Advanced grav tanks - why do they have turrets?

[ThunderChilde]

About this table hockey, pucklike idea. If its inytu, I don't see civilian AG vehicles ever being adopted. They'd be an awful menace riccocheting around town, crushing people, pets, fences, each other.

I don't buy it, it doesn't feel right. Hell, that'd put players off ever getting a Gravbelt, and they'd suck in military use, a whole platoon skidding all over the place, it'd be the Melberg Incident all over again. Hockey Puck indeed. Not imtu, Thankyou very much.

 

[Klaus]

Well I think it's been established that the grav tank is not a universal fighting vehicle.

It's primary theatre is NOE hide and seek. However, before it can get there, in a 'classic' planetary assault, it will have to negotiate an exposed and dangerous atmosphere. They have speed, but will that be enough. Might they require secondary characteristics akin to a combat aircraft?

Might there be all sorts of designs of AFV's using different modes of operation. Look at all the (nowadays seeming) crazy designs that were deployed in WW2. After all, modern tanks have never actually fought the 'classic' tank battle as seen back then, so it's likely that if we ever got into shooting wars between advanced industrial nations many of the theories and tactics that modern MBT's are based on would turn out to be wrong or irrelevant.

Anyway, even if tanks are tanks, where are the other classes of grav AFV? There was a scout gunship in 'Against Gravity' but that's the only one I've can remember from any edition of Trav. What does lift cavalry use...?

One last thing. The grav tank is the 'big ticket' army kit, that gets the attention of the kids and the media (and the game designers). However, it is probably very uncommon in the OTU for grav tank to face grav tank. Asymmetric warfare seems more likely, and we can see from RL that 'jeeps' protected from IEDs and close air support are arguably much more useful in that environment than an MBT. Also, the players are much more likely to face and use this kind of AFV rather than the heavy mob. So what would these types of vehicles look like with grav tech?

 

[far-trader]

...What does lift cavalry use...?

Classically (iirc) they use G-Carriers and Air/Rafts. The Grav equivalents of APCs/AFVs and Jeeps.

The Classic Grav Tanks (Trepida and such) have never seemed so much MBT (heavy and super heavy) equivalent to me, but more like Light Tanks.

 

[Greylond]

After all, modern tanks have never actually fought the 'classic' tank battle as seen back then, so it's likely that if we ever got into shooting wars between advanced industrial nations many of the theories and tactics that modern MBT's are based on would turn out to be wrong or irrelevant.

Uh.... excuse me? You need to read the history of the Arab-Israeli Wars and read up a bit on Gulf War I (1991).

 

[Icosahedron]

About this table hockey, pucklike idea. If its inytu, I don't see civilian AG vehicles ever being adopted. They'd be an awful menace riccocheting around town, crushing people, pets, fences, each other.

I don't buy it, it doesn't feel right. Hell, that'd put players off ever getting a Gravbelt, and they'd suck in military use, a whole platoon skidding all over the place, it'd be the Melberg Incident all over again. Hockey Puck indeed. Not imtu, Thankyou very much.

YTU can have anything you like, of course, and I don't actually like the puck principle myself for the reasons you suggest, but I find it difficult to argue with the physics.

A ground vehicle brakes and turns by using friction against the ground, and an aircraft brakes and turns by using the aerodynamics of a large wing area and low mass. Both of these principles allow braking and turning forces far in excess of the vehicle's thrust.

The grav vehicle has access to neither of these methods and, in the absence of another 'handwaved' system, has its braking and turning limited to the available thrust. Some of the listed canon thrusts suggest that deceleration by thrust alone will inevitably point to the puck principle.

Either the craft need a new braking and turning system, or they need much higher thrust ratings, yet lower speeds.

If you have a logical rationale that allows a grav vehicle to obtain extra thrust for deceleration and turning, but not for acceleration, I really would be pleased to hear it and banish that pesky puck principle of physics.

