THE increasing speed of modern aircraft has brought to the forefront the necessity for making a careful drag analysis of all aircraft in order to separate out the essential drag, that is to say the drag that is unavoidable, from the non‐essential drag. Most designers, we believe, now do this in order to see what progress is being made in the streamlining of their products. By this means we are enabled to see the relative importance of the drag terms and to arrive at a figure of merit. The ideally‐streamline aeroplane, though not at present a precise proposition, is like other ideals unattainable. It is the standard to which designers may aspire, but which they cannot achieve.