Analyzing the Pitch Agility of an Ornithopter Undergoing Passive Compliant Element Induced Shape Change
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2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Ornithopters, or flapping wing robotic birds, represent a unique category of aerial vehicles that fill a need for small-scale, agile, long range and payload-capable flight vehicles. This study focuses on understanding the physics responsible for pitch agility of an ornithopter and its dependency on the plant dynamics. An analysis to determine factors that influence the Pitch Stiffness (KPitch) for an aeroelastic flapping wing was performed. Using blade element theory, the aerodynamic moment acting upon a wing undergoing aeroelastic flapping is calculated. The results indicated that ornithopter pitch agility has a strong dependence on the shape of the wing during flight. Passive compliant elements that were capable of providing shape control with a weight penalty that is minimal were then inserted into the wing. These contact-aided compliant mechanisms had nonlinear stiffness which varied during the upstroke and downstroke sections of the flapping cycle. The elements were designed and optimized using commercial finite element software. A Polyoxymethylene based plastic (Delrin) was used to fabricate the compliant elements. Using a motion tracking system, kinematic data for the wings of an ornithopter in level flight was captured. This information was used to calculate the pitch stiffness of the ornithopter for different configurations of compliant mechanisms. Results of the analytical analysis reveal that there was a compromise between agility and other flight performance measures such as stability and propulsive forces.
