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 Psienesis wrote:
Unless you use a multi-stage stepped magnetic field to pull the round down the barrel before pushing it from behind.

Doesn't matter. The magnet pulls the shell towards itself, and pulls itself towards the shell.

Seriously, there are no tricks (other than handwaving a magic "momentum remover" technology) to let you get around conservation of momentum. The shell + tank system starts at (relative) rest, momentum = 0. If the shell gains momentum X then the tank must gain momentum X in the opposite direction. It doesn't matter how you fling the shell, you must satisfy that simple equation.

IN regards to the railgun recoil thing.
allegedly the hammerhead gets around a railguns recoil using those big engines on it.
WHen the gun fires it puffs its engines so that the recoil of the gun is counteracted by the engines pushing the tank forwards.

I would imagine If imperial hover tanks had cannon they would have a similar system. When the cannon fires, thrusters push in the opposite direction of the recoil keeping the tank relatively stable.

That level of recoil wouldn't be enough to disturb a heavy enough tank, and given design refinements it would be possible to eventually have a floating breech that would hardly move. Hence, railguns don't have recoil enough for it not to be practical in a tank, admittedly after a lot of development to make them far smaller than current tech.

I think from what I have read the gun BAe developed works on the same principle as the maglev train with the magnets being rapidly cycled to propel the shell along, hence and the moment its not practical to be anything other than a solid mount on the ground.

In the future it may be possible on a tank as the coils could be solid mounted onto the turret with a "floating" breech like in the video. A foot or so of recoil wouldn't affect a tank much - a Sherman for example only budges very slightly (if at all) when you fire its main gun.



But anti-grav and railguns would only work if you used the method the Hammerhead is said to use as they would be moved a lot more from even a small amount of recoil from the breech. Something like a plasma or laser cannon would be fit more I would think. But then a recoil suppressor system is fairly easy to develop, lot more from even a small amount of recoil from the breech. Something like a plasma or laser cannon would be fit more I would think as that would be a lot easier to deal with (laser especially).

The problem with Anti Grav is, that any AG vehicle would essentially be frictionless. So instead of the tank firing it's weapon on solid ground, imagine him doing the same thing while standing on skids on ice.

There could be an inbuilt system to deal with the recoil, but then the techpriests probably would have to find a complete STC since I highly doubt that the marsians have enough understanding of the interaction of forces to create said system themselves...

Not necessarily.

Anti-grav may have some sort of "friction" like effect when interacting with the ground. The force which keeps it aloft is pushing on the ground, which would be friction in the strictest sense.

DrunkPhilisoph wrote:
The problem with Anti Grav is, that any AG vehicle would essentially be frictionless. So instead of the tank firing it's weapon on solid ground, imagine him doing the same thing while standing on skids on ice.

There could be an inbuilt system to deal with the recoil, but then the techpriests probably would have to find a complete STC since I highly doubt that the marsians have enough understanding of the interaction of forces to create said system themselves...

See that isn't necessarily true, there is less friction on a grav tank to be sure, but all of its friction is viscous friction against a fluid (the atmosphere), which is still a fair amount and you could additionally make the rear of the vehicle as unaerodynamic as possible allowing you to generate even more.

Before you start arguing about friction you should do the math on just how fast a Hammerhead would be kicked backwards by its own railgun. If you approximate the numbers based on the real-world railgun in development the final answer is very small (IIRC around walking speed) and easily corrected by the tank's engines. Making your tank deliberately less aerodynamic to reduce that minor problem would just be stupid, all you do is make sure your fire control system can handle shooting on the move and you stop worrying about it entirely.

Really only about walking speed? Why does that seem, I don't know a bit slow? Got a link to the numbers for a modern railgun? I'd like to check the maths myself.

 Krellnus wrote:
Really only about walking speed? Why does that seem, I don't know a bit slow? Got a link to the numbers for a modern railgun? I'd like to check the maths myself.

I did it in a previous thread here, just google the railgun numbers. You don't need anything precise, just rough estimates. Though maybe I used a conventional tank shell, which shouldn't be all that different.

The TL,DR of it is that the railgun shell is very fast but doesn't have much mass, while the tank has a lot of mass so it doesn't need to move very fast to have the same momentum.

Based on the round used by the us navy in the 2000s.

Momentum = 3.2kg x 2400m/s
= 7680kg.m/s

Mass of hammerhead (from lexicanum): 24000kg
Velocity of hammerhead = 7680/24000 = 0.32m/s

Huh, that's about a quarter walking speed give or take. Put some springs on the weapon assembly and your practically not even going to move.

