1 Copyright © 2010 by ASME Proceedings of the ASME 2010 Conference on Smart Materials, Adaptive Structures and Intelligent Systems SMASIS2010 September 28 – October1, 2010, Philadelphia, PA, USA SMASIS2010-3637 DESIGN OF A PASSIVELY MORPHING ORNITHOPTER WING USING A NOVEL COMPLIANT SPINE Yashwanth Tummala Graduate Research Assistant Dept. of Mechanical and Nuclear Engineering The Pennsylvania State University University Park, PA, USA Mary Frecker Professor Dept. of Mechanical and Nuclear Engineering The Pennsylvania State University University Park, PA, USA Aimy Wissa Graduate Research Assistant Dept. of Aerospace Engineering University of Maryland National Institute of Aerospace Hampton, VA, USA James E. Hubbard Jr. Langley Distinguished Professor Dept. of Aerospace Engineering University of Maryland National Institute of Aerospace Hampton, VA, USA ABSTRACT A new scheme to design morphing ornithopter wings using a passive compliant spine is presented in this paper. The objective of this work is to optimize steady level flight performance of an ornithopter by passively implementing the Continuous Vortex Gait (CVG) which requires bending, twist and sweep coupling during the upstroke. An optimization problem is formulated to design a compliant spine for pre- specified bending, sweep, and twist deflections. As a first step to achieving these 3 DOF kinematics, a 1 DOF compliant spine is considered to produce a specified bending deflection during the upstroke for drag reduction while remaining stiff during the downstroke for increased lift. The effect of the relevant geometric design parameters, namely contact gap, angle, and hinge geometry, are considered and optimized to achieve the aforementioned kinematics for both single and multiple joints, which make up a compliant spine. Results presented include the spine design optimization procedure, as well as a complete analysis for a 1DOF compliant spine to illustrate the efficacy of the methodology. This compliant spine design methodology and optimization procedure will be used, in the future, to design the 3-DOF compliant spine for the passively morphing ornithopter. 1. INTRODUCTION Over the last few decades, flapping wing Unmanned Aerial Vehicles (UAVs), or Ornithopters, have shown an enormous potential for advancing and revolutionizing UAV performance in both civil and military sectors [1]. An ornithopter has unique potential in that it can combine the agility and maneuverability of rotary wing aircraft with excellent performance in low Reynolds number flight regimes. These traits could yield optimized performance over multiple mission scenarios. Nature achieves such performance in birds using wing gaits that are optimized for a particular flight regime [2]. The goal of this work is to passively improve the aerodynamic performance of ornithopters during steady level flight. The aforementioned goal can be realized through passively implementing a bio-inspired flight gait, known as the Continuous Vortex Gait (CVG) [3]. In this gait, vortices are shed continuously during both the upstroke and the downstroke, as illustrated in Figure 1.