1. A computer-aided method for assisting in a design of an aircraft by providing aerodynamic forces, skin values or values distribution around a complete aircraft or an aircraft component, comprising: a) selecting a set of parameters of said complete aircraft or said aircraft component, for computing said aerodynamic forces, skin values or values distribution dependant of said parameters; b) performing flow field Computational Fluid Dynamic Reynolds Averaged Navier-Stokes (CFD RANS) computations and calculating and storing said aerodynamic forces, skin values or values distribution for different combinations of values of a limited set of parameters; c) computing Proper Orthogonal Decomposition (POD) modes of flow variables; d) expanding the flow variables using said POD modes; e) obtaining POD coefficients of said expanded flow variables using a genetic algorithm that minimizes an error associated with expansion of Navier-Stokes equations; f) generating a reduced-order model using the POD modes and the POD coefficients; and g) obtaining said aerodynamic forces, skin values or values distribution for different combinations of values of the selected set of parameters through reduced-order model.