Would have assumed that's higher. oO

Then, where do we get all that recoil in conentional guns from, just the expanding gas?

There's also matters of cost and ability of every world to produce the technology. Astartes get their stuff built on Forge Worlds, handcrafted by the best tech priests the IoM has.

However the Imperial Guard needs tanks, lots of them, quickly and cheaply. Most fluff I've read indicates that on Imperial worlds there is some kind of currency system, and as most of the Imperial Guard's equipment is produced on less advanced worlds more geared to mass production there wouldn't be the facilities, resources, money, or expertise to produce anti grav tanks in large numbers.

DrunkPhilisoph wrote:
Would have assumed that's higher. oO

Then, where do we get all that recoil in conentional guns from, just the expanding gas?

You get all that recoil in conventional guns because the gun is mounted on a spring so that it kicks backwards instead of putting a lot of stress on the bolts holding it to the turret. The momentum isn't going into the main hull of the tank (most of the tank's mass), and you'll notice that the tank itself doesn't move very much when it fires the main gun.

This was an interesting read. Thanks for starting a conversation that lead me to read this.

http://www.utexas.edu/research/cem/IEEE/PR%2052%20Weldon%20Publications.pdf

 Peregrine wrote:
Before you start arguing about friction you should do the math on just how fast a Hammerhead would be kicked backwards by its own railgun. If you approximate the numbers based on the real-world railgun in development the final answer is very small (IIRC around walking speed) and easily corrected by the tank's engines. Making your tank deliberately less aerodynamic to reduce that minor problem would just be stupid, all you do is make sure your fire control system can handle shooting on the move and you stop worrying about it entirely.

Provided the engines are pointing in the opposite directio to the gun. however a little lateral drift is unlikely to cause many problems either.

Another solution is one that is often quoted in Peter F Hamilton's sci-fi, where you project a forcefield into the ground to brace the firing platform. Add the mass of the planet to your tank to help with the recoil

 Flinty wrote:

 Peregrine wrote:
Before you start arguing about friction you should do the math on just how fast a Hammerhead would be kicked backwards by its own railgun. If you approximate the numbers based on the real-world railgun in development the final answer is very small (IIRC around walking speed) and easily corrected by the tank's engines. Making your tank deliberately less aerodynamic to reduce that minor problem would just be stupid, all you do is make sure your fire control system can handle shooting on the move and you stop worrying about it entirely.

Provided the engines are pointing in the opposite directio to the gun. however a little lateral drift is unlikely to cause many problems either.

Another solution is one that is often quoted in Peter F Hamilton's sci-fi, where you project a forcefield into the ground to brace the firing platform. Add the mass of the planet to your tank to help with the recoil

Or just have a guy get out and hold the back of the tank

 Grey Templar wrote:

 Flinty wrote:

 Peregrine wrote:
Before you start arguing about friction you should do the math on just how fast a Hammerhead would be kicked backwards by its own railgun. If you approximate the numbers based on the real-world railgun in development the final answer is very small (IIRC around walking speed) and easily corrected by the tank's engines. Making your tank deliberately less aerodynamic to reduce that minor problem would just be stupid, all you do is make sure your fire control system can handle shooting on the move and you stop worrying about it entirely.

Provided the engines are pointing in the opposite directio to the gun. however a little lateral drift is unlikely to cause many problems either.

Another solution is one that is often quoted in Peter F Hamilton's sci-fi, where you project a forcefield into the ground to brace the firing platform. Add the mass of the planet to your tank to help with the recoil

Or just have a guy get out and hold the back of the tank

And here we run into the momentum problem again... Sure the tank is only moving at walking pace (assuming all the previous maths is correct), but would you like to try and stop a tank moving at any speed by standing in front of it?

Yeah, holding the tank wouldn't help. A tank only moving a tiny bit would still knock you flying because its tiny velocity multiplied by its huge mass, then divided by your tiny mass, would equal your very high velocity the other way.

the big problem that railguns have is that they burn out there rails pretty quickly. Guass guns are alot better but they require a shed load more energy to do the same task

Tau obviously have magic future-tastic-space-materials to deal with the practicalities (graphene nanocomposites are in there somewhere, probably... They seem to be the silver bullet solution for everything else)

If a race can overcome Gravity (with Anti-grav), I think recoil mitigation would be somewhat basic, and not really certain how a Railgun "Burns out " their rails, since al it does is us a magnetic current to propel a projectile, the Projectile never contacts the "Rails" floating in a push/pull bottle of mag force. And if you are referring to burning the Rails out due to electrical powering the rails...pretty certain that would not be a issue. But again we are trying to rationalize tech that's hundreds if not thousands of years more advanced than what we currently have with our basic Rail weapon designs.

