UNSTEADY AERODYNAMICS OF A FLAPPED AIRFOIL IN SUBSONIC FLOW BY INDICIAL CONCEPTS

An approach based on indicial concepts is described to model the unste ady airloads on a thin airfoil in subsonic compressible now caused by the arbitrary motion of a trailing-edge flap, Exact indicial aerodynam ic responses at small values of time as a result of flap deflection an d angular deflection rate about the nap hinge are obtained from linear unsteady subsonic theory in conjunction with the aerodynamic reverse flow theorems, Using the known exact initial (piston theory) and asymp totic values of the airloads, along with an assumed analytic form for the indicial functions, these exact results are used to help obtain co mplete approximations for the respective indicial responses. The airlo ads from arbitrary flap motion in subsonic flow are subsequently obtai ned in state-space form. Validation of the method is conducted with ex perimental data for time-dependent flap motions.