Author Topic: Railguns (Read 517 times)

davidpt40 · « **on:** March 31, 2003, 06:03:56 AM »

I remember watching a tv show about railguns a few years ago. By railguns I am referring to projectiles fired electromagnetically. They said that this new technology would allow tanks to fire projectiles 50 to 100 times faster (in velocity) than they do now. However, I havent heard much about this in the past few years. Is research still on going for railguns?

majic · « **Reply #1 on:** March 31, 2003, 07:56:22 AM »

It is, but the sticking point as I understand it is the power source. It takes alot of electricity to work.

EDIT: Last I heard, the smallest practical generator they have is about the size of my living room.

Saurdaukar · « **Reply #2 on:** March 31, 2003, 08:46:34 AM »

Aye - I think at this point the size of the genrators needed would make the weapon more suitable to a small cruiser than a tank - but it will come.

Rino · « **Reply #3 on:** March 31, 2003, 11:32:43 AM »

This is going back a few years, but a friend of mine worked
at Picatinny Arsenal in NJ, home of artillery R&D for the US Army.

They were working on an alternator based rail gun to be
mounted in a tank chassis. The reason being is that you could
spool up the alternator very quickly by linking it to a turbine
engine. An added bonus is that you wouldn't have all that
potential energy sitting around if you got hit like you would if
you used batteries.

I have no idea about the success or progress of the project
as A: I don't have clearance, and B: my friend retired a while
back and so is no longer in the loop.

As armor warfare seems to be taking a bit of a backseat now
engagement>, it's very possible the program was cancelled.

Rino

Mini D · « **Reply #4 on:** March 31, 2003, 12:57:34 PM »

One of our Field Service Engineers worked on the rail gun at Livermore (I think it was...). They never managed to get the velocity they were hoping for (4000 fps). It was huge too. Basically, they couldn't get it to do anything artillery couldn't already do and they couldn't get the size down either.

MiniD

gofaster · « **Reply #5 on:** March 31, 2003, 01:04:34 PM »

We'd be better off studying phaser technology. Projectile weapons are just so 15th, 16th, 17th, 18th, 19th, and 20th century, man. This is the dawn of a new age!

Tuomio · « **Reply #6 on:** March 31, 2003, 02:57:31 PM »

Yeah, beam me up scotty, shields are down to 20 percent!

Preon1 · « **Reply #7 on:** March 31, 2003, 03:15:49 PM »

I worked on this project for the Air Force for a year. The US is still very interested in deploying railguns but the materials science isn't quite up to it yet. There are two solutions to the problem when you want to push your projectile to huge velocities:

1: Increase the power. Sure, with enough energy you can pack at least a small percentage of it into getting your bullet fast enough but then you're lugging around a lot of waste

2: Increase efficiency. A railgun is essentially a long barrel filled with electromagnets that turn on and off as the slug passes. You want to turn each magnet on when the slug approaches it so the magnetic field will increase the velocity of the slug. You then turn it off again as the slug passes through.

This is fine for your first 1000 fps or so, but once you get going REALLY fast, the timing is nearly impossible. If you turn the magnets on too early, you're wasting energy. If you turn the magnets off too late, the magnetic field pulls the slug in the wrong direction and slows it down.

We're working on it. Uncooled super conductors are speeding up the response time of our magnets but a deployable weapon is still a good time in the future.

Hope that helps.

miko2d · « **Reply #8 on:** March 31, 2003, 03:49:24 PM »

Preon1: 2: Increase efficiency. A railgun is essentially a long barrel filled with electromagnets that turn on and off as the slug passes. You want to turn each magnet on when the slug approaches it so the magnetic field will increase the velocity of the slug. You then turn it off again as the slug passes through.

I do not believe what you are describing is a railgun but a magnetic cannon where the projectile acts as a plunger inside of a solenoid. Of course it si entirely possibly that the army would confuse teh terminology.

A railgun consists of two parallel conductors, the "rails", bridged by a non-ferromagnetic conducting armature. The railgun is fired by creating a current loop that flows from some large power source, down one rail, across the slug, and back up the other rail. This current loop induces an enormous magnetic field which, in turn, pushes the armature down the rails with a force proportional to the magnitude of the current, the separation distance of the rails, and the magnetic field.

The main problem is armature (projectile) being spot-welded to the rails.

National Research Laboratories' shot a 1 gram object at 16000m/s while Maxwell Lab' railgun fired a 1.6 kilogram projectile at about 3300m/s.

This is fine for your first 1000 fps or so, but once you get going REALLY fast, the timing is nearly impossible.

This is not entirely true, pardon my french. Huge (hundreds of yards in diameter) particle accelerators successfully accelerate the subatomic particles close to the speed of light by making them fly around the circumpherence several times and them diverting them into a target outside the circle - all by turning on the electromagnets in the proper sequence.

If you turn the magnets on too early, you're wasting energy.

