Estimation on location of subsonic aerodynamic center for tandem airfoil configuration or multiple-lifting-surface system

With the effect of the aerodynamic interaction between lifting surfaces, the position of the airfoils' subsonic aerodynamic center will deviate from the quarter chord, so as to that of the whole aircraft. A method to estimate the location of subsonic aerodynamic center for tandem airfoil configuration or multiple-lifting-surface system is presented, which applies the increments of the aerodynamic force caused by the small change in angle of attack combined with the aerodynamic interaction between lifting surfaces. To simplify the calculation, the traditional approximation and the Taylors expansion are used. A series of tandem airfoil configurations with different parameters, such as the horizontal distance, the vertical distance, the incidence angle and the wingspan, are calculated by computational fluid dynamics and Prandtls lifting-line theory. The results indicate that the aerodynamic center are significantly influenced by the aerodynamic interaction between the two lifting surfaces. In the tandem airfoil configuration with the bigger horizontal distance, the negative vertical distance, the negative incidence angle and the smaller wingspan of the canard, the position of aerodynamic center is closer to the point without aerodynamic interaction.