Naturally, if you’re [Daniel Riley] of RCTestFlight, then you have to 3D ... toroidal propeller that made waves a while ago, mostly in the field of flying drones, but commercial toroidal boat ...

[PDF via NewAtlas] Inspired by some of the experiments with “ring wings” in the early 20th Century, researchers iterated on various toroidal propeller ... fabricated via 3D printing they ...