Harnessing instability for deployable propeller blades

Launching in highly constrained environments such as battlefields and undersea requires aerial vehicles to reconfigure rapidly and radically. Deployable structures present an effective solution to package aerodynamic surfaces for launch and expand midair for cruise without the need for actuation. Here, we propose to exploit an elastic instability adopted by insects in wing folding to achieve tight packaging and fast deployment in propeller blades. The instability is imparted into the blade structure by introducing slits and making the cross-section open. Through folding and deployment experiments, we demonstrate that open-section blades exhibit compliant post-buckling response that allows extensive folding and rapid unfolding behavior solely driven by strain energy. Propeller thrust test results show that the proposed blade retains sufficient stiffness in the pre-buckled state to resist aerodynamic loads and generates the same thrust performance as solid blades. These findings pave the way for next-generation aircraft that employ long-span deployable surfaces to enable flexible launching or take-off while achieving aerodynamically efficient flight.