Round-barrel(-ish) Railgun

[andykhang]

Just today I saw that video of the US Navy firing their railgun from a barrel at highspeed. I only seen it firing from 2 straight rail parralel to each other though, so how does firing from a round barrel work, and is there a calculation for it?

[p1t1o]

A railgun is called a railgun exactly because the "barrel" consists of two "rails" between which a large voltage is applied. Electromagnetic effects cause a large force to appear when this is allowed to discharge through the projectile. Or something.

Ergo, there is no calculation for a "round barrel". I suppose one could imagine a circular barrel being constructed out of many pairs of rails, but I think its pretty likely that it would merely simulate a single large pair of rails, which is probably a much more efficient arrangement.

A "coilgun" however, works by rapidly switching electromagnets on/off in a sequence down a barrel and magnetically drawing the projectile without physical contact, and is much more suited to circular apertures.

**edit**
Quick google turned up something called a "helical railgun", a design from the 1980's which appears to be a hybrid rail-coil-gun. It is apparently not a practical design as yet.

[andykhang]

You could save alot of space by just splitiing the rail and place it in circular fashion though. IIRC, rail size doesn't matter much aside from durability

[p1t1o]

You could save alot of space by just splitiing the rail and place it in circular fashion though. IIRC, rail size doesn't matter much aside from durability

Im not a huge buff on electronics so the mathematical details escape me, but the voltages, currents and forces are very high - for example, enormous repulsion is set up between the rails that requires heavy reinforcement. And not for nothing but durability is a major concern, in the heavy-duty versions the USN is testing, the rails are only good for a handful of shots before they wear out, there is tremendous friction between the rails and the projectile as well as electrical vaporisation of projectile/rail substrate.
I would wager that splitting them into a circular geometry wouldnt end up being much smaller or lighter.

[andykhang]

You can't really be lighter with these kind of thing anyway, since a rail need a certain level of size and weight to withstand such force. You could be significantly shorter though, by splitting the load between multiple shorter rail (though I guess you still need some revolutionary engineering to do that, or there is some significant drawback to that method that I can't see it)

[p1t1o]

You can't really be lighter with these kind of thing anyway, since a rail need a certain level of size and weight to withstand such force. You could be significantly shorter though, by splitting the load between multiple shorter rail (though I guess you still need some revolutionary engineering to do that, or there is some significant drawback to that method that I can't see it)

The drawback of a shorter design though, if the advantages you assume pan out, is the proportionally faster timing in which the power must be discharged. Increasing the speed of the discharge is non-trivial and is essentially the major limiting factor in railgun design - how much electrical energy can you pump into a piece of equipment in a short space of time. When you are talking about tens of Megajoules being released in vanishingly tiny fractions of a second, it is not a simple thing to say "Can we do this twice as fast?".

[andykhang]

The electricity itself is also split between the rails though, so the only problem I see right now is how to time the discharge rather than make it faster than in the long version though.

[p1t1o]

The electricity itself is also split between the rails though, so the only problem I see right now is how to time the discharge rather than make it faster than in the long version though.

What I was getting at, to obtain a certain muzzle velocity, shortening the barrel means the switching must occur faster as the projectile must be accelerated harder. Increasing the speed of discharge may not be trivial since it is probably already fairly maxed out in current designs.

There is no real need to design a shorter weapon unless your space requirements are more important than your firepower requirements, and then you may be better off using a different weapon.

In the grand scheme of things, the reason why railguns are still on the drawing board is that missiles can pretty much do all the things railguns can and more.

[andykhang]

Yeah, too bad...with all the craft relying on missile for their primary fire, all you need is a well placed kinetic kill weapon too fast and too heavy for the missle to react against. (Applied for warship only, I think)

[Mutex]

In the grand scheme of things, the reason why railguns are still on the drawing board is that missiles can pretty much do all the things railguns can and more.

Railguns still have an advantage that makes them sought after. The ammunition is literally inert lumps of metal. As opposed to things containing explosives and flammable fuels, which can detonate if a well aimed shot hits the part of your ship where you're storing them. The only other thing a railgun needs is electricity, which on a nuclear-powered warship is plentiful.

[p1t1o]

Yeah, too bad...with all the craft relying on missile for their primary fire, all you need is a well placed kinetic kill weapon too fast and too heavy for the missle to react against. (Applied for warship only, I think)

Dont underestimate missiles, they are ballistic projectiles just like gun rounds only their propulsion is in a different form. Once their fuel is expended, they are kinetic projectiles just like the rest - In fact there are missiles which function exactly like that, using KE instead of an explosive warhead.

Just for reference, and because they are my fave, here are some facts about a particular missile:

The Sprint missile, put in service 1972
Accelerated to Mach 10 in 3 seconds
100G manouvre capacity
Can hit a Mach 20 target
Capable of physically hitting said target (undesirable, was deliberately made less accurate)

Railguns still have an advantage that makes them sought after. The ammunition is literally inert lumps of metal. As opposed to things containing explosives and flammable fuels, which can detonate if a well aimed shot hits the part of your ship where you're storing them. The only other thing a railgun needs is electricity, which on a nuclear-powered warship is plentiful.

True, but at the moment they are just not good enough at being weapons to make those advantages worthwhile. Honestly, I doubt if they will ever make great Naval weapons, other uses sure, but we have [largely] discarded the Naval gun for good reason. Its just that at the moment, ships are the only things big & powerful enough to carry & power them!

[morriswalters]

I believe only the propellant is replaced. The shells themselves still have explosive charges. The only gun I'm aware of that shoots just inert material is the Phalanx CIWS, which is designed to stop missiles. Which I believe shoot depleted uranium shells(Wiki says they also shoot tungsten). The limitation wouldn't seem to be firing rate. The guns as the navy will use them appear to still be ballistic weapons like any other artillery. They seem to be saying that you can get the range of a 16 inch gun from a 5 inch. And their mission is apparently shore bombardment.

@andykhang

You are aware that to hit a target at distance with any gun regardless of type that you must use a ballistic trajectory? At 20 miles + any target at ground level would not be line of sight.

[p1t1o]

Honestly its way too soon to be saying what is in the projectiles. Railguns are still highly experimental and an operational weapon could be very different. The projectile will be as experimental as the weapon at this point.

Its interesting, a railgun projectile has to conduct the entire firing charge through its chassis. Think about that while adding an explosive warhead!

[morriswalters]

Yeah, it appears that all the weapons are KE only. My apologies.