The Practicality of Hovering Vehicles

[m4inbrain]

As far as the tank idea goes, there's way more drawbacks that a hovering vehicle brings to the table than upsides. The only argument for a hovertank would be, if you're generous, the "strafing". But in modern combat situations (speaking from experience), you actually don't attack around a corner, exposed. You call for support, which is always with you (soldiers/airsupport/flanks/artillery/or simply fog). If you don't know that you have a tank in your flank somewhere, you wouldn't know it in either tank. Few other issues that weren't mentioned: turretrotation would shift weight and accelerate the tank into a specific direction except if stabilized by computers, your gimballing engines would need to be immensly powerful to accelerate a, let's go easy on you and say, 20t tank (which is nothing for an MBT, in reality we're talking 60+ tons, 20 is generally not even enough for APCs) up a hill, or even worse: rough terrain, which would bring the need for the gimballing engines to accelerate the tank, keep it stable in height, AND do the "countersteer". You said, these vehicles would be used for urban combat, meaning that a relatively small mine (or even handgrenade/pipebomb) under the tank would render it unable to move (i suppose you can't armor the propulsion devices, correct me if i'm wrong though). You also said the tank wouldn't need a turret, which is impractical since you can't (in urban combat) turn the tank everywhere (there's a reason why tankdestroyers with fixed guns died out - and in urban combat rockets are pretty useless, that's why MBTs still use cannons, and APCs have AT rockets only as secondary weapon). Another problem would be, if the tank hovers "a couple of feet above ground", what happens if it gets trapped, by rubble or other cars/trucks? I can't believe that you could make those engines powerful enough to push a 20t tank and whatever is in front of it away. But i might be wrong on that one, it's just a guess.

There's two things though that render the tank actually useless to me as a former gunner on a tank: for the ability of strafing (if needed or not doesn't matter in that argument) you give up on two very important things. First, you want your tank to be as low in profile as you can get. Hovering a few feet above ground would make your tank stand out alot, and render alot of potential cover (walls etc) useless. And the fact that you try to build a tank that is supposed to drive (strafe) into the crosshair of an enemy, intentionally (which btw wouldn't work either, since no matter what you do, the other tank will have the first shot - and while the front is the toughest part on a tank, it's not invincible - especially if weight is such an issue).

Now, i sound overly negative, but don't worry. I am. As a tank, that idea is flawed horribly, and i never ever see it working. But.

That doesn't include civilian vehicles. I'm not sure that your idea has the same energy consumption as modern cars (which get more and more efficient too), but that's because i can't do the math for it. I do see applications, maybe not really in the sense of "cars for people" (alot of people can't drive a car properly, let alone something that reacts so differently to steering inputs like a hovercraft, and i had the enjoyment of driving a small one on an event, for like 5 minutes or something), but rather public transport.

You asked for opinions about advantage for hovervehicles - i don't know enough about complexity, theoretical fuel/power consumption and whatnot for civilian vehicles - but for military vehicles, i see so many drawbacks already out of the top of my head, i don't think it'll ever be worth it. Not even for those drawbacks, but for the simple fact that modern warfare has no use for it. There's no upside to a hovertank, all our military strategies and tactics are based around how to fight in an urban enviroment with conventional tanks. That entangles with soldiers, supportunits, aircrafts and all kinds of things, you'd need to change all that just to get literally no upside. A military vehicle nowadays has to integrate into the existing force, i don't see that working for hovertanks.

I don't mean to attack you though, if i come off like that.

[KerikBalm]

Now now KerikBalm. I know your stance on the system, this thread isn't about that. Utilizing the drive in a hover-vehicle IS a patentable idea. If it turns out the drive doesn't work, well then the patent is useless but still existent. And yes, you can get patents on things that don't work out or are declared infeasible. Mostly because the patent office does not have the budget to have people on staff that can definitively declare things one way or another.

I'm well aware of what can and cannot be patented.

If the drive worked, the idea of using it to make a hover vehicle would probably be contested due to lack of an inventive step/obviousness.

If there was some particular problem with the implementation that he had solved, then he'd probably be able to get a patent.

But generally very basic ideas and concepts are not patentable, and you need to be pretty specific in what you want to patent.

The examiner would not let stand such broad claims. If the claims were granted, they would be easily challenged and invalidated in a court.

That said, I never made any mention of the patentability of the EM drive or applications thereof, rather I expressed skepticism that there would ever be a "generation 2" EM drive before its even shown that "generation 1" works (which it most likely doesn't)

[KerikBalm]

It isn't an ion engine. It contains a bubble of plasma and repels off of it. It doesn't constantly expel plasma.

If you could magnetically contain a bubble of plasma for practical periods of time, Fusion reactors are where you would want to focus your efforts.

You wouldn't be able to contain the plasma, let alon contain the plasma outside a structure.

Assuming you could, what happens when your "plasma wheel" contacts the ground? Your plasma wheen gets destroyed.

It wouldn't work.

[K^2]

It isn't an ion engine. It contains a bubble of plasma and repels off of it. It doesn't constantly expel plasma.

Gravity constantly transfers momentum over to the craft. You have to bleed that momentum off. That means either applying a force to a static object (ground) or expelling reaction mass. In other words, you cannot repel from plasma without expelling it. That simply does not work.

[KerikBalm]

I think that he thinks that the plasma bubble would repel off thr ground.. I guess through direct contact with the ground.

Obviously, the plasma would be rapidly depleted from colliding with the ground.

