Railguns

[Sturgeon]

Curious Droid, as always gives us a great treatment of his subjects:

 

 

[Ramlaen]

Just as a note, the clips where the projectile was spinning are because a traditional chemical (rifled) gun was used.

 

Those HVP projectiles in 127mm and 155mm guns will be a boon to the navy.

[Sturgeon]

2 hours ago, Ramlaen said:

Just as a note, the clips where the projectile was spinning are because a traditional chemical (rifled) gun was used.

 

Those HVP projectiles in 127mm and 155mm guns will be a boon to the navy.

 

Yep, they were sabot separation tests with conventional guns. You can see the same projectiles being used with actual railguns in the tests below:

 

 

 

 

[Gripen287]

Hello all,

 

Gripen here. Long-time reader, first-time poster here. I'm drinking Founder's Breakfast Stout and come bearing documents about railguns (is there a preferred method of posting/uploading documents?):

 

https://drive.google.com/open?id=1bZeNQNqLwoOxyGORELf7H80qI0ENFJ5M

 

https://drive.google.com/open?id=0B21XX6zvOt4fdHpxVGdvaFdpR28

 

https://drive.google.com/open?id=1QUAUdaP_QGBmA9DTby6pWYINon8XZFn_

 

https://drive.google.com/open?id=0B21XX6zvOt4fWHJRdHZIdGlRWDQ

 

https://drive.google.com/open?id=0B21XX6zvOt4fQjVyYkpWaG1CRkk

 

And for the inductively minded:

 

https://drive.google.com/open?id=0B21XX6zvOt4fZDM3SHM3SWE5N2M

 

Did I do it right? 

[Belesarius]

4 hours ago, Gripen287 said:

Hello all,

 

Gripen here. Long-time reader, first-time poster here. I'm drinking Founder's Breakfast Stout and come bearing documents about railguns (is there a preferred method of posting/uploading documents?):

 

https://drive.google.com/open?id=1bZeNQNqLwoOxyGORELf7H80qI0ENFJ5M

 

https://drive.google.com/open?id=0B21XX6zvOt4fdHpxVGdvaFdpR28

 

https://drive.google.com/open?id=1QUAUdaP_QGBmA9DTby6pWYINon8XZFn_

 

https://drive.google.com/open?id=0B21XX6zvOt4fWHJRdHZIdGlRWDQ

 

https://drive.google.com/open?id=0B21XX6zvOt4fQjVyYkpWaG1CRkk

 

And for the inductively minded:

 

https://drive.google.com/open?id=0B21XX6zvOt4fZDM3SHM3SWE5N2M

 

Did I do it right? 

Epic firstpoast. Well done! Welcome to SH!

 

[Collimatrix]

Welcome to SH @Gripen287.  We don't really have a preferred format for sharing information online; whatever you can find and think is most resistant to the dreaded link-rot.

[Walter_Sobchak]

On 11/18/2017 at 9:22 AM, Gripen287 said:

Hello all,

 

Gripen here. Long-time reader, first-time poster here. I'm drinking Founder's Breakfast Stout and come bearing documents about railguns (is there a preferred method of posting/uploading documents?):

 

https://drive.google.com/open?id=1bZeNQNqLwoOxyGORELf7H80qI0ENFJ5M

 

https://drive.google.com/open?id=0B21XX6zvOt4fdHpxVGdvaFdpR28

 

https://drive.google.com/open?id=1QUAUdaP_QGBmA9DTby6pWYINon8XZFn_

 

https://drive.google.com/open?id=0B21XX6zvOt4fWHJRdHZIdGlRWDQ

 

https://drive.google.com/open?id=0B21XX6zvOt4fQjVyYkpWaG1CRkk

 

And for the inductively minded:

 

https://drive.google.com/open?id=0B21XX6zvOt4fZDM3SHM3SWE5N2M

 

Did I do it right? 

+1 for the founders reference.

[Mogensthegreat]

I suppose I don't really understand the electromagnetism involved in this, I understand that there is one positively charged and one negatively charged rail on either side of the barrel, and that there is an electrical current running through them and the projectile housing, but how does this propel the missile?

[Belesarius]

12 hours ago, Mogensthegreat said:

I suppose I don't really understand the electromagnetism involved in this, I understand that there is one positively charged and one negatively charged rail on either side of the barrel, and that there is an electrical current running through them and the projectile housing, but how does this propel the missile?

https://www.wired.com/2014/08/the-physics-of-the-railgun/

[juretrn]

Question.

What's you opinion on using railguns as AAA? Viable? 

[Belesarius]

3 hours ago, juretrn said:

Question.

What's you opinion on using railguns as AAA? Viable?

It's something that I'm curious about as well.  Velocity loss is pretty high from what I understand. I think we might have to wait for the tech to miniaturize and ROF to  increase significantly before that's a better choice for AAA than standard options, and I think at that point lasers as triple A may be more viable, as that tech is rapidly advancing as well.

