1) Oerjan is right in a sense - Grav kills other manouvre tech not a
weapons system. My point was it kills ground mobile arty. Arty that can fly
probably uses something more like helicopter armaments (Mavericks, Hellfires,
Rockets, etc) rather than something like a 200mm gun, I'd think. Though there
may be a niche for flying arty platforms that still land to shoot.
2) A tank is loud and noisy. So is a GEV. Either can be made lower in
singature by the application of a) money and b) engineering. Grav might
actually be the quietest and lowest signature possible.
3) Can we build a hovercraft that ways 80 tons, carries the kind of armour a
Leopard II or Challenger or late model Abrams does, mounts a
120-140mm CPR gun or another big main weapon? I have my doubts. If you
could, it'd eat deisel at a far faster rate than even a tank! It has
to pay gas costs to hover - even when it is stationary (if it wants to
not have a lag in getting moving). I think if we had Fusion or
A-Matter power, that'd be a non issue. But with gas engines or power
cells, it is an issue.
4) GEVs can move through swamps and if packing non-recoil weapons
could even fight there. I agree CPR arty would be problematic.
Oerjan, you can cuss me out for making you pick up DS2 - but you
undoubtedly have a lot of first hand info of interest here so I don't
apologize one bit;)
> On Mon, 29 Nov 1999 kaladorn@fox.nstn.ca wrote:
> 1) Oerjan is right in a sense - Grav kills other manouvre tech not a
Why not shut down the grav/GEV drive when doing fire missions?
Conventional SP guns lock their suspension and deploy recoil spades. Grav
vehicles would do the same thing. Slammer's tanks shut down and drop to the
ground when they do company level fire support missions.
> 3) Can we build a hovercraft that ways 80 tons, carries the kind of
This is already covered by the HMT/Fuision power plant rules...
> On Mon, 29 Nov 1999 18:06:30 -0500, kaladorn@fox.nstn.ca wrote:
> 1) Oerjan is right in a sense - Grav kills other manouvre tech not a
Chemical propellent is still pretty efficient. You launch a load into the air
and let gravity drop it where you want it. I think you'll always be able to
launch heavier warheads using chemical (or mass driver) propellent. In fact,
mass driver artillery may be a better bet for grav vehicles, particularly if
they are already using fusion power for the anti-grav units. Recoil
won't be a problem.
> 3) Can we build a hovercraft that ways 80 tons, carries the kind of
You also have to ask yourself "why". What do you gain out of ground effect
tank. Ground effect tanks are actually not THAT useful, David Drake not
withstanding. There is a very real limit to the slope a GEV could scale,
regardless of the slope's potential traction. You raise the skirt too much and
you lose lift. For that matter, you can't easily tilt the vehicle. I think you
could probably kill a GEV with deep, wide trenches. True, that kills tracked
AFVs too, but I'd imagine that narrower trenches would have a nasty effect on
GEVs but allow tracked vehicles to pass. Likewise, anti-tank "dragon's
teeth" wouldn't need to be as big. This is just off the top of my head, too. I
sure wouldn't want to be infantry riding beside a GEV. You couldn't be that
close (due to the ground effect) and imagine standing beside one when it gets
hit in
the side with an anti-tank weapon. Ever play table air hockey? Imagine
you're an ant and the GEV is a puck! Nasty!
> I think if we had Fusion or
I think that tracked movement would still be more efficient. You don't have to
lift and propel the tank, just propel it forward. I think a tracked vehicle
would be able to move faster than a GEV given the same power plant. Of course,
ground pressure would be more of a problem in a tank, as the weight is spread
over a smaller area.
> 4) GEVs can move through swamps and if packing non-recoil weapons
That's about the only type of terrain where it has an advantage. Okay, mud and
snow would be advantageous. But you still have that whole "slopes cause
spilling of air out of the curtain" problem.
Anti grav, however, shouldn't have this problem...
> -----Original Message-----
[snip]
> In fact,
----End Origninal Message -----------
Why would recoil not be a problem? Even if you use magnetics to propel an
object, there is still an equal and opposite force applied against the
launcher. Or did they repeal Newton's Law?
