Testing of novel compliant spines for passive wing morphing

Flapping wing Unmanned Aerial Vehicles (UAVs) or ornithopters are proliferating in both the civil and military markets. Ornithopters have the potential to combine the agility and maneuverability of rotary wing aircraft with excellent performance in low Reynolds number flight regimes. These traits promise optimized performance over multiple mission scenarios. Nature achieves this broad performance in birds using wing gaits that are optimized for a particular flight regime. The goal of this work is to improve the performance of ornithopters during steady level flight by passively implementing the Continuous Vortex Gait (CVG) found in natural avian flyers. In this paper we present new experimental results for a one degree of freedom (1DOF) compliant spine which was inserted into an experimental test ornithopter leading edge wing spar in order to achieve the desired kinematics. The lift and thrust along with electric power metrics at different flapping frequencies were measured using a six-channel load cell and a current senor, respectively. These metrics were determined for the test ornithopter both with and without the compliant spine insert. Initial results validate the ability of our compliant spine design to withstand the loads seen during flight at flapping frequencies of up to and including 5 Hz. For the ornithopter test platform used in the study, inserting the compliant spines into the wing leading edge spar accurately simulates the CVG increasing the mean lift by 16%, and reducing the power consumed by 45% without incurring any thrust penalties.