Hovertanks

[Skrim]

A thread to discuss whether hovertanks are actually logically feasible.

This thread is inspired by the fairly widespread use of glass cannon-ish hovercraft units in WZ2100, especially NEXUS' complete obsession with them. WZ2100, as I take it, is a pretty realistic game, not counting the acceptable breaks from reality such as the truck turret, repair turret, the simplistic logistics, etc.

The hovertanks in question are actually combat vehicles with weapons mounted on a hovercraft propulsion as we know it - which works by riding on a cushion of pressurized air - and not attack-helicopter-like VTOL machines (which are anyway represented as, well, VTOLs) or phlebotinum-powered antigravity tanks which float for no apparent reason.

Their advantages include:

• - They're amphibious, and can cover water, swamps, ice and other bad but relatively smooth terrain without much difficulty. (demonstrated by PACVs in Vietnam, and by LCACs)

• - They're faster than wheeled/tracked vehicles (well, theoretically at least if they use bigass-fan propulsion, but definitely if they use jet propulsion - not that that's ever been done AFAIK).

• - They, unlike helicopters, can assume a stationary hull-down position and hold ground without having to constantly spend fuel.

• - They seem to be able to carry a pretty decent amount of weight (at least in case of LCACs), more than helicopters. (LCACs of course, are bigger than the theoretical hovertanks, but the hovertanks will still need to carry much less weight than they do- they won't have 60+ ton tanks to haul around, save for maybe themselves if they get that heavy)

Their disadvantages include:

1. - They can't traverse rocky terrain easily, because they hover pretty damn low above the ground.

1. - They would have to counteract recoil from weapons fire if they use cannons, though this isn't a problem if they use missiles or railguns (which, AFAIK, get their 'recoil' in the form of the rails getting pushed apart, not as a backwards kick).

1. - They'd probably still have to be a good deal lighter than tracked vehicles of a similar technology level, meaning less armor and/or weaponry.

1. - The propulsion (whether fan or jet) and air cushion skirt make extremely easy targets unless they have armor focused around them. The above-mentioned PACV wouldn't last a moment against an RPG.

1. - They'd most likely be more expensive than tracked vehicles, though that's no problem for, say, someone like NEXUS.

In my imagination, a hovertank's defense would rely on relatively lightweight defensive mechanisms like active protection systems (whether interceptor-based, like Trophy or Quick Kill, or 'barrier'-based, like Iron Curtain) and electric reactive armor, and always be lightly armored compared to contemporary tanks, more suited for roles such as that of amphibious IFVs or highly mobile MLRS/SAM batteries instead of as MBTs. What armor they do have would be concentrated around the air cushion and propulsion so as to help prevent immobilization.

Any opinions?

[TVR]

Ground-effect vehicles cannot perform any of the tasks required by manoeuvrer warfare.

The air they're supported on is relatively frictionless, although that means high maximum velocities, it also leads to poor acceleration and deceleration rates. In addition, any weapon producing recoil can't be fired while air cushion is active, ie they cannot fire cannons, pressure and magnetic induction included, on the move.

Although this means GEVs are a poor choice for manoeuvrer warfare, they are still excellent for hover-by rocket attacks, and the turret means they aren't vulnerable to the predictable flight patterns of a gunship.

They are most efficient platform for transporting heavy cargo, which includes it's own vehicle armour, over any distance, as they easily beat even ground-effect seaplanes by the sheer virtue of being able to move onto land safely.

The actual exposed propulsion mechanism can't be a jet-engine, as proximity to salt-water will easily cause engine stalling, electric motor, turboshaft, or rocket are feasible alternatives.

[JDW]

Eh? Me thinks, this topic is better off in general discussion.

[Zarel]

Moved.

[Skrim]

Ground-effect vehicles cannot perform any of the tasks required by manoeuvrer warfare.

The air they're supported on is relatively frictionless, although that means high maximum velocities, it also leads to poor acceleration and deceleration rates. In addition, any weapon producing recoil can't be fired while air cushion is active, ie they cannot fire cannons, pressure and magnetic induction included, on the move.

Although this means GEVs are a poor choice for manoeuvrer warfare, they are still excellent for hover-by rocket attacks, and the turret means they aren't vulnerable to the predictable flight patterns of a gunship.

They are most efficient platform for transporting heavy cargo, which includes it's own vehicle armour, over any distance, as they easily beat even ground-effect seaplanes by the sheer virtue of being able to move onto land safely.

The actual exposed propulsion mechanism can't be a jet-engine, as proximity to salt-water will easily cause engine stalling, electric motor, turboshaft, or rocket are feasible alternatives.

