> and propellers can operate even with very low air pressure How does that work exactly? Of course, my intuition is that lower air pressure means less to "pus

> and propellers can operate even with very low air pressure How does that work exactly? Of course, my intuition is that lower air pressure means less to "push off of" but also less drag. And you've got certain constant overhead, like internal friction. Is there some sweet spot of air pressure where you'll get the best efficiency?