Odd question for the thinkers: Assume we have one AFV of mass X. On wheels, it
probably has 8 wheels to distribute its weight between thus giving a certain
ground pressure. On tracks, it has even more area to divide its pressure
across, giving a lower ground pressure (assuming drive systems are roughly
comparable, thus allowing mass X to stay about the same). Now, is this taken
to an even greater extreme with GEV?
I'm a little unaware of the physics of a plenum chamber. Is pressure
concentrated around the skirts, where air is contained? Is it greatest under
the fans? Is it equally distributed?
My question was this:
Given that a GEV is higher off the ground than a conventional tank, given that
a GEV may have significantly lower ground pressure, is it possible that GEVs
will have better luck penetrating minefields?
I assume with mine pressure detectors that you set AT mines for a certain
minimum pressure, which probably makes them harder to sweep and less likely to
go off on a jeep or false and go off on their own. If you crank this down, so
you can target a GEV, then don't the mines become easier to sweep?
Just thinking of scratchbuilding some engineering vehicles for SG2 and trying
to figure out if GEVs are at all practical for engineering
vehicles. I have GEV-mobile forces, and having
their engineering elements capable of manouvre at the same speeds seems vital,
but some options (ie the mine plow) seem a little unlikely. Other options may
present themselves (autonimous robot minesweepers, penetrating sensors
combined with precision mine
detonation systems, tractor/pressor beams (if
you buy AG, why not?), etc).
Thomas Barclay schrieb:
> On tracks, it has even
Yes, the ground pressure would be even lower (Weight of Vehicle divided by the
Area under the skirt)
> I'm a little unaware of the physics of a plenum
The lifting medium is a gas, so as a first approximation the pressure would be
equally distributed. There may be some minor pressure variation and heavy
turbulence. I think the pressure would be marginally higher under the fans.
> Given that a GEV is higher off the ground than a
Conventional (present-day) minefields could be more easily crossed,
yes. If GEV vehicles ever become a significant part of a nation's arsenal, I
have no doubt that Oerjan and his colleagues would have little trouble in
coming up with mine designs that explode when a GEV (or even a Grav
vehicle ;-) passes over them. Ideas for mechanisms would be trip-wires,
barometers that react to a sudden change in air pressure, optical sensors that
note the shadow of a vehicle, small radar systems, etc.
For game purposes, you can define minefields either way - though your
opponent may prefer to have minefields that work against GEV :-)
> Just thinking of scratchbuilding some
GEV vehicles slide easily over the ground. Thus they are easily moved and
pushed aside and they cannot exert much sideways pressure. Also they are not
very stable and could be unbalanced by asymmetric loads. For any tasks that
include lifting heavy loads, pushing earth or strong recoils, the GEV would
have to rest on the ground or, perhaps, on
hydraulic rams - think of modern crane trucks. If the task involves
moving as well, auxiliary wheels or tracks would be needed.
For a highly mobile force, it might make sense to have engineering
vehicles that use Ground-effect mobility for fast movement. But they
would need auxiliary tracks/wheels for actual work - complex and likely
to be expensive.
Greetings
KH.Ranitzsch@t-online.de schrieb:
> > Just thinking of scratchbuilding some
> If the task involves moving as well, auxiliary wheels or tracks
Another option for auxiliary movement might be legs - probably four or
more rather than two. Some kind of insect-like arrangement with folding
legs might also be easier to combine with a GEV skirt than wheels or tracks.
Greetings
On 30-Oct-01 at 04:50, KH.Ranitzsch@t-online.de
(KH.Ranitzsch@t-online.de)
wrote:
> For a highly mobile force, it might make sense to have engineering
Unless...
You use portable grav units powered off the GEV. The engineer hops out, places
the grav units at predisgnated positions, and flips the switch. The Disabled
GEV rises into the air and is slowly towed home. Decelleration would be fun to
watch.:)
***
You use portable grav units powered off the GEV.
