Analysis of Railgun vs Coil gun technologies

Edited by John Abom (Fall 16)

The rail gun and coil gun are both alternative methods of launching a projectile at high speeds compared to conventional chemical methods. If perfected, these technologies could potentially launch projectiles many times farther and faster than current chemical based methods. The US government has already demonstrated a proof-of-concept rail gun weapon, and is set to begin testing a ship-mounted rail gun in the near future.

But what are the main differences between the two technologies? In this page we will explore the physics and conceptual understanding of both the rail gun and the coil gun.

Introduction

The main difference between a rail gun and a coil gun is how each gun propels its projectile.

The rail gun uses Lorentz Force by passing a current through two metal rails and the projectile, causing a magnetic field to be produced that interacts with an external field, and thereby produces force via F = ILB equation. The rail gun works by storing power in an external source. Once this source builds up enough energy, it sends an electric pulse creating the current and therefore the force needed to launch the projectile.

The coil gun uses simple magnetic configuration to generate the field to propel a projectile. Multiple solenoids are connected in series, and each one is activated sequentially in such a manner to add kinetic energy with each pass of the solenoid. The current in the loops induce a magnetic flux through the center of the loop so that as the projectile moves toward them, loop inductance increases and it becomes magnetized and accelerates through them. In order to keep the projectile moving as quickly as possible, the current in the coil is turned off as the projectile passes through so that it is not still attracted to the magnetic field when it exits.

A Mathematical Model

To generate the massive amounts of energy required to accelerate a projectile to high speeds, capacitors are most often used. They have the capability to provide a large amount of current in a very short amount of time.

Rail Gun: This simple model shows the fields and forces created due to the current in the rails, creating the magnetic force needed to shoot a projectile. The blue arrows represent the magnetic field of the current in the wires, the red arrow is the electric current and the gray is the magnetic force.

Coil Gun: This model depicts the general idea of the movement of the projectile through the coils.

Video Examples

US Rail Gun https://www.youtube.com/watch?v=ygHN-vplJZg

Homemade Coil Gun https://www.youtube.com/watch?v=jr5lHY5vrO4

Real World Use

Railgun The biggest problems faced with actually implementing and using the rail gun is that it takes a lot of power and the fact that the rail gun destroys itself each time it fires. It can fire a 25 pound projectile at seven times the speed of sound, and the contact between the sabot and the rails themselves erodes the gun itself.

Coilgun Also known as Gauss' Rifle, it was first developed by Norwegian scientist Kristian Birkeland in 1904. Small coilguns can be made fairly easily. The biggest problem with advanced coilguns is switching the power in the coils. A less effective way to do this is to use a spark gap, but a better option is to use solid-state switches.

External Sources

1. http://www.popularmechanics.com/military/weapons/a21174/navy-electromagnetic-railgun/ 2. https://www.wired.com/2014/08/the-physics-of-the-railgun/ Pictures 1. https://301o583r8shhildde3s0vcnh-wpengine.netdna-ssl.com/wp-content/uploads/2014/05/coilwork.gif 2. https://www.wired.com/2014/08/the-physics-of-the-railgun/