Starting from a finite state model for a two-dimensional aerodynamic n
ow over an airfoil, the eigenmodes of the aerodynamic now are determin
ed. Using a small number of these aerodynamic eigenmodes, i.e., a redu
ced-order model, the aeroelastic model is formed by coupling them to a
typical section structural model with a trailing-edge flap. A free-pl
ay nonlinearity is modeled. Results are shown from the finite state mo
del, the reduced-order model, and previous theoretical and experimenta
l work, All results are in good agreement.