The recently issued Report of the Aeronautical Research Committee draws attention to the fact that much work, apparently of academic interest only, is now of direct practical utility. In particular, the theories of the boundary layer and of turbulence, though admittedly very incomplete and uncertain and lacking a secure scientific foundation, have been developed to the stage in which they can be applied to explain and predict the behaviour of aircraft, and to show how aircraft may be improved. The physical structure of the boundary layer will be described, and the methods by which the problems have been attacked mathematically to get useful results and to check the theories.

In conclusion, the theory of the boundary layer will be applied to the calculation of the drag of an airship or aeroplane fuselage under full-scale conditions, and to an explanation of the behaviour and performance of different types of aerofoils.