I think that has less to do with strange aerodynamics and more to do with the deadly whirling blades interacting poorly with the solid vertical surfaces if ther

I think that has less to do with strange aerodynamics and more to do with the deadly whirling blades interacting poorly with the solid vertical surfaces if there happens to be, say, a gust of wind. A ducted-fan based system would be much safer, and could work in a constrained urban environment.