 

[far-trader]

...If you have a logical rationale that allows a grav vehicle to obtain extra thrust for deceleration and turning, but not for acceleration, I really would be pleased to hear it and banish that pesky puck principle of physics.

I touched on this briefly above but it might work for you with more explanation.

My take on grav thrust is the main thrust is down to keep the craft airborne. Directional thrust can be applied off axis one of two ways. First and most commonly by manipulating the field so it falls-off in the direction you wish to apply the thrust, and second by tilting the craft itself to gain a better attack angle for the field.

This is based on the field having a set orientation on construction and the thrust being less as you deviate from that orientation.

Overall speed calculated for thrust is the same, but it takes longer getting there in normal operation. Ditto for braking speed.

Hence my "flip" maneuver for quick full thrust for stopping on a dime from speed. Also useful for faster acceleration. Sort of like a helicopter that lifts straight up to gain a little altitude then noses over to make better speed at a sacrifice of some lift.

Of course I also have the inertial damper and artificial grav associated with the grav thrust orientation and power. So normal accel and decel are totally compensated, but use the flip maneuver and you will feel the extra gees. Better be buckeld in.

I also see air-brake spoilers for additional stopping and turning in my TU grav craft.

An emergency drogue chute for stopping wouldn't be amiss for civilian grav craft used in atmo. I seem to recall building a fast sport grav bike that had a dual purpose chute that served as both an emergency drogue brake and an emergency parachute in case of high altitude power or grav failure.

So basically I guess it's air-hockey pucks with special maneuvers and gear to compensate.

 

[aramis]

Either the craft need a new braking and turning system, or they need much higher thrust ratings, yet lower speeds.

If you have a logical rationale that allows a grav vehicle to obtain extra thrust for deceleration and turning, but not for acceleration, I really would be pleased to hear it and banish that pesky puck principle of physics.

Keep in mind, aside from the thrust agency being above rather than below the majority of mass, a helicopter is thrust driven. Quite literally, it's the closest comparison available in terms of movement capabilities.

Now, most helos operate with 1.5-2.5G's.. much the same regime as most published MT grav vehicle designs.


The most nimble have stubby but functional wings and tail fins... plus the tail rotor is useful in repointing as well (in addition to its use in countering Rotor Torque).

THe addition of these types of features to a grav vehicle (stubby wings and a basically flat design, plus fins and sideways thrusters on the ends of the craft), and you get something that bites enough air to reduce its turn radius below that of thrust alone.

Even the trepida and astrin, with large flat underbodies, can cut into the air somewhat by banking while turned off-vector. It's not much, but it will more than at least quadruple their cross-sectional area (and probably increase drag by about the same, maybe a little more.) (from about 20m² & SL to about 105m² and essentially not... which puts the mass/surface ratio from 7T/m² to 1.3T/m². Which cuts coasting distance by quite a bit, but I don't remember the formulae... which involve airmass disturbance, amount of deflection, rate of deflection over form, speed regime, and several other ugly variables.)

Stopping distances are akin to those of helicopters and harriers, and for the same reasons... But unlike helos, where the lift mechanism is external to the body (and is circular), the gravitic lift is generally presumed below the main cabin, but inside the armor.

(Note that Renegade Legion: Centurion has the gravitics external but also providing a limited shielding effect... so RL gravitics are subject to direct underside attack, but have inherent side-on resistance to kinetic weapons. Therefore they have a much better reason to stay low. Plus RL:C gravitics are most effective at NOE level. Elements that are not present in Traveller. BTW, most of the FASA guys had exposure to Traveller...)

Also note that TNE grav vehicles are entirely different; they use mass reduction instead of gravitic thrust. When you drop the weight of the tank to 2% (140 tons would be 3.2 tons of thrust up required), and generate that thrust by other means, usually HEPlaR. (Which has it's own .9c+ exhaust issues... essentially it's a firing high-energy alpha and beta radiation....)

 

[Zparkz]

I can see some very special maneuvers that grav tanks can use, regardless of ruleset used. HEplar drives may be vectored and in CT/MT (and possible MgT) the gravitic system seems to be able to thrust in any direction regardless of facing.

