Abstract: An aircraft comprising an envelope (6) that is inflatable with a lifting gas that is lighter than air that, at least when inflated has curved upper and lower surfaces. The aircraft has a payload carrying means (5), and an aerodynamic lifting means (8) for creating a vertical annular flow of air that induces a flow of air over the respective upper or lower surface (12, 14) of the envelope (6.). One form of aerodynamic generator (8) comprises a plurality of aerofoil blades (20) mounted for rotation around a periphery of the envelope (6).