1. Method for determination of a rigid value of an aerodynamic coefficient of an aircraft for a given set of conditions, in which measurements made in a wind tunnel on a model representative of the said aircraft for the set of conditions involved and, on the basis of these measurements at least one experimental value (C Z-flexible-model ), known as flexible model value, of the said aerodynamic coefficient is determined, characterized in that a rigid value of the aerodynamic coefficient is calculated on the basis of the said flexible model value or values and a correction taking into account the flexibility of the model.