The title of this paper clearly has a wide scope. None will dispute the presence of many problems in aircraft development. It was suggested in the first place that this paper might take the form of a description of the workings of a chief designer's mind when a new aeroplane is conceived. Such a paper would deal largely with technical considerations, such as choice of engines, wing loading, plan form and so on.

The diversity of uses to which the modern aeroplane is put gives rise to great differences between types. A jet fighter, for example, will be influenced by considerations far removed from those controlling the design of a long—range civil transport. To attempt to cover in detail such a wide field would result in an encyclopaedia rather than a paper; to tackle it in general terms would beget a vagueness lamentably devoid of interest.

Therefore, it has been thought wiser to attempt an assessment of some of the more fundamental problems confronting aviation.

It has long been the practice in engineering to use direct manual operation of the controlling parts of a machine, so long as it was within the strength of the operator, and so long as design of the operating gear was relatively simple. In innumerable applications, however, the increased demands for power by the controls, and the need for greater accuracy, have necessitated the development of servo mechanisms to drive them; that is, we have to sever, partially or completely, the direct mechanical link from operator to control, and use the inserted backlash, elasticity, and so forth, to meter power from an external power source.

In the flying control field we have come at this time to the transition stage, in that we have realised that, for a large number of applications, direct manual operation is impractical, and we are feeling our way towards suitable forms of servo controls for our various needs.