We're talking about cargo drones, so I'm assuming the rotor would be relatively heavy duty compared to the size of the craft. And since we're talking unmanned,

We're talking about cargo drones, so I'm assuming the rotor would be relatively heavy duty compared to the size of the craft. And since we're talking unmanned, you can probably accept higher landing speeds than normal. You are really just interested in preventing a catastrophic landing, so navigating towards an empty area and not exploding on impact.