Method of estimating an angle of attack and an angle of sideslip of an aircraft

Abstract

A method for estimating an angle of attack and an angle of sideslip of an aircraft having a plurality of control surfaces each adjustable with respect to an associated reference surface. The method includes measuring quantities representative of the angle formed by each control surface with respect to the associated reference surface, and measuring an effective rolling speed, an effective pitching speed, and an effective yawing speed of the aircraft. A linearized model of a state observer is defined according to the following equations: wherein u is a vector containing the values of the quantities of each control surface, x is a vector including an estimated angle of attack, an estimated angle of sideslip, an estimated rolling speed, an estimated pitching speed and an estimated yawing speed, δy is an error vector including the errors between the measured speeds and the respective estimated speeds, y is a measure vector including the values of the measured speeds, A,B,C,D are matrices representative of the behavior of the aircraft in unperturbed motion and L is a feedback matrix including the gains of a predetermined numeric control filter. The estimated angle of attack and the estimated angle of sideslip are obtained from the model to use as an actual angle of attack and an actual angle of sideslip of the aircraft.