Twice the lift of hot air, and it's dynamic for buoyancy control.
OTOH Bucky Fuller's Cloud Nine cities used one degree of temperature difference inside a one-mile sphere.
Quote:
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Fuller suggested that the mass of a mile-wide geodesic sphere would be negligible compared to the mass of the air trapped within it. He suggested that if the air inside such a sphere were heated even by one degree higher than the ambient temperature of its surroundings, the sphere could become airborne. He calculated that such a balloon could lift a considerable mass, and hence that 'mini-cities' or airborne towns of thousands of people could be built in this way.
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https://en.wikipedia.org/wiki/Cloud_Nine_%28tensegrity_sphere%29
Steam in ballonnettes could control altitude.
drrbc -- cross-post. I just wanted to post that old cartoon and mock it; where it goes from there is open (nanomachines?) but hopefully steam related.
I'll check the article.
Edit:
What do you think? He uses an equation that he doesn't give, and suggests the Vs (I assume velocity?) drops from 1700 to 1440fps. Which suggests a smaller volume over time, but steam is going to expand the volume.
I can see reducing radiant heat off the pipes to keep velocity up, that's why thermal wraps. This
maybe uses heat of vaporization to reduce the energy in the gas so it doesn't heat up the pipe it's passing through, instead.
I don't know why it would be limited to two-strokes; but what's the advantage over injecting the water into the combustion chamber?