Actually I think the slug does contact the rails in the current design.

Or the rapid movement and compression of the air molecules in the gun itself cause the friction.

True Based on our current designs..but as to a alien race and superior tech..who knows, they already use some kind of nano-crystaline substance for armor on suits and tanks, so some form of super conductive material with superior heat dissipation seems likely..Since they use the weapons..extensively.

The most simple design is to have the projectile as a mobile bridge between 2 rails to forma complete circuit.Tthe magical effects of physics then kick in to fire the projectile sideways resulting in friction. If you don't have contact you don't complete the circuit and it doesn't work. The free floating alternative is the coilgun that uses pure magnetism to propel a projectile.

If you can make the rails themselves frictionless, then you don't have a problem with overheating from physical contact, but I have no idea what that might do to the electical contact the alternative is to just make the rails so robust that they don't take much damage by individual shots and easy enough to manufacture that you just replace the rails after x number of shots.

 Flinty wrote:
The most simple design is to have the projectile as a mobile bridge between 2 rails to forma complete circuit.Tthe magical effects of physics then kick in to fire the projectile sideways resulting in friction. If you don't have contact you don't complete the circuit and it doesn't work. The free floating alternative is the coilgun that uses pure magnetism to propel a projectile.

If you can make the rails themselves frictionless, then you don't have a problem with overheating from physical contact, but I have no idea what that might do to the electical contact the alternative is to just make the rails so robust that they don't take much damage by individual shots and easy enough to manufacture that you just replace the rails after x number of shots.

I suspect that regarding Tau its a bit of both..more of a materials science thing, with some form of extremely heat resistant alloy, but then again they may be more akin to a coil gun like you described..but as always, we don't get much detail on non-human weaponry.

I still say if anyone can make a ANTI-GRAV vehicle, then everything else is Kindergarten stuff.

"Anti-grav" in 40k also may not literally be countering the force of gravity, but simply some advanced force generator that lets you float at whatever elevation you want.

Land Speeders for example use the planet's magnetic field to float. Thus they wouldn't work on a planet with no magnetic field.

Maybe Eldar and Tau skimmers are really more akin to hovercraft. Using some sort of field generator to create a cushion of air for the vehicle to float on.

 Grey Templar wrote:
"Anti-grav" in 40k also may not literally be countering the force of gravity, but simply some advanced force generator that lets you float at whatever elevation you want.

Land Speeders for example use the planet's magnetic field to float. Thus they wouldn't work on a planet with no magnetic field.

Maybe Eldar and Tau skimmers are really more akin to hovercraft. Using some sort of field generator to create a cushion of air for the vehicle to float on.

Also as pointed out in Consider Phlebas (RIP Banksy), AG devices that react against a planet's gravity also won't work on a ring orbital... "fake" gravity created by spinning =/= actual gravity

 Soo'Vah'Cha wrote:

 Flinty wrote:
The most simple design is to have the projectile as a mobile bridge between 2 rails to forma complete circuit.Tthe magical effects of physics then kick in to fire the projectile sideways resulting in friction. If you don't have contact you don't complete the circuit and it doesn't work. The free floating alternative is the coilgun that uses pure magnetism to propel a projectile.

If you can make the rails themselves frictionless, then you don't have a problem with overheating from physical contact, but I have no idea what that might do to the electical contact the alternative is to just make the rails so robust that they don't take much damage by individual shots and easy enough to manufacture that you just replace the rails after x number of shots.

I suspect that regarding Tau its a bit of both..more of a materials science thing, with some form of extremely heat resistant alloy, but then again they may be more akin to a coil gun like you described..but as always, we don't get much detail on non-human weaponry.

I still say if anyone can make a ANTI-GRAV vehicle, then everything else is Kindergarten stuff.

Well, the Necrons one-up the Tau in having both anti-grav tech as well as the ability to travel through time. As the Tau do not yet have time-travel, I don't think anti-grav is quite the super-science you suggest that it is.

Railgun theory 101 has been informative, thanks.

Personally, I am willing to believe that the Adeptus Mechanicus have the STC to do it if they wanted to. I would state the fact that Space Marines have their Land Speeders.

But the AM, tend to be knowledge hoarders to the leasLet's not forget the fact that, Adeptus Munitorum, is a galaxy spanning bureau of paper pushers. The orders could put in and the paperwork could be lost in the shuffle.