> Yeah rotor tip speed is Mach .7

The thin atmosphere cuts both ways. It generates less lift. But it inflicts less drag.

It also lowers the speed of sound. This poses some design limitations and since traditionally designed rotors get less efficient near Mach 1- they still work, but not as well. So you have to spin the rotors fast to generate enough lift, but you want to keep them slow so the tips don't go supersonic. Helicopters/drones on Mars are a tough design problem in areas beyond just the atmospheric- you can't use a gas engine because you can't refuel it, recharging a battery with solar energy takes forever because there is less solar radiation. You can't replace the rotors if you crash, so you need to make it robust, but you can't make it too heavy. On and on...

Maybe a balloon to provide most of the lift, then attach a few electric props? And if you have access to ice, maybe we can use solar panel to electrolise it into fuel.

What about solar-powered aircraft?

Would they work in Mars' atmosphere?

I'd like to see it tested in mars equivalent dust. I assume that the higher speed will correspond with more wear from sand blasting.