***
Doesn't it seem that, if there are grav units in abundance, you'd do the
machines in grav? However, even with a temporary add-on gev unit/skirt,
decel is always a fun concept. ;->=
I never could get my rather conventional mind around this one. Knowing the
need to have both your recovery and engineer assets keep up with the maneuver
elements.The simple solution I came up with in my MTO&Es for both Grav and GEV
units is a large flatbed GEV on the same principle as the USMCs' large
hovercraft. This can carry a conventional tracked recovery and engineer
vehicle.The main reason for all this is I just couldn't see how you made a
plow work on either a GEV or Grav vehicle. And towing a GEV would be bad....)
> > For a highly mobile force, it might make sense to have engineering
> --- KH.Ranitzsch@t-online.de wrote:
> Conventional (present-day) minefields could be more
Depends. Tilt-rod minefields are so sensitive that
they would go off if you run a couple tons of tank over on FANS.
> vehicle ;-) passes over them. Ideas for mechanisms
IR sensors, magnetic sensors...
> --- Thomas Barclay <kaladorn@fox.nstn.ca> wrote:
> I assume with mine pressure detectors that you
For pressure fuzes, yes.
> which probably makes them harder to sweep
No, they become more dangerous to sweep--more likely
to blow up some poor sapper. AT mines are a breeze to
clear manually--if there are no AHDs on them.
> unlikely. Other options may present themselves
Probably all would be better. A PLS-style system on
the back carrying a couple drones is almost ideal, as your actual breacher is
completely unmanned and hence expendable.
> On 30-Oct-01 at 10:07, devans@uneb.edu (devans@uneb.edu) wrote:
It all depends on how expensive and fragile they are. A set attached to an
engineering vehicle that isn't "supposed" to take fire is a whole different
maintenance problem than grav lifters in 100 vehicles.
> KH.Ranitzsch@t-online.de wrote:
> For a highly mobile force, it might make sense to have engineering
The other option being to build smaller engineering vehicles and put them on a
GEV transport.
KH Ranitzsch wrote in reply to Tom Barclay:
> > On tracks, it has even
The pressure differences can be quite large, but it depends a lot on the
geometry of the outlet from the fan ducts. The pressure is most likely lowest
along the skirts where the air escapes from the air cushion.
> >Given that a GEV is higher off the ground than a
No need to wait that long; such mines are already in service. For side-
or
top-striking mines it doesn't matter whether or not the target touches
the ground <shrug>
Later,
> Thomas Barclay wrote:
> Odd question for the thinkers:
Pretty much. The air cushion does not need that much pressure to lift a very
heavy object if the area is great. A 200 ton craft with a footprint of 200
square metres would need an aircushion with a guage pressure of about 10
kilopascals (1.4psig). This hypothetical craft should float, as the air
cushion need only form a depression in the water with an average depth of one
metre (why I love metric). Hammer's Slammers style hovertanks have a problem
(with floating) that, even if they could generate the requisite aircushion,
their center of bouyancy and center of mass are too far apart for stability
(like standing on someone's shoulders, as they stand in a canoe).
> I'm a little unaware of the physics of a plenum
As the air goes from the fan to the edges of the skirt, the laws of fluid
mechanincs dictate that the air pressure is greatest in the middle, and lowest
at the edges.
> My question was this:
Like everything else in the world, it depends. If I do not operate any
aircushioned vehicles, but know that you use them to the exclusion of all
other vehicles, my mines will be triggered barometrically. AC vehicles will
not get far, but my wheeled, tracked, walking units are in the clear
(assumption: weather on the particular planet is not extreme). A Hammer's
Slammers hovertank is an unspecified size, but known mass. If they are three
by six metres, and 180 tonnes, they apply a whopping 1atm of pressure.
Although this is slightly less than half of the pressure exerted by a car
against the road, or only three times the ground pressure of a typical
infantryman, there are still circumstances when these hovercraft will bog
(Therefore, HS hovertanks have a larger footprint than eighteen square
metres).
