Brian and another fellow hit it on the head.
The GEV of 2183 will
A) use a limited form of vectored thrust and maybe skirts to enhance the
effect but can use thrust alone for limited periods to transit
from hills to flats - and the thrust from a turbine parallel to the
hillside WILL push a GEV up a hill
AND/OR
B) Have other methods like null-grav packs or active skirts or who
knows what.
If we can believe in abundant power, we can believe a GEV can climb a
hill. Or at least, I can. If I can buy anti-gravity, I can buy GEVs
climbing hills. And moving through scrub. Heavy forest is bad, but it is for
tracklayers too. And if anyone has ever seen Alberta or Saskatchewan, there is
plenty of GEV playground there. The same with
other plains/deserts. And lakes, swamps, rivers, the arctic, the
antarctic, etc.
They aren't the be all end all (I think that is grav) but they sure do have a
lot of features that make them attractive for a lot of operations).
Additionally, someone said something about a hockey puck analogy. Think about
it. You may have a lower coefficient of friction than a tracklayer, but you
still mass a huge amount. A round striking you would certainly impart a very
minimal change in your vector, even if it was a big one. It would be more than
to a corresponding tracklayer (unless the GEV was grounded) but still not
huge. The round just does not have the energy to alter the momentum of the
mass effectively.
As for the recoil reduction from using small projectiles gradually
accelerated:
Gradual acceleration must take some length of barrell. This may penalize the
AFV in close terrain. It looks fine on a static platform
with fish-tank attached, but try to put something like that into a
tank and get meaningful damage output without significant impulse to the tank
firing the weapon. I'm not saying it won't be better than a CPR gun, but it
isn't a low recoil weapon. Especially if you want
ROF - that means the round must clear the barrell (even if you do
multi-round simultaneous staggered fire) reasonably expediently, which
means a gradual acceleration is a problem. As does target movement -
if I press the firing stud after lining up my shot, I want it there NOW not
later. So a slow launch isn't in line with that. I want the round GONE. That
probably involves recoil. If I want a low recoil weapon, I pick a MD over a
CPR gun. But even lower, I pick a HEL over either of those other two.
> On Thu, 2 Dec 1999 12:26:43 -0500, kaladorn@fox.nstn.ca wrote:
> The GEV of 2183 will
I'm curious how this will happen. I think aeordymanics are against you. Little
tiny blades travelling very fast still won't give you the lift necessary, I
don't think, even for short periods of time.
The other problem I see is one of mass of the propulsion system to overall
mass of the vehicle. It seems with a GEV far too much of the vehicle has to be
used for propulsion. You need air ducts, the engine, the blades, the motor
drive attached to the blades... lost of stuff there that takes up space
(increasing the vehicle's volume) or weight. I haven't done a study on it, but
it wouldn't surprise me if the power to weight ratio of a GEV is higher than
that of any other tank.
I will say that there is enough leeway to suspend my disbelief for the
purposes of a game (or a novel). I mean, we're not talking plasma farting bugs
the size of houses (ala the Starship Troopers movie).
Still, I don't think these will make an appearance in the real world. I think
in the real world the emphasis will be on avoiding being hit. I see very small
tanks, smaller than the Swedish S-Tank, but similar in design. I see
them run by AIs or remote piloted. I see the gun mounted on a rising platform
that allows 360 degree traverse but no need for a turrent. I see them being
relatively easy to mass produce, low em signature and visual profile, and no
training time required.
I did think of something, though... I think with a thicker atmosphere you get
more lift from a slower moving propellor (also more drag due to the thicker
"fluid" through which the craft travels). A thick atmosphere might make GEVs
with "hop" capability more feasible.
This is something DS2 and SG2 don't take into consideration THAT much. There
is little in the way of rules for extreme atmospheres. It would be fun to run
some games in extreme conditions (high gravity, thick atmosphere, corrosive
atmosphere...). Mobility, firepower, even morale would all be affected...
> AND/OR
> kaladorn@fox.nstn.ca wrote:
> The GEV of 2183 will
Um. I've always supposed that the solution from 1983 would work. That is, a
set of small, retractable treads on the skirt edge. Also used with
differential braking for rapid turns. Very similar to many vehicles in service
now (eg BRDM) which run on 4 wheels, with another 4 (usually solid metal not
tyred) which can be lowered to cover rough ground.
