<< The air powered transport would indeed work, but the losses in a pneumatic
system are awesome for tubes large enough to carry passengers and freight.
The air in front of the car is compressed, and the air behind is compressed,
and this causes heating. A pump big enough to pull an active vacuum in front
of the car would be a very impressive piece of machinery.
There are physical limitations to flow in pipes without huge frictional
losses. I am not an aeronautical or fluids engineer, so I cannot give
precise limits, but i know they exist.
Heinlein described above ground ballistic transports running in air at
supersonic speeds, with accelerator coils on hilltops at intervals. A neat
idea, but I doubt anyone would let us build one..
>>
The tubes could have gills in them, like in front of the craft the gills are
open, so it wont create compressed air in front of it (or not as much), since
it will escape into the outside air, and as the craft passes over the gills
they become temporarily sealed to hold the seal-tight air bursts behind the
craft, then they would have to be opened again for the next craft after the
first craft passes the next charging station.
The gills would have to be like super thin and lightweight (but still able to
be sealed), so it wont create very much friction for the craft. Where and
when to get out have to be worked out, like perhaps the tubes split, and they
are diverted in a station, so it wont hold up the crafts behind it as they
pass through.
danny
danny