Study on shapes of Double Cylindrical Structure for Wing Twist Morphing

We previously developed a twisted morphing wing system based on a double-cylinder structure that consists of outer and inner parts. Here, trade-off studies on the shape of the outer part of the double-cylinder structure are carried out. The open section of the outer part has four beams. The equivalent bending stiffness, equivalent torsional stiffness, and buckling force are calculated for various shapes of the open section using previously derived formulas, and their relationships are obtained. The effects of the shape parameters, namely beam height, width, aspect ratio, and length, on the equivalent bending stiffness, torsional stiffness, and buckling force are investigated, and the optimal cross-sectional shape of the outer part for wing twist morphing is determined. The open section should have low torsional stiffness to achieve wing twist morphing, high bending stiffness, and a large buckling force to bear the aerodynamic load. The results indicate that the smallest equivalent torsional stiffness is achieved by using a cross-sectional shape with a large aspect ratio. Moderately small torsional stiffness and moderately large bending stiffness are achieved with a small aspect ratio. Therefore, the shape of the open section can be designed by considering the trade-off between bending and torsional stiffness. Furthermore, the open section length should be set to avoid buckling of the beam and realize a large twist angle.