US Navy preps railgun for tests The US Navy’s Office of Naval Research is preparing to test a prototype railgun delivered by BAE Systems under a $US21 million contract signed in 2010. The industry prototype – a kind of dream machine for Mythbusters’ fans – is due for tests in coming weeks at a facility in Dahlgren, Virginia. The ONR’s aim is to develop a …
You've got to give it to the US, they learn from their mistakes. 68 years ago this June, some stupid general, in the fashion of Haig, sent thousands of his soon to be dead men onto a beach without any protection because the boffins' mine clearing devices looked (and I quote) "funny."
Even so, he lost a lot less men than General (you'd be a war criminal now with such crass stupidity,) Haig's "You don't need to charge the enemy, cos' we've blown them up, so you should just walk to the edge of the Somme.
Can you imagine D-Day all over again, where nops amis yankees don't lose thousands of men, because of this crass stupidity, and they turn up, a mile offshore with a nuclear reactor powering one of these, and literally turn the Normandy beach front in front of them into a gentle blood and sand covered, landmine free, slope.
I'd really like to seem them get this working (while still an ally, of course.)
A rather simplistic, one-sided view.
If we assume some foreign power has managed to invade and hold Europe, between Russia and the Atlantic coast we must assume they have some neat toys of their own. For example they probably have their own railguns able to fire 100nm.
Now add that in to your view of WW2 and you have the whole US invasion force being killed on the South coast of England as they board the ships to France...
"If we assume some foreign power has managed to invade and hold Europe, between Russia and the Atlantic coast we must assume they have some neat toys of their own."
We don't really need to assume that, the Germans had been working on "neat toys" of their own for quite some time prior to D-Day - the V1 had been under development for almost 2 years by that point (and was pushed into service very soon after D-Day), and von Braun had been working on the ideas that eventually led to the V2 since before the outbreak of war. And although they weren't railguns, the cannons that formed the heart of the V3 projects had the same basic principle in mind - long range bombardment using relatively cheap and practically impossible to detect/intercept projectiles.
It's a question for debate that, had German industry been left to make up its own mind about what weaponry to develop, rather than being pushed and pulled in a variety of incompatible/incomprehensible directions on the whims of certain members of the German High Command, the Germans would have been able to deploy some seriously effective weaponry against the allied forces far sooner and in greater number than they eventually did.
"Routemaster" is the only kind of bus I know the name of, and here's why:-
True story:
A few years ago a colleague was giving me a lift to the station. All of a sudden he exclaimed "F**k me! It's a type 53 Routemaster!", did a "U" turn and headed off in the opposite direction at an insane speed.
I had no idea what a "Routemaster" was at the time, so just sat there spluttering "err, train... Station,..... ARRRRGH Cyclist, OH MY GOD"
I eventually twig that the object of his desire was a bloody bus. The bus pulls into a stop, and Nigel (for that was his name) pulls in in front of it, blocking it in, whips out his camera and proceeds to take pictures of the bloody thing. The bus driver just looked bored, as if this kind of thing was a regular occurrence if you happen to drive a Type 53 Routemaster. I just slid down in my seat and pretended I wasn't there.
Nigel finished his photography, got back in the car, the glazed, insane look, lifting from his eyes. He drove me to the station for me to catch a later train, and we never spoke of his dirty little bus spotter secret agaiin.......
Until.....
A year or so later (this was during the 1st Gulf war) I received a phone call:
caller: Hello, is that Mr Anonymous Coward.
me: Err, yes.
caller: This is sergeant Plod of the MOD Police. Do you know a Mr Nigel Nerd?
me: Err, yes.
caller: Can you tell me anything, err, unusual about him?
me: He's quite fat.
caller: With regard to his hobbies?
me: Oh god. You don't mean busses, do you?
caller: Yes, thank you, we'll release him.
Nigel had been out photographing busses outside the naval base. The MOD Plod didn't like the look of that and pulled him in, not believing his "I'm a bus spotter" plea.
I have often wondered how things would have progressed if I'd said "Errm, well, He's a founder member of the Sadam Hussein fan-club" when asked about his unusual attributes.
So you should divide by the square root of 7.7 = 2.8, so 36mph.
But the figures don't add up, 32MJ with a one ton (1016Kg) projectile would be 561mph, and a Routemaster 202 mph (OK, until you consider the G-forces when it stops at the bus stop!)
A one tone projectile at 100 mph would be 2MJ, so they are loosing 94% of the energy to... Well, I guess they won't need central heating.
I, for one, welcome our Routemaster-throwing overlords.
Using E = 1/2 * m * v^2, and rearranging for v = sqrt (2E / m), a 1 ton car would be doing 594mph, and a London routemaster (using dogged's mass) would do 224mph.
Also, dogged's maths is off - multiplying mass by 7.7x reduces speed by 2.77x, for the same energy.
One you are assuming that all of the energy goes into the projectile, I seriously doubt that.
Also dogged seems to be equating the projectiles momentum and you are equating KE. Now in this instance I am trying to work out who is right but I do know when a gun goes off momentum is conserved but KE isnt.
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We've been given values for mass and velocity from which we can easily calculate momentum (p = mv), in that we're given 1 imperial ton and 100 mph for m and v respectively.
Now, when you scale up the mass to a London bus (7.7 tons) that momentum should remain equal thus p = mv = 100 * 1 = 7.7*12.99.
The megaJoules measurement is irrelevant since at no point are we supplied acceleration and cannot infer it from the given values. One Joule is equal to the energy expended in applying a force of one newton through a distance of one metre. We could convert miles per hour to meters per second but that won't help us calculate a force (m*a).