> I assume with mine pressure detectors that you
Current landmines are set for a given weight. Serious overpressures can take
the place of a vehicle (why explosives can clear mines), but pretty much if a
sufficiently heavy object is placed on a mine, it detonates. To bury mines,
some account must be made for the weight being spread out, but that is need to
know information that I do not care to find out. Barometric mines are harder
to sweep, if they can differentiate a shockwave from a passing hovercraft.
Gravimetric mines are the hardest
> KH.Ranitzsch@t-online.de wrote:
> Thomas Barclay schrieb:
> Roger Books wrote:
> On 30-Oct-01 at 04:50, KH.Ranitzsch@t-online.de
Hiding wheels/tracks under the skirts of an air cushion vehicle is not
as difficult as people make it sound. According to an episode of TLC's
"Extreme
Machines" the SRN-4 hovercraft, used as a Channel ferry, is equipped
with hydraulic jacks to raise the vehicle up off of the ground for inspection
and maintenance of the skirt and plenum. They do not have wheel trucks on the
ends of these jacks, because they have no need for them, but there is no
reason that it would be difficult.
The only sticking point for a tracked hovercraft hybrid is how to raise the
skirts off of the ground, but furling sails is a similar problem that has been
solved. Once you have picked your preferred method of raising the skirts, you
either put the air cushion between the tracks, or the tracks under the skirt.
In both cases the powerplant of the hybrid vehicle has a power train that can
> Don M wrote:
> I never could get my rather conventional mind around this one.
***
The recovery vehicle has a selection of thin plastic skirting that it wraps
around the stricken vehicle, held on by a superglue and caulked to be
airtight. An auxillary lift fan supplies the air to raise the stricken vehicle
through an umbilical, and tow cables take the strain of pulling it along.
***
I alluded to this earlier, though superglue seems a mite on the weak side. A
good deal of the weight of the carried item transfers to the skirt, right?
Where it joins to the damage vehicle?
Anyway, I thought folks were balking at the idea of how you control the towed
item. Not insurmountable, though.
Can we call time on this one, or are there further actual game points to be
raised?
The_Beast
> devans@uneb.edu wrote:
> ***
First, the skirt is not bearing the weight of the vehicle, the air cushion is.
The temporary skirting is really only needed to patch up the skirt of the
damaged vehicle. Finally, that drop of superglue (between polished surfaces)
would continue to support that guy in the hardhat, even if he gained another
two thousand pounds [Time-Life Science: Giant Molecules].
> Anyway, I thought folks were balking at the idea of how you control
Given that it did not have brakes before it broke down, it is not that much
harder to control (not that this is an easy task, just not much harder than
controlling one).
> Richard Bell wrote:
> >I alluded to this earlier, though superglue seems a mite on the weak
The air cushion just has to be able to survive the air pressure in the air
cushion.
> The temporary skirting is really only needed to patch up the skirt of
It also has to cover the umbilical's connection to the damaged vehicle's
skirt.
> Finally, that drop of superglue (between polished surfaces)
Polished surfaces? On a GEV which has been knocked out in combat and crashed?
Yeah, *right*... how many hours did you say your recovery crew spent polishing
those surfaces after they arrived at the crash scene?
> >Anyway, I thought folks were balking at the idea of how you control
No, but it *did* have its own control surfaces and maneuvering thrusters. To
tow a GEV over rough terrain without having it bang into every nearby
obstacle, you need either a rigid (and very strong) umbilical or at least some
cooperation from the towed vehicle.
Later,
***
The air cushion just has to be able to survive the air pressure in the air
cushion.
***
True, if simplistic.
***
Polished surfaces? On a GEV which has been knocked out in combat and crashed?
Yeah, *right*... how many hours did you say your recovery crew spent polishing
those surfaces after they arrived at the crash scene?
***
Easily debated, but fiddly.
***
No, but it *did* have its own control surfaces and maneuvering thrusters. To
tow a GEV over rough terrain without having it bang into every nearby
obstacle, you need either a rigid (and very strong) umbilical or at least some
cooperation from the towed vehicle.
***
Which, I think, was my point in the first post, missed entirely in the
followup, and WAY too detailed in the last. Can we drop yet?
The_Beast