[restalis]

"For jet engines, the only thing that comes to mind is electric aircraft. No single-crystal turbine blades needed at all. I may have picked a bad example, but the principle stands."

I understand the idea you wanted to convey and that commenting on the technical detail is not something we're supposed to do, but the technical side of your example is just too glaring to ignore. A people-carrying aircraft, be it of electric propulsion, or of other type, is heavy. Like, several tons (at minimum) heavy. To acquire the necessary portance, the aircraft has to be accelerated (on its inert wheels) on the runway up to the take-off speed and then to be able to hold the cruising speed, using engines capable of generating such thrust by only moving the air. That's a lot of force right there, and the engine that has to do this, will have to be pretty tough. Regardless of the fact that the source of the on-board energy is electric or not, that same air will have to be moved, somehow, at the needed speeds, and it will be by an engine that will look and work pretty much the same way the current jet engines do, since the shape is dictated by the aerodynamics and the internal design is given by the (air) fluid dynamics it has to work with. The single-crystal turbine blades are just an optimization. Weaker (regular fine-grained casting) materials can be used, but that will mean limiting the performance to lower tolerance levels (and most likely be heavier as well, to compensate for the lower mechanical strength).