I recall reading about the craft using gasoline as an incompressible floatation fluid, but I hadn't realized the scale: 100 tons of gasoline, making up 2/3s of the craft's mass.
Basically the equivalent of a lighter than “air” craft but in a different fluid. I wonder if there’s a word for a craft that controls its buoyancy regardless of medium?
borrowed from French aérostat, probably back-formation from aérostatique "of aerostatics," with -stat (after héliostat heliostat) taken as the Greek agentive element -statēs "one who causes to stand" — more at -stat
I never knew the scale either. But the book says gasoline has a specific gravity of 0.7. So 100 tons will make roughly 30 tons of buoyancy. The negatively buoyant craft is 50 tons so combined with the air inside that is probably the displacement required to make it positive