 

[Gripen287]

Report to Congress on Navy Laser, Railgun and Hypervelocity Projectiles

[FORMATOSE]

Found on my hard drive :

 

[LostCosmonaut]

Edit: already posted here

[Sgt.Squarehead]

The weathering sucks too. 

[A_Mysterious_Stranger]

huh I've always meant to post something in this thread but never got around to it.

 

Anyhow, to start I've read that one simple way to visualize how a railgun would work is the Jacob's Ladder:

 

https://www.youtube.com/watch?v=bKD1wsBOo2M

 

Kinda silly I know, but I couldn't resist.

 

Howstuffworks has an explanation as well that I thought was good and may be useful for others: https://science.howstuffworks.com/rail-gun.htm

 

Obviously the armature is a crucial component to railguns (I think of it as combining propellant and sabot though I'm not sure how accurate that is.).  But like a sabot, it represents parasitic mass that you want to minimize and other factors.   There are approximately four kinds of armatures I am aware of:  solid, hybrid, transitioning, and plasma each with their own tradeoffs.  A good description of Armatures can be found here along with the impact of various armatures on railgun performance:

 

Efficiency Scaling for Railgun Armatures

 

Quote

The armature is one of the key components of a railgun system since it serves as the medium whereby electrical energy delivered by the power supply is converted into projectile kinetic energy.. The efficiency with which this conversion is accomplished is an important consideration in the assessment of railgun systems because it directly influences the requirements placed on the prime power and power conditioning components. Several mechanisms such as armature parasitic mars, armature resistance, viscous drag between the armature and the bore, and ablation of bore materials and entrainment of those materials into the armature (commonly referred to as ablation drag) can all have a deleterious effect on the armature efficiency. In addition, two of these loss mechanisms, viscous drag and ablation drag, impose a limit on the maximum velocity that can be achieved. The principal purpose of this paper is to develop a methodology for examining how armature efficiency and velocity limits scale with key gun performance parameters--such as projectile mass, bore size, and gun current per unit rall height--and to apply that methodology to the various hypervelocity armature concepts. (In this paper , the term hypervelocity is used to denote velocities in excess of 7 km/s.)

 

Our analyses are focused on only three of the four commonly used armature concepts, shown in Figure 1, since it is generally believed that the solid armature, which relies on solid-to-solid contact for current transfer to and from the rails, is limited, because of bore gouging and because of the difficulty of maintaining solid contact at high velocities, to a maximum velocity in the range of 3 to 5 km/s, In the plasma armature, current transfer is achieved through a moderate temperature, high-pressure arc which is typically several centimeters or 10's of centimeters long. The hybrid and the transitioning armatures are actually variations on the more basic designs of the solid and the plasma armatures. The hybrid armature consists of a solid conductor with plasma brushes bridging a small gap between the solid conductor and the rails. Its design is intended to overcome the velocity limitations on solid-to-solid contacts while preserving some of the advantages of the solid armature. The transitioning armature begins as a solid armature and transitions, after accelerating over severa) 10's of centimeters of bore, to a plasma armature as aresult of ohmic heating. The intent of the transitioning armature is to eliminate plasma heating of the bore near the breech where it is most severe, aecause of the long transit time. The relative advantages and disadvantages of the four armature types have been discussed in detail in Reference 1.[/quote]

 

Unfortunately I cannot find a copy of Armature options for hypervelocity railguns but I persist.    But to summarize the other armatures than solid (self evident I hope):  Hybrid armatures are mostly solid but plasma between the armature and rails.  Sources about the Navy Railgun sometimes mention Lubrication and I think they're talking about hybrid armatures.    Transitioning armatures start out solid but turn to plasma.   Plasma armatures are basically using a plasma to push the projectile down the rails (and often have the least parasitic mass I've discovered, but plasmas aren't kind to the interior of the railgun.) 

 

Other sources include discussion of metal armatures here and plasma armatures here. 

 

Other interesting documensts include Concepts for Fieldable Electromagnetic Gun Barrels which gives a good idea of how railgun barrels will differ than conventional gun barrels.  The need to reinforce the rails against recoil but also keeping the barrel as lightweight as possible.  AFAIK most rails are copper whilst most armatures are aluminum.  Although you could use other materials IIRC these seem to be considered the most favorable in the stuff I've read. 

 

As a final note this paper is a discussion of performance parameters on railguns. 

