Drone flies as both biplane and helicopter using one propeller
 

There are helicopter drones and fixed-wing drones, but creating a hybrid of both is tricky. Even Parrot's Swing, as clever as it is, needs four propellers and elaborate wings to pull off its stunt. However, TU Delft (with backing from Parrot) has a...

https://www.engadget.com/2016/10/02/...one-propeller/