Prev: Re: [ds] Modern Tanks. Next: [DS2] Vehicle Design Application

Re: GEV capabilities

From: Adrian Johnson <ajohnson@i...>
Date: Tue, 17 Nov 1998 11:26:53 -0500
Subject: Re: GEV capabilities

>> In a message dated 11/16/1998 11:26:48 AM Central Standard Time,
>> ScottSaylo@AOL.COM writes:
>> >  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.
>> The reason why hovercraft are so bad at climbing hills (except
>> 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,
>> your propulsion fans.
>if the hull stays parallel to the ground, then yes. however, if it
>horizontal, then the tank will climb the hill as thrust will escape on
>downhill side. of course, your power consumption will skyrocket.

You'd have to have selective venting around the skirts or lift fans at
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
limiting factor would be the maximum possible thrust of the lift fans. 
the end, having lift fans capable of lifting the vehicle (for brief
periods) solely through their lift and not just with the contained
of pressurized air in the skirts may be the best way to go.  If you have
lower the front of the skirts to go up a hill, what happens if you have
hill with broken/rough surface terrain?  You'd dig in the nose of the

>>  To overcome that you'd have to install almost enough
>> thrust to make the whole thing fly, making it, in effect, a VTOL.
>not quite; it still has the advantage of the ground effect, which makes
>flight far easier than in the free-flight regime.

Well, almost.  This is maybe straying a bit far from the point of the
but the "ground effect" in "ground effect vehicle" (al la hovercraft) is
different from the "ground effect" which makes flight more efficient
to the ground.	Or, maybe I should say it's the same basic idea, but
different practical applications.  A hovercraft generates "lift" solely
from riding on a cushion of compressed air, contained by its' skirts. 
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
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
hills, etc - the vehicle has to give up its' cushion of air to do so -
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). 
airfoil generates its lift by the differential in pressure on the top
bottom surfaces as the airfoil passes through air in flight.  Airfoils
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
cushion under a hovercraft.  I may be forgetting some of the details
(been a while since I was flying) - but the end result is that
do not take advantage of the "ground effect" the same way that a fixed
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
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
to describe 'cause it is very unfamiliar looking).  It moves like a boat
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
of the airfoil in ground effect).  It can only stay within about 6 feet
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
roughly equiv. in size to the cargo capacity of a Hercules
 It was part of a tech. development program for this technology.  I
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
remember what the results of the program were - certainly we don't see
tech used anywhere - though it seemed like a good idea.  The Soviet
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
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
on land (be a drag to need a 10k foot runway to land and take off),
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...


Prev: Re: [ds] Modern Tanks. Next: [DS2] Vehicle Design Application