Rocket propulsion wouldn't work too well, given the very short burn times of rocket motors. Diesel-electric or turboshaft are the most practical - turboshafts are what are used on actual hovercraft.

I think the 2 roles that hovers could fulfill pretty well are those of the MLRS and the EFV. The MLRS-hovercraft would be good for providing off-shore fire support before moving inland. It would be pretty good for shoot-&-scoot style bombardment. As for the role of the EFV, it would be a landing craft that carries infantry provides fire support for them, through rocket/grenade launchers and smaller-caliber guns/cannons. The machine would be something like the Russian Zubr, but much smaller. The main problem is that it's in-land mobility would be worse than that of a tracked EFV, being restricted to relatively flat terrain and with slower accel/decel rates. The MLRS could still work in-land pretty well, since it doesn't quite need the mobility and fast start-stop characteristics of a front-line vehicle.

Why would a hovercraft be unable to fire railguns, though?

[3drts]

railguns (which, AFAIK, get their 'recoil' in the form of the rails getting pushed apart, not as a backwards kick).

Absolutely wrong. Railguns produce a lot of recoil in the opposite direction the projectile is fired.
Conservation of momentum.
There is no sideways recoil, there is a force pushing the rail apart, this is analagous to the force on the walls of the firing chamber in a gun.
As the rails push the projectile forward, they push themselves back in a way described by M1V1= M2V2 (where the numbers are meant as subscripts)
So for a 1kg projectile going 10,000 m/s, a 10,000 kg tank (ie, 10 metric tons), will be pushed backwards at 1 m/s, which isn't that bad - only 3.6 km/h or 2.2 mph.
If you use a 5 kg shell, or a 10 kg shell, like some tank guns today
http://en.wikipedia.org/wiki/Ordnance_QF_20_pounder
Then the recoil gets quite significant, if we are still assuming its launching them at 1 km/s (rather than the modern tanks, which fire shells between 1-2 km/s)

Hovertanks (using air cushions and a fan) cannot climb steep inclines, this will get worse as your armor them up, their acceleration will also get worse.
Increasing engine power necessitates increasing fan diameter (or else you get diminishing returns for added engine power)- making them rather visible.
Sure you can armor their side skirts, like the armored sides that protect tank tracks.
The fan wouldn't actually be that vulnerable, unless you hit the center, you will only hit individual blades, it could be desigend to be able to withstand a few blades flying off (indeed, even some turbines are remarkably durable, still runing with many of the fan blades all chewed up)

To counter the traction problem, they could have a system like what cog trains use to go up steep inclines- a cog wheel, or spike wheel, that they lower down to dig into the ground and help them climb - or to brace for recoil.
Such cog wheels would be useless in swampland or muddy floodplains, but thats where hovercraft operate normally today, and where a tracked tank would find itself mired in mud (tracks are better than wheels for that, but that poor terrain mobility advantage is used to add more armor, making the vehicle heavier, and will not perform better than an offroad wheeled vehicle in that terrain).

Also for the recoil thing, the hover tank could easily reduce airflow to the skirt, and settle down on the ground, a second or two before firing (think siege tanks from SC), and be on the move again in another second or two.
But as mentioned, without a huge fan, or some wheel that digs into the ground (when over solid ground), their acceleration will suck.

As to fan size, we can also look at M1V1=M2V2.
Except now you calculate the mass of air being moved-> smaller diameter means smaller mass of air, which means it must be moved faster- at which point we run into the equation KE=1/2 MV^2
If you move air twice as fast, it takes 4x as much energy. Small fans moving a small amount of air very fast, are exceedingly energy inefficient. Its one thing for a light jet, but a heavy armored tank..... its just not feasible unless said tank mounts a fusion/nuclear reactor....
Thats why passenger jets have high bypass turbofans, not turbojets, the diameter of each turbofan is roughly double that of a turbojet of the same thrust, for 4x the area- allowing the exhaust to be much slower to supply the same thrust.

Of course, you can't go faster than your exhaust speed - so there is good reason to have exhaust moving at mach 3 or 4, but for a passenger jet that isn't meant to go mach 2, such exhaust speeds are wasteful.

[Skrim]

railguns (which, AFAIK, get their 'recoil' in the form of the rails getting pushed apart, not as a backwards kick).

