THE design of aerofoils, after years of research, has about reached its maximum development. The comprehensive research of the National Advisory Committee for Aeronautics has resulted in several new highly efficient aerofoils. The systematic nature of this research indicates that the possibility of further marked improvement is remote, and would be of comparatively small value and costly to discover. Various attempts have been made to so design an aerofoil that it would develop an especially high L/D ratio, better minimum drag at cruising speed, etc.