With the return of British civil aviation to normal operating conditions after the war it was found that several problems which had previously given little cause for concern had become acute. More especially, the increase in the volume of traffic, particularly under instrument flying conditions, together with certain indirect consequences of the greater sizes and weights of aircraft, had brought about greatly increased congestion around major airports, and there was, therefore, an urgent requirement for an effective system of close air traffic control to ensure the safety and rapid movement of the traffic.

The Ministry of Civil Aviation immediately gave much attention to this problem of air traffic control, but at once found itself in serious difficulties on account of lack of sufficiently precise knowledge of the traffic and the traffic pattern. The then Controller of Technical and. Operational Services, Sir Conrad Collier, realised that the obtaining of the necessary data concerning air traffic control and other matters of technical interest was essentially a matter of operational research, and in 1947 a small operational research section was established which began work in the autumn of that year.

As time passes more and more knowledge of the flow of fluids past bodies accumulates and of this increase some becomes applied to the problems of the day. Boundary layer theory is being applied at the present time to the problem of the degree of polish which should be given to a wing in order to reduce its profile drag to a minimum. Tests in the compressed air tunnel at the National Physical Laboratory and in flight at Cambridge and Farnborough have recently been directed to this point and give quantitative assurance of the correctness of theory. In what follows, a survey is made of a group of theorems relating to the resistance of various bodies such as aerofoils and flat plates and more generally to streamline forms. The theorems are partly physical and partly mathematical and approximations are numerous and of very different degrees of validity.

During the last twenty years a revival of interest in the subject of map projections has taken the form of a renewed attack upon certain basic limitations which face the cartographer. A necessary stimulus has been provided by the growth of a technique of air navigation, which in many ways has departed from the traditional practice of the marine navigator. From this and other directions emphasis has been laid on the need for precise cartographic representation of distance, direction and position on the earth. But although certain problems may be treated by devising new projections to meet special needs, it is obvious that there is a limit to any purely cartographic approach.

The requirements of the new navigation are, briefly, that its methods should be rapid, convenient to use, and of an accuracy consistent with the limitations imposed. The traditional solution by means of spherical trigonometry is thus ruled out on at least two of these counts. In its place, there are now available a number of graphical, mechanical and simplified tabular methods, many of which have no cartographic basis. Since a map projection is an obvious medium for the measurement of spherical relations, the needs of long-distance air navigation have encouraged the adaptation of certain projections in the form of special instruments and devices.

Explicitly or implicitly the yield strength of a material is often used as a measure of incipient structural damage. With the yield strength determined by conventional methods, however, it cannot be said in general for two structural elements geometrically alike but of different materials that similar loads, producing maximum stresses equal to the yield strengths in the two cases, are simply related to the yield strengths. A definition of yield strength is proposed in this paper which often has the advantage that, for geometrically similar structures of different materials, loads producing maximum stresses equal to the yield strength are proportional to the yield strength.

In view of recent adverse publicity I must begin this paper by stating that anything I say must not be taken to imply any criticism of the Aircraft Industry. Any conclusions I draw, probably from insufficient evidence, must be regarded as purely intentional!

It has been difficult to decide how to prepare this paper. Should I confine myself to technological matters or should I range wide over the Industry's past, present and future problems, and run the risk of displaying my ignorance? I decided to range wide.

The possibility of sustained flight by heavier-than-air-machiaes was fully recognised during the last century by those who had studied the aerodynamic problems involved and it was realised that its accomplishment awaited only the development of a prime mover of sufficiently light weight.

Of all the known forms of prime mover, the internal combustion engine alone held out any promise of fulfilling the conditions necessary .for sustained flight, namely, light weight not only of the engine itself but also of the fuel it consumes. Early attempts had, however, been made to fly with steam, propulsion and it is of interest to note that the very remarkable and cleverly-designed steam plant employed by Sir Hiram Maxim in 1894 was actually very considerably lighter per h.p., even including the boiler and condenser, than the petrol engine used successfully some nine years later by the Wright Brothers.

Second in importance only to the problem of increasing the safety and reliability of aeroplanes is the question of reducing their head resistance. If aviation was to take its place as an established means of commercial transport the first essential was obviously to make it reasonably safe and certain, and the main energies of investigators and designers immediately after the War were directed to this object. Economy of operation, of which the reduction of head resistance is one of the major factors, was, by comparison, somewhat neglected. But in the last three or four years, with the safety and reliability problems essentially solved, more attention has been devoted to the reduction of drag.

In reviewing the progress that has been made, and the possibilities of further improvement, it is helpful to inquire what is the best we can hope for. We know that the generation of the lift required to carry weight in heavier-than-air aircraft is inseparably associated with a certain drag—the induced drag.