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Rail Technology
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Old 03 May 2009, 16:21   #1 (permalink)
Shas'Vre
 
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Default Rail Technology

I've heard a lot about Railguns, Rail Rifles, and even rumours about Railpistols.
Here is what I know/have deduced about Rail Technology.

The Hammerhead railgun is a remarkable piece of physics (Yes I know it's not real, but us modern day humans do have Rail-weapons at present).

Many people have said that the Hammerhead Railgun would be far too small, and would do no more damage than punching the target. The only reason the modern day Railguns are so huge (around 30m) is because they are firing projectiles that weight about 750g, thats 500 times more than the Hammerhead's bullet (which is a tungsten slug in a nickel-cobalt casing).

The Tungsten bullet leaves the barrel after being accelerated to 99% of the speed of light by superconductive magnets. 99% of the speed of light is 297,000,000 m/s, or 668,250,000 mph. Nice. This means it has a momentum of 445,500 kgm/s: That's has the same momentum as a Shelby GT500 travelling at just under 600 mph.
The amount of reactant force this produces would probably be enough to push the Hammerhead back a long way, but we can assume that Tau have mastered recoil dampening.
Also the amount of magnets required would probably mean that the barrel would have to be dozens of metres long, but we could also assume that the Tau have access to much more efficient and powerful magnets than us.


So, what are your views on Rail technology, both in the 40k Universe and today?



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Old 03 May 2009, 16:38   #2 (permalink)
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Default Re: Rail Technology

I would like to say "who cares as long as it can kill stuffs for the greater good". But yeah, that is kind of rude.

Any source states that Tau Railgun fires Tungsten ammunition? I don't see any mention on that in my codex.
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Old 03 May 2009, 16:39   #3 (permalink)
Shas'El
 
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Default Re: Rail Technology

Is there anything in paricular you want to know, or is this just a random discussion?

Quote:
Originally Posted by LordZanuu

Many people have said that the Hammerhead Railgun would be far too small, and would do no more damage than punching the target.
I have to disagree with anyone who says this, the Tau are very technologically advanced, I don't find it that hard to believe that they'd have a strong enough power source. Though to be honest, it is a fools errand to apply today's logic to 40k, it is after all a world where monsters from another dimension kill people for the twisted pleasure they get from doing it :P

Quote:
Originally Posted by LordZanuu

So, what are your views on Rail technology, both in the 40k Universe and today?
If you want to talk about the modern day, you have the wrong board Unless what you intend with this thread is to compare the modern day to 40k (Oh wait, I said that that was stupid earlier didn't I? :P
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Old 03 May 2009, 18:06   #4 (permalink)
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Default Re: Rail Technology

I think that one thing that would prove many of the people wrong who think that it is underpowered is air. Something traveling through air at almost the speed of light would generate an incredible amount of friction. The effect would end up being similar to space shuttle re-entering atmosphere and meteors burning up in the sky. The extreme heat of this object combined with its extreme momentum would probably produce the effect referenced in the codex.
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Old 03 May 2009, 18:07   #5 (permalink)
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Default Re: Rail Technology

I think that if the tau where a real race in our universe and a hammerhead is what we had to face. i'd surrender without a second thought.

Tau are very technologically advanced, as their fluff states. so i would also assume that they would improve systems to account for re-coil and energy usage. by my understanding of physics (A Level), i wouldn't want to be the target if you know what i mean.

Warhammer isn't the only game to involve Railguns. MGS 1 and 2 had railguns in them, the first had it for display while the second you had to survive a non-stop bombardment from a woman who couldn't be hurt by anything.

