Do superfluids lack inertia and/or don't exist with a finite speed of sound? I've been reading a few things on other sources about superfluids and what kind of propulsion would work in them. Supposedly a propeller won't work in a superfluid, but I'm having a hard time understanding why.
As the propeller spins, it pushes against the fluid which should have an equal and opposite affect on the propeller, no? Is it that there is also fluid on the other side pushing the propeller in the other direction?
If so, this can only work when the speed of sound in the superfluid is >> than the speed of rotation of the propeller, right? If I somehow had a propeller that could spin an appreciable fraction of the speed of sound, would it be able to cause cavitation in the fluid and actually accelerate forward?
And why is a propeller, which can be seen as being a truncated corkscrew with less than a full rotation, unable to work in a superfluid, but a corkscrew with several rotations can work in a superfluid?
Edit:
I seem to have mis-read about the corkscrew.
http://echochamber.me/viewtopic.php?t=64408
 A: I am not convinced that your corkscrew will work. Do you have a reference for where you got that idea? 
Notice that the superfluidity case is completely different from the ultra-low Reynolds number situation of swimming microorganisms. It's virtually the opposite: In the latter case you are in fact dealing with a fluid at a nondimensionally very high viscosity, which means the differential equations of fluid flow become (approximately) linear and spatio-temporally symmetric as you go from the Navier-Stokes to the Stokes equations. See Purcell's classic "Life at Low Reynolds Number". Thus reciprocating motion cannot be used for swimming propulsion, and amoebas and such use e.g. corkscrew designs or various kind of flagellar motion.
As for the supersonic flow case, well, sure, in that case you can in theory generate (singular) vorticity sheets through the development of discontinuity surfaces. I don't know enough to tell you off the top of my head whether or not you could use this for propulsion purposes. I'm not planning to spend time thinking about this, since it's fairly clear that this is not a very realistic scenario that anyone is likely to ever contemplate seriously.
