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-   -   ULTRATECH guass weapon system design rules? (http://forums.sjgames.com/showthread.php?t=156351)

AlexanderHowl 03-09-2018 08:18 AM

Re: ULTRATECH guass weapon system design rules?
 
Titanium possesses a higher friction coefficient and a lower heat capacity though, and it burns in an oxygen atmosphere. At the energy levels of a man portable railgun, a titanium armature will ignite. Of course, you can have titanium as the support structure, just as long as it does not contact the round you should be fine (a railgun made from bronze and titanium would actually be quite beautiful).

Fred Brackin 03-09-2018 08:46 AM

Re: ULTRATECH guass weapon system design rules?
 
Quote:

Originally Posted by hal (Post 2163948)
Hello Folks,
Does anyone have a design system they've been using for use with describing the ultratech guass weapons?

Using Doug's spreadsheet formulas - I get a 442.9 grain (28.7 grams) bullet moving at 2650 feet per second,

Note that contrary to much of the later posts at this quite modest performance regime railguns that are in danger of melting themselves are not necessary. It wouldn't be that hard to achieve with cordite much less more modern powders.

For this ballistic profile I would expect instead of railguns that a "contactless coilgun" would be used instead. Such a weapon has no friction issues.

Or propellant issues either. Much of the fire and fury seen in prototype railguns comes from the plasma arc that travels along the rails and pushes the projectile forward.

The advantages of the coilgun over a conventional chemical propellant weapon of similar output would be the relative lack of thermal signature and less recoil due to no mass of propellant gasses. 30-40% less recoil.

A sabot might be useful if the actual projectile is poorly conductive but that sabot itself would be chosen for electrical conductivity. Plastics are improbable.

Any field-ready EM gun would be TL9. We are very close (probably) to the end of TL8 and no one has a deployable weapon yet. I have no idea why a Chinese version would be definitive. They are generally several years behind the Western defense/aerospace establishment in any area except press releases.

DouglasCole 03-09-2018 11:48 AM

Re: ULTRATECH guass weapon system design rules?
 
Quote:

Originally Posted by Fred Brackin (Post 2164103)
Note that contrary to much of the later posts at this quite modest performance regime railguns that are in danger of melting themselves are not necessary. It wouldn't be that hard to achieve with cordite much less more modern powders.

This is a 15% velocity boost on a .416 Rigby cartridge, for example. One could probably work up this load in a jiffy and maybe not even break anything. Well, except maybe your shoulder.

hal 03-09-2018 01:15 PM

Re: ULTRATECH guass weapon system design rules?
 
Some of what I'm reading is that the energy required to send the projectile moving isn't 100% efficient. In other posts, I think I came across the figure that David Pulver was using 25% efficient. So, if the figure (say, 400 joules) were to be required to get a projectile moving, presumably, the applied energy is closer to 1600 joules - no?

If so, what happens to the remaining 1200 joules applied to the process?

If the projectile is jacketed Tungsten or depleted uranium for instance, then you'd get the mass with the relatively small volume. If using a dart form, then you're dealing with out having to spin the projectile for stability purposes. Right now, I'm just trying to keep things reasonable so that anything that I want to use in game, has some reasonable structure behind it. What I miss the most about the GURPS VEHICLES 2nd edition rules were the weapon design rules. If I'm going to have gauss pistols, or gauss submachine guns, or what have you - I'd like to be able to craft something that makes sense.

Back when I created stats for the Cohen Battle Tank, using a rail gun cannon system, I also created battle suits along with a battle suit taxi (think battle taxi but for battle suits) along with what I called the integrated combat team system.

Long story short - the tank contained the main battle computer, and was a network node for all of the battlesuits assigned to work with the tank as a team. The gatling gauss and the Heavy Automatic Gauss Gun (HAGG) had definite roles in the concept, and it was FUN designing the weapon systems for what I called the Narco-Terrorist War set in Columbia in the near future.

Problem is - there has never been any real conversion system between the older "Classic" GURPS and the newer 4e GURPS. The design system modifications are all ad-hoc with no real foundation one way or another.

