[Vehicles] Low-grav, high-pressure aircraft

[Anthony]

Originally Posted by Anaraxes

Yes. I was focusing just on the pressure effect. If the OP wants Earth-normal humans to breath this atmosphere (and preserve an otherwise Earthlike environment), he'll have to reduce the proportion of oxygen. And that will, of course, mean less fuel per unit of air

Less fuel per unit mass. Per unit volume is the same, though if you're using a compressor you need more pressure. The big worry is that the presence of neutral gases significantly affects combustion (the neutral gases absorb some of the heat of the reaction; if there's too much, there isn't enough left over for a self sustaining reaction), possibly meaning your fuel won't ignite at all.

Fuel cells will be fine, though.