Aircraft engines are classed as air-cooled or water-cooled, accordingly as they are cooled directly by contact with air or indirectly by air through the intermediary of the water which surrounds the cylinders. The method of cooling used has been a cause of wide divergence in design and arrangement between the two types. The air-cooled engine, except for the smaller powers, appears in the radial form in which exposure of each cylinder to the air stream is simplified at the expense, however, of a large frontal area while, with obviously greater latitude, the water-cooled engine can take a form having a smaller frontal surface.

The following Paper comprises some of the results of an investigation originally undertaken by the writer to determine the effects of the humidity of the atmosphere and other secondary factors upon the static lift of airships. It is almost invariably found on completion of such a craft that a considerable deficiency is revealed between the designed lift and the apparent value deduced, for example, from a “ lift and trim ” trial. Clearly, it is of considerable importance that the reason for this discrepancy should, if possible, be determined; for whilst the loss may be only a small percentage of the total displacement of the ship, and hence difficult to trace, yet considered in terms of disposable lift, it frequently is very serious.

In the later part of autumn last year, I was invited by your President, Colonel the Master of Sempill, to read a paper about the work of the “ Deutsche Versuchsanstalt fur Luftfahrt ”( i.e. “ German Aeronautical Research Institute ” ) . The Royal Aeronautical Society can look back to a long and successful development. Your Society has always aimed at the promoting of the technical work of your country and at the fostering of close scientific relations between air–minded countries. It is therefore a great honour for me to lecture before your Society.

I regard co–operation in discussing areonautical matters between the various countries as very necessary. Representatives of aeronautical science have, during the past year, held international congresses at Stockholm, in the Hague and finally in Paris. Common problems were treated at these congresses by the representatives. New personal relations were formed during the meetings held there.

In this first lecture upon the origin and development of the heavy oil aero engine to be delivered under the Akroyd—Stuart foundation, it is appropriate to devote some space to the early history of oil engines generally, for it is certain that the aero engine of the future will claim a direct descent from some terrestrial parent. The early history moreover, of the heavy oil engine is of quite exceolional interest, both technical and personal.

Herbert Akroyd—Stuart was born in 1864.His father, Charles Stuart, owned a small engineering works at Fenny Stratford, and it was here that the son gained his training as an engineer. Between 1885 and 1890 he took out several patents for the improvement of oil engines, which appear to have been the outcome of his experience with a “ Spiel ” petroleum engine used for power generation at his father's works.

It is not possible to go fully into all the aspects of this problem in the time at my disposal. I am accordingly confining myself to a discussion of the feasibility of operating heavier-than-air craft in fog with reference to the instrumental equipment required. The meteorological aspects were dealt with in a paper by Captain Entwistle two years ago.

In order to obtain a correct perspective on the problems of flying in fog it is necessary to realise that many cases of impaired visibility, which would not normally be regarded as fogs, may seriously increase the risks of flying. This reduction of visibility may be caused by fog proper or by haze, drizzle, rain, snow or dust. The problem I wish to consider then is that of flying, navigating and landing when the visibility is such, that flight would be impossible or unduly dangerous without special equipment.

The subject I have to talk about this evening is one on which many previous papers have been read before this Society, so I am afraid I must ask you not to expect much original material from me. Practically the whole of the material I have gathered together is the result of practical experience, and from this point of view I hope it will prove interesting.

During recent years considerable development has been done and good progress made with both the design and operation of big flying boats.Also, the Schneider Cup races have caused a considerable amount of research work to be done on the development of twin float seaplanes, particularly with regard to taking off the water at very high speeds and also to the air resistance of the floats.

In the last year we have seen the advent of the Dornier Do.X the largest flying boat yet constructed, whose total flying weight approximates to 50 tons.

The Gliding and Soaring Flight movement is as old as History. The observation of bird flight must have shown the men of former centuries in the same way as our own generation, that apart from power flight with wing beats there must be another flight possibility, enabling the use of the energy in the movement of air masses for flight without the expenditure of other power. The experiments undertaken in these times on the solution of the flight problem have come down to us only through myths and sagas, and we cannot differentiate between truth and imagination in these stories.

Experimental research, which can certainly be considered as the foundation of modern physics, has also in the realm of aerodynamics laid the basis for modernaeronautics. In this gliding and soaring flight plays the rôle of full–scale experiments, not as an end in itself, but as a proving-ground and last station before the invention of power flight.

Noise is becoming of increasing importance and interest in modern life, and we appear to be approaching the time when much that we endure now will be regarded as intolerable. Public protests arise spasmodically on every hand and noise has been the subject of a certain amount of attention in the medical and popular press. With many persons the chief deterrent to air travel is understood to be the discomfort caused by the noise experienced. Whilst we may not wish to investigate the physiological reason for such discomfort, it is of interest to notice that in a recent paper, Laird (Acous. Soc. Am. J., I, p. 256, 1930), has summarised experimental data on the effect of sound on living beings.

No fully representative commission of medical, legal, acoustical and engineering interests has yet been set up in England, but in 1929 the Aeronautical Research Committee appointed a Sub–Committee in connection with the reduction of aircraft noise, and traffic noises have been considered in conferences by the Ministry of Transport.

This paper describes an investigation conducted at the request of the Aeronautical Research Committee, who made a grant to one of us for the purpose. It is submitted by permission as an essay to compete for the R.38 Memorial Prize.

