change barrels so the heated barrels can be swapped for cool ones to maintain a high rate of sustained fire. It is very easy to overheat a machine gun with continuous fire till the barrel exceeds design limitations and actually begins to droop, leading to a permanent deformation that destroys it. Now this is for weapons with low cyclic rates (compared to our 22mm cannon,) in thick atmosphere, designed to exploit convection effects to maximize the cooling benefit. In addition, our contemporary earthly firearms also benefit from using brass cartridge casings - the reason caseless ammunition hasn't replaced it yet, despite all the advantages, is because the brass absorbs much of the heat of the chemical reaction before being ejected from the chamber - effectively serving as a heat sink. The effect is significant enough that the German G11 design never fully came to grips with the overheating issues introduced by eliminating the brass casings... and at the rates of fire our stock cannons use - plus the impetus to keep mass as low as possible, on spaceships - it's reasonable to assume that caseless ammunition is being used. Thus, conventional cannons are ducking the heavy hand of thermodynamics as it stands, achieving fire rates almost four times conventional weapons we're used to in a hard vacuum without slagging themselves. I've been trying to figure out how one would model barrel/chamber heating in a conventional firearm in vacuum. Sadly I've not been able to find much; the best I've seen is this wikipedia article on the energy efficiency of firearms. Sadly there's no specific information on the consequences for firing a gun in vaccum, but I was at least able to find a freely available reference book (written in 1943,) on the Thermodynamics of Firearms. Unfortunately I'm nowhere near equipped to utilize this information (I can barely manage simple algebra.) Cooling is obviously much slower without convection, but I'm terribly curious as to how much barrel heating comes from the hot gasses in the barrel after the projectile has been expelled - would the rapid evacuation of said gasses from the barrel (because of external vacuum) reduce the heat imparted to the barrel? I can't begin to say. tl;dr liberal arts major uses his fancy words to beg STEM for help
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Post by dragonkid11 on May 2, 2017 4:44:32 GMT
Honestly if you are trying to ask a question, you should at least move the question away from the wall of text.
Anyway,hot gas certainly has an impact on gun firing in atmosphere as they tends to stay in the barrel instead of getting evacuated in vacuum.
There's also the factor of how fast the bullet moved in the barrel.
A 5.56mm rifle round usually reach around 300 to 400 meter per second.
22mm conventional cannon reach 3 times of the velocity, thus the hot gas will also evacuate out of the barrel faster. It also has a bigger firing chamber to absorb the heat, 22mm diameter circle is bigger than 5.56mm diameter circle after all.
Of course, that mostly doesn't matter with how fast the gun is firing.
But then there's the issue of mass.
A M249 weighs 5 kg, a 22mm conventional cannon weighs around 200 kg, with maybe 50 in the barrel. That's more than enough mass to absorb heat from the barrel.
I have also made some optimized gun that weigh much lighter, but still has dozen of kilogram of mass for the barrel, enough to absorb heat from the firing.
Whether or not that's enough to stay within realistic realm of thermodynamics, I have no idea.
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Post by bigbombr on May 2, 2017 5:59:18 GMT
I think a big issue is that barrels can heat up to just below their melting point, but in reality, many metals/materials become more malleable close to their melting point. In the real world, you can't fire a machinegun to just below the melting point of it's barrel. The barrel (and possibly the chamber) would have deformed significantly before that, rendering the gun inoperable.
The same issue crops up elsewhere in the game: coolant pumps, rocket nozzles, ...
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Post by demetrious on May 2, 2017 6:46:06 GMT
I think a big issue is that barrels can heat up to just below their melting point, but in reality, many metals/materials become more malleable close to their melting point. In the real world, you can't fire a machinegun to just below the melting point of it's barrel. The barrel (and possibly the chamber) would have deformed significantly before that, rendering the gun inoperable. The same issue crops up elsewhere in the game: coolant pumps, rocket nozzles, ... I humbly submit that a fire rate of 40 rounds per second - in vacuum - will, in fact, bring the barrels to their melting point in short order.
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Post by RiftandRend on May 2, 2017 11:08:54 GMT
I think a big issue is that barrels can heat up to just below their melting point, but in reality, many metals/materials become more malleable close to their melting point. In the real world, you can't fire a machinegun to just below the melting point of it's barrel. The barrel (and possibly the chamber) would have deformed significantly before that, rendering the gun inoperable. The same issue crops up elsewhere in the game: coolant pumps, rocket nozzles, ... I humbly submit that a fire rate of 40 rounds per second - in vacuum - will, in fact, bring the barrels to their melting point in short order. Barrel overheat and melting is one of the things the game calculates fairly well. If the module is not giving an overheat value than it is reasonable to assume that it is not going to melt.
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Post by Rocket Witch on May 2, 2017 11:55:27 GMT
I humbly submit that a fire rate of 40 rounds per second - in vacuum - will, in fact, bring the barrels to their melting point in short order. Radiation of heat becomes very rapid at temperatures like 3800K. The gun probably reaches an equilibrium at an elevated temperature where the heat radiated becomes equal to the heat from firing, and then it doesn't get any hotter. This could be wrong but radiation does occur quicker than people tend to expect.
