Drone design features an autorotating body
One of the big worries regarding the widespread use of drones is that if their motors fail, they could plummet out of the sky and hit us on the head. Equipping them with parachutes is one option, although that adds weight and complexity. Meteorological forecasting company Meteomatics is taking another approach, in the form of a quadcopter that can spin its way down like a top.
The Swiss firm recently received a US patent for the "Meteodrone" concept, in which at least two of the drone's four symmetrically-arranged propeller arms are flat and twisted – not unlike propeller blades, actually. In the event of a motor failure, once the drone starts falling, those arms will act as passive lift elements. This will cause the aircraft to spin horizontally, around its yaw axis.
That spinning motion will keep the drone stabilized, so it comes straight down instead of tumbling erratically. Additionally, the motion will generate some dynamic lift, so the aircraft won't simply drop like a stone – that said, you probably still wouldn't want to be standing beneath it.
When and if the Meteodrone reaches production, plans call for it to be used for measuring weather parameters within the lowest region of the atmosphere.