 

The armature is a big influence on projectile design obviously and highlights a key limitation.  A railgun projectile is by definition sub-calibre and cannot (AFAIK) be spin-stabilized.   Which means it looks like a dart.  Which is fine for kinetic penetrators but presents problems for artillery (fin stabilization IIRC isn't as good as spin stabilization and sub caliber projectiles have less internal volume than a full caliber projectile.)   A peculiar side note here is that a few documents on DTIC discuss 'alternative' projectile designs:

 

SMALL SCALE TESTING OF A MASS-STABILIZED ELECTROMAGNETIC PROJECTILE

 

Examination of a High-Explosive Round for a High-Aspect Ratio Railgun Bore

 

With the second one that is from 2001 and might be dated.  AFAIK the BAE Hypervelocity Projectile can carry HE payloads but given its sub-caliber design it obviously has limits on top of the guidance package.

 

Another novelty worth bringing up: THEORETICAL DESIGN AND MODELING OF AN INFANTRY RAILGUN PROJECTILE.

 

I've actually posted about the EM gun small arms before, but here's the link anyhow:    I'm always amazed what you can find on DTIC. 

 

Here's another general throw out on EM gun development.  As a bonus, it discusses Electrothermal guns as well.  ELECTROMAGNETIC/ELECTROTHERMAL GUN TECHNOLOGY DEVELOPMENT.

 

To wrap this up, I'll also bring up that while railguns usually have single pairs of rails, there have been other discussions with multiple pairs and other such concepts:

 

Multi-turn railguns: Concept analysis and experimental results (PDF is available to view/download on site)

 

Parametric study of an augmented railgun  (like above, PDF available to download/view)

 

A Multiple Armature Railgun Launcher

 

And though coilguns are an entirely different kettle of fish I notice the Sandia Coilgun mortar got mentioned so here's another EM MORTAR TECHNOLOGY DEVELOPMENT FOR INDIRECT FIRE  

[Xlucine]

Do you really need HE fill at railgun velocities? >2.9 km/s you're matching TNT for energy density in pure KE, and for a typical ~23% TNT mass in a whole artillery shell you only need to impact at 1.4 km/s to match the energy delivered

[DD000]

21 hours ago, Xlucine said:

Do you really need HE fill at railgun velocities? >2.9 km/s you're matching TNT for energy density in pure KE, and for a typical ~23% TNT mass in a whole artillery shell you only need to impact at 1.4 km/s to match the energy delivered

 

Yes. Just because it has the same energy doesn't mean it's going to do the same thing.

 

The point of an HE fill is to create a cloud of fragments to cover a wide area. A metal slug impacting at 3 km/s is just going to create a big hole at the point of impact.

[Xlucine]

So you develop a railgun shrapnel round, which won't need a major HE fill. More mass for the fragments (without a proper HE fill) means more area covered

[Jägerlein]

19 minutes ago, Xlucine said:

So you develop a railgun shrapnel round, which won't need a major HE fill. More mass for the fragments (without a proper HE fill) means more area covered

Railgun PELE

[Gripen287]

39 minutes ago, Xlucine said:

So you develop a railgun shrapnel round, which won't need a major HE fill. More mass for the fragments (without a proper HE fill) means more area covered

 

Which seems to be exactly what BAE is doing with their "Dispensing" charge. There's barely any room for explosives anyway  Things might get more interesting with larger bore rail and coil guns due to the scaling factors of the various components. This paper contemplates a 12" coilgun firing projectiles 155mm in diameter, excluding the fixed control fins. The guidance package volume fraction isn't nearly so bad. 

[Lord_James]

7 hours ago, Gripen287 said:

 

Which seems to be exactly what BAE is doing with their "Dispensing" charge. There's barely any room for explosives anyway  Things might get more interesting with larger bore rail and coil guns due to the scaling factors of the various components. This paper contemplates a 12" coilgun firing projectiles 155mm in diameter, excluding the fixed control fins. The guidance package volume fraction isn't nearly so bad. 

 

I've been looking for a reason to place 12" and larger guns on warships again

 

Thank you. 

[Belesarius]

2 minutes ago, Lord_James said:

 

I've been looking for a reason to place 12" and larger guns on warships again

 

Thank you. 

Return of the battleship.

 

[Ramlaen]

8 hours ago, Gripen287 said:

 

Which seems to be exactly what BAE is doing with their "Dispensing" charge.

 

Also why I believe the USN wants HVP rounds for Zumwalt's 155mm guns.

[Alzoc]

Ammunition concept for railguns by the ISL :

 

Sabot 120 mm (scale 2/3 rd) with a projected range of ~200 km :

 

Salvo ammuntion for CIWS railgun applications (3D printed model, scale 1 : 1):

Since railguns don't do well regarding rate of fire, the idea is to launch five of those within a 1/10th of a second allowing fire them within one discharge cycle.

With a low dispersion, those rounds could intercept an hypersonic missile at a range of 1 km (which doesn't leave much time for reaction).

 

Last concept presented (no photo here) is a hollow aluminum round used to test the resistance to acceleration (30 000 g) of electronics.

 

https://www.forcesoperations.com/eurosatory-de-nouveaux-concepts-de-munitions-pour-le-rail-gun-de-lisl/