Divergence instability of a simply supported orthotropic composite shell reinforced in both axial and circumferential directions is considered. The shell is subject to an axial static load and to the action of an external supersonic gas flow in the direction parallel to the shell axis. Two variants of the solution considered in the paper include discrete widely spaced stiffeners and closely spaced stiffeners; the latter case can be treated using a smeared stiffeners technique. © 1990.