Flutter, a destructive self-excited phenomenon due to mutual interaction of inertial, elastic, and aerodynamic forces is studied by Theodorsen and Garrick using simple typical section model. This model is a practical approximation of high-aspect-ratio wing with two or three degrees of freedom and is considered as benchmark for performing flutter and freeplay analysis. The progress in the development of unmanned aerial vehicles, high altitude long endurance (HALE) vehicles, and wing inground (WIGs) vehicles have introduced new consideration, challenges, and opportunities. Among all, aeroelastic stability is one of the important design challenges. Thus, the present work interest is to investigate the effects of ground proximity on aeroelastic instability of an airfoil with flap. Because, the airfoil near ground experience increase in lift thus, effecting the dynamic stability of airfoil.
The present work is based on the unsteady vortex-lattice method to study the aeroelastic behavior of a two-dimensional airfoil with trailing edge flap near the ground. The airfoil near the ground is modeled by using the mirror-image method. The numerical solution involves an iterative scheme based on Butcher’s fifth-order Runge-Kutta method where the coupled aerodynamic forces and structural forces are integrated simultaneous and interactively in the time domain. The critical speeds for an airfoil at different height above the ground for given model parameters are shown in Fig. 2. The flutter occurs at lower airspeed when the airfoil is closer to ground. As the height increases, the flutter speed approaches that of Theodorsen’s (Uf* = 2.98).