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.
About that Hypothetical Earth, with 10x actual atmospheric pressure. I’ve already made the point, that internal-combustion engines would not work. But what about steam engines?
Well, by analogy, the efficiency of a steam-engine is also dependent, not only on how high the high-side pressure can be, but on how low the low-side pressure can be. And so, if the hypothetical steam engine was just to vent its exhaust-steam into the air, as the earliest locomotives did, then its low-side pressure would already need to be higher, than the high-side pressure was, of an actual locomotive.
But ultimately, an external combustion engine should work. And my main reason for saying that is the observation, that in the real world, we were able to build refrigerators by the 1970s, which had a closed-cycle working fluid (Freon at the time). And our hypothetical Civ would be able to devise a tailor-made fluid-cycle, with an efficient pressure-ratio, sealed into a closed loop.
(Edit 05/11/2017 : The point of sealing this loop would be, to keep the high atmospheric pressure out of it, so that its low-side pressure could be as low as needed, and the most-efficient working-fluid available recycled. The resulting system would not be optimized for low power, high-cooling, but would instead be optimized for tapping a low amount of heat-transfer, and generating as high an amount of electrical power as possible.
Also, there exists no specific reason for why this working fluid would need to be steam. Steam was used since the early Industrial Revolution, because water was cheap, and because the properties of water were about-right. If the working fluid is to be recycled fully, a more-expensive substance can be chosen and charged once. There are often several reasons why steam is not chosen, including the corrosive nature of water on several alloys, as well as the fact that water would freeze, at the fluid-temperatures present in a refrigerator or freezer – even if the temperature inside is not intended to go below 0⁰C .
In big, thermal power-stations that are modern, another consideration for using steam is, the fact that the steam escapes. Experiments have been done on thermal power-stations, where some more-expensive working-fluid was used, but then additionally, the cost of sealing the system 100% became prohibitive.
In practical examples of nuclear power-stations, steam is allowed to escape from the outer loop, which is non-radioactive. And any water that might escape from the inner loop would be radioactive, and needs to be caught. This water stays liquid, and only serves to transport heat to the steam-generators, that turn water from the outer loop into steam. It stays liquid because the inner loop is under much higher pressure than the outer loop.
But I do not see how such a contraption would become airborne, until a later point in the hypothetical evolution, of an Earth with 10x our real atmospheric pressure. Becoming airborne is always a proposition of achieving high power-to-weight ratios, and not just high power. If the flying contraption needs to transfer its power through 2 sets of heat-exchangers, one generator and one motor, before feeding it to propellers, I do not see good, lightweight design.
And yet, electric drones do achieve high power-to-weight ratios, mainly just by being very lightweight. )
(Edit 05/11/2017 : )
It’s a fact known by Rocket Scientists, that actual rocket engines lose efficiency due to ambient atmospheric pressure. They take this into account, in the calculations for every space-launch in our actual Civilization, as well as for rocket-assisted landings on Mars, etc..
If the effect happens to be negligible in one case, they have to prove it’s negligible. They have to translate the reduction in short-term thrust – which might seem negligible at first glance – into how much additional fuel a rocket needs to carry, in order to carry out a lengthier maneuver. And then, if the increase in fuel to be carried is less than one gram, the effect is indeed negligible.
(On the note of electric motors designed to operate under 100 atmospheres of pressure:
It would be important not to design them, to contain a cavity which the external gas is blocked from entering. Considering that every electric motor has at least 2 parts which move with respect to each other – such as a rotor and a stator – this means that gas will eventually need to separate those two component-assemblies, and that this gas will also need to be under 100 atmospheres of pressure.
If this was not permitted, then the risk would prevail, that the external pressure would crush the assembly around this gap.
OTOH, Whether that gap may be filled with external, atmospheric gas, would depend on whether that gas conducts electricity or insulates against its flow. If the external fluid was one which conducted electricity, then the gap inside the motor would need to be charged with 100 atmospheres of some other gas, so that external and internal pressures match. We could charge the space inside the motor with 1500 PSIA of Hydrogen, and it would work fine. And in fact, high densities of certain gasses can act as lubricants, as coolants and even as gas-bearings. )
(On the note of electrical drones which are able to carry People:
I have heard that there exists a company in the USA, which is currently in the process of designing a drone, meant for emergency medevac purposes. Its concept is that it would fly into a disaster zone mainly-empty, but with large containers designed from the inside to hold patients.
People would load patients into these compartments, and the drones would fly out of the disaster-zone, carrying those patients to safety.
My only problem with that, is that according to my latest information, those medevac drones have not advanced into their production-phase.
Until they do, I must consider them to be hypothetical.
In general, I try to measure the worthiness of my own hypotheses, against established facts, and not against other hypotheses.
If those drones are ever proven, I would say that in our counterpart-world, we would simply have achieved manned flight for the first time. In the year 2017.
Going a bit further with that, there might exist a type of solar-powered airplane, which has by now carried one pilot. But to the best of my knowledge, such airplanes tend to be very lightweight, and much larger than conventional planes today, so that they can also hold the required surface-area of solar panels. They barely meet the specification of heavier-than-air, and do not meet most of the practical requirements made of airplanes in fact. They tend not to be practical lifters.
And was the first manned, solar-powered plane built and flown before or after the year 2000 ? )