Performance and stability of a winged vehicle in ground effect

The present work deals wit h the dynamics of vehicles that intentionally operate in the ground proximity. The dynamics in ground effect is influenced by the vehicle orientation with respect to the ground because the aerodynamic force and moment coefficients, which in turn depend on height and angle of attack, also vary with the Euler angles. This feature, usually neglected in the applications, can be responsible for sizable variations of the aircraft performance and stability. A further effect, caused by the sink rate, determines the unsteadiness that modifies the aerodynamic coefficients. In this work, an analytical formulation is proposed for the force and moment calculation in the presence of the ground and taking the aircraft attitude and sink rate into account. The aerodynamic coefficients are first calculated for a representative vehicle, and its characteristics in ground effect are investigated. Performance and stability characteristics are then discussed with reference to significant equilibrium conditions, while the nonlinear dynamics is studied through the numerical integration of the equations of motion.