Normal tanks will have problems with armor facing if they need to change position during an engagement. However a grav tank with vectored thrust may slide sideways keeping the front towards the enemy, and even engaging it.

 

[Klaus]

Uh.... excuse me? You need to read the history of the Arab-Israeli Wars and read up a bit on Gulf War I (1991).

I do know my history. I know both sides had tanks that were of a comparable marque but could not easily find any info on tank vs tank battles. As for Gulf War I, those are not 'classic' tank battles in the WW2 sense but essentially turkey shoots with one side equipped with far more advanced and superior kit - that just proves that you cannot go head to head against forces that have a TL up on you. (And anyway, Apaches and A-10's accounted for a good portion of the kills, showing the import of air superiority and combined arms - now where are those types of vehicles in Trav?).

Apart from the Zhodani and the Solomani, who else sharing a border with the Imperium can field forces of TL13+ grav tanks? Since the Imperial military has to be everywhere, but the tech-equal threats are localised, it may well be the average imperial marine has never seen a grav tank.

 

[shadowdragon]

Also note that TNE grav vehicles are entirely different; they use mass reduction instead of gravitic thrust. When you drop the weight of the tank to 2% (140 tons would be 3.2 tons of thrust up required), and generate that thrust by other means, usually HEPlaR. (Which has it's own .9c+ exhaust issues... essentially it's a firing high-energy alpha and beta radiation....)

ok this has been driving me crazy...according to TNE, HEPlaR is only heating the hydrogen to a plasma state, not to the fusion or even fission level. Its hot, yes, but giving off alpha or beta radiation? I dont think so. .9c exhaust velocity? that i dont know but is seems a tad on the high side..

 

[robject]

Apaches and A-10's accounted for a good portion of the kills, showing the import of air superiority and combined arms - now where are those types of vehicles in Trav?

= Grav tanks? Maybe? (Dunno).

 

[mike wightman]

As I posted earlier - TL12 and above they are called gunships

 

[ThunderChilde]

Okay, here goes.
IF you accept the handwave of ships easily landing on millenium falcon like struts. IF you accept there are gravbelts, air rafts, G-carriers and all the other associated handwavium of inertial sumps and what not, why is it so hard to picture a grav tank being a very accurately controled, braked, gimballed whatever, grav vehicle??

It already can fly at mach speeds, make re-entry, achieve orbit from the ground, etc etc etc. if it has enough oumph to do all that, why can it not finely modulate low speed noe movement? Just seems rediculous that it can't.

 

[Greylond]

I do know my history. I know both sides had tanks that were of a comparable marque but could not easily find any info on tank vs tank battles. As for Gulf War I, those are not 'classic' tank battles in the WW2 sense but essentially turkey shoots with one side equipped with far more advanced and superior kit - that just proves that you cannot go head to head against forces that have a TL up on you. (And anyway, Apaches and A-10's accounted for a good portion of the kills, showing the import of air superiority and combined arms - now where are those types of vehicles in Trav?).

Look up the Israeli 7th Armored Brigade History vs the Syria and their involvement in the Battle of Suez. Classic Tank Operations/Tactics.

As for the Gulf War I? Yea, I'd call that a "Classic Tank" Operation simply because to pull it off involved a massive movement of Tanks over unfamiliar terrain at night. Even with state of the art night vision/thermal systems, I've been told it is a challenge. And using the advantages of your equipment and training is the obective of a fight.

And there were incidents where plain stupidity played it's part on our side too.


Also, you have to remember that our Armored Warfare Operations and Tactics are tried and tested all the time at the U.S. Army NTC in the Mojave desert.

 

[aramis]

ok this has been driving me crazy...according to TNE, HEPlaR is only heating the hydrogen to a plasma state, not to the fusion or even fission level. Its hot, yes, but giving off alpha or beta radiation? I dont think so. .9c exhaust velocity? that i dont know but is seems a tad on the high side..

