Direction Controlled Descent of Samara Autorotating Wings (SAW) with N-Wings

The seeds of Maple trees (Samara) use autorotation as a unique mechanism to disperse their seeds. By exploiting gyroscopic stability of a spinning wing, the Samara is able to cover large horizontal distance despite having no form of propulsion. We applied and adapted this natural ability in our novel concept, the Samara Autorotating Wings (SAW), and extended its stability and direction controllability by generalizing the mechanism to incorporate designs with more than 1 wing. By conceiving cyclic control, the translational motion of autorotation is regulated. A nonlinear model of SAW with $n$ wings is derived and control schemes developed to control the translational position during autorotation. Numerical simulations were performed to investigate the performance of the multi-wing SAW prototypes to track a conical spiral autorotation trajectory. Direct experiments were conducted in a vertical wind-tunnel through a special ball joint that allows z-axis translation and all three rotational degrees of freedom. Finally, free-fall drop tests are used to verify the directional controllability and performance of SAW.