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don't be so harsh. If someone wants to compare Sci-Fi with Sci-Fact, let them. it isn't going to kill you.
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Old 03 May 2009, 19:26   #6 (permalink)
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Default Re: Rail Technology

There is one highly flawed assumption that you've stated and that I see far too often. That is in the speed of the projectile. 99% of light speed is flat-out not possible for several reasons:

1) The slug itself would become apprx. 12 times heavier at that velocity
2) It takes several hundred quads of power to do it (for reference, 4 quads runs all of humanity's current needs for a year)
3) Action-reaction would mean the recoil would either send the tank/suit flying halfway across the solar system or disrupt the rotation of the planet you're on, depending on how securely you're fastened to said planet.

The tau linear accelerators use a rail weapon that's long enough, given the tech advance, to shoot the slug to right around Mach 50 or so, which is PLENTY fast enough to do what it is described as doing. Current rail weaponry shoots a projectile at around Mach 12.
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Old 03 May 2009, 20:11   #7 (permalink)
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Default Re: Rail Technology

Quote:
Originally Posted by PsyBomb
3) Action-reaction would mean the recoil would either send the tank/suit flying halfway across the solar system or disrupt the rotation of the planet you're on, depending on how securely you're fastened to said planet.
*laughs like a loon* the idea of a braodside flying acros the Damocles gulf just seems so funny to me. how much bad luck would you need for that to happen?

But you're kinda on the right track about the momentum change. to make the total momentum of the projectile and the tank = 0. the projectile and the tank would have to have equal and opposite momentum. BUT. the tank will have more mass and so will be acelerated to a solower velocity.

think of it as a shotgun in your armpit. when you fire that small cartidge, the tiny metal fragments are traveling uber fast, but your arm isn't jerked back at a similar speed because your entire body is used to conter-act the pellets momentum. meaning the velocity at which you're thrown back isn't as fast as the bullet shot forward.

make sense?

Quote:
Originally Posted by PsyBomb
1) The slug itself would become apprx. 12 times heavier at that velocity
that would be true if Tau were just pumping energy into the projectile. your statment is essentially refering to E=mc^2 rule.

this is simplely aceleration at its fastest.

Quote:
Originally Posted by PsyBomb
2) It takes several hundred quads of power to do it (for reference, 4 quads runs all of humanity's current needs for a year)
ok i can see where you're coming from with this statement.
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Old 03 May 2009, 22:43   #8 (permalink)
Shas'El
 
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Default Re: Rail Technology

Quote:
Originally Posted by Buster Sword
@Mr X
don't be so harsh. If someone wants to compare Sci-Fi with Sci-Fact, let them. it isn't going to kill you.
Except that Science fiction often has little to do with science fact (the key word being "Fiction"- someone has made it up.)

I wasn't trying to be harsh, so please allow me to expand a little, it annoys me when somebody points at fiction and says "ha, that's wrong",

I'm just saying that Tau are probably so technologically advanced that they have discovered many things about this technology that we haven't, so its fair to assume that comparing it with what we do know and saying that it shouldn't work is pointless, you want to know why? Read some Tau background, doesn't matter what anyone says because in the fluff rail technology does work, and for that reason (because that's all you really need in a fictitious universe- the writer saying that it should), it works. Its impossible to explain because the whole idea of the Tau making it work is that they know things that we currently don't.

What I'm basically saying is, you can point out "flaws" all you like, the point is that it does work.

I don't mind discussions like this in the slightest, in fact I'm interested to see how the Tau might go about making it work, so long as no-one tries to suggest that it doesn't work when what they actually mean is that we today don't have the technology to make it work.
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Old 03 May 2009, 23:11   #9 (permalink)
Shas'O
 
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Default Re: Rail Technology

I agree the physics presented is all fantasy.

If we assume that a Tau projectile weights 750g (seriously that's about a bag of sugar or a small bottel of water in weight. Then it's kinetic energy will be given by;

1/2 mv[sup]2[/sup], as you can see the velocity is the important factor here.

Hence let's do some physics!!!

Now assumption. Tau railguns use a system whereby the projectile is propelled by a current carrying plasma, maintained by whatever 'force field' technology that the Tau use (because there are massive gaps in Tau Hammerhead railguns (the railrifles might not go to this scale of complexity and simply use the firing tube to contain it.