And where would that "wasted" energy go? If you turn on a lightswitch without a bulb in the socket, do you draw any energy? The same here with a plunger of a solenoid. The energy is expended to draw it in. No plunger - the resistance to current increases, less current flows, etc. Plunger appears - the resistance drops, the curent increases, the energy is expended to be stored as a kinetic energy of the projectile.

miko

Preon1 · « **Reply #9 on:** March 31, 2003, 04:26:06 PM »

Quote

Originally posted by miko2d
I do not believe what you are describing is a railgun but a magnetic cannon where the projectile acts as a plunger inside of a solenoid. Of course it si entirely possibly that the army would confuse teh terminology.

True

Quote

Originally posted by miko2d
This is not entirely true, pardon my french. Huge (hundreds of yards in diameter) particle accelerators successfully accelerate the subatomic particles close to the speed of light by making them fly around the circumpherence several times and them diverting them into a target outside the circle - all by turning on the electromagnets in the proper sequence.

You mention the scale. Timing problems are mitigated when the distance traveled between magnets is increased. It also helps when you have plenty of time and distance to accelerate the ions. Once you scale the barrel down to the size of an M-16, or even the GAU-8A (the cannon on the A-10) and then increase the size of the slug then timing becomes a serious issue. Right now it just takes too long to turn on a magnet and then turn it right back off.

Quote

Originally posted by miko2d
And where would that "wasted" energy go? If you turn on a lightswitch without a bulb in the socket, do you draw any energy? The same here with a plunger of a solenoid. The energy is expended to draw it in. No plunger - the resistance to current increases, less current flows, etc. Plunger appears - the resistance drops, the curent increases, the energy is expended to be stored as a kinetic energy of the projectile.

That's not the way my physics teacher taught it to me. With the plunger in, the solenoid causes a sympathetic current in the plunger. That current makes another magnetic field which reacts to the one in the solenoid pushing it in/out. Without that plunger, the resistance decreases because there's nothing that reacts to the creation of the magnetic field.

In my view, you would waste energy because of two reasons.
1. The generation of a magnetic field sends out an electromacnetic wave. It's the same principle for accelerating magnetic fields and charges. You move or change it, it expends energy.

2. There's no point in generating that magnetic field too early because the field dissapates with the inverse cube of the distance. Plus it will generate sympathetic currents in the magnets closer to the slug that will decrease overall effectiveness.

miko2d · « **Reply #10 on:** March 31, 2003, 04:50:42 PM »

Preon1: You mention the scale. Timing problems are mitigated when the distance traveled between magnets is increased.

Scale? How many yards a particle travelling at the 99% of the speed of light will travel while a projectile travels 3 feet even at 100,000 fps? We are talking about 1000 difference time dilution effects, the time it takes electrons to travel, etc.

Timing effects on such scale were solved long time ago - in the detonators for the nuclear bombs, for example. If the explosive is not detonated exactly right from dozens/hundreds of points, the nuclear reaction will not occure or much smaller fraction than designed would react.

That's not the way my physics teacher taught it to me. With the plunger in, the solenoid causes a sympathetic current in the plunger. That current makes another magnetic field which reacts to the one in the solenoid pushing it in/out. Without that plunger, the resistance decreases because there's nothing that reacts to the creation of the magnetic field.

You could consider that situation from the energy or force perspective.
You start with an unpowered solenoid and end with a powered solenoid and projectile travelling at a certain speed. Whether you turn that solenoid on before or after shoule not make a difference to the total sum of energy.

1. The generation of a magnetic field sends out an electromacnetic wave. It's the same principle for accelerating magnetic fields and charges. You move or change it, it expends energy.

True, it does produce a magnetic field that contains stored energy, but you have to turn the current on sooner or later. Solenoids do store energy.
Once you stop the current, this energy is gount to be released. It can be done two ways - if you breake the circuit, the energy will be emitted into space as the magnetic field dissipates.
Or you can just remove voltage from the circuit but leave the circuit closed - or cose it on the capacitor or resistor. In that case teh magnetic field will maintain the current flowing and the energy with some losses will be passed from that of the magnetic field into one stored in a capacitor or used to heat the resistor. That is how the impedance contours (coil/capacitor) work - moveing energy from the one stored in a capacitor as electric field into one stored in (around) a coil as magnetic field.

2. There's no point in generating that magnetic field too early because the field dissapates with the inverse cube of the distance.

I see your error. The static field does not dissipate - it's intensity is reduced with distance from the source. Like gravity. The further you are from the planey, the lower the gravity, but there is no gravitic energy dissipating anywhere.
So you can safely power your coild and the only energy lost/dissipating will be the energy used to heat the wire due to the wire resistance.
A super-conductive coill with no loss in the wire will have stored energy that does not dissipate for years.

There is a need to synchronise to make sure the coil does not pull the solenoid back in and for other engineering reasons but the coil that is powered in advance and is shut off once the projectile passed the middle would work.

miko

N1kPaz · « **Reply #11 on:** March 31, 2003, 05:05:36 PM »

jeez. and i thought magnets were only good for sticking my crayon drawings on the fridge.