A Wind Tunnel Experimental Study on the Flexible Flapping Wing with an Attached Airfoil to the Root

With the purpose to improve the performance of the flexible membrane flapping wing, a kind of flapping wing with an attached airfoil to the root is designed and tested in a wind tunnel. In order to study, the actual performance improvement of the flapping wing, the flight performance is calculated and compared instead of the aerodynamic performance. A method to establish a semi-empirical cycle-averaged mathematical model for the flapping wing with high precision based on the wind tunnel experiment is proposed to calculate the flight performance. The established continuous mathematical model can solve the problem of how to obtain the trimmed state by using discrete experimental data. By attaching the airfoil EPPLER 378 with a thickness of 4.07% chord length to the root, the cruise velocity envelope is expanded, especially with a small cruise velocity. Although the attached airfoil to the root can cause a slight decrease in endurance and range of the flapping wing, it will greatly enhance the climbing performance and effectively reduce the demand for the takeoff sites. Besides, the flapping wing with an attached airfoil to the root will result in a significant reduction in the radius of steady turning and will improve the maneuverability. In addition, the airfoil EJ 85, which is similar to the airfoil EPPLER 378 in shape and camber but has a larger thickness of 6.5% chord length, is attached to the root of the original flapping wing. The same experiment and modeling procedure are performed on the airfoil EJ 85 to analyze the difference in performance of the flapping wing with different airfoil thickness.