Longitudinal Model Parameter Estimation of a Small Aircraft

An aircraft aerodynamic forces and moments depend on the pressure distribution on the airframe, its exact description defies the available computational and experimental means. However, for many purposes a more simple description can be used. Dimensional analysis allows to express the aerodynamic forces and moments as functions of the dynamic pressure, the aircraft dimensions and dimensionless, attitude dependent, aerodynamic coefficients, referred to the wing dimensions. Therefore, the aerodynamic coefficients are a very important part of an aircraft model. They can be estimated from the aircraft dimensions and geometry. But these estimations must be experimentally verified. This paper deals with the estimation of the aerodynamic coefficients related to the longitudinal behaviour of the aircraft. To estimate these, a linear model of the aircraft is used, and from it, the aircraft modes characteristics identified. The linear model can be split in two, almost independent models, the longitudinal and the lateral-directional model. The coupling due to the propeller. This gives linear model gives us a description at equilibrium points of flight. Yet the model used in the experiments is nonlinear. The paper presents the analysis and results of implementing basic manoeuvers with the aircraft's elevator to excite the longitudinal modes and allow the estimation of the aircraft modes and the stability and control derivatives.