I have wondered how far you can get without an engine and with computer stabilization. A plastic bag flies in the wind, and sailships can sail upwind to some degree, so surely someone is experimenting with solely wind powered drones?
The easiest version of that is a balloon, they go where the wind goes but they can go very far and if the winds are favorable then you can do 800 km on a couple of AA batteries while powering up your controller every 10 minutes or so.