It's not my math... someone on the TML worked out that, given the volume/mass of fuel used, the thrust generated, etc, the exhaust velocity was essentially particle beam speeds.

 

[ThunderChilde]

In WWII, the germans consistantly held a clear edge over US and British armour in the field. It wasn't until the mid 50's that the US fielded a tank gun that out preformed the 88L70. German tank guns were a decade ahead of anyone elses. Thier Armour doctrine was superior aswell.

THe US buried them under a tidalwave of inferior tanks with high losses to win. That and artillery and close air support, which we did better than the Germans. We did logistics better too, it helped.

Very few "classic" armour battles were ever fought with equivalent equipment and training on both sides. The Israeli's have shown on several occasions that inferior equipment, in the hands of well trained and led forces can defeat superior equipment and numbers.

Honestly, tanks very rarely get fielded in the worlds hot zones against each other. Isreal has been a crucible for equipment, doctrine and tactics.

 

[shadowdragon]

It's not my math... someone on the TML worked out that, given the volume/mass of fuel used, the thrust generated, etc, the exhaust velocity was essentially particle beam speeds.

weeeelllll.....
using the F=m(p)v(e) formula i get 4032 km/s, about .01344 c....

did I do that right?

 

[Starviking]

It's not my math... someone on the TML worked out that, given the volume/mass of fuel used, the thrust generated, etc, the exhaust velocity was essentially particle beam speeds.

Also akin to having a nuke going off behind you. I handwave this away by using 'em on low power in atmospheres to heat up scooped up air like a jet does.

 

[Starviking]

In WWII, the germans consistantly held a clear edge over US and British armour in the field. It wasn't until the mid 50's that the US fielded a tank gun that out preformed the 88L70. German tank guns were a decade ahead of anyone elses. Thier Armour doctrine was superior aswell.
<SNIP>

The problem with the German equipment was that a lot of it was just too complex. I recall reading about a comparison between US and German artillery: the US gun had 6 moving pieces, the German one 70! So many more things to go wrong - a maintenance nightmare.

 

[aramis]

http://traveller.mu.org/house/thrusters.html includes the expected result of 20km/s for the energy available, but then notes that this produces 1/1980 the thrust listed, so...

Date: Mon, 20 Nov 1995 16:04:13 +0200
From: Antti Lahtinen (al76188@cs.tut.fi)
Subject: HePlaR efficiency
HePlaR efficiency I was trying to design better thrusters to be used with FFS rules, and first I decided to try some real-world efficiency calculations for the existing FFS thrusters. However, during the very first calculations I noticed that something was wrong with HePlaR thruster: HePlaR thruster appears to have a curious way to generate extra energy from nothing.

According to FFS, 1 MW HePlaR thruster consumes 0.25 m3 of liquid hydrogen in one hour. This amount can be converted to (0.25 m3 * 0.07 ton/m3 *1000 / 3600 s =>) 0.0049 kg/s.

Thrust: F = v * m/t [Newtons]
Power consumed by generated thrust: P = 0.5 * m/t * v^2 [Watts]
m/t = 0.0049 kg/s

Thrust in Newtons can be converted to tons by dividing the Newton value by (9.81 m/s^2 * 1000 =>) 9810.

With 1 MW input power and 100% efficiency, the exhaust velocity of plasma is:
v = sqrt(P/(0.5 * m/t)) = 20284 m/s

Thrust produced by this plasma stream is:
F = v * mt / 9810 = 0.0101 tons = 10.1 kg thrust

However, according to FFS, this thrust should be 20 tons, which is 1980.2 times the calculated value.

While thrust is proportional to exhaust velocity, the power consumption is proportional to the square of this exhaust velocity. Because of this, it is more efficient to have heavy exhaust with lower speed than light exhaust in high speed.

so it uses about .00000025 the power it should...

I stand corrected on the value. It's a negative entropy drive, drawing some form of energy that isn't supplied by fuel or power inputs.

So... HEPlaR is still putting out mach 40+ exhaust. it's a cutting torch.