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davejames
02-29-2012, 05:54 PM
Hello Forum Wizards,

Why would a magnetic rail gun throw a projectile amidst a bunch of flame and smoke? :confused:

http://news.yahoo.com/navy-railgun-tests-leading-ship-superweapon-2020-201003095.html


Curious in San Jose...

ElectricAye
02-29-2012, 06:10 PM
Hello Forum Wizards,

Why would a magnetic rail gun throw a projectile amidst a bunch of flame and smoke?....


I'm going to take a wild guess and say it's the result of an ablative material used to keep the rails from melting down due to friction and the immense energy being used. Perhaps this flame and smoke carry away heat that, if not vented, would destroy the rails.

But that's just a guess.

Lawson
02-29-2012, 06:34 PM
Hello Forum Wizards,

Why would a magnetic rail gun throw a projectile amidst a bunch of flame and smoke? :confused:

http://news.yahoo.com/navy-railgun-tests-leading-ship-superweapon-2020-201003095.html


Curious in San Jose...

The reason is burried in the details of the article. Basically, that gun dumps 22-32 MEGA joules into that projectile in 1-4mS. (btw for scale, a "normal" bullet has around 300 Joules of kinetic energy when fired) Rail guns are comparatively high efficiency high velocity launchers, 20% is a ball-park number I've seen from hobby launchers. So the peak power while firing is in the 10s of gigawatts to terrawatt range. At these power levels if stuff DOESN'T melt or explode, it's because someone has done a lot of work. (the fireball is likely burning copper, molybdenum, and aluminum melted off the rails and projectile)

davejames
03-01-2012, 12:25 AM
...this smoke/fire thing has bugged me all day (jeez, get a life!).

I found some interesting information here:

http://www.powerlabs.org/railgun.htm

This guy built his own rail gun, powered by a supply that I wouldn't even want to be with in the same room!

This is his second attempt:

http://www.powerlabs.org/railgun2.htm

Anyway, due to the heat generated by the magnetic fields, the rails actually erode when the gun is fired; a partial source of the smoke/fire.

Also (buried in the article), the author noted that if the projectile remains stationary for any length of time, the aforementioned heating rises dramatically (due to nasty amounts of induction) and the rail assembly destructs. In order to prevent this literal melt-down, the projectile is pushed by a gaseous charge to get it moving first. This charge is evidently an appeciable amount, and factors into the smoke/fire. Even the type of gas used affects smoke/fire.

I learned some stuff today!

Mark_T
03-01-2012, 09:18 PM
My guess is:

Because you initiate the gun with a conventional charge so that the projectile is travelling fast when current first flows (otherwise the rails will simply melt at the point of contact because the contact lasts too long at one place).

Smaller rail guns have pneumatic initial acceleration (see the links someone just posted)