My question has been:
Assume that there exists a species similar to Man, but on a hypothetical Earth, with an atmospheric pressure of 150 PSI – i.e. with 10x the actual atmospheric pressure. The atmosphere should still contain free oxygen, so that early, primitive tools and fire remain possible. But my Civ seems to have a very late-onset Industrial Revolution.
The reason for this seems to be, that internal combustion engines just wouldn’t work. An actual gasoline engine needs to achieve pressure-ratios of 1:8 or better, to be efficient, and should not need to be made from super-alloy. An actual diesel might seem prohibitively expensive already, just because it uses a pressure-ratio of 1:12 or so. You see, the fact that a simple, cheap solution already exists, can prevent our actual civilization from developing solutions that could ultimately be better. We still don’t see a lot of electric cars on the road, just because the internal combustion engines are so much more-affordable.
Flying-machines already exist, that use the infernal-combustion engines, so why try to invent (presumably more-expensive) flying machines that would be electromagnetic?
But on the hypothetical Earth, electric motors that spin propellers would work just fine. In fact, electric motors should work just as well, at 100x actual atmospheric pressure. So the obvious question should be, where would our counterpart-Civ derive its electricity, if not again, from an internal-combustion engine?
And so one observation which might be useful to me, is that drones such as our electric drones should work well for this hypothetical Civ. But then, that would also seem to be the earliest-possible onset of their version, of heavier-than-air flight. By that analogy, flight would have to wait, until they have invented a lightweight source of electricity, comparable in performance to our Lithium-Ion batteries.
But I don’t have my full answer yet. Our actual drones today are still not powerful enough, to lift a Man into the air and fly way with him. Apparently, Lithium-Ion Batteries are not lightweight and/or high-energy enough yet. Our Civ has gotten unmanned drones to fly, but no manned flight yet.