Railguns
mi...@maple.sover.net
possible, can anyone tell me how to construct one, or some other device that
will launch metal items at high velocity electromagnetically?
Michael John Charles Boehm
Railguns are not just possible, they exist- in the laboratory, however.
The principle is actually rather simple- you line up a bunch of toroidal
electromagnets and have them seitch between positive and negative in a
carefully (i.e., computer controlled) synchronized pattern. Any metallic-
or, so I hear, in some cases non-metallic- object will be accelerated by
the force of the electromagnets. Projectile velocities in the range of a
rifle bullet (or even higher) can be achieved.
There are two major drawbacks to this system. the first is that it
requires a huge power supply. As such, a man-portable railgun is probably
a long way off. However, a railgun for a tank or a ship is technically
possible. This would result in smaller, lighter ammo with the same punch,
since no gunpowder propellant charge is needed; therefore, more ammo could
be carried and a faster rate of fire could be achieved. Also, since no
explosions will be going off inside the turret (to propel the shell, you
see), there will be less wear and tear on the gun (and the crew).
That brings us to the second problem- emissions.
Every time you generate an electromagnetic field of the strength required
to launch a projectile, you create a gigantic electromagnetic signature
that can be detected from very far away. In an era where "stealth"
technology is becoming more important, this is a serious drawback.
Nevertheless, there are developments in this field. The US Navy is
considering replacing the steam catapults on their carriers with
electromagnetic catapults. This will take up less room and weigh several
hundred tons less. also it will create a "smoother" launch than a steam
catapult does, thus reducing the wear and tear on the aircraft (and the
pilots as well). I suppse the Navy figures a carrier is so big a target a
bit larger EM signiature is an acceptable trade-off.
I don't know any more of the actual physics than what I've listed here,
so if anyone else out there knows more about the topic, feel free to post.
-Michael Boehm
gt2...@prism.gatech.edu
--
Michael John Charles Boehm
Georgia Institute of Technology, Atlanta Georgia, 30332
uucp: ...!{decvax,hplabs,ncar,purdue,rutgers}!gatech!prism!gt2995b
Internet: gt2...@prism.gatech.edu
FolsomMan
>In article <Pine.BSD/.3.91.9506101551...@maple.sover.net
>> mi...@maple.sover.net writes:
>>Do railguns really exist or are are they just science fiction? If they
are
>>possible, can anyone tell me how to construct one, or some other device
that
>>will launch metal items at high velocity electromagnetically?
>Railguns are not just possible, they exist- in the laboratory, however.
>The principle is actually rather simple- you line up a bunch of toroidal
>electromagnets and have them seitch between positive and negative in a
>carefully (i.e., computer controlled) synchronized pattern.
...
That's not a railgun. A railgun has two rails and a sliding armature that
makes contact between the rails. A humongous current runs up one rail,
through the armature and down the other rail. The magnetic field of the
rails, interacting with the current in the armature, expels the armature.
Pulse generation and switching are very difficult. The mechanical and
thermal demands on the rails are hellish. You will need a lot of time and
money to make a good rail gun.
Mark Folsom
Paul Johnson
> In article <Pine.BSD/.3.91.9506101551...@maple.sover.net
> > mi...@maple.sover.net writes:
> >Do railguns really exist or are are they just science fiction? If they are
> >possible, can anyone tell me how to construct one, or some other device that
> >will launch metal items at high velocity electromagnetically?
> >
> Railguns are not just possible, they exist- in the laboratory, however.
> The principle is actually rather simple- you line up a bunch of toroidal
> electromagnets and have them seitch between positive and negative in a
> carefully (i.e., computer controlled) synchronized pattern. Any metallic-
> or, so I hear, in some cases non-metallic- object will be accelerated by
> the force of the electromagnets. Projectile velocities in the range of a
> rifle bullet (or even higher) can be achieved.
No. This is a coilgun. A railgun is slightly different.
