UNSTEADY LIFT OF A FLAPPED AIRFOIL BY INDICIAL CONCEPTS

A practical method is described for computing the unsteady lift on an airfoil due to arbitrary motion of a trailing-edge flap. The result fo r the incompressible case is obtained in state-space form by means of Duhamel superposition and employing an improved exponential approximat ion to Wagner's indicial lift function. For subsonic compressible flow , the indicial lift at small values of time due to impulsive trailing- edge flap deflection is obtained from linear theory in conjunction wit h the aerodynamic reciprocal theorems. These results are used with exp erimental results for the oscillating case to obtain complete exponent ial approximations for the indicial response due to impulsive flap def lection. The final result for the unsteady lift due to an arbitrary fl ap motion in subsonic flow is obtained in state-space form. Numerical results and comparisons with experimental data are shown.