Design, Fabrication and Testing of a Passively Morphing Ornithopter Wing for Increased Lift and Agility

Abstract

Abstract : Over the last few decades, flapping wing Unmanned Aerial Vehicles (UAVs), or ornithopters, have shown the potential for advancing and revolutionizing platform performance in both the civil and military sectors. An ornithopter is unique in that it can combine the agility and maneuverability of rotary wing aircraft with excellent performance in low Reynolds number flight regimes. The objective of the proposed work was to develop methods to design novel ornithopter wings that allow passive wing morphing. Passive morphing was achieved through an optimally designed compliant spine that mimics the function of a bird s wrist. A multi-objective optimization was carried out and several designs resulting from this optimization were bench-top and free flight tested. The presence of a 1DOF compliant spine in the ornithopter wing was found to introduce an asymmetry between the upstroke and the downstroke. For any given flapping frequency or throttle setting, the ornithopter with the compliant spine consumed less electric power, produced more mean lift and did not incur any thrust penalties when compared to the ornithopter without the compliant spine. Power reduction of 44.7% was achieved at the steady level flight flapping frequency, lift gains of up to 16% of the ornithopter's weight was also realized without incurring any thrust penalties. Also during the free flight test, the ornithopter with the compliant spine inserted in its wings reduced the overall negative center of mass acceleration during one flapping cycle by 22 %. The negative acceleration reduction may translate into overall lift gains. Thus the steady level flight performance was improved due to the presence of the compliant spine. Therefore compliant mechanisms proved to be not only feasible, but also beneficial for application to general air vehicle design.