Magnetic field strength is proportional to two factors, the current flowing in a conductor (or through free space) and the distance from that conductor. If we make the assumption that tge railgun constitutes two rather long straight conductors then we can use;

B = [mu][sub]0[/sub]I / 2[pi]r

Where r is the perpendicular displacement of a point in the field from the conductor, and I is the current flowing through it and mu is just some constant of proportionality called the permeability of free space.

There are two rails in this combination, hence we use the superposition of fields theorem to state that;

B[sub]T[/sub] = B[sub]1[/sub] + B[sub]2[/sub]

As the current is flowing in a loop;

---------------------------------------------------->
. A |
v
<--------------------------------------

Then from Flemings law of the orthogonal nature of magnetic fields to the current that produces them then, the vector sum of the two fields is positive rather than negative. Hence the total magnetic field generated by the current flowing in the loop at some point I have called A will be given;


B = [mu][sub]0[/sub]I / [pi]r

And will be directed in a direction into your computer screen from where you are sitting. r here will now be the total separation distance between the two wires.

Again using Flemings law F=BIL where F is force in Newtons, and L is the length of a conductor in the magnetic field in meters. We can see that r = L for a conductor spanning both rails (i.e. the plasma). So the total force on the projectile is given;

F = [mu][sub]0[/sub]I[sup]2[/sup] / [pi]

So current production is now our most important factor.

Using F=ma now, we can find an expression for the acceleration of the projectile down the railguns barrel.

a = [mu][sub]0[/sub]I[sup]2[/sup] / m[pi]

So we don't really want that large a projectile mass.

Assuming a linear acceleration curve (hence we are going to ignore the inductive property of the build in magnetic field and assume that the current wave is of a square nature).

v[sup]2[/sup] = u[sup]2[/sup] + 2as

Where the initial velocity is 0 and s is the length of the railgun barrel. We find that the overall formula at perfect efficiency for this scenario (muzzle velocity) is given;

v = sqrt( 2s[mu][sub]0[/sub]I[sup]2[/sup] / m[pi] )

to find the kinetic energy;

KE = s[mu][sub]0[/sub]I[sup]2[/sup] / [pi]

Stolen from wikipedia;
Quote:
As a typical example, the American General Dynamics KEW-A1 has a muzzle velocity of 1,740 m/s (5,700 ft/s).
This is a Sabot tank shell, at roughly 4kg in mass. Hence let's find how much current needs to flow in the railgun for it to have the same capacity as a normal tank round;

KE[sub]Shell[/sub] = 1/2 4 1740[sup]2[/sup] = 6x10[sup]6[/sup]J

Let this equal the formula from before;

s[mu][sub]0[/sub]I[sup]2[/sup] / [pi] = 6x10[sup]6[/sup]J

Make a 6m approximation for the barrel length

I turns out numerically to be: 1.6x10[sup]6[/sup] Amps. Well that is rather large eh? But possibility practical, you just need a way to store a massive charge somewhere (in a capacitor bank) and discharge it very quickly through the rails.

Now of course your spacing of the rails needs to be such that an electric breakdown can occur so close spacing is a must, you also want the current to peak quickly and stay high for the duration of the projects transit down the barrel. Hence tuning the inductance of the gun is very important, and finally you want to adjust the parameters for optimum performace.

Well now you can go calculate your perfect railgun. I hope this has been informative. If your interested the law for the long wires comes from Biot and Savant, and involves some calculus, so if you wanted to compare linear railguns against coilguns, then you need to take a line integral for the number of circular coils. Interestingly, coilguns far out perform railguns at the small scale. I have personally built one that can embed a nail in my skin and is fed off a small 9v battery. Multiply that by three, and you have something that could be classed as a dangerous firearm. The trouble is that the peak field is at the center of the coil, and coils are limited by the crossection of wire, and the current that can pass through it. Hence while they are better the laws of scaling let them down.

