Aerodynamics is naturally associated with the external air flow past aircraft, but with the advent of the gas turbine it has also become of the greatest importance for the internal flow through such engines. The efficiency and bulk of the compressor and turbine components in gas turbines are largely an aerodynamic matter, and their design is determined by a knowledge of the lift coefficients, drag coefficients, Mach numbers, and so on that can be used. The same fundamental laws, if they were fully known, would apply to both internal and external flows, but there are at present considerable differences in practice between the data obtained, and the detail methods used, for the two categories of flow. This lecture attempts to cover in a general way the internal aerodynamic flow through gas turbines.

There are various possible interpretations of the title of this lecture and because of this and the fact that I have not had complete responsibility for the design of any one aeroplane, I regarded this lecture and title with some diffidence at first. Nevertheless in recent years no lecture has dealt with the general problem of how an aeroplane design progresses stage by stage, from the first ideas to the prototype flight trials and I have tried to make that the basis of my lecture.