Absolutely wrong. Railguns produce a lot of recoil in the opposite direction the projectile is fired.
Conservation of momentum.
There is no sideways recoil, there is a force pushing the rail apart, this is analagous to the force on the walls of the firing chamber in a gun.
As the rails push the projectile forward, they push themselves back in a way described by M1V1= M2V2 (where the numbers are meant as subscripts)
So for a 1kg projectile going 10,000 m/s, a 10,000 kg tank (ie, 10 metric tons), will be pushed backwards at 1 m/s, which isn't that bad - only 3.6 km/h or 2.2 mph.
If you use a 5 kg shell, or a 10 kg shell, like some tank guns today
http://en.wikipedia.org/wiki/Ordnance_QF_20_pounder
Then the recoil gets quite significant, if we are still assuming its launching them at 1 km/s (rather than the modern tanks, which fire shells between 1-2 km/s)

Ok, yeah. The electromagnetic forces between the rails and projectile, driving the projectile forward, will also drive the rails backward, while the force between the rails will drive them apart.

The U.S Navy's 90mm prototype railgun fired a 3.2 kg projectile at 2,520 m/s. If mounted on a 60-ton tank, it would push it back at ~0.5 km/h. Recoil would be less of a problem with very fast but not very massive projectiles. So relatively low-caliber railguns firing fast kinetic-energy projectiles would be comparatively better-suited to hover tanks than big cannons like those on real tracked tanks. The lack of propellant would mean that the railgun barrel can be smaller in diameter without actually having to use a smaller projectile than a cannon.

The most unlikely thing to be mounted on a hover would be indirect-fire cannons of any sort, like mortars or howitzers, since those would generate downwards recoil that forces you to land and means that you can't use them when positioned over water or bad terrain like swamps. Rockets/missiles or lasers could be used pretty easily, though.

As to fan size, we can also look at M1V1=M2V2.
Except now you calculate the mass of air being moved-> smaller diameter means smaller mass of air, which means it must be moved faster- at which point we run into the equation KE=1/2 MV^2
If you move air twice as fast, it takes 4x as much energy. Small fans moving a small amount of air very fast, are exceedingly energy inefficient. Its one thing for a light jet, but a heavy armored tank..... its just not feasible unless said tank mounts a fusion/nuclear reactor....
Thats why passenger jets have high bypass turbofans, not turbojets, the diameter of each turbofan is roughly double that of a turbojet of the same thrust, for 4x the area- allowing the exhaust to be much slower to supply the same thrust.

Yeah, you'd basically want to maximize fan area. You could have one huge fan, which can be knocked out if the hub is hit. Alternatively, you could have 2 or 3 slightly smaller fans, or 4 half-size fans while maintaining the same amount of area. The 4-fan configuration would probably be slightly heavier and more complex, but is probably more resilient since it can't be completely disabled with one lucky hit.

[Assault Gunner]

Personally, I would go with the many-fans approach for any combat vehicle. As for the projectiles utilized by a railgun, they are generally very small and lightweight (comparatively speaking), usually massing 5-6 pounds, compared to the 50-pound shells used by the M1A1 Abrams. They are so small and light because their velocity makes them energy states, not matter. If they hit something, they will explode in a very big way.

[Lancefighter]

while id agree that rocket engines have no place on a hovercraft, what is wrong with jet engines? fans arent the only thing that produce thrust..

[Verin]

lol jet engines,
Speed: 1200

[Lancefighter]

lol jet engines,
Speed: 1200

Jet engines can be small too. For instance.. model jet airplane
I cant be sure, but i seem to recall some jet engines being used on hovercraft by the navy on one of those engineering shows i watch during the day when im bored >.>

[Jorzi]

About the railguns: they provide less recoil for the same amount of kinetic energy compared to ordinary cannons, since the projectiles have lower mass and higher velocity, but a large railgun still inevitably produces a huge recoil impulse. (Even lasers produce a small recoil impulse because the photons have a momentum) It is true that the railgun produces large outward forces on the rail, but so do the powder gases do against the barrel walls of a cannon too.

Hovertanks like in warzone would indeed have several limitations in reality that seem to be mysteriously overcome in the game, but I still think they are good as they are, warzone isn't that realistic

[Verin]

http://www.thekoalition.com/wp-content/ ... rcraft.jpg

A logical hover tank

[Tren]

(Even lasers produce a small recoil impulse because the photons have a momentum)

It would be true, if photons had mass.

[Tren]

(Even lasers produce a small recoil impulse because the photons have a momentum)

It would be true, if photons had mass.

Then again, you could be confusing it with any form of particle accelerator, which would produce a little bit of recoil as you said, seeing as they have mass, not enough to show any sign, but mass is mass nonetheless.