propellors et al.

any medium our crafts pass thru should remain as undisturbed as much as possible, be it air, water, or space-time (maybe?)

e.g. the vortices in air after an aircraft passes thru mean we wasted energy creating those

propellors should help us move our craft forward, but any other effect happening would mean they are not 100% efficient

on the same thought large grills on automobiles are a testament of our failure to engineer efficient propulsion systems! we are generating waste heat!