Even before 1939 the problems of high-speed flow were receiving a great deal of attention in the German aeronautical world. Their leading aerodynamicists, Prandtl, Busemann and Schlichting among others, had contributed largely to the theory of compressible fluid flow, and basic experimental research in the high-speed field had begun both at Aachen and at Göttingen. The activity in Germany in this particular field before the war was, in fact, much greater than in Britain, where Mr. Lock and his co-workers at the National Physical Laboratory carried practically the entire responsibility for such work.

The great increase in aircraft speeds during the war, and in particular the arrival of jet propulsion, completely changed our attitude to the subject in Britain. What had been an absorbing fundamental study became, quite suddenly, an important operational problem, looming large in every new fighter design.

In being honoured by the request to deliver a lecture on “ The Problems of Blind Landing,” I am set to some extent a task different from that normally presented to the Society's lecturers. In general the results of successful research are presented to you, whereas I am merely asked to outline the problems — with the implication that constructive suggestions for their solution may result. Personally, I feel that this is a most appropriate type of lecture, particularly in regard to a problem which embraces specialist fields in radio and radar, in aerodynamics and aircraft instruments, to an extent that few can claim to be expert in all.

The problem of blind landing can best be discussed after reviewing existing methods of blind approach and proposals now current for solving the landing problem.

The photo-elastic method can be used for either of two main purposes:

1. a) As a qualitative design tool to obtain indications of possibly unsuspected sources of stress concentration.

2. (b) As a means of obtaining a complete analysis of a two-dimensional stress problem, i.e., the determination of the separate magnitudes of the principal stresses at any point, as well as the direction of the principal planes relative to some axis of reference.

All that is required for (a) is the stress pattern which becomes visible and can be photographed when a loaded model cut from a sheet of suitable material is placed in a field of circularly polarised light.

Experience with the installation of guns in aircraft in recent years suggests that there has been little co-operation between gun designers and aircraft designers. This becomes more apparent as gun calibres increase and if satisfactory fighting aircraft are to be produced in the future, closer co-operation between gun designers and aircraft designers will be necessary. In consequence, a brief review of the progress of gun design in recent years, with special reference to its effect on installation, may be of interest.

From 1918 to 1938 the standard guns used in the Royal Air Force were the Lewis gun and Vickers Maxim gun, both Army guns modified for air cooling. The installation of these guns had reached a standard form by 1918 which was adhered to for the best part of 20 years.