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| ramses |
 Posted: 02/27/2010 20:34 PM Post subject: |
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Major General
Joined: 29 May 2008
Posts: 1519
3981.54 Spud Bux
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| Ragnarok wrote: | | I do have a project with a frictionless barrel (and indeed, frictionless "rifling"), but it's electromagnetic, not pneumatic. |
be careful, magnetic projectiles in a metal barrel produce eddy currents... |
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| spudtyrrant |
| Posted: 02/27/2010 20:48 PM Post subject: |
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Colonel
Joined: 02 Jan 2009
Posts: 582
959.61 Spud Bux
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| ramses wrote: | | Ragnarok wrote: | | I do have a project with a frictionless barrel (and indeed, frictionless "rifling"), but it's electromagnetic, not pneumatic. |
be careful, magnetic projectiles in a metal barrel produce eddy currents... |
he's probably is thinking the other way around  |
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| MrCrowley |
| Posted: 02/27/2010 21:22 PM Post subject: |
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Kaleun
Joined: 23 Jun 2006
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| Ragnarok wrote: | | I do have a project with a frictionless barrel (and indeed, frictionless "rifling"), but it's electromagnetic, not pneumatic. |
May I ask how many projects or designs you actually have? 
I swear you've designed everything  |
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| jackssmirkingrevenge |
| Posted: 02/27/2010 23:13 PM Post subject: |
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aspiring machinist
Joined: 15 Mar 2007
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32519.23 Spud Bux
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| Brian the brain wrote: | | Friction allows for pressure buildup. |
This is a fairly "obvious" point that not many people take to heart, btrettel had mentioned it here and it's worth keeping in mind, especially if using a less than optimal valve.
| MrCrowley wrote: | | I swear you've designed everything |
I'm guessing his student digs are insulated with piles of blue-prints  |
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| Ragnarok |
| Posted: 02/28/2010 5:09 AM Post subject: |
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Lord of Karma
Joined: 19 Dec 2006
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16113.53 Spud Bux
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| ramses wrote: | | be careful, magnetic projectiles in a metal barrel produce eddy currents... |
When I say it's electromagnetic, I mean the "launcher" as a whole - it's a reluctance coilrifle.
Provided you've done it right, a coilgun's magnetic fields can support the projectile on their own, so while it's useful to have something to align the coils with and protect them from the projectile, the "barrel" (which should be non-conductive) and projectile need never touch one another during firing.
| MrCrowley wrote: | | May I ask how many projects or designs you actually have? |
Projects currently going anywhere... a couple, but slowly. As my currently low posting rate might suggest, while I'm not quitting spudding, I'm not currently going at it with my normal exuberance - I haven't really the funds to spare at the moment (and frankly haven't really had them for ages).
Designs... well, last I checked, there were nearly two thousand separate files in my ideas/designs folder. There's usually a few to any given idea, so I'd guess anywhere up to about 500 sets of designs. |
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| psycix |
| Posted: 02/28/2010 8:21 AM Post subject: |
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Donating Member
Joined: 25 Jun 2007
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17.61 Spud Bux
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*sigh*
That single pound of friction is nothing compared to the thousand pounds of force accelerating the projectile.
On top of that you are wasting air, and putting air in front of the projectile AND venting air from behind the projectile out.
But hey, atleast this guy tried to use his mind and tried to think of something new. It failed even in theory, but better luck next time. |
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| jimmy101 |
| Posted: 02/28/2010 12:28 PM Post subject: |
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Lieutenant General
Joined: 28 Mar 2007
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| Lentamentalisk wrote: | inonickname: "Vacuum alone" can accelerate anything to the speed of sound (actually to the speed of the fastest moving particles) it just takes a damn long time and zero friction. Assuming, of course, that both sides aren't vacuumed.
Its called unbalanced forces. They cause acceleration. End of story. |
Make that "to the local speed of sound assuming zero drag on the air flow".
Air expanding into the barrel behind the projectile will drop in pressure which in turn drops the temperature and the local SOS will decrease. The exit velocity of the projectile will be relative to that reduced SOS and not to the ambient SOS.
In addition, it assumes zero blow-by around the projectile. But that means the ammo is touching the barrel which means there is friction which means the SOS is probably not obtainable.
If there is no contact then air flow past the projectile will be at the local SOS chocked by the geometry of the system.
Any vacuum only based gun is very nearly the same as a gun operating at ~15 PSIG. Even taking into account the mass of the air in front of the ammo (in the case where the ammo is extremely light which is the only time the air mass really matters) you probably only need to boost the pressure by a few PSI or so to overcome that increased mass. |
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