Airplanes have always always been an interest, since I was a kid (though theoretic, not actual).
Simple basic facts about aeroplanes: long thin wings tend to more efficient (aerodynamically, not structurally) than wider/thicker/shorter wings. For much the same reason - propellers are more efficient than jets. Ducted fans are less efficient than propellers, but more efficient than pure-jet engines. Turbofan engines are basically ducted fan turboprops. Gains in jet efficiency over than past few decades are in part due to higher bypass turbofans (basically moving from pure jets closer to propellers).
Even propellers are not ideal. Swirling a couple curved sticks of metal through the airstream at high speeds is going to chew up energy without adding to propulsion. Many-bladed turbofans chewing through the airstream have got to be worse. Lots of energy wasted - could there be a more efficient way? Nothing especially obvious … or something better would be in practice.
Ideally we would like a way to throw back the bulk of an airstream without lots of extraneous physical churning. The only certain way we know is to use propellers - like oars in water. Could there be another way?
There is a well-known phenomena in Physics known as “electric wind”, that moves air without physical contact, but is by no measure efficient. Is there any way this could be used?
Is there any way to efficiently push an airstream without physical contact?
The “electric wind” is a stream of charged particles. A magnetic field deflects an charged particle moving through. The deflection exerts a force on the magnet (assuming the force is not sufficient to capture the charge). Movement against that force consumes energy. That energy presumably could accelerate the charged particles.
The mean free path of a charged particle at normal atmospheric pressures is short. Any accelerated ion would give up about half it’s energy at each collision. Short mean free paths mean many collisions. The net result would be (presumably) to accelerate a bulk of the airstream. Maybe.
Magnetic fields deflect charged particles. Strong magnets rotating on opposite directions could deflect and accelerate, then re-deflect and further accelerate charged particles - maybe. Would the result be significant? Would the result be efficient? I have no idea.
This might be an approach only possible if the “controller” is sufficiently smart, and with quite intense magnets (superconducting?). Matching the acceleration and deflection of charged particles through alternating magnetic fields through changing atmospheric conditions may not be possible with simpler control.
Is a “magnetic propeller” is practical possibility?