The gun consists of two parallel conductors. The projectile is
mounted as a cross-bar short-circuiting the two conductors. The gun
is fired by putting a mega-amp pulse in one conductor and out of the
other, connected to the *end* of the gun.
Here is how it works (if I have it right):
Say the left hand conductor is positive. As you look down the gun the
left hand conductor will have an anti-clockwise magnetic field, and
the right hand conductor will have a clockwise magnetic field. So
between the conductors the field direction will be upwards, like this:
<- ->
^
| O | O |
V ^ V
-> <-
The two "O"s are the conductors, and the arrows show the direction of
the magnetic field. Note that this is *not* the direction that a lump
of iron will move when placed in this field. Its the direction that a
compass will point.
If we now add the cross-bar, then we have charge moving from left to
right, at right angles to the magnetic field. To work out what
happens, hold your left hand with the thumb pointing up, the first
finger pointing forwards, and the second finger pointing to your
right. The thumb and two fingers stand for, in order, Motion, Field
and Current (conventional). UK readers may remember this as
Manchester Football Club. We have a field pointing upwards and
current from left to right. If you twist your hand to the appropriate
direction your thumb (motion) will be pointing towards you. So that
is the direction the projectile will move.
The problem with railguns is that the conductors are big, expensive,
and only good for one shot. The pulse of current tends to melt them.
Perhaps someone who knows more than me could post some numbers for
currents, forces, efficiency etc.
--
Paul Johnson | GEC-Marconi Ltd is not responsible for my opinions. |
+44 1245 473331 ext 2245+-----------+-----------------------------------------+
Work: <paul.j...@gmrc.gecm.com> | You are lost in a twisty maze of little
Home: <Pa...@treetop.demon.co.uk> | standards, all different.
Michael John Charles Boehm
>No. This is a coilgun. A railgun is slightly different.
Coilgun? First time I've heard it called that, but I guess it makes sense.
The reason I described it that way was because I saw a working model of this
in a lab at U. C. Berkeley and they called it a "railgun" there. But I
guess you need a rail to have a railgun, right? :)
>If we now add the cross-bar, then we have charge moving from left to
>right, at right angles to the magnetic field. To work out what
>happens, hold your left hand with the thumb pointing up, the first
>finger pointing forwards, and the second finger pointing to your
>right. The thumb and two fingers stand for, in order, Motion, Field
>and Current (conventional). UK readers may remember this as
>Manchester Football Club.
Argh! The dreaded "left hand rule!" I remember that from back in my
undergraduate years! It was painful.
>The problem with railguns is that the conductors are big, expensive,
>and only good for one shot. The pulse of current tends to melt them.
Say, do you think the new (i.e., since 1986) Yttrium-Barium-Copper Oxide
superconducting magnets could have useful applications in this field?
You'd need an LN cooling system, but the pulse wouldn't generate
significant amounts of heat then. I'm sure DoD researchers thought
of this years ago, I was just looking for an opinion.
ste...@rain.org
velocity of 27ft/sec. Used about 80 pounds of capacitors to get 2/3
farad. Efficiency of the whole system: 1/10 of 1 per cent. Not much to
write home about, but it really scares the horses if there's a loose wire
in the system: lotsa sparks and loud noises.
One of the lurkers at sci.physics.electromag is the current
(ha-ha) head of the electromagnetic armaments division of the US Army.
He's got a homepage with lotsa abstracts and much other useful
information. try: http://k-whiner.pica.army.mil/ (I think that's right).
Another place to look is at the Survival Research Laboratories
homepage. These folks have acquired a surplus railgun which they
occasionally trundle out and fire at various venues in the Bay Area, at
their impromptu events... Homepage: http://canuck.com.Srl/srl.html
For more info. I write a newsletter for amateur scientists in my
area and I wrote up some of the findings from building the coilgun,
including equations to calculate muzzle velocity, using a stopwatch and
some other handy stuff. Send me a snail-mail address and I'll stick one
in the mail for whoever wants it. No charge, no spam: information is a
river, let's keep it flowing...
--
"Steamboat Ed" Haas : Co-founder of the
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