---
> Date: Mon, 29 Nov 1999 18:06:30 -0500
[snip]
> 2) A tank is loud and noisy. So is a GEV. Either can be made lower in
[snip]
i agree. a grav propulsion unit would be quiet, but it would not necessarily
have the lowest signature. signature not only depends upon physical
visibility, but also the level of sensor tech the opposing race(s) possess. if
the enemy also had grav tech, they probably also have grav detection gear
(pick up grav distortions upto a certain distance).
a low-tech race, OTOH, must rely on simple methods (Mk 1 eyeball, etc.).
this note is not to directly pick on you Thomas, but to point out that
everyone's FT/DS2/SG2 universe should work out relative tech factors
for things like sensors/detection, etc. a simple rule for stealth is
that the level purchased is the effective signature to races of the same tech
level. for each tech level greater than the enemy, stealth = +1
(minimum
signature = 1). for each less than the enemy, stealth = -1 (minimum
stealth = 0). for example, it is possible for an advanced race to ignore a
lesser races stealth! one's universe, therefore, must assign general tech
levels to each race.
> Thomas Barclay wrote:
> 1) Oerjan is right in a sense - Grav kills other manouvre tech not a
Until you get Mavericks or Hellfires which you can fire indirectly at
ranges of 40 km and above, indirect-firing artillery will have a niche.
Whenever you have a supply dump (which isn't mounted on grav vehicles)
within 50-150 km of the enemy, indirect-firing artillery will have a
niche.
> 2) A tank is loud and noisy. So is a GEV. Either can be made lower in
Grav might be low-signature, but I doubt it. If something starts
messing with the local gravity field, I suspect it would be fairly easy
to detect :-/ It
probably wouldn't be anywhere near as noisy as a GEV, but it would have other
signature problems to cope with.
> 3) Can we build a hovercraft that ways 80 tons, carries the kind of
you could, it'd eat deisel at a far faster rate than even a tank!
Considering that even the Challenger (the heaviest of the current Western
tanks) is "only" 62 tons fully loaded, and the various
ex-Soviet tanks average around 45 tons, I'm not entirely sure why you'd
want to make the GEV tank 80 tons :-/
> I'm also not sure why you are talking about GEV tanks, when I wrote:
"... I wouldn't be surprised at all if you could build GEV SPs and APCs with
today's hovercraft technology. Not particularly economic, of course, but
probably possible."
Note the complete omission of tanks from the list; it was entirely
intentional. Modern 155mm SP guns average around 25-30 tons when fully
combat loaded, ie about half the mass of an MBT.
> It has
Of course. That's why I considered it "not particularly economic", you know.
Looking at today's military hovercraft and assuming that track transmission is
about as heavy overall as skirts (the skirts themselves are probably lighter,
but the extra turbines and fans aren't), we'd need to increase their cushion
pressure by about 75% from the 1989 level to make an M113 APC hover. I'd be
quite surprised if this were not *technically* possible today. Why you'd want
to do this beats me,
though <shrug> It'd definitely have severe problems with dust/spray
clouds and noise, too.
An M109 or CV90120 (SP arty and severely overgunned light tank, respectively)
would need almost three times the cushion pressure; that'd be more difficult
but may still be possible to do.
An M1A2 would need about four times the ground pressure of today's hovercraft.
This starts sounding a bit too heavy for today's
technology. The most serious problem isn't the energy supply, though -
it is finding space for the lifting and maneuvering fans and air intakes,
preferrably somewhere where they won't be wrecked by the first
burst of small-arms fire directed at the vehicle <g>
> 4) GEVs can move through swamps and if packing non-recoil weapons
There are no non-recoil weapons. Only low-recoil ones... and I'd want
to be *very* certain of my platform's stability (and ability not to drift into
various nearby objects) before I fired any large weapons
from it while hovering over a swamp :-/ Particularly if I am to fire
them in any direction other than straight ahead of the vehicle.
In a message dated 11/29/99 11:40:23 PM Eastern Standard Time,
> agoodall@interlog.com writes:
> On Mon, 29 Nov 1999 18:06:30 -0500, kaladorn@fox.nstn.ca wrote:
In fact,
> mass driver artillery may be a better bet for grav vehicles,
Mass drivers would still create plenty of recoil--I am assuming by
saying
that recoil won't be a problem you are assuming the anti-grav could just
dial up a bit more "thrust" in order to counteract the recoil. Unfortunately,
if it had the capability to dial up that thrust, wouldn't it just be a
higher-rated grav unit (faster, higher flying, whatever)?
