OK.

Back to my prop in a glass of water.

If you dropped some steel balls into the glass and activated the prop, wouldn't those balls begin to roll around in the bottom of the glass?





Alternatively, if there were no helical flow of air from a prop, how would the engine's shaft experience any torque? I mean, if the airflow was purely axial, then the propshaft would experience thrust, but no torque ... I think that this would be impossible.