Now Doug did write the Pyramid Article Interior and Terminal Ballistics for GURPS a while back (back in 2002). He also provided us all with his spreadsheet for estimating damages for weapons based on actual physical world data. So, there seems to be little reason not to try and determine the following:

How much energy from a power cell is required to send a round flying towards its target (that determines how many shots per cell is required). There is nothing to keep us from determining how fast the projectile is travelling (Muzzle velocity) nor diameter of bullet nor its mass.

In reality? The only thing missing from the design sequence is how much material goes into the rest of the gun proper, and how much it costs.

So, if we're really talking about a weapon that requires roughly four times the actual energy in joules produced by the gun's handling characteristics - then knowing the muzzle velocity in joules for a 5mm round with a given mass - let's us say how many shots from what power cell, how much damage it does, half damage range, max damage range etc. Determining acc or recoil or what have you seems to be the other "seat of the pants" stuff or ad-hoc stuff that I wish didn't have to be pulled out of thin air. Then again? Until we see the vehicle design system, or a weapons design system comparable to what I'm seeing for armor design - but for weapons, we'll just never have those tools.

:(

Maybe the Vehicle Design System will never see the light of day. If so, then those of us who want a little more differentiation in weapons are either going to give up or make up their own system. Before GURPS HIGH TECH firs edition came out, I remember using the AFTERMATH! system for gun design. It worked out ok, but I liked it even better when GURPS VEHICLES 2nd edition came out. ;)

On that note... I'll catch you guys a bit later.

Anthony 03-09-2018 01:23 PM

Re: ULTRATECH guass weapon system design rules?
 
Quote:

Originally Posted by hal (Post 2164161)
Some of what I'm reading is that the energy required to send the projectile moving isn't 100% efficient. In other posts, I think I came across the figure that David Pulver was using 25% efficient.

I don't think an efficiency number has ever been given for gauss weapons (and 25% seems low), but it's a realistic estimate for conventional firearms.
Quote:

Originally Posted by hal (Post 2164161)
If so, what happens to the remaining 1200 joules applied to the process?

Heat, noise, escaping propellant (for conventional guns), escaping magnetic pulse (for EM guns). A tiny amount (usually less than 1%) goes into recoil.

starslayer 03-09-2018 02:25 PM

Re: ULTRATECH guass weapon system design rules?
 
An important thing to consider in this discussion:

Gauss != Rail.

A railgun (so called because of the linear rails) accelerates due to lorentez force, you put a tremendous difference of voltage on rail A and Rail B, and the arcing through the projectile causes the projectile to move forward. Much like how in a jacob's ladder the arc will happily climb up between the two antennas, but much faster and carrying a projectile.

You radically increase efficiency by shortening the arc distance required, so ideally you want the projectile touching the rails, and this actually reduces heat (open arcs = arc welder running on the inside of your railgun). Using any kind of sleeve or sabot would be bad as most low friction materials are also high insulating (teflon, etc), and you want to encourage the arc, not resist it. Bronze is about as close to ideal as possible because it has a low friction coefficient, is soft, AND is conductive.


In a gauss weapon you are using multiple magnetic rings to accelerate your projectile, each ring pulls the object one more 'click' forward until it exits the barrel. Closer is better for magnetic transference, but the ultimate loss from having an air gap is actually quite minimal. You can also use an ultra low friction sleeve or sabot (or both) on the projectile, as long as the magnetic force (gauss) can reach the projectile all is well. As a downside you need VERY sophisticated electronic controls to manage the magnetic activation. An ideal gauss weapon would balance the magnetic forces to actually levitate the projectile in a tiny air gap in the middle of the barrel.

Humabout 03-09-2018 04:16 PM

Re: ULTRATECH guass weapon system design rules?
 
Quote:

Originally Posted by AlexanderHowl (Post 2164099)
Titanium possesses a higher friction coefficient and a lower heat capacity though, and it burns in an oxygen atmosphere. At the energy levels of a man portable railgun, a titanium armature will ignite. Of course, you can have titanium as the support structure, just as long as it does not contact the round you should be fine (a railgun made from bronze and titanium would actually be quite beautiful).

