Dynamic Modeling of a Thin Airfoil Pitching in Ground Effect

This paper considers how the presence of a ground plane alters the aerodynamic force on a thin airfoil pitching about its leading edge. A discrete-vortex model of the pitching thin airfoil generates time-series data of the pitch acceleration and the resulting lift for various altitudes from the ground plane. The structure of Theodorsen’s aerodynamic model provides a starting point for system identification of the lift response in ground effect. The lift response varies nonlinearly with changes in the airfoil’s altitude, and the identified dynamics can be represented by a linear transfer function from pitch acceleration to lift coefficient with zeros, poles, and gain that vary nonlinearly with altitude (i.e., the height of the pitch axis location). The dynamic response of the lift coefficient is well-approximated by a 5th-order, triple-zero, triple-pole transfer function.