Static structural and modal analysis of Micro Air Vehicle flapping wing with varying stiffness structures

Abstract

Increased demand for undetected surveillance along with data sensing and gathering capabilities has encouraged the researchers to explore new avenues in micro and nano air vehicle technology. Successful employment of fixed and rotary wing micro air vehicles in a vast array of roles have encouraged the scientists to develop bio-inspired flapping-wing micro air vehicles hence surpassing them in hovering and sharp turning at low-speed capabilities. These vehicles mimic birds such as hummingbird and many more. Their wings are constrained from the root; flexible nature of their material inhibits deformations and torsion during the flapping motion. Static deflections may lead to buckling or loss of lift due to higher torsion angles. Moreover, the cyclic motion of the wings may lead to material degradation resulting in an increased twist. This effects their aerodynamic performance and in the worst case may lead to fatigue failure. Therefore, it is of paramount importance to design the flexible wing with appropriate stiffness distribution for deformation, which may result in desirable aerodynamic and structural performance. Material selection for the flapping-wing unlike fixed wings is complex in nature due to the anisotropic property of reinforcement members and membranes used in the design. In this research, a comparison of different wing designs has been carried out using commercial finite element analysis software. In the first step, different wings of varying stiffness structure patterns of a Zimmerman planform (mimicking the humming-bird) have been designed. They consist of thin flexible carbon fiber and latex rubber membranes of varying strengths. Wing designs of different membrane materials and structural reinforcement patterns have been analyzed and compared in this work. Four such wings with an aspect ratio of 7.65 (wing length and root chord of 75 mm and 25 mm root, respectively) have been designed with different placement patterns of stiffness battens. This paper focuses on the stress, strain, deformation and modal analysis of the wings of various design configurations as a reaction to static forces applied at leading edge tip of the wing. After the analysis of the obtained results, the thickness of reinforced material has been decreased to three-fifth and one-fifth of the original thickness. The refinement in wing design has enabled the selection of the optimum design for given models and materials. The results show that Spread Batten Wing made of Capran membrane, with batten and membrane thickness of 0.2mm and 0.014mm is better amongst the designed wings to handle a load of 6g at higher operating frequencies (>100Hz). Whereas at lower operating frequencies (<50Hz), reinforcement of 0.6mm members along with 0.14mm thick Capran membrane is suitable for Leading edge reinforced wing and Leading & Trailing Edge reinforced wing. This study will augment in the appropriate selection of material and stiffness members in design finalization of the micro aerial vehicle wing to avoid buckling, twisting, and failure at high frequencies.