Exit the need for extreme performance power packs etc. Just requires a bit of
lateral thinking, rather than vertical:)
> On 2-Dec-99 at 22:36, Allan Goodall (agoodall@interlog.com) wrote:
So why use little tiny blades. Maybe auxilliary jets? Compressed gas?
Null-G packs.
> Still, I don't think these will make an appearance in the real world.
Too late, already been used.:) The Navy has used them and I believe they were
used in Viet Nam.
One other thing I still am not sure I believe is part of the vector of the GEV
pushing it down hill. If the skirts follow the terrain and the GEV stays level
it appears to me as if the GEV would experience the same (or maybe even less)
downhill force than the equivalent ground vehicle. The fan isn't blowing at
the ground, the fan is forcing air into the plenum, your fans could be on the
side of the GEV aimed toward the center hand the vehicle would still hover.
However, I am encountering another problem that could be insurmountable. GEV
over water, when the pressure required to hover (say 10psi) exceeds the mass
of the water underneath (not very well put, but I hope it gets the idea
across) wouldn't the vehicle sink? Anyone know at what pressure this would
occur.
> Roger (I don't remember the Slammers going over water, did I
In Rolling Hot - combat cars can just make it over water but
tanks can't - a tank has a bridge go under it and sinks like
a stone.
An interesting question. A GEV must displace an amount of air equal to or
exceeding its mass in order to hover.
I would assume that the water would be displaced. Place a small puddle of
water on a table (about 2" diameter), then take a can of compressed air, point
it at the edge of the puddle and release the air (not the can) while
traversing the puddle. If it has enough pressure, you will see the table
surface while moving the straw across.
Don't forget that water is self-leveling, so you are pressing not only
against the water under you and the entire body of water. You would reach some
equlibrium point. The area under any air cushion vehcile on water is always
VERY slightly lower than that of the surrounding water due to the water that
is being displaced. The GEV would be designed with this in mind. Then again, I
usuall add 'Amphibious' to my GEV's during the DS2 design phase, so that they
can shut down and float if they need to.
I don't think that it would present a problem. You will either have enough
water to support the GEV or the pressure will displace the water and be
supported on semi-dry land.
Perhaps I misunderstood the question, but it seems like you are asking what if
you took a battleship that you know will float in Lake Erie and put it in a
pond. It would sink because there is not enough water to support it. But then
a battleship is not designed to work on both land and water like a GEV.
-----
Brian Bell bkb@beol.net
http://members.xoom.com/rlyehable/ds2/
> On 3-Dec-99 at 12:00, Bell, Brian K (Brian_Bell@dscc.dla.mil) wrote:
Not quite, it must put enough pressure in the plenum that there is as much
pressure on the ground as the mass of the GEV.
> Perhaps I misunderstood the question, but it seems like you are asking
Let's get extreme so I can make my point.
I have an 80 ton block of iron sitting on a 1 cm x 1 cm skirt. This skirt
has air in it equal to 80 tons/cm^2. I put it over the a 300 foot deep
lake. It's pretty obvious it will bubble wonderfully as it sinks to the
bottom. We have to pay attention to wether our tanks will do this also. If the
pressure required to lift them is greater than what the water will support
they will sink.
If our Slammer Tank sinks in water that means it is going to sink in swamp. As
a matter of fact, much as I would like it to be, I can't see a situation where
a GEV that sinks would be more useful than a tracked tank. I guess with proper
equipment it could jump short puddles, but it won't do an amphibious assault.
So, anyone have any idea what the max is we could use on the cushion? Sounds
like a little empiricle testing with an air compressor, a tub of water and
some bricks is necessary.
> On Fri, 3 Dec 1999, Roger Books wrote:
> > Still, I don't think these will make an appearance in the real
Yep. PACV Patrol Air Cushion Vehicle US Riverine Forces used them in the
Delta. The VC hated them. By the time you heard the things they were right on
top of you. The were perfect for riverine delta patrol since then could ride
right over the tall reeds that were impassable to normal hulled PBRs and
LCP's.
One of the tactics they would use was flying up into a bed of reeds and
hiding. They'd wait for VC boats to come through then pop out and swoop in.
Also note that the USN has the LCACs and the Russians have several Air Cusion
vehicles including a monster that is used for coastal deployments.
See members.xoom.com/cmpotter/sk5.html for a rather nice group of images
of PACV's. Armament was 2.50 cal MGs on top, 2 M60's inside out hte side
> However, I am encountering another problem that could be
exceeds
> the mass of the water underneath (not very well put, but I hope it
It would have to be pretty damn high. I would think the size of the skirt
would alleviate this. The US has the LCAC which is huge and can carry an
M1. The Russians have even bigger monster hover craft.
> On Fri, 3 Dec 1999, Roger Books wrote:
> The size really isn't relevant, it's the mass/surface area that
Perhaps my terminology is imprecise. Size speaks to the mass/surface
area. The LCAC is much larger than an M1 much wider and longer. Its got a
bunch o' big gas turbines (tm) and thus has the thrust to put air under
that big/wide skirt and lift that M1 or LCAC full of marines.
> On 3-Dec-99 at 12:53, Ryan M Gill (monty@arcadia.turner.com) wrote:
> > However, I am encountering another problem that could be
exceeds
> > the mass of the water underneath (not very well put, but I hope it
The size really isn't relevant, it's the mass/surface area that counts.
I understood what you meant (even if I did a poor job of describing it).
It is the same principal of design used in making ships. In designing a ship,
you need to make sure that the hull will generate enough pressure on the water
to equal or exceed the mass of the ship (and in doing so, it will displace a
mass of water equal to the mass of the ship).
I do not know how much mass a given surface of water can support. But it wold
be the same for ships as GEV's (except that all ships are partially sunken).
Take a ship of 10 tons. Mark the waterline on the hull of the ship while it is
at rest. Compute the suface area of the marked area of hull. This is the
minimum area that a GEV, of 10 tons (minus the mass of the air in the skirt)
would need to cover to float on the air trapped in the skirt alone. Now as you
add pressure within the skirt and start to move air through the skit, the
craft will begin to hover (the air escaping out the bottom of the skirt
effectivly also adds to the surface area being used by the GEV to stay
afloat/hover. You can now reduce the size of the skirt as long as you
maintain the same volume of air passing through the skirts. Although it may be
a good idea to keep a larger surface area incase your engines are hit.
To take your example and add the output of a Saturn V rocket engine through
the skirts, you can now hover your 80 ton block (but you better have good
gyros to keep it from tilting).
-----
Brian Bell bkb@beol.net
http://members.xoom.com/rlyehable/ds2/
-----
> -----Original Message-----
> Ryan M Gill wrote:
> Yep. PACV Patrol Air Cushion Vehicle
If it is the one I think it is, the cushion pressure was about 0.3 psi.
> > However, I am encountering another problem that could be
> > put, but I hope it gets the idea across) wouldn't the vehicle sink?
Of course it would - just like a boat which is too heavily loaded :-/
Let's see - the density of water is pretty close to 10^3 kg/m^3
(depending on salt contents, etc), and the pressure at depth h (meters) below
the mean surface (ie, don't measure where the cushion pressure pushes the
surface down <g>) should be roughly 10^3 * 9.8 * h Pa. I think this
corresponds to about 0.44 * h' psi in imperial units (h' measured in feet).
Unless I've made a major though error somewhere (which I quite likely have,
since it is 3 am and I've recently caught a bad cold), the hovercraft will
sink to the depth where its cushion pressure equals the pressure of the water.
If this depth is far enough down that the water reaches the air intakes, bad
things will happen <g>
If my reasoning and unit conversion is correct, a 10 psi-cushioned GEV
would sink about 22 feet down into the water before reaching the equilibrium
pressure.
> It would have to be pretty damn high.
Only if your GEV is very high <g>
> I would think the size of the skirt would alleviate this.
The size of the skirt determines the cushion pressure - a bigger skirt
for the same Mass means a lower pressure.
> The US has the LCAC which is huge and can carry > an M1.
Cushion pressure approx. 0.8 psi. Displacement (fully loaded) 182 tons.
> The Russians have even bigger monster hover craft.
Cushion pressure roughly 0.6 psi for all of them, including the 550 ton one.
Regards,
> Bell, Brian wrote:
> Take a ship of 10 tons. Mark the waterline on the hull of the ship
> the skirt) would need to cover to float on the air trapped in the
Not entirely correct. Only the area of the vertical projection of the
underwater part of the ship counts (since the horisontal component of the
pressure tries to push the ship sideways, not keep it afloat), and since the
pressure varies quite rapidly with the depth of the water you get more
buoyancy from a deeper hull than you get from one with less draught.
See my other post for the depth a GEV might sink to :-/
> To take your example and add the output of a Saturn V rocket engine
If you add the output of a Saturn V through the skirts, you'll blow the
skirts off and use the reaction force from the engine to "hover" - IOW;
you are a VTOL rather than a
> On 3-Dec-99 at 12:00, Bell, Brian K (Brian_Bell@dscc.dla.mil) wrote:
I think this can be simplified to: If the pressure required to support the
vehicle exceeds atmospheric pressure, it will sink. At some point, the weight
of the surrounding water will be sufficient to balance the supporting air
pressure, but unless the vehicle has tall snorkels, this won't happen until
long after the air intakes are flooded (which won't do the blades any good!).
> If our Slammer Tank sinks in water that means it is going to sink in
If the swamp is shallow enough that the displaced water can't enter the air
intakes, the vehicle should just displace the water and muck until it reaches
a solider base. If there is no such solider base, it will sink until it the
intakes are flooded. 'Course, I suppose one could design a vehicle to function
as a GEV on land and as a submarine in water. Stop the fans during air to
water transition, then restart them at a lower speed. Moving from water to air
would be a problem, though.
- Sam
On Fri, 3 Dec 1999 10:07:01 -0500 (EST), Roger Books
<books@mail.state.fl.us> wrote:
> So why use little tiny blades. Maybe auxilliary jets? Compressed gas?
In order to lift the GEV? Well, then by definition it isn't a Ground Effect
Vehicle. You do make a point with the null-g packs (auxilliary jets and
compressed gas I think would be one use only due to "fuel" use and would still
be unpractical).
But null-g packs are fantasy. Sure you could build GEVs with them, but
we
haven't found anything to support anti-grav ability either. I'll change
what I
said and stipulate that GEVs, without resorting to some other sci-fi
macguffin, probably wouldn't be feasible.
However, if you have a world with anti-grav ability, then GEVs might
make a reasonable vehicle.
> Still, I don't think these will make an appearance in the real world.
The Navy had Hammer's Slammers style hovertanks in Vietnam? Wow! *L*
I know hovercraft have been used in real life, but they weren't used as a
replacement for tanks, and were restricted to some pretty specific terrain
conditions. Which was a point I conceded earlier. GEV tanks might make sense
on some planets.
> One other thing I still am not sure I believe is part of the vector
The GEV is level. The force would be straight down. If the skirt follows the
contour of a slope, part of the force would be down into the back of the
skirt, pushing the skirt down the slope. Thus part of the vector is still down
the hill. You'd also have uneven pressure in the skirt from the front to the
back, which I think would tend to push the front of the GEV upwards parallel
to the slope. And then there's the turbulence effects within the skirt itself.
I don't know enough about aerodynamics, but I'd guess this would NOT be a nice
situation...
> However, I am encountering another problem that could be
Yep, the vehicle would sink. I'm not sure what pressure you'd need, but the
GEV would sink if the pressure exceeds the mass of the water. Floating on a
cushion of air over water is similar in effect to floating a boat.
> Roger (I don't remember the Slammers going over water, did I miss a
I remember they mention water at one point. Can't remember the story though...
[snip]>
> However, I am encountering another problem that could be
exceeds
> the mass of the water underneath (not very well put, but I hope it
IIRC, the Combat Cars can cross water but the tanks can't, for the reason
given above - they're just too damn heavy..... one bit of plot centred
around needing a bridge for the tanks to cross a river, not sure which book
- was it Rolling Hot?