It makes perfect sense, because the Kinetic Energy can be calculated using E = ½mv²; the acceleration and distance fall out. (For constant acceleration, take E = Fd and substitute in F=ma to get E = mad. Now use s = ut + ½at² with an initial velocity of 0, to get d = ½at²; and substitute in to produce E = ½maat² = ½m(at)². Finally substitute in v = u + at, again starting from rest—i.e. v = at—to get E = ½mv². ∎)
By contrast, the final momentum will depend on the length of time the force is applied (F = ma and v = at so F = mv/t; i.e. Ft = p) or, equivalently, the distance over which it is applied.
Forces are the means by which Energy is transferred around a system. So the gun will take a fixed amount of energy, "turn it into a force"*, and apply it to the projectile. The heavier the projectile, the lower the acceleration that force will produce, and so the slower it will end up travelling. But an ideal system will transfer all its energy to the projectile.
Momentum, by contrast, is stolen from the Earth's rotation, and there can be as little or as much as necessary. It can only be from the forces and times (back to F=ma), or via Energy. We don't know the forces and times, so the kinetic energy is the only way to do it.
And despite knowing all that, my initial reaction was to scale it linearly, too. :oops:
* An electromagnetic force is a bunch of virtual photons transferring energy and momentum from one particle to another. Kinda.
That's 6 to 10 rounds a minute for a naval battleship sized gun. The smaller anti-missile guns will produce a lot less waste heat, be a lot smaller and thus take a lot less power to fire and recharge. You can expect the anti-missile versions to fire a couple of rounds per second.
Still not very high compared to currently CIWS solutions, but then railguns can be considerably more accurate so they won't have to spray 50 rounds at an inbound missile and hope one will hit.
1. 6-10 RPM will be for artillery-style use... the sorts of things that cruise missiles might be used for these days.
2. This particular device is unlikely to be used for missile or aircraft defense, but if it were it would like as not be used in a lower velocity or lightweight projectile mode.
Read Reg warporn articles passim for talk about the other naval railgun project going on.
That sort of warship displaced a good 40000t and needed to be enormous to support those sorts of guns and the huge amount of infrastructure they required. The guns weight about 100t each without any ammunition, needed huge crews and threw their projectiles about 20 nautical miles at best and managed perhaps 2 rounds per minute at best.
This means that the low-end range goal for this prototype railgun, 50 nautical miles range at only 4 rounds per minute, would utterly outclass those old cannons and be capable of being mounted on a much smaller and more manoeverable vessel.
Whilst you're there, have a quick think about the relative safety merits of a ship carring hundreds of tonnes of explosive propellant, vs one carrying a load of spare gun barrels and a crate of little metal rods.
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"A London routemaster weighs 7 tons 14cwt unladen according ot the internets, which means to match the force of a 1ton object moving at 100mph, it would have to move at 100/7.7mph or in real money, 12.99 miles per hour (2 decimal places)."
We're talking about kinetic energy here, not force. A 1 ton car travelling at 100mph has a kinetic energy of about 1.1 Megajoules, not 32 Mj (correct me if I'm wrong). A 7.7 ton bus would have to be travelling at around 36mph to have the same energy. (E = 0.5mV^2)
32Mj would require speeds of 561.55 and 202.37 mph respectively (2dp) i.e. bloody fast!
At a range of 100 miles, and travelling at 5600 mph, it's going to take more than a minute for the projectile to reach it's target (and that's assuming it doesn't slow down along the way, which it will). A minute is plenty of time for the target ship to change course to avoid the incoming projectile... all they need to do detect the launch and plot the trajectory (OK so that will be tricky but give it some R&D and it's probably do-able).
Unless... we combine giant-rail-gun technology with steerable-projectile technology, then there's no escape!
At a sailing/steaming/turbine speed of 30 knots, the ship would travel 0.5 nautical mile in a minute. The turning rate of large warships is not too impressive, but let's pretend that it can be instantaneous.
Ergo, the target could be anywhere in a circle of radius ca. 0.5 nautical mile. That's what the shooter has to aim for, and that's part of the reason the old fashioned battleship guns frequently have multiple barrels, to be able to fire barrages. I've heard that navies that have nuclear weapons are loathe to forsake them, because they have a large destruction radius, and, after all, you don't make permanent holes in the water.
From the point of view of the target, the trick is to use, e.g., radar, to find the projectile (the horizon is 50 miles away, so you won't see the projectile until it is already half way to you), predict its path, and avoid the patch of ocean where it will hit. Not an easy task, especially if the projectile is a slender 10 kg tungsten rod.
Actually around 40 seconds (assuming that the round doesn't slow down as you pointed out so call it a minute) ... Large Ships don't necessarily maneuver that well, the firing ship will fire a barrage most likely (over the horizon so you aren't going to know there incoming rounds) so it's not as silly as it sounds.
Cheers
Most modern warships have relatively thin hulls. Such a slim projectile needs to hit something with substantial mass to impart a good proportion of its energy otherwise it will just go through like a rifle bullet through paper. There might be local damage but it could easily be insignificant to a ship-sized object.
Its also an unguided shell equivalent so it need to follow a ballistic curve and allow for the curvature of the earth. This is likely to increase errors in aiming.
For close quarter defence there might be a different picture.
I calculate the 1 ton kinetic energy as ~1.5MJ so there is a large mismatch somewhere
(Imperial AND SI units - urrgh!!)
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