Nonlinear Models for Representing Aerodynamic Coefficients of a Wing in Ground Effect

摘要

The aim of the present work is to develop a model for representing lift, drag, and pitching moment coefficients of a wing and/or flight vehicle in ground effect when the height is a function of time. By assuming that the airplane is a rigid-body, the altitude variations are sufficiently small that the flow density, the kinematic viscosity, and the dynamic pressure remain constant, and by including the non-dimensional height into the aircraft states, it was possible to obtain a general longitudinal aerodynamic model of an airplane in ground effect. In this model, the non-dimensional stability derivatives are functions of the non-dimensional height, and the nonlinear effects in ground effect are represented by a group of terms, which are equal to zero in steady flight close to ground. Three cases are considered to represent the nonlinear effects that occur in a dynamic ground effect phenomenon: 1) They can be represented by the h derivative, 2) the It derivatives are also functions of the angle of attack, and 3) there is an additional term to represent the unsteady flow effects. It is concluded that the non-dimensional h derivatives are linked to a specific history of the flight path or trajectory due to the flow downstream.