> >3) Can we build a hovercraft that ways 80 tons, carries the kind of
I think that assumes that we're dealing with the "marginal" powerplant type
GEV's currently in use. If we were talking about something that basically
had the "thrust" (with the help of limited ground effect) to hover--like
a
helicopter--then we aren't really talking about something that would
need a vulnerable skirt. Of course, such a vehicle would almost definitely
require
a fusion or a-matter plant and could basically fly like a VTOL, but what
the heck!
snip
> wouldn't need to be as big. This is just off the top of my head, too.
I sure
> wouldn't want to be infantry riding beside a GEV. You couldn't be
Imagine you'
> re
Ouch--not a pleasant thought, especially for those of us that like
grunts.
> > I think if we had Fusion or
Of
> course,
And you'd have to watch for throwing tracks--supposedly (and I'm not a
tanker, so this is hearsay) the speed governors placed on the Abrams were
there to prevent some hot dog to scoot around at speeds that increased the
chances of throwing tracks.
> >4) GEVs can move through swamps and if packing non-recoil weapons
Okay, mud
> and
Rob
On Tue, 30 Nov 1999 08:31:44 -0500, "Bell, Brian K"
<Brian_Bell@dscc.dla.mil>
wrote:
> Why would recoil not be a problem? Even if you use magnetics to propel
I said it wouldn't be a problem, but there would still be recoil. What I
should have said is that it would be much LESS of a problem than an explosive
propellent.
Basically with a gun or a mass driver you're trying to apply energy to a
target. With a gun a good chunk of the energy comes from mass. With a mass
driver, more of it comes from velocity.
So, you've got energy being produced by mv**2 (mass times velocity squared).
However, momentum is based on mv (mass times velocity). Since the projectile's
mass can be pretty tiny, you've got a lot of energy for not much momentum. And
since the vehicle's mass is pretty big, you don't have a lot of reverse
momentum.
That's, of course, assuming you're using a mass driver with magnets. I believe
you get even LESS recoil from a mass driver that uses a plasma flow, with part
of the projectile eaten up to form the plasma bridge...
> On Tue, 30 Nov 1999 18:53:49 EST, RWHofrich@aol.com wrote:
> Mass drivers would still create plenty of recoil--I am assuming by
Unfortunately, if
> it had the capability to dial up that thrust, wouldn't it just be a
Sorry, yes you get recoil. It just won't be much of a problem.
Remember, energy is mv**2, but momentum is mv. In other words, if you have a
very small projectile and accelerate it relatively slowly, you will build up a
lot of energy without much reverse momentum. The "v" component would be more
important than the mass component. The launcher and vehicle would have a lot
of mass compared to the projectile. I think it was in the end of Gibson's Mona
Lisa Overdrive that a mass driver fired from a blimp. Recoil wasn't much of a
problem.
That's also assuming you're using a mass driver with magnets. You can also
build a mass driver with two rails, a magnetic field, and a plasma flow. Part
of the projectile would be eaten up by producing the plasma bridge. The result
is even less recoil. I'm not sure this is feasible in a tank based mass
driver, though...
This last one I'm remembering from physics class more than a dozen years
ago...
> I think that assumes that we're dealing with the "marginal" powerplant
If the vehicle can hover ala a helicopter, it would need to generate more lift
than you get just from ground effect. I think then, by definition, you don't
have a GEV but a rotary wing tank. Or, perhaps, a hybrid GEV/helicopter.
But the lift required would be enormous for a helicopter. I'm not sure you
could lift a tank with a bottom mounted propeller. I'd imagine you'd either
need very long blades or an incredible amount of speed to generate the
necessary lift. I'm not sure that's feasible. I'd love to see a calculation on
the speed of the blades and the temperature they'd build up from spinning fast
enough.
Oh, and the skirt... You'd need SOMETHING around blades to protect it, I'd
think.
