Process and device for optimising the performance of an aircraft in the presence of a lateral dissymmetry

A process for optimising the performances of an aircraft (A) in the presence of a lateral dissymmetry, during a flight of the aircraft (A), comprising automatically, via a device on-board the aircraft:

• a) monitoring said aircraft (A) such that the lateral dissymmetry can be detected;
• b) when a lateral dissymmetry is detected, measuring flight parameters of the aircraft (A), on the one hand, for calculating aerodynamic coefficients relating to control surfaces (18) of the aircraft (A), and on the other hand, measuring an equilibrium position of said control surfaces (18), said control surfaces (18) being preliminary brought to these positions for minimising effects of the lateral dissymmetry by generating a null sideslip of the aircraft (A);
• c) using said measured flight parameters, aerodynamic coefficients relating to said control surfaces (18) are calculated;
• d) using said thus calculated aerodynamic coefficients and said measured positions of the control surfaces (18), an optimum sideslip βop likely to generate a sideslipping for minimising an overall drag coefficient of the aircraft (A) is calculated using the following expression:
• βop=−(Cλδp1·δp1+Cλδr+Cλδp2·δp2)/Cλβ
• wherein:
• δp1 and δp2 are the equilibrium positions of roll control surfaces (18A, 18B) of the aircraft (A) ;
• δr is the equilibrium position of a rudder (18C) of the aircraft (A);
• Cλδp1, Cλδp2 and Cλδr are the aerodynamic coefficients relating respectively to the roll control surfaces (18A, 18B) and the rudder (18C);
• and
• Cλβis the derivative of the roll moment coefficient with respect to the sideslip;
• e) determining commands for controlling at least one rudder (18C) for generating said optimum sideslip βop, when they are applied to said rudder (18C);
• and
• f) applying said commands to said rudder (18C).