Abstract: An air cushion vehicle is provided with a lift system including a flexible keel. The vehicle has a rigid body which is supported on an air cushion. The air cushion is divided into two longitudinal semichambers by a flexible keel and is further defined by flexible skirts provided at the periphery of the rigid body. The flexible keel directs lift air to the semichambers and controls the attitude of the vehicle by automatically distributing lift air to one of the two longitudinal semichambers to provide a stabilizing force. The flexible keel is constructed of a plurality of flexible segments, each of which has two triangular portions which are joined by a trapezoidal portion having a curved bottom. When the flexible sheets are formed into a working configuration the two triangular portions are joined at a fastening point so that the top edge each of the flexible segment form a triangle.