Several Attempts have been made lately to reduce the drag due to lift of wings by means of camber and twist. Slender wings in particular have been considered and a typical theory is that by Tsien on the supersonic conical wing of minimum drag, where the lift forces on the wing are calculated from conventional aerofoil theory so that the overall lift of a flat wing turns out to be proportional to the angle of incidence. For convenience, this is called a “ linear theory.” It is usual to consider two cases: (1) Wings where the drag is calculated by the same theory so that the full thrust component and the suction at the leading edge are included. (2) Wings where the drag is not calculated by the same theory as the lift but where the thrust at the leading edge is omitted.