Re: [DS2] GEV mechanics

In a message dated 9/1/1998 11:48:33 AM Central Daylight Time,
lesack@unixg.ubc.ca writes:

<< There is one thing about GEVs that has always bothered me. DSII
allows
 GEVs (except fixed mount) to move then shoot. Hammer's Slammers'
 hovertanks had no problem firing when moving. 
 
 Being suspended on a cushion of air, gun stabilisation should not be
too
 much of a problem. The main thing is recoil from the main gun. It seems
 to me that a hovertank would experience severe effects from firing a
 hypervelocity round. (Think air hockey).I suppose using directional
fans
 could compensate somewhat, but I don't think they could be that
 effective. 
 
 Then again, I've never been in a tank, let alone seen one firing its
 main gun, so I could be completely wrong.
 
 I'm considering making a house rule that GEVs must fire before moving,
 but this would put them at a serious disadvantage.
 
 Does anyone have any (even purely speculative) information on this? Am
I
 the only one who has a problem with this?
 
 Thanks for your comments,
 
 Paul Lesack
 
 If I wanted complete suspension of disbelief, I could play Warhammer.
  >>

You are not the only one to have a problem with this, Paul.  I've long
thought
hovertanks and GEVs are one of those areas where sci-fi writers just
plainly
got it wrong.  I doubt we'll ever see hovercraft displacing tracked and
wheeled vehicles.  The US Army just released its "Army After Next" study
which
makes no mention whatsoever of hovercraft as combat vehicles.  

However, GEVs have taken root so well in various sci-fi setting that
there is
no getting around their existence.  So I've been using a couple of house
rules
(I'll put them on my site in a few weeks, along with other homegrown
stuff) I
drafted to clip hovercraft wings (or skirts, if you will) and make them
conform to reality.

According to my rules, GEVs treat Open terrain as Normal (as opposed to
Easy)
and Hills as Difficult.  No terrain is perfectly flat, and if you have a
hovercraft zooming along at movement allowance of 30 (which is
equivalent to a
couple of hundred miles per hour), guess what happens if it encounters a
small
dip or gully or even a gentle incline?	Since air is a compressible
medium,
the hovercraft is likely to plow right into the ground as it won't be
able to
raise its nose fast enough.  Hovercraft are also notoriously poor at
climbing
hills.	You can overcome both problems by installing more powerful
engines,
but then you end up with a VTOL design, rather than a GEV.

Air hockey analogy is quite apt. Here are a couple of recoil force
figures for
modern tank guns:

120mm 
KE 550kN,  56,1t (I believe the data is for the DM13 round) 
MZ (HEAT) 550kN,  56,1t 

105mm 
APDS 476kN,  48.0t 
HEAT 591kN,  60.3t 
HESH/HEP 233kN,  23.8t 
The data is for the Leopard 1 and 2... 
source W.J. Spielberger ISBN 3-613-01198-0 

By way of comparison, F-15's engines develop "only" about 25 tons of
thrust.

So, according to my rules, no GEV may mount a HKP, MDC, HVC, or RFAC
greater
than half of its size rating (fractions rounded down).	No restrictions
on
low-recoil weapons (i.e., directed energy and missile weapons).  

Comments?

Mike Jasinski