Flexible duct assemblies

In a rocket motor a flexible duct assembly for high temperature gases comprising axially first and second duct parts, a mounting system adjustably supporting the second duct part with respect to the first about a center located on the longitudinal axis of the duct assembly, generally axially extending portions on said duct parts, which protions interfit to provide a first pair of radially facing surfaces and a second pair of such surfaces located radially outwardly from the first said axially extending portions including an annular axial extension on the first duct part extending into an annular channel on the second duct part, a radially inwardly facing surface of the extension providing a surface of said first pair and a radially outwardly facing surface of the extension providing a surface of the second pair, the surfaces of the first pair being complementary and relatively movable, there being a primary seal between the surfaces of the first pair and an annular block of elastomeric material bonded between the surfaces of the second pair so as to present a major thickness against passage of gases between the surfaces of the second pair and so as to be deformable in shear upon adjustment of the second duct part relative to the first, the block being afforded protection from the interior of the duct assembly by the primary seal.