ponderance of the day: Just how small could one make a turbojet? Would a turbofan necessarily be larger? Could you make a ramjet even smaller?
jet wank
@Felthry idk how small you could theoretically make them but RC turbojets about the size of a coffee mug are totally a thing.
A turbofan is a turbojet with a ducted fan wrapped around it so yes, the smallest possible turbofan will necessarily be larger.
I would bet the lower bound on ramjet would actually be larger than turbojet but that's instinct, I can't back that up empirically.
jet wank
@machariel I was thinking a ramjet could be smaller because you don't have to deal with moving parts and manufacturing isn't a problem, but you do still need to have a good size air intake, so maybe not
jet wank
@Felthry yeah that's exactly my thinking.
jet wank
@machariel the reasoning I had for thinking a turbofan _might_ be able to be smaller is along similar lines, actually; a turbofan works at lower velocities because it moves more air than just what it uses for combustion. I'm not sure the entire thing, fan and everything, could be smaller, but the turbine and combustion chamber probably could.
jet wank
@machariel Ah, I am thinking in terms of practical output. Even given perfect manufacturing capability, there would be a lower limit on possible size simply because the coefficient of performance would (probably) go below 1 at some point, and at that point you're getting less power out than it takes to compress the air in the first place.
jet wank
@machariel That said, someone did mention yesterday that smaller turbojets are more efficient. I imagine there's a limit on that at which point smaller starts to become less efficient, but I don't know where it lies, or if it even exists.
jet wank
@Felthry same. I'm not an engineer, just a nerd who reads a lot.
And yeah if your criteria is output ratio > 1, then it might be that the smallest turbofan is smaller.
(Don't repeat the word small too many times in the same breath. Weird things happen 😃)
jet wank
@Felthry interesting, interesting.
when talking about "as small as possible" I'm not thinking in terms of practical output, just a "will it work at all." if you're not concerned about output then any tiny turbine you make for a turbofan will be a turbojet in its own right, inherently smaller than the turbofan it was built to be the heart of. that's where I was going with my thinking.