No essential alteration has been made in the form of presentation adopted in our preliminary reports, but to meet the needs of the general reader we have added the introductory paragraphs which follow. These explain briefly the nature of the problem which we have set ourselves, the range of our solution, and the bearing of our results on practical questions which confront the designer of a rigid airship hull.

The development of aviation, particularly since the War, has led to a growing demand for information on various aspects of meteorological science as applied to flying, and the investigation of the problems thus raised has helped considerably towards increasing our knowledge of the atmosphere and its mechanism.In so far as the subject of wind structure is concerned, attention has been concentrated mainly on the accumulation and interpretation of data regarding the average direction and speed of the wind currents at different levels in various parts of the world.The horizontal variations of wind and the vertical currents which disturb the regular flow of air have received, in comparison, little consideration. The latter aspect of the subject is of paramount importance in connection with the problem of soaring flight; it is also related to the more general question of the stability of aircraft.

The work for the development of air traffic in Europe into a generally recognised means of communication in conjunction with railways and steamships,has hitherto mainly been done through the conveyance of passengers and goods. Mail has certainly been carried by the aeroplanes, but as a rule only in small quantities. As managing director of the Aerotransport Company, the Swedish Air Line, I have seen this development with a certain amount of worry and distrust, and submitted therefore to the International Air Traffic Association a suggestion lor organising, at the earliest possible moment, a general European air mail net, mainly for night traffic. My suggestion was dealt with by a Committee appointed at the Iata's last session in Antwerp, and the suggestion was discussed also at the Postal Congress which was held at Brussels in October,1930.

I realise that the question of establishing air mail conveyance between London and the various parts of the Empire is of great importance from a British point of view, but as this object has nothing to do with the aims for which I am working, I shall not touch upon it to—day.

In January of this year Mr. R. McKinnon Wood read a paper before the Society on the new American. wind tunnels, and in his paper he emphasised the importance of making tests at values of the Reynolds number which are actually obtained in flight. These modern developments of wind tunnel design comprise firstly the compressed air tunnel in which high values of the Reynolds number are obtained by testing models of the usual dimensions in a stream of air compressed to 20 atmospheres, and secondly the large wind tunnel with a free jet of 20 to 25 ft. diameter in which it is possible to test the airscrew and fuselage of an aeroplane of moderate size. Mr. Wood also emphasised the importance of a high speed wind tunnel for certain special classes of experiment.

In this paper a study has been made of certain cases of airflow in which various means are employed to control the behaviour of the air so as to prevent breakdown in the flow and the resulting turbulence. It is mainly an attempt to analyse the evidence which exists on such phenomena as slots, rings and boundary layer control by means of blowing through backwardly–directed slots in the surface, and to determine, if possible, the extent to which their apparent similarity corresponds, if at all, to an identity of physical principle.

A great deal of experimental work has been done at various times on such devices, and in this paper some of the published results are discussed and an attempt made to correlate them. In addition, some further experiments have been made to fill up gaps in the data available, or to extend their scope. They include other examples of control of airflow at sharp corners (Part I.); some of the cases considered differ widely from others, but all exhibit the reduction in eddying which results from assisting air to negotiate sharp corners or bluff obstacles with the least disturbance possible.

Before beginning this lecture I have first of all to thank the Air Ministry for permission to give it and to explain that any opinions expressed are my own and do not necessarily reflect the opinion of the Air Ministry.

Secondly I must express my appreciation of the honour conferred on me by the Society in asking me to deliver a lecture before them; though I wish they had chosen a less difficult subject.

As regards the title of this lecture it sounds very circumscribed, but you can't test anything without having a fair idea of what its complete function is or without some standard of reference; and in trying to discuss these parts of the problem I am afraid you will find that I have been, if anything, too. general.

An accurate knowledge of the strength of materials is more essential in aircraft construction than in any other branch of engineering, as every aircraft component has to be reduced in weight to a minimum compatible with safety. Equally essential in aircraft construction is the use of every available refinement in calculation, although it is not possible as yet to estimate with sufficient accuracy from calculations alone the strength of many of the components. At every stage hv aircraft construction, mechanical tests are therefore made, first to determine the qualities of the materials, then to verify the strength of each part and finally to. check the strength of the complete machine.

Owing to the wide range of my subject and to the limited time available, I propose to deal briefly with some of the aspects of mechanical testing of special importance in aircraft research and development, describing more particularly some of the test apparatus and methods of testing I have had opportunities of developing.

The statement that aviation is in its infancy is now the commonest of platitudes and it is possibly not unbecoming in conscientious parents or guardians to take stock of the growth from time to time of the infant they are interested in—to weigh and measure it with a view to ascertaining whether such growth is normal and uniform, and more important still, whether the rate of growth is being maintained, is increasing or diminishing and to try to ascertain what external influences have the most beneficial effect.

A lecture on Deck Flying must include a good deal about carriers and the development of the seaplane carrier into the modern flush decked ship from which high performance aeroplanes can operate in almost any kind of weather, and as I believe this is the first occasion upon which a paper has been read to the Society on deck flying I propose to trace briefly the development of the modern aircraft carrier from the improvised auxiliaries commissioned to meet war exigencies.

The design of the ship has throughout directly influenced the design of the aircraft until to—day a stage has been reached which within certain limits enables the fleets to use aeroplanes which are no longer hampered by extra strong undercarriages and appliance for picking up wires used with the original arresting gear, details of which I will describe later.