Re: GEV and Grav Vehicles

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
>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...

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
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?

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
>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...

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
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 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
Slammers'
>size by using bottom mounted rotors, that's for sure...  

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
fun
>at all :)

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*

Allan Goodall		       agoodall@interlog.com
Goodall's Grotto: http://www.interlog.com/~agoodall/

"Surprisingly, when you throw two naked women with sex
toys into a living room full of drunken men, things 
always go bad." - Kyle Baker, "You Are Here"