[batuhandirek]

I mean propellers are around for a long time, I cannot believe no one thought about optimizing their tip vortice energy loss.

[rawicki]

People do! there were many different approaches - small winglets on propeller tip, propeller with a ring, propeller in a tunnel (turbine) - and they all improve performance by a bit.

This is a next iteration, seems to be harder to simulate but improves on previous ideas.

[karmakaze]

This is so simple and brilliant. It's like the winglets on planes but so much more so.

Just looking at it says efficiency and power.

[julienfr112]

the equivalent for plane wing would be to have two wings on each side connected like that :

---------\ | ---------/

[beecafe]

Those exist too! Every so often NASA tries it out.