On the other hand, with a fusion plant maybe you could do it. I'm still not
sure it's feasible. I have my doubts, but they are kind of fun. I always did
like the Slammers stories (even if Drake does have a problem with 2-D
characters...).
> Ouch--not a pleasant thought, especially for those of us that like
There's got to be a Slammers parody in here somewhere!
> And you'd have to watch for throwing tracks--supposedly (and I'm not a
I guess if you have a fusion plant you can assume you have tracks strong
enough to handle the load. But, ground pressure is still a big problem with
tracked vehicles.
Personally, I'm a big follower of strong AI (I know... I've been down this
road before on this list! *L*). I personally think the way to go is turretless
tanks. Essentially self propelled anti tank weapons mounted on a rising,
rotating mount. Just a chassis with an autoloading gun that can rise from a
hull down position. Then, do away with the human driving it, by replacing the
driver with an AI. There's a limit to how small they could be, as they would
have to hold ammunition. Couple it to a small calibre projectile fired from a
mass driver, and you have something very hard to hit and very powerful...
> Remember, energy is mv**2, but momentum is mv. In other words, if you
Heh. Keeping in mind, of course, that Gibson himself is not exactly a
techno-genius... He's a guy with a vivid imagination, but wrote all
those books on a TYPEWRITER because he didn't own a computer...
Someone more physics-literate than me correct me here if I'm wrong, but
how do you get around the Newtonian "for every action there is an equal and
opposite reaction" thing...? If a 1 kilo projectile is accellerated to
1000m/s in a combat-useful length of time (ie relatively immediate) then
there's going to be a recoil whether it was fired out of a present day cannon
or accelerated by a mass driver. Recoil doesn't go away just 'cause
you're using electro-magnetism rather than chemical explosives, does it?
(leaving aside such stuff as recoil compensators, inertial dampers, etc etc).
If a tank (65 tonnes) now gets rocked back on its tracks by a shot from the
main cannon, then a gev is going to suffer the same effect
achieving the same result, no? If you're using a mass-driver on the
gev, it will still have to deal with substantial recoil, won't it? If the GEV
is of the same mass as the tank (65 tonnes), it will have to have some kind
of counter-force to the recoil, or it will be shoved around...
> If the vehicle can hover ala a helicopter
...then it isn't a GEV...
, it would need to generate more lift
> than you get just from ground effect.
remember to keep in mind the difference between "ground effect" a-la GEV
(pressurized cushion of air contained inside a flexible skirt which
supports the mass of the GEV) and "ground effect" a-la aerodynamic-lift
aircraft (such as helocopters and airplanes). Quite different...
You don't really get "lift" per-se from hovercraft. The active
aerodynamic force "lift" keeping the craft up off the ground is minimal (you
get a bit off the lift fans, but not much... certainly not enough to keep the
hovercraft up. Helocopters derive their "staying-up" power from
aerodynamic lift (ie lower-pressure air on top of their wings, in this
case rotor blades, and higher pressure air below the wings... the high
pressure pushes into the low pressure, thereby keeping the wing up... but the
pressure differences are achieved by the speed of the wing moving through the
air and the shape of the aerofoil) whereas hovercraft are just creating an
enclosed cushion of air to ride on. Same as how an avalanche
can travel so far, so fast - riding on a cushion of compressed air which
hugely reduces friction.
I think then, by definition, you don't
> have a GEV but a rotary wing tank. Or, perhaps, a hybrid
I'd say impossible. Or at least WAY unlikely. You'd need rotors so long as
to be impractical for the bottom of an armoured vehicle - spinning them
fast doesn't do you too much good 'cause then they go supersonic and it really
starts to screw things up... That's the main limiting factor for
top speeds of helicopters today - they have to avoid getting their
rotors
over the speed of sound or nasty things happen - especially since it
happens to the advancing rotor on one side of the aircraft and not to the
retreating rotor on the other side.
> Oh, and the skirt... You'd need SOMETHING around blades to protect it,
I like 'em too. But you aren't going to have flying tanks of the Slammers'
size by using bottom mounted rotors, that's for sure...
