skin may be formed by one or more fiber fabrics this skin surrounds a core material 23 such that said skin defines a cavity with a closed section filled with said core material said core material is chosen to be rigid enough to be able to form a molding core and light enough not to cause weight gains inherent to the choice of a composite material to form the skin of the 12 o 39 clock beam as previously indicated hard synthetic foams such as rohacell u00ae wf 100 or honeycomb structures may for example be appropriate the rails 13 15 allowing sliding of the corresponding thrust reverser half cowl may be made from the same composite material as the skin 21 either at the same time as that skin or by later fastening or gluing alternatively these rails may be made from a material other than that of the skin 21 such as a metal alloy and may in that case be attached on said skin although it is not shown in fig6 the beam 1 b may also comprise hinge yokes similar to those of the beam of the prior art in particular shown in fig3 and 4 said yokes being able to be made in a single piece with or attached on the skin 21 like the rails 13 and 15 the beam 1 b according to the present disclosure may also.