Well,
Having made quite a few craft designs, and then looking at the
problem of grav belts from that perspective, I'd have to guess
that the 300kph limit for speed has more to do with the drag
and structural integrety than the max force of output of the
belt.
MegaTrav puts an upperlimit of 300kph on all craft that are
considered 'unstreamlined'. A streamlined craft has an upper
limit of 1000kph, and an airframe craft has an upper limit of
4200kph (or 5000 in COACC). That is my opinion on why the
limit is set where it is. However, we have seen from the
high altitude parachute jump that higher speeds are possible.
(In a thinner atmosphere). This is the source of my confusion.
However, Grav belts are probably not designed to be a FAST mode
of transportation. It is much cheaper to design a grav vehicle
that is faster than a grav belt. So, for the most part the
belt will be operating at lower altitudes where 300 kph is
indeed reasonable.
Mark pointed out the problems of windburn and the difficulty in
breathing. Well, IMO, anyone who is out there trying to travel
at the speeds we're talking about is gonna be in some sort of
protective clothing, like a biker. A helmet will certainly be
needed. I would imagine that a helmet would provide enough of
a windbreak that breathing would be normal. Witness the formula
1 racers at the Indy 500. Cars there are open topped and travel
at 200mph (320kph) and the driver has no special breathing gear.
Admittedly, he's got a small windshield as a windbreak, but I
still think the helmet would prove effective. And if helmet
configurations that you and I are familiar with wouldn't do the
job, a helmet could be designed for the purpose. After all,
there just isn't a market for grav belt helmets here on Earth is
there? :-)
Scott "2G" Kellogg