There is no reason to use a metal at all. Titanium was simply listed as one of many materials that have lower thermal conductivity than bronze. Personally, i'd look at ferromagnetic ceramics.

AlexanderHowl 03-09-2018 04:24 PM

Re: ULTRATECH guass weapon system design rules?
 
1200 J is not a lot of energy though (three hundred milligrams of sugar possesses that much chemical energy). If you are talking about a 25% efficiency, that means the projectile possesses on 400 J, which is less than the energy of a 9mm. If you want a powerful weapon, the equivalent of a .50 BMG, you need a minimum of 18,000 J, which would mean that you would have 54,000 J of wasted energy at 25% efficient (you could actually reach 50% efficiency using a bronze railgun due to the low friction coefficient, though you would still have to deal with 18,000 J of wasted energy).

If we assume a 25% efficiency though and that 2/3 of the waste energy is heat from friction, that ends up being 36,000 J of heat for a .50 BMG equivalent (18,000 J for the bullet and 18,000 J for the armature). The problem is that the heat is being created on the magnetic armature, and the armature will lose magnetism if is not allowed to cool down. A 2 kilogram armature with a generic specific heat of 450 J/K/kg will heat up by 20 K every shot, meaning that you will lose magnetism within a few shots if you fire more than once every few seconds (using the same assumptions, the 50 gram bullet will gain 800 K).

Rupert 03-09-2018 06:10 PM

Re: ULTRATECH guass weapon system design rules?
 
Quote:

Originally Posted by DouglasCole (Post 2164139)
This is a 15% velocity boost on a .416 Rigby cartridge, for example. One could probably work up this load in a jiffy and maybe not even break anything. Well, except maybe your shoulder.

It's only 6% more energetic than a standard .416 Weatherby Magnum load. A .460 Weatherby would out-recoil it quite handily.

starslayer 03-09-2018 06:25 PM

Re: ULTRATECH guass weapon system design rules?
 
Quote:

Originally Posted by AlexanderHowl (Post 2164217)
1200 J is not a lot of energy though (three hundred milligrams of sugar possesses that much chemical energy). If you are talking about a 25% efficiency, that means the projectile possesses on 400 J, which is less than the energy of a 9mm. If you want a powerful weapon, the equivalent of a .50 BMG, you need a minimum of 18,000 J, which would mean that you would have 54,000 J of wasted energy at 25% efficient (you could actually reach 50% efficiency using a bronze railgun due to the low friction coefficient, though you would still have to deal with 18,000 J of wasted energy).

If we assume a 25% efficiency though and that 2/3 of the waste energy is heat from friction, that ends up being 36,000 J of heat for a .50 BMG equivalent (18,000 J for the bullet and 18,000 J for the armature). The problem is that the heat is being created on the magnetic armature, and the armature will lose magnetism if is not allowed to cool down. A 2 kilogram armature with a generic specific heat of 450 J/K/kg will heat up by 20 K every shot, meaning that you will lose magnetism within a few shots if you fire more than once every few seconds (using the same assumptions, the 50 gram bullet will gain 800 K).

This is not quite as horrible as it seems on the surface

This is only if the armatures have no:
Active cooling
Heat sinking
Other methods for dealing with heat.

Further as the barrel heats up the more heat that the projectile will absorbe.

Again we are getting gauss and rail confused as the 'same type of weapon'. Rail won't care if it heats up enough to loose magnetic coefficiency, it propels via lorentez force, not inherit magnetisim (It will care that resistance increases, but that is an entirely different temperature scale that will allow a much more significant temperature delta for faster radiation, of course being that amateur science projects can melt copper rails in a lab setting using no more than wall power and some capacitors that may be moot.).

Gauss by comparison will actually IMPROVE in efficiency as the coils heat up (It is unlikely that any sort of gauss weapon will use permanent magnets since the goal is to selectively subject the projectile to magnetic force then turn it off, 'toy' gauss gun demonstrations today that use permanent magnets do so because the software for electromagnet control is really hard to get right).[1]

[1] https://www.omicsonline.org/open-acc....php?aid=75409


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