Surface Roughness and Wing Drag: An American Opinion upon a Problem Becoming of Ever‐Increasing Importance

DURING the past eight or ten years the speeds of most types of aeroplanes have been practically doubled. Part of this impressive advance has resulted from the use of increased power, but most of it has come from the reduction of aerodynamic drag. The largest and most obvious “built‐in head winds” such as exposed engine cylinders, landing gear struts and wires were first eliminated and attention was then directed to successively smaller factors. The stage has now been reached where it is necessary to consider the effects on drag of such items as rivets, sheet‐metal joints and other irregularities on the surfaces exposed to air flow.