I guess he thinks you can push the same plasma mass against the ground almost indefinitely - which is not the case.

[Wanderfound]

I think that he thinks that the plasma bubble would repel off thr ground.. I guess through direct contact with the ground.

Obviously, the plasma would be rapidly depleted from colliding with the ground.

I guess he thinks you can push the same plasma mass against the ground almost indefinitely - which is not the case.

The cartoon in post #29 is looking more appropriate as this goes on.

[MockKnizzle]

My interpretation is that he imagines the plasma bubble to be analogous to the air trapped under a hovercraft's skirt - a region of high-pressure fluid trapped between the vehicle and the ground that provides the necessary lift. A hovercraft contains the high-pressure air underneath itself by blowing a relatively small volume of air at high velocity through slots in the bottom edge of the skirt, creating a curtain of air that traps air inside (just like the air-curtain doors that some supermarkets use to keep their conditioned air inside when the solid doors are open). The vehicle only needs to move a relatively small amount of air to maintain both the air curtain and pressure in the plenum, and thus requires significantly less power to hover than a momentum-based helicopter.

Theoretically, an electromagnetically contained, pressurized plasma plenum would keep a vehicle aloft the same way - but good luck trapping it beneath the vehicle for any useful length of time. Electromagnetically containing plasma is already difficult enough in the lab, and when you need one side of your containment vessel to be the ground, you make that job essentially impossible. Now, you might then decide to re-think the idea and pressurize the plenum with regular air, and have the skirt be the fancy bit: maybe you use your ionized air as a "plasma curtain" instead of an air curtain. This seems slightly more practical to me, but again, creating and controlling the plasma curtain is a big problem.

Regardless, I'm still left with one giant question... why would you ever want a plasma hovercraft instead of a regular one?

Edited October 28, 2014 by MockKnizzle

[cantab]

A practical issue with any sort of hovering vehicle is that your acceleration and braking are the same. Wheeled cars can brake much more quickly than they accelerate with brakes much smaller than their engines. A hovercar will need an 'engine' that's overkill for acceleration in order to have a stopping distance that's short enough for safety.

And no, turning off the hover and dumping the car on the ground as an emergency brake isn't a good idea, because you'd have no control over the car as it skidded. Turning off the hover and dumping the car onto regular wheels equipped with steering and brakes would work, but if you're carrying around regular wheels why are you hovering at all?

[Mazon Del]

I think MockKnizzle's thoughts are probably close to the what JMBuilder imagines with this setup. I think I can see what he is going for, he wants to create a hovercraft that unlike conventional versions, does not have a physical skirt. One reason we don't have giant hover-land battleships (amidst all other kinds of problems with it) is that it just takes one sharp boulder or mine to blast a hole in the skirt to immobilize the entire thing.

However, in addition to the other technical issues going on with this, one of the bigger points being that if you are ionizing the air, this is in effect just trying to hold onto a giant ball of lightning under your craft. Even assuming you do manage to get the electromagnetic skirts going correctly, then you still have a fairly significant problem of the charged air trying to constantly dump its charge somewhere, anywhere. This is likely to be into the ground itself, and worse, it should also definitely include water. If your tank started going over a water source, its very likely to dump all the charge into the water.

You are probably thinking about using your magnetic fields to try and keep the charge from escaping. Like someone pointed out, if you have found a way to effectively pressurize plasma to that degree, then you need to be building fusion reactors, not hovercraft. Right now I am assuming that your idea is just what has been presented, and that you do not have solid design data on the magnetic system (unfortunately some drawings on design paper of coils with the label 'magnetic containment system' doesn't count. I really really wish it did, that would make my job much easier).

As far as a 2nd gen of anything, it is easy to come up with a mk2 of something, so that statement about someone being unlikely to make a mk 2 is kind of pointless.

[Nibb31]

I think MockKnizzle's thoughts are probably close to the what JMBuilder imagines with this setup. I think I can see what he is going for, he wants to create a hovercraft that unlike conventional versions, does not have a physical skirt. One reason we don't have giant hover-land battleships (amidst all other kinds of problems with it) is that it just takes one sharp boulder or mine to blast a hole in the skirt to immobilize the entire thing.

We don't ?

The main reason we don't have hovercrafts bigger than the Zubr-class is that they require so much power when most of that power is wasted by fighting gravity. The other big reason is that the tactical advantage these days is more in stealth than in speed.

As far as a 2nd gen of anything, it is easy to come up with a mk2 of something, so that statement about someone being unlikely to make a mk 2 is kind of pointless.

Indeed. You can quite easily make a Mk2 than doesn't work any better than a Mk1 iteration that doesn't work.

[Kryten]

Ironically, there's a much easier to make a hovercraft without a skirt-take the skirt off of a hovercraft. They increase efficiency, but they aren't vital; SR.N1 managed a complete channel crossing without being fitted with one.

The main reason we don't have hovercrafts bigger than the Zubr-class is that they require so much power when most of that power is wasted by fighting gravity.

Nonsense; a hovercraft isn't constantly thrusting into the ground like a helicopter, it's floating on a cushion of pressurised air; the only energy needed is to top up losses from the cushion (which can be very small in the right circumstances) and for moving around. Oh, and there are hovercraft about twice the size of Zubr.

Edited October 28, 2014 by Kryten

[Mazon Del]

We don't ?

While various militaries have giant hovercraft like this, they are used for ship-to-shore transport for the most part. I was more meaning, we don't exactly have battleships floating across the plains of Kansas.