A duct assembly comprising: a first duct ; a second duct ; and a flexible joint assembly coupling the first duct to the second duct and comprising: a bellows having a first end and a second end ; a mounting assembly having a first support and a second support and wherein one of the first support and the second support surrounds at least a portion of the bellows ; a set of rod assemblies , with each rod assembly of the set of the rod assemblies including a rod bundle and two bushings that are attached to each end of the rod bundle , with the set of rod assemblies operably coupled to the first support and the second support and spanning a length (L) there between and where the set of rod assemblies are configured to act as rotational flexures to allow three rotational degrees of freedom at the flexible joint assembly ; and a protective sheath that wraps at least a portion of an exterior of the rod bundle for each rod assembly of the set of rod assemblies , characterised in that the protective sheath includes one of a helical coil or a set of apertures to tailor a bending moment loading for the set of rod assemblies . a first duct ; a second duct ; and a flexible joint assembly coupling the first duct to the second duct and comprising: a bellows having a first end and a second end ; a mounting assembly having a first support and a second support and wherein one of the first support and the second support surrounds at least a portion of the bellows ; a set of rod assemblies , with each rod assembly of the set of the rod assemblies including a rod bundle and two bushings that are attached to each end of the rod bundle , with the set of rod assemblies operably coupled to the first support and the second support and spanning a length (L) there between and where the set of rod assemblies are configured to act as rotational flexures to allow three rotational degrees of freedom at the flexible joint assembly ; and a protective sheath that wraps at least a portion of an exterior of the rod bundle for each rod assembly of the set of rod assemblies , characterised in that the protective sheath includes one of a helical coil or a set of apertures to tailor a bending moment loading for the set of rod assemblies . a bellows having a first end and a second end ; a mounting assembly having a first support and a second support and wherein one of the first support and the second support surrounds at least a portion of the bellows ; a set of rod assemblies , with each rod assembly of the set of the rod assemblies including a rod bundle and two bushings that are attached to each end of the rod bundle , with the set of rod assemblies operably coupled to the first support and the second support and spanning a length (L) there between and where the set of rod assemblies are configured to act as rotational flexures to allow three rotational degrees of freedom at the flexible joint assembly ; and a protective sheath that wraps at least a portion of an exterior of the rod bundle for each rod assembly of the set of rod assemblies , characterised in that the protective sheath includes one of a helical coil or a set of apertures to tailor a bending moment loading for the set of rod assemblies . <EOS>