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Post by bigbombr on May 2, 2017 12:10:33 GMT
I humbly submit that a fire rate of 40 rounds per second - in vacuum - will, in fact, bring the barrels to their melting point in short order. Radiation of heat becomes very rapid at temperatures like 3800K. The gun probably reaches an equilibrium at an elevated temperature where the heat radiated becomes equal to the heat from firing, and then it doesn't get any hotter. This could be wrong but radiation does occur quicker than people tend to expect. Exactly my point, if barrels can only heat to the point where the barrel becomes malleable instead of the melting point of the barrel, they'll overheat much easier.
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Post by Enderminion on May 2, 2017 12:28:29 GMT
you mean deform
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Post by demetrious on May 2, 2017 18:28:02 GMT
Oooh, no kidding? I presume that's the same physical affect that makes radiators vastly more effective the hotter the coolant temperature is, then? What's the name of the effect or law that causes this? I'm curious. The interesting thing about a gun barrel is - as qswitched noted in his blog posts - that they're fairly effective as radiators, since they're a good shape for it (a cylinder.) Since we can now make composite barrel armor we could even exploit some of the principles of actual radiator design (main materiel layer and surface coating) to maximize heat radiation. If the rise in radiation efficiency is exponential rather than linear (which is the gist I'm getting,) than you would indeed hit an equilibrium point sooner or later, as you say - as long as the barrel can handle very high temperatures. Now I see what bigbombr was driving at - in real life, metals lose a lot of their structural strength as they're heated, whereas CoADE's model ignores that effect till the point of actual failure. So we can build guns with barrels that are heated to just under their melting point, and instead of bending or bursting like a real weapon would, they just reap the benefits of much more efficient heat radiation. I didn't give qswitched enough credit then, his model is considering thermodynamics, it's simply not complete yet. Of course that raises the issue of how to model this; again as bigbombr points out, ignoring this effect is present in the whole game. The basic dynamic relationship shouldn't be too hard to model (modify effective strength of <part> by temps its exposed to before doing the <forces involved> vs. <part strength> check,) but having good data to work with on that would be. Steel in all its varieties won't be an issue, simply because modern industry has worked with it so extensively in engineering applications - you could probably find the heat/strength curves on Google Scholar in short order - but more exotic materiel is a different matter. A lot of that stuff (like the various carbons/ceramics) do not lose structural strength when they heat up, (I think?) which would make them more in those high-temp applications. It'd be more challenging to implement however, because it'd play merry hell with module design, and that's a core of the game and the User Experience; it becomes a lot harder to isolate variable A to play with the sliders on variable B, when variable A and B both affect one another in a feedback loop. Every tweak in a rocket engine design would see your turbopump throwing error messages for either melting or bursting as temps and pressures change, for instance. Solving the UI feedback question is probably the thornier issue.
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Post by Rocket Witch on May 2, 2017 19:10:57 GMT
Oooh, no kidding? I presume that's the same physical affect that makes radiators vastly more effective the hotter the coolant temperature is, then? What's the name of the effect or law that causes this? I'm curious. Indeed it is. Stefan-Boltzmann law; "the total energy radiated per unit surface area of a black body across all wavelengths per unit time is directly proportional to the fourth power of the black body's thermodynamic temperature."
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Post by Enderminion on May 2, 2017 19:14:24 GMT
I don't know enough science yet to answer that question, I would have said something about blackbody radiation
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Post by dragonkid11 on May 3, 2017 0:39:34 GMT
I'm still not supporting making material strength dependent on temperature.
For one, it make making new module from abeit difficult to literally a fucking engineering task.
It's gonna drive a lot of new player away just from how awfully hard it would be, exponentially so than the current system.
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ndeo
Junior Member
It's not a flashlight... It's a High-frequency relativistic boson cannon
Posts: 67
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Post by ndeo on May 3, 2017 3:11:36 GMT
I'm still not supporting making material strength dependent on temperature. For one, it make making new module from abeit difficult to literally a fucking engineering task. It's gonna drive a lot of new player away just from how awfully hard it would be, exponentially so than the current system. Well considering CoaDE is going for realism I don't see why it's an issue. The barrier of entry for your average gamer is already moderately high so raising it a bit isnt going to do much. Material strength dependant on temperature would just be yet another error message to worry about for us anyway not unlike beam deflection stress etc., and means that more reason to use red-hard materials or different materials for different goals instead of a one module/material fits all roles
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Post by Enderminion on May 3, 2017 3:23:37 GMT
a lot of ceramics fuction fine white-hot (tantaium hafnium carbide) but when you cool them (or heat them up) thermal expansion wreaks havoc, basicly instead of using boron at lower temps we would only use diamond thermal rockets
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Post by kaiserwilhelm on May 4, 2017 18:25:13 GMT
a lot of ceramics fuction fine white-hot (tantaium hafnium carbide) but when you cool them (or heat them up) thermal expansion wreaks havoc, basicly instead of using boron at lower temps we would only use diamond thermal rockets I refuse to belive that BORON will not always be the ultimate answer. Also all hail Boron.
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