A model of a machine, ship, aircraft, etc., so constructed as to imitate the movements or mechanisms of the thing that it represents.
Mid 18th century; earliest use found in Charles Labelye (d. ?1781). From working + model.
working model/ˌwəːkɪŋ ˈmɒdl/
A model used or intended as an aid to the execution of the final form of a sculpture or similar artefact; a maquette.
Mid 19th century; earliest use found in The Athenaeum. From working + model.