Stability of high-aspect-ratio flexible wings loaded by a lateral follower force

Follower force could induce flutter instability of elastic systems. Parametric studies on the aeroelastic stability of high-aspect-ratio flexible wings subject to a lateral follower force are performed, with the lateral follower force and concentrated mass representing the engine thrust and engine mass or external payload, respectively. The effects of variations of several parameters are investigated, including the ratio of flapwise bending stiffness to torsional stiffness, the concentrated mass, a lateral follower force and the location of a concentrated mass, and the wing sweep and dihedral. The geometrically exact, fully intrinsic theory for dynamics of a moving beam is coupled with unsteady ONERA dynamic stall aerodynamic model, which yields the nonlinear aeroelastic model of high-aspect-ratio flexible wings used in the present numerical studies. The nonlinear aero-elastic model considers geometrical nonlinearity, dynamic stall and material anisotropy. Results obtained indicate that the lateral follower force may stabilize the wing, the performance of which depends specifically on several parameters. The aeroelastic stability of high-aspect-ratio flexible wings with the engine nacelle or external payload can be improved by the following designs or configurations: reducing the ratio of flapwise bending stiffness to torsional stiffness, mounting the engine nacelle close to the wing root, keeping the thrust location in the flapwise direction close to the wing's elastic axis, avoiding the existence of a concentrated mass in the middle region of the wing span, and moving the concentrated mass forward before or downward below the wing's elastic axis.