Dynamic soaring. No motors, no engine, no thrust of any kind. Just harnessing the power of the wind that accelerates up hill. The trick is to know the currents of the wind and to accelerate up the hill and knowing when and where to come up and not lose any speed. Picking up tailwind speed with each successive loop.
The black footed albatross harnesses the wind differential in the ocean swells in a similar way to traverse great distances without expending any energy and even while sleeping.
No sleeping or even so much as blinking at these speeds with these models!
https://youtu.be/4eFD_Wj6dhk