Anyhow I'm waffling now...
Gen

EDIT:
What I'm basically saying is, you can point out "flaws" all you like, the point is that it does work.

The point is it doesn't work as the laws of physics do not allow it to... We know a hell of a lot about how railguns work, the theory is good and strong. The trouble is the physical practicallities of building the machine. The Tau have just perfected it to a point whereby it can be used in the millitary.

Mankind doesn't need railguns planetside, because unfortunatly chemical explosive is still a better option until we have got to the stage where we can replace conventional arms with better.

The interesting thing about comparing fiction with reality is it allows you to explore what ideas are plausible and those which are just 'magic'. For instance if we take CAP troopers from Starship Troopers. The entire idea is perfectly physically possible. Sure it would cost about 300,000 to build a CAP without all the instrumentation, so each drop would be expensive, but it would be almost the perfect paratrooper attack, as most SAM attacks would not be able to even target you, you travel too fast for most systems and your on the ground about as fast as a HALO jump. So it will be (in my opinion) a millitary tactic that will come to be used.

Another example comes from another novel, but I've forgotten it's name. Anyhow after the novel was written a set of engineers did a study into exactly how mankind would fight in space. As the idea put forth in the novel was that we humans would use satilites as 'intelligant mines' that would sit in space on odd orbits with really low radar cross sections untill they passivly picked up another satilite and fire on it.

At which point it lights up to everybody, hence it has very little chance of escape from counter attack, and would most probally die, hence they would have a lifespan of 2-5 attacks. Attacking would be cluster shots of ball bearings, blanketing an area of several thousands of cubic km at ranges of 100s of millions of km. After an attack takes place it would be hours/days/ even months before the projectiles hit, but course corrections in space are expensive for any ship (in terms of fuel), hence they would be 'destined' to die, unless by accident they had a 'hole' in the scatter of projectiles coming their way.

All these ideas were discussed in the novel and proved to be both resonable, and physically accurate. Finally you have A.C Clarks GEO idea, while not in fiction strictly, the idea of asking questions, then applying some science can get you rather useful ideas;

http://lakdiva.org/clarke/1945ww/194...t_305-308.html

Gen
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Old 04 May 2009, 00:00   #10 (permalink)
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Default Re: Rail Technology

Whoa there people... a few things I feel I have to say as a weapons engineer, designer and a man who has built his own hunting rail gun (but doesn't have the strength to lift it, much less shoot it).

1. at Genmotty What in the hell, I thought the upper theoretical limit to Chemical Propellant based weapons was 1500 M/s, Is it just a giant ridiculously small caliber sabot in a giant caliber barrel or a rocket assisted round, I can't find any info on it.

2. Railguns work on the principal of Inducing a magnetic field in a ferro magnetic projectile. Current designs require either large capacitors. So large in fact that they're unfeasible as real weapons. OR they require superconducting materials to concentrate the energy into the projectile itself by way of ... I think it's gauss's laws, Could be Kirchoff's laws though. My design uses the large capacitor bank and I've only been able to get velocities of about 100m/s with a 70 gr projectile. So don't start thinking of these things as ultra powerful because they are not an end all to anti-tank weapons. They only offer the potential for high efficiency. The hyper velocity offers only increased accuracy and range. While the kenetic energy penetrator will be outclassed by it's rail cousins, the primary tank killer will remain, and will forever remain THE SHAPED CHARGE. (all hail the great Munroe, and Nuemann I guess... well mostly just Nuemann)

3. Feasible railguns aren't so far into our future the navy is looking at incorporating some for long range bombardment sometime within the next 20 years.

4. Don't take 40k physics into real equations, it's like dividing by 0. you can't do it.

5. Because I know someones going to do it, and it's my pet peeve. Don't under any circumstances call it a gauss rifle, the two are entirely different and the only thing they have in common is that they use electricity to accelerate projectiles.

End rant.
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