According to the invention, a shell handling carriage (19) is provided with grippers (194) which grip the end edges of a shell (2) made of composite material still fixed to a molding drum (11). An expeller strut (13) prevents the drum (11) from moving while the carriage (19) translating 5 removes the shell (2) from the drum (11). The shell (2) is then transported by the carriage (19) to a working station in which robots rivet the transversal ribs on it. The transversal ribs reach the robot working position orderly arranged on a self-moving rib store, which is inserted in the shell (2) itself.