Wow, there's innovation in propeller shapes (which i thought we're close to optimal for a century): toroidal propellers https://newatlas.com/aircraft/toroidal-quiet-propellers/ >50% performance improvement at midrange rpms in liquids!

@mtyka It's a common trend for technology to improve rapidly, get "good enough", and then only be incrementally improved because the gains aren't worth the effort. No one looks for radical change because everyone's satisfied with the thing as it is.