The other option is to use coanda-effect vehicles which I'm not sure if there is an efficiency gain. The other thing too I brought up with somebody else is to

The other option is to use coanda-effect vehicles which I'm not sure if there is an efficiency gain. The other thing too I brought up with somebody else is to use muscle wire or memory wire and put that into blades that are otherwise soft. So if it's about to strike something the blades go limp.