Nonlinear Aeroelastic Modeling and Experiments of Flexible Wings

High Altitude Long Endurance (HALE) aircraft exhibit aeroelastic behavior that is quite different from conventional flight vehicles. For such aircraft, large static structural deformations that occur during standard flight conditions could severely reduce the flutter speed. Limit cycle oscillations may occur, reducing their operational life. In this paper, a non-linear aeroelastic model is proposed as a design/diagnostic analysis tool. A geometrically exact non-linear structural model for large deformations by Hodges and Dowell, modified according to Da Silva second order geometrical non-linear terms, has been adopted. The structural model has been coupled with an unsteady aerodynamic model for an incompressible flow field, based on the Wagner aerodynamic indicial function, in order to obtain a non-linear aeroelastic model. Within the analysis, linear and non-linear static and dynamic aeroelastic responses have been considered. The approach enables one to expedite the calculation process. In addition to analytical and computational results, a high aspectratio wing model has been selected as a candidate for a feasibility study case and to validate the theoretical model. Preliminary tests have been conducted and more experiments are underway.