> Personally, I'm a big follower of strong AI (I know... I've been down
But boring to game with.... it's the human element that makes the games fun at
all:)
> On 30-Nov-99 at 20:59, Allan Goodall (agoodall@interlog.com) wrote:
> Sorry, yes you get recoil. It just won't be much of a problem.
component
> would be more important than the mass component. The launcher and
The easiest way to think of this is the kinetic energy (mv**2) of the
projectile will be the _same_ as the kinetic energy of the firing
platform. So yes, it is a problem, no matter how slowly you accelerate the
projectile. You could correct for this with a circular accelerator approach I
guess, but I can't see this being small enough to fit in a combat vehicle.
You might take a look at an earlier discussion about Kr'vak (sp?) railguns
where it turns out the ship would be accelerated backwards
to the order of Km/S.
> That's also assuming you're using a mass driver with magnets. You can
Doesn't matter how you accelerate the particle newton still applies.
> On Wed, 1 Dec 1999, Roger Books wrote:
> On 30-Nov-99 at 20:59, Allan Goodall (agoodall@interlog.com) wrote:
that is incorrect.
Newton's third law of motion tells us that when something is fired from a
gun, the magnitude of the _momentum_ of the projectile will be the same
as that for the firing platform. it is possible to look at this a little more
closely.
<maths>
i'll work in scalar units to keep things simple.
quantities:
m mass v speed p magnitude of momentum E kinetic energy
relationships:
p = mv
E = mv^2/2
i'll prime things which apply to the projectile, so x is x for the tank and x'
is x for the projectile.
let's say the things we know are m, m' and E', and the thing we want to know
is v; that is, for a given projectile energy, and given masses of vehicle and
projectile, how much recoil is there? what we're really interested in is the
way v varies with m'.
E' = m'v'^2/2 // by definition
m'v'^2 = 2E'
v'^2 = 2E'/m'
v' = (2E'/m')^1/2 // call this 'A'
p' = m'v' // by definition
p = mv // by definition
p = p' // newton's third law
p = m'v'
mv = m'v'
v = (m'/m)v'
v = (m'/m)(2E'/m')^1/2 // using A to substitute for v'
v = (2E'm'/m^2)^1/2
so (where | means 'is proportional to')
v | E'^1/2
v | m'^1/2
v | 1/m^2
</maths>
so, for a constant projectile energy and vehicle weight, the recoil produced
by a gun is proportional to the square root of its mass. thus, if we use a
smaller round, we get less recoil *even though we are putting the same amount
of energy into it*. we are also more power efficient, as less energy is going
into recoil.
> So yes, it is a problem, no matter how slowly you accelerate
it wouldn't work anyway - if you shoot out a projectile of a given mass
and speed, you get a particular recoil, irrespective of how you do it. to ref
another thread, TANSTAAFL.
tom
On Wed, 1 Dec 1999 14:26:54 +0000 (GMT), Tom Anderson
> <thomas.anderson@university-college.oxford.ac.uk> wrote:
> so, for a constant projectile energy and vehicle weight, the recoil
THANK YOU!!! This is what I was getting at in my previous posts. You can
impart a fair amount of energy with a very small mass, and get very little
recoil in return. Not zero recoil, but little recoil.
On Wed, 01 Dec 1999 02:26:05 -0500, Adrian Johnson
<ajohnson@idirect.com> wrote:
> Heh. Keeping in mind, of course, that Gibson himself is not exactly a
Well, his physics was sound. And he didn't write ALL those books on a
typewriter. By Count Zero he had a (albeit vastly obsolete) computer.
> Someone more physics-literate than me correct me here if I'm wrong, but
then
> there's going to be a recoil whether it was fired out of a present day
I didn't say it went away. I said that recoil is relatively minor. Tom
Anderson explains this in another message in the thread. Basically, energy is
a function of mass and the square of the projectile's velocity. But recoil is
based on momentum, which is the projectile's mass times it's velocity. Mass of
the tank times the recoil velocity is equal to the mass of the projectile
times its forward velocity. The huge mass of the tank (compared to the
projectile) counters the huge velocity of the projectile. Thus, high energy
with comparatively little recoil.
> (leaving aside such stuff as recoil compensators, inertial dampers, etc
The problem is that cannons are heaving large masses. It's a spiral. You have
a small projectile which you want to impart a lot of energy on. So, you need
chemical propellent to do that. But, the chemical propellent needed is a
considerable size compared to the projectile. You could make the propellent
long and narrow, but that doesn't make for the most efficient explosion, and
is a pain to load into the weapon. So, you make it shorter and fatter. This
requires a wider projectile. Since you want a dense projectile (you don't want
the projectile absorbing the impact energy, you want the target to do that),
you have to increase the diameter of the projectile. This increases mass,
which means more propellent, etc. etc.
So, in a cannon you have a fairly massive projectile accelerated to
comparatively low velocities. Say you have a 10,000 gram (10 kilo) projectile.
Say you accelerate it to 1000 m/sec. To get the same energy out of a 1
gram
projectile, you'd only have to accelerate it to 100,000 m/sec. The
momentum of
the first projectile is 10,000 times 1000 = 10,000,000 gm/sec. The
momentum of
the second projectile is 1 times 100,000 = 100,000 gm/sec.
Assume a tank of 1,000,000 grams weight. In the first case, it would have a
momentum equal to the projectile, or 10,000,000 = 1,000,000 times x, where x
is its velocity. In this case, it would have a recoil of 10 m/sec. In
the second case, the same tank would have a momentum of 100,000 = 1,000,000
times
x, and x would in this case be .1 m/sec.
For the same energy, the small projectile has a MUCH lower recoil than the
larger projectile.
> ...then it isn't a GEV...
That was my point. *S*
> I'd say impossible. Or at least WAY unlikely. You'd need rotors so
That's what I said. *S* I thought it was improbable too, if not out and out
impossible. Also, imagine the turbulence effects underneath the tank...
And I completely forgot about what happens at the speed of sound on helicopter
rotors. Okay, this isn't likely at ALL.
> I like 'em too. But you aren't going to have flying tanks of the
That was my point. And if they can't fly, then they aren't going to be much
good the moment they come to their first hill. *S*
> But boring to game with.... it's the human element that makes the games
Oh, I don't know. I never found it boring playing the Ogre in Ogre. I also
never found it boring playing robots in Rivets. In fact, the dispassionate
"robots fighting robots" sphere of gaming has merit. You could ignore morale
considerations. But it's still humans who lose or win based on the ability of
their robots.
But that's not how Jon invisioned his universe, so the point is moot.
*S*
On Wed, 01 Dec 1999 06:44:29 -0500, Nyrath the nearly wise
<nyrath@clark.net> wrote:
> But if we are postulating antigrav technology, why
I was postulating floating tanks, ala Hammer's Slammers. But you're right, if
you have anti-grav tanks you might as well have anti-grav weapons...
While y'all are doing your maths--what power level and what units
should we be talking about for beam weapons? This is occasioned by finding a
"Walk Softly and Carry a Megawatt
Laser" button--would a "megawatt" be the right order of
magnitude--don't get a swelled head, here, Keith... : ) -- or
should we be talking about gigajoules or teraergs or what?
> Oerjan Ohlson wrote:
> Until you get Mavericks or Hellfires which you can fire indirectly at
They exist already. The US (them again ;-) have the Copperhead, a 155mm
laser guided AT round. Indirect fire arty will always have its place.
> Ludo wrote:
> > Until you get Mavericks or Hellfires which you can fire indirectly
You seem to have missed the context. Thomas's thesis was that VTOL-ish
grav tanks with Mavericks or Hellfires would make indirect-fire
artillery obsolete. The sentence you quoted above was part of my antithesis.
The Copperhead is fired from an indirect-firing tube artillery piece,
so can hardly make indirect-firing tube artillery obsolete... no
support for either side.
Later,
In a message dated 11/29/99 10:40:23 PM Central Standard Time,
> agoodall@interlog.com writes:
<< That's about the only type of terrain where it has an advantage. Okay, mud
and snow would be advantageous. But you still have that whole "slopes cause
spilling of air out of the curtain" problem.
> [quoted text omitted]
The problem here is just what excactly is a GEV. The Drake books pretty much
state that the panzers can lift over obstacles, and there seems to be enough
power in one of them to get off the ground a substantial distance, so maybe
they are really VTOL's with ground effect skirts... in which case the problems
you stated become dead issues...
John