In the design of a fan drive regard should be had to possible critical or resonant speeds which may result in failure of the system. It is not sufficient to arrange for the ordinary whirling speed to be well above the maximum running speed. In whirling the forced vibration arises from static or dynamic unbalance of fan and/or its shaft and the frequency of the forced vibration is the frequency of revolution of the fan shaft. Other important forced vibrations may however be set up.

When men of the first Elizabethan era looked to the Arctic, they dreamed of a North–West Passage over the sea to enable them to reach by a short cut the fabulous riches of the Far East. Between 1576 and 1578, Martin Frobisher doggedly took three expeditions beyond Greenland to explore what he thought was an open channel but which in reality is the bay of Baffin Land and today bears his name—as tribute to a great pioneer. Others to take unsuccessful expeditions North were Davis, Baffin and Hudson, and their names too have been immortalised in the geography of the Arctic. These men had to contend not only with the severity of the elements and with inadequate equipment in their frail sailing craft; mutiny at sea was prevalent in those days. Thus in the huge bay which now bears his name, Hudson with eight of his companions was put ashore by a mutinous crew and abandoned to his fate. Not until 1847 came Sir John Franklin's triumph in which he and his expedition perished after the moment of discovery, his two ships Erebus and Terror being crushed in the ice.

Probably few realise that a self–contained organisation for maintaining an air fleet would need many more different types of ground vehicles than aircraft. This is true in the case of the Royal Air Force even if all vehicles of a purely military nature are excluded. It is highly probable that a civilian air organisation of similar magnitude would have fewer types of aircraft, but if it were to be self–contained and operate in different parts of the globe, it could not do with many less types of ground vehicles than the R.A.F. finds necessary.

Obviously this depends on the interpretation of the term “self–contained.” Most of the small aerial transport companies have their own ground transport organisations, but they are far from being self–contained in the sense in which the author wishes to use the term to–night. We would all like to see a vast civilian air organisation operating in and between all the different units which comprise the British Empire. Nothing would do more to knit us and the Dominions and Colonies into one impregnable whole.

A considerable amount of attention has been devoted to the study of the position of the centre of shear for straight beams but there appears to have been Uttle or no consideration of this position for beams of which the centre line is either shghtly or heavily curved. The reasons are probably twofold. Firstly, no demand for such an investigation has been made by designers, and secondly, and probably not least, any very general inquiry into this problem will lead to complex expressions which would not only be difhult and tedious to evaluate but will also be of uncertain accuracy.

This problem of taking beam curvature into account starts from the point where it normally ends for most mechanical engineers, who usually require to estimate the bending stresses in members of large curvature such as hooks and chain-links. Now the classical theory of elasticity applied to these latter members has yet to be seen to conform with experimental results to such a high degree as makes the added labour attending such methods worth while.

The spin is a mode of motion of which we know very little. The general public are inclined to look upon it as necessarily dangerous, but this we do know it is not. It is only in rare circumstances and under fortunately rare conditions that danger arises. Nevertheless there is ample warrant for its study, and for that study to be treated as one of high importance. New conditions of aeroplane operation are continually arising, the very increase of speed itself would ensure an entry into regions never before penetrated. Hence it is ever necessary to seek for remedies even before serious difficulty has arisen; this anticipating action always seems to me to be absolutely essential, and I am comforted by support in this view from no less an authority than Francis Bacon, who, in his essay “ On Innovations,” wrote: “ Time is the greatest innovator; and if time in course alters things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?”

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.

The Sixth Louis Bleriot Lecture was given in London by General Guy du Merle on 19th March 1953 at the Institution of Mechanical Engineers, Storey's Gate, S.W.I. Mr. G. H. Dowty, F.R.Ae.S., President of the Society, presided and welcomed particularly M. Jules Jarry, President of the Association Francaise des Ingenieurs et Techniciens de l'Aeronautique, and members of A.F.I.T.A., who had come over from France for the occasion.

Introducing the Lecturer, the President outlined his career. After leaving school General du Merle went into the corps of aeronautical engineers, which was then of civil status but had since been militarised. He spent two years at the Ecole Nationale Supérieure de l'Aéronautique, graduating in 1932, and obtained his certificate as a pilot of military aircraft including seaplanes. For the next two years he served as an engineer pilot at the Centre d'Essais en Vol (Flight Testing Centre) testing prototype aeroplanes at Villacoublay, during which time he flