> Just curious, what kind of terrain do you guys believe GEVs can
Is GEV "Gravitic Effect Vehicle" or "Ground Effect Vehicle"?? If
Gravitic, then I figure it could fly like a helicopter - to orbit
potentially (though the vehicle would have to be vacuum tight). If Ground
Effect, you'd have to have a REALLY powerful set of lift fans to get an
armoured vehicle to hop over any significant terrain (say, larger than a
car). Hovercraft float on a contained cushion of air - remove the
containment and down they go. Present hovercraft can go over limited
obstacles, but mostly by momentum/inertia not by the lift power of the
fans
- these are really just to keep the cushion skirts "inflated".
Just to throw in a monkey wrench:
Q: if a Ground Effect (hovercraft) tank fires it's main gun, won't it be
propelled in the opposite direction - in other words, there's nothing to
push back against the recoil... This would not be a problem if you had
directional fans providing propulsion AND the gun was firing in a direction
opposite to the thrust of the fans AND you had "burst" thrust capability on
the engines to compensate for the momentary thrust of the cannon recoil...
There are some potentially very serious performance
issues/considerations
for ground effect armoured vehicles...
For example: How do you stop them once they are moving... A tank has LOTS
of inertia, and a GEV is like an air-hockey puck...???
Armoured vehicles have a maximum side incline rating (the vehicle can climb an
incline of x degrees, descend a y degree incline, and traverse an incline of z
degrees tipped to the side without rolling over...). How
would a ground effect vehicle traverse ANY side incline - would it not
just "slide off" to that side...????
Any GEV vehicle would require ducted fans or turbo fans to hop over
obstructions, couter-act side tilt, etc. Ducted fans could be used today
for VTOL craft, but still have bugs to work out. (After all helicopters work
NEARLY all the time) As far as side tilt rolling over a GEV, it isn't much
different than rolling any other vehicle, except it slides instead of rturning
turtle. The fans should be able to crab it up the hill at a reduced movement
rate.
> On Mon, 16 Nov 1998, Adrian Johnson wrote:
<snip>
> >SO the point I'm getting at is, a GEV could not traverse a cliff, or
(snippage)
> Just to throw in a monkey wrench:
Combat-capable GEVs (and it is Ground Effect Vehicle in all the SF I've
read) would have to have gimballed fans for movement, steering, etc. With a
few exceptions, GEV tanks don't have external thrust fans and rudders,
so the bottom-mounted lift fans would have to swivel around to provide
steering and accel. There are already, I believe, real-world hovercraft
that operate on these principles.
As for power supply and availability of enough thrust, we're already positing
battlefield lasers, FTL, some energy weapons, combat railguns,
and a host of other futuretech in vanilla DS/SG. Assuming a big enough,
efficient enough power plant exists for armoured GEV tanks isn't that big a
stretch.
(I must admit a certain bias here: I really like hovertanks, and I have a
DS2 Size 5 super-hovertank that regularly appears in my forces, to great
effect. Most of the rest of my force is also GEV mobile.)
DS2 standard GEV combat vehicles do have certain mobility problems already:
they can't move thru forests, and they really slow down in slopes
and rough ground. The open-ground mobility and the absolute
amphibiousness tend, I find, to make up for the restrictions.
Just my $0.02,
In a message dated 11/16/1998 11:26:48 AM Central Standard Time,
> ScottSaylo@AOL.COM writes:
> Any GEV vehicle would require ducted fans or turbo fans to hop over
The reason why hovercraft are so bad at climbing hills (except through
momentum) is that as soon as you start moving up a incline, a component of
your lift thrust vector suddenly begins to push you down hill, counteracting
your propulsion fans. To overcome that you'd have to install almost enough
thrust to make the whole thing fly, making it, in effect, a VTOL.
> Any GEV vehicle would require ducted fans or turbo fans to hop over
The Slammers' ground effect vehicles in the Hammer's Slammers novels have fans
in ducts, but they don't adjust the duct position to change the thrust
vector (correct me if I'm wrong here) - they selectively change pitch on
the thrust fans themselves (or maybe this in combination with directional
vanes/nozzles under the fan. To go up a hill, they drop the thrust on
the
"up-side" fans, lowering that side of the vehicle, while increasing the
thrust on the "down-side" fans - the net effect is to add a much greater
lateral thrust component, reducing the "hill effect". A significant slope
would be a real problem, though, because if you tip the vehicle too much, you
will let out the air cushion and the vehicle will ground.
If you have "power is no option" generators driving
"really-super-duper-effective" fans, you could say that the lift fans
have the ability to *temporarily* provide direct lift (al la VTOL) for the
vehicle, in short bursts (to prevent damage to engines, bearings, etc by
prolonged overpowered running) - to overcome obstacles, short steep
slopes, etc. You could use the same effect for braking (sudden high power in
direction opposite to that of travel) thereby removing the need for
drag-brakes (though the image of the driver pressing the "anchor" button
brings a smile). I guess the air cushion would allow the vehicle to travel
in "fuel efficient" mode (or low-maintenance-needs mode?), while the
"VTOL" type movement would be used only in special circumstances.
The problem with considering vectored thrust fans on the underside of this
type of vehicle is that if you vector the thrust into a confined space
attached to the vehicle (the air-cushion area inside the skirts), you
would basically negate your thrust. You need somewhere for the pressurized air
from the fans to escape the confines of the vehicle, ie from one edge of the
skirts. Maybe you vector the thrust and have vents in the skirts open up. I
don't imagine big propulsion fans on the outside of the upper deck
area (like today-era hovercraft) - 'cause these would be EASY to damage,
difficult to shield (from a thermal and radar standpoint), etc. I
much
prefer the whole idea of countra-grav. technology.
My Bad. When I said GEV I was talking Gravatic Effect Vehicle. I see them
working as they do in Battlezone, with only limited vertical lift capability.
Due to rappel to weight ratio of their power plant's output to the actual
conuter grav generator..
> Just to throw in a monkey wrench:
<SNIP>
> There are some potentially very serious performance
Drop an Anchor....(semi-serously) Mount hefty spikes or something that
can
be lowered to rake the ground - create a source of ground friction where
there otherwise is none (or very little). I have heard of something like
this, but using side mounted 'outrigger' style arms - you drop one side
and
it imparts a significant drag on that side of the vehicle - enough that
it helps the vehicle change direction more quickly (creating an external pivot
point). (don't ask for sources - I don't remember. It has been a while
and it was probably a concept drawing anyway.)
<SNIP>
Why not use fusion-plasma ejection to provide a jet lift to the fans.
Thusly, you could hop over obstacle of offset going sidwise along a ridgeline,
or lift for 10 seconds at a time or so (can't overheat or fuse the fans after
all) to cross broken ground that would otherwise overtax the air skirt. The
blast of
hot exhaust could lift the hover vehicle an extra few feet. As an anti-
personnel weapon it would also be bad news for dug in troops to put them on
"air-pop" as you cross their foxholes.
> On 16 Nov 98, at 10:14, Adrian Johnson wrote:
> Q: if a Ground Effect (hovercraft) tank fires it's main gun, won't it
Sounds like a good reason to use beam weapons;)
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> On 16 Nov 98, at 10:14, Adrian Johnson wrote:
That would be too easy. Besides, I'd rather have solutions for the technical
problem I posed, which would let me off the hook for proposing a technical
problem with a blatently obvious answer...
....ah....wha... what about the recoil effect from all those propelled
coherent light photons... or... the.. um... shock effect from the
matter-antimatter matrix tranciever...
fiziks? bah!
> At 06:09 PM 11/16/98 -0500, you wrote:
Let's see...
Let's say that an HKP/5 fires a non-rocket assisted 4kg projectile
at 3000m/s (Mach 9.1, I believe that that is quite a bit faster than
current tech...).
If the GEV vehicle firing is 60 tonnes, then the velocity of the tank after
firing (assuming it was initially stationary) would
only be 0.2m/s=0.7km/h. Now, most tanks will have recoil damping
through the use of hydraulics, so this could be reduced even more.
As you can see, any powerplant capable of propelling the tank at combat speeds
could easily keep the vehicle stationary while firing. Not to mention that
hovercraft can come to rest on their skirt, which makes them much more
difficult to move than wheeled or tracked vehicles of comparable mass. They
would likely do this with the engines on standby while in hull down position.
> On Mon, 16 Nov 1998 Pmj6@aol.com wrote:
if the hull stays parallel to the ground, then yes. however, if it stays
horizontal, then the tank will climb the hill as thrust will escape on the
downhill side. of course, your power consumption will skyrocket.
> To overcome that you'd have to install almost enough
not quite; it still has the advantage of the ground effect, which makes
flight far easier than in the free-flight regime.
Tom
> On Mon, 16 Nov 1998, Tony Christney wrote:
one minor quibble: the total change in velocity due to recoil (which you
find to be 0.2 m/s) will take effect regardless of damping. such is the
conservation of momentum. it may, however, be spread out over a longer time,
reducing the strain on the turret and the acceleration to be countered by the
drive. If spread out over 20 milliseconds, it becomes a
lesiurely 10 m/s2, or 1 gravity. over a second it is 1/50 of a gravity.
