1. A computer-aided method suitable for assisting in the design of an aircraft by providing the dimensioning aerodynamic forces, skin values or values distribution around the complete aircraft or an aircraft component, characterized by comprising the following steps: a) Selecting a set of parameters of said complete aircraft or said aircraft component, being said aerodynamic forces, skin values or values distribution dependant of said parameters; b) Performing flow field CFD RANS computations for a number N1 of different combination of values of said parameters; c) Obtaining said aerodynamic forces, skin values or values distribution for whatever combination of values of said parameters through a reduced-order model, generated by computing the POD modes of the flow variables, expanding the flow variables using said POD modes and obtaining the POD coefficients of said expanded flow variables using a genetic algorithm that minimizes the error associated to the expansion of the Navier-Stokes equations.