Leading-Edge Twisting Mechanisms for Flapping Wings

This paper is to focus and evaluate the effects on aerodynamic forces due to the leading-edge twisting on a flapping wing. Three flapping mechanisms were fabricated using the fused deposition modeling (FDM) 3D printing. They are type-A1 (normal servo) mechanism for simple flapping motion, type-B (servo-bevel gear) mechanism for flapping with continuous leading-edge twisting, and type-B1 (servo-bevel gear with adjustable mechanical stopper) mechanism for flapping with restricted leading-edge twisting. Time-averaged lift and net thrust forces were measured using a low-speed wind tunnel. Results revealed that the type-B1 mechanism with restricted leading-edge twisting to have 32.9% better performance than the type-A1 mechanism with simple flapping, and to have 64% better performance than the type-B mechanism with continuous leading-edge twisting. The leading-edge twisting is sketched using a visual motion sensing technique. A high-speed photography was performed for all three flapping mechanisms and the Kwon3D software was applied to find the trajectories accordingly. Through MATLAB software the wing trajectories were converted into 3D surfaces and 2D airfoil cut sections were generated at mean aerodynamic chord at different time frame of flapping cycle. Finally, the instantaneous angle of attack was found for each instance to help understanding the corresponding lift force value. Furthermore, a theoretical rigid body dynamics was applied to create the 2D profile and verify the 2D cut sections from MATLAB. The comprehensive study and evaluation of lift and net thrust forces due to leading-edge twisting were conducted for all three flapping mechanisms in this study.