> Allan Goodall wrote:
This was all about hopping, not about continued use. You get a run on
normal ground affect, when you get to ditches/small hills you use your
jets/compressed gas/short duration null-g pack and hop. Sure, they
only last 6 seconds and have to be charged again for a minute, but it gives
you more options.
> But null-g packs are fantasy.
So do you run grav-tanks?
> >One other thing I still am not sure I believe is part of the vector
The part of the force pushing backwards on the skirt is exactly balanced by
the force on the frame of the vehicle. There is NO net thrust from the air
cushion EXCEPT for that of the escaping gas.
Thus part of the vector is still down
> the hill. You'd also have uneven pressure in the skirt from the front
That's the wonderful thing about compressed air, it balances to the same
pressure at all points.
You are making the mistake of thinking of this as a fan blowing air down. It
is not, it is compressed air in a plenum. It doesn't press harder at any
point, it has a standard 1 or 3 or 5 or whater psi. All the fans do is put
more air in to replace that escaping under the bottom of the plenum. The only
way you get an affect of lifting one part more than another is if the design
is poor and one part weighs less than another, and in this case it will do
this on level ground.
> >However, I am encountering another problem that could be
exceeds
> >the mass of the water underneath (not very well put, but I hope it
I can see it now, you drive your tank across the swamp, going fine over the
muck as the water is pushed away, when you hit the main channel where the
water is 20 feet deep. At least you make lots of bubbles as you go
down. :)
On Sun, 05 Dec 1999 15:11:03 -0500, Roger Books <books@mail.state.fl.us>
wrote:
> But null-g packs are fantasy.
Yep. I'm perfectly happy to suspend my disbelief.
You have to understand that any "objections" I may have are to the thinking
that some of the stuff we use in games is likely to occur at some point in our
real future. But I'm perfectly willing to accept them as part of a story or
game environment. Jon's geo-political spectrum is far more flawed than
his science (I still snicker at the NAC... *L*) but it's fun to think about. I
enjoy the Slammer books (well, most of them... there were a couple where Drake
was just going through the motions). That doesn't mean they are likely to
occur, or that their lack of liklihood takes away from the story for me.
As a good friend, and science fiction anthology editor (as well as head
librarian for one of the largest public collections of sci-fi in the
world) once told me, science fiction has nothing to do with predicting the
future...
> The part of the force pushing backwards on the skirt is exactly
Okay, now that I'm actually more awake, I thought about that. You're right.
That leaves the air going out the cushion, with the force vector parallel to
the ground, not straight vertical. Thus the vector has a downward component.
> Thus part of the vector is still down
Then as soon as you hit the slope the air pressure will drop. You will have to
run the fans up to a higher power as the volume in the skirt increases, or you
risk grounding the vehicle.
I suppose it would work... except for the thrust vector on a slope. And I'm
not sure you could generate enough force for a grav tank. Depends on the size
and weight of the vehicle. But one thing that got lost in my original post:
with all the weight and energy going into pushing the tank so that it hovers,
you're taking away from weight for armour and armament (and crew space,
electronics, etc...). Except in special terrain situations you'd have a more
efficient vehicle if you used something like tracks.
> I can see it now, you drive your tank across the swamp, going fine over
*L* Yep. On the other hand, you can get around this by making a BIG vehicle.
The Russians have a huge ground effect vehicle (that looks a lot like an
aircraft) for landing troops amphibiously. It uses aerodynamics and speed to
create the ground effect. They would be good for amphibious operations.
they're just too damn heavy..... one bit of plot centred
> around needing a bridge for the tanks to cross a river, not
Yes.
> On 6-Dec-99 at 00:21, Allan Goodall (agoodall@interlog.com) wrote:
> Then as soon as you hit the slope the air pressure will drop. You will
This is pretty academic because we've (as far as I'm concerned) shot this idea
down, however, how do you get the air pressure dropping? I would see the tank
hit the slope, the front skirt would raise, at which point the pressure would
go up. When the whole tank was on the slope the front skirt would be
compressed and the back extended. Pressure back to normal. Are you not
assuming active skirts?
The problem with a fantasy system is to get everyone having the same fantasy.