Anyone ever seen some of the new toroidal propellers that claim to increase efficiency by limiting the tip vortices and propeller slip:
It seems to me this accomplishes a similar thing to a high aspect wing - where the pressure loss across the tips is minimized by increasing the span. A propeller is just a spinning wing.
I wonder how a toroidal foil wing (think biplane - but with a loop connecting the lifting surfaces) would handle. It seems Wikipedia refers to this as a Closed wing
Theoretically you may be able to control the water flow more effectively to create more lift (without drag) without increasing the wingspan. After all lift is created by imparting a momentum change on the fluid a wing is passing through. It seems a toroidal wing design may be able to more effectively control the lateral flow of water across a wing. But maybe I am understanding this wrong.
Total speculation / nerd out here.
