The design of structures to resist jet noise fatigue demands a knowledge of a wide range of subjects from pure acoustics at one end to metal physics at the other. At the present time the various aspects of the problem are not sufficiently well known quantitatively for a purely theoretical design study to be made. Nevertheless a knowledge of the behaviour of typical forms of construction in noise environments can be used with a limited amount of theoretical work to indicate the most efficient types of structure. This approach to the problem is adopted in this lecture as it seems to be the most promising one available at the moment. It must be emphasised, however, that although some progress has been made in discovering the behaviour of a structure subjected to noise it is not possible to estimate the life of any component at the drawing board stage. Some prototype strain measurements and proof testing are therefore essential if one is to prove the integrity of the design.

Last year the Royal Aeronautical Society and the Wissenschaftliche Gesellschaft für Luftfahrt agreed to organise lectures in honour of Osborne Reynolds and Ludwig PrandtI, to be given every two years, and alternating between Great Britain and Germany. The purpose of these lectures will be to show how closely English and German aeronautical research is related, and to recall the great scientific work of Osborne Reynolds and Ludwig Prandtl for the benefit of the younger generation. Without their contributions our scientific and technical achievements in aeronautics today would hardly have been possible.

Today I have the great honour to present the first Reynolds-Prandtl Lecture, and I wish to thank the Royal Aeronautical Society and the Wissenschaftliche Gesellschaft für Luftfahrt for this high distinction.

Aerial top-dressing, or the spreading of inorganic fertilisers from aircraft, introduces stringent flying conditions at extremely low altitudes. During release of the fertiliser there are large load and centre-of-gravity changes, and aerodynamic effects the cause of which has hitherto been conjectural. The experiments described in this paper were aimed at obtaining a knowledge of the aerodynamic effects of the cloud of falling material beneath the plane, and the effects of air flow through the empty hopper. The implications upon aircraft design are discussed. The high accident rate experienced in this industry emphasises the necessity for the production of a suitable aircraft designed solely for top-dressing.

This paper describes the plasma jet which has recently been put into operation in tha Department of Aeronautics. A brief outline of the apparatus and its equipment is given, and methods are described for obtaining data from the high temperature gas stream. Finally some results of a recent test programme are outlined.

For many years certain similarities between the mechanics of the sailing yacht and of the slow speed aeroplane have been recognised and the wealth of knowledge in the science of “Aerodynamics” has undoubtedly led, by the slow process of evolution, to increased ability of the yacht in skilful hands to beat to windward. Interesting comparisons in this respect have been made by Davidson. But there are essential differences between the yacht and the fixed-wing aircraft, apart from the more obvious ones, which are so profound that a study of yacht dynamics would appear to be worthy of more attention than it has yet been given.

In this note a brief description is given of some interesting results obtained in smooth pipes of circular cross section during an investigation of the steady flow losses in a 90° mitre bend at the Endicott Product Development Laboratory of I.B.M. The tests indicated that in a certain Reynolds number range the presence of a mitre bend was sufficient to cause flows of different types to exist in the upstream and downstream tangents of the bend. The definition of the bend loss in the light of this phenomenon is considered.

It is hoped that this paper will stimulate comment on similar occurrences, which would lead to a better understanding of flow behaviour in this rather neglected area of fluid mechanics.

In many internal flow problems, the velocity profile of the flow in a duct is of major importance. A recent survey has shown that the study of the effect of different velocity profiles on the performance of various components has been hampered because no general means of generating profiles was available.

Livesey, Parker and Jones have described a baffle specially developed in connection with gas turbine combustion chamber work, with which velocity profiles can be generated, having Vmax/Vmean ratios of up to 1·42, for an inlet profile of Vmax/Vmean = 1.15.

The determination of the critical axial load of a strut having one or more intermediate supports and varying stiffness is made difficult by the highly transcendental nature of the simultaneous equations involved. It is therefore usual to make a test of the stability of the strut at some arbitrarily chosen load, as for example when applying the convergence technique. The behaviour of the strut then indicates whether the chosen load is too high or too low, and another load is selected and another test made. Although the true critical load is eventually reached, it is clear that if its value can be fairly closely approximated at the outset, then the labour of calculation will be greatly reduced.