type can fill in the space between the longeron 38 and the front part of the aerodynamic shell 24 just as filler material 56 can fill in the space between the longeron 40 of the core 34 forming the caisson and the rear part of the aerodynamic shell 24 the hollow secondary core 34 u2032 in the form of a caisson can optionally also be filled with any filler material in the second preferred embodiment of the invention shown in fig5 the secondary structural assembly 34 u2032 fully forms the secondary core for this to happen the assembly 34 u2032 comprises not only the longerons 38 u2032 44 u2032 of the first preferred embodiment but also a longeron 40 u2032 flat against the second longeron 40 of the principal core as well as a longeron 42 u2032 flat against the third longeron 42 of the principal core these longerons preferably being attached in pairs this concerns veritable duplication of the principal core 34 made inside the latter in the third embodiment shown in fig6 coatings made of shock absorbing material have been added to reinforce resistance of the vane to projectile impacts if this third mode is described with a configuration in which the assembly 34 u2032 fully forms the secondary core it is also applicable to any other configuration in particular that of the first mode wherein the two cores 34 34 u2032 comprise common elements in this third preferred embodiment.