Tom
> In a message dated 11/16/1998 11:26:48 AM Central Standard Time,
The fans
> > should be able to crab it up the hill at a reduced movement rate.
You'd have to have selective venting around the skirts or lift fans at the
edges of the vehicle platform with variable thrust - both of which seem
possible. And yes, your power consumption will go through the roof. If you are
using fusion powerplants with oodles of excess power, then the real limiting
factor would be the maximum possible thrust of the lift fans. In the end,
having lift fans capable of lifting the vehicle (for brief periods) solely
through their lift and not just with the contained cushion of pressurized air
in the skirts may be the best way to go. If you have to lower the front of the
skirts to go up a hill, what happens if you have a
hill with broken/rough surface terrain? You'd dig in the nose of the
craft.
> To overcome that you'd have to install almost enough
Well, almost. This is maybe straying a bit far from the point of the list, but
the "ground effect" in "ground effect vehicle" (al la hovercraft) is different
from the "ground effect" which makes flight more efficient close to the
ground. Or, maybe I should say it's the same basic idea, but very different
practical applications. A hovercraft generates "lift" solely from riding on a
cushion of compressed air, contained by its' skirts. It has no "aerodynamic"
lift, ie lift produced by the difference in air pressure above and below an
airfoil. Think of a hovercraft as an air
hockey puck. It rides the cushion of compressed air - take away the
air, and it hits the ground (this is why selective venting and tipping the
vehicle to adjust for rough terrain is a very limited way of dealing with
hills, etc - the vehicle has to give up its' cushion of air to do so -
ok in very brief moments ie if you have lots of inertia and you are going up a
small incline, but not very practical if you are going up a long hill). An
airfoil generates its lift by the differential in pressure on the top and
bottom surfaces as the airfoil passes through air in flight. Airfoils get a
"boost" in effectiveness when they ride in "ground effect", the max height of
which is a distance above the ground usually taken to be equivalent to the
wingspan of the airfoil. There is some compressing of the air between the
airfoil and the ground, which acts, in effect like the cushion under a
hovercraft. I may be forgetting some of the details here
(been a while since I was flying) - but the end result is that
hovercrafts do not take advantage of the "ground effect" the same way that a
fixed wing
aircraft does, because they don't use aerodynamic lift to stay up -
certainly they never experience a free-flight regime.
Where this gets interesting is with the development of transport vehicles
designed specifically to use the aerodynamic aspects of "ground effect". There
is a company in the US now marketing a small personal vehicle (I think it has
4, maybe 6 seats) which looks like a cross between a Cessna
and a boat - it has a lifting surface hull, with a prop on the front
(hard to describe 'cause it is very unfamiliar looking). It moves like a boat
at slow speeds, but when it travels faster, it lifts out of the water and
"flys" above the surface in ground effect (so it can use a much smaller
airfoil surface than a real airplane, because of the increased efficiency of
the airfoil in ground effect). It can only stay within about 6 feet of the
surface, but can travel relatively fast (maybe 120 mph). This craft was based
on research that the Soviets used in the '80s to develop a military transport
version of this type of craft. Theirs was BIG (I think roughly equiv. in size
to the cargo capacity of a Hercules
transport?????).
It was part of a tech. development program for this technology. I believe the
objective was eventually to design craft big enough to have the carrying
capacity of small transport ships, but with speeds similar to aircraft (say,
carry 1000 tons at 140 mph across the Bering strait...). The Soviet craft had
jet engines, and was supposedly successful. I don't
remember what the results of the program were - certainly we don't see
the
tech used anywhere - though it seemed like a good idea. The Soviet
designs supposedly had the ability to "fly" through relatively rough oceans
(10,
maybe 20 foot waves - I think they had a maximum "altitude" of around 50
feet, but my memory on this is quite hazy, it's been a while since I read
about it).
See any applicability in the GZG universe for this technology? Giant "ocean
going" transports using efficient "ground effect" lift to carry armoured
formations. If you could figure out how to set one of these down on land (be a
drag to need a 10k foot runway to land and take off), there's
no reason why they wouldn't work over land - doesn't require water, just
easier to take off and land on water.
Anyway - just some thoughts...
> On 16 Nov 98, at 17:50, Tony Christney wrote:
> Let's see...
I think that you will find that due to conservation of momentum that recoil
damping does not alter the overall change in velocity of the tank, it serves
to make the force act more weakly for a longer period, rather than massively
all at once, and tearing the gun off the mount.
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> At 12:13 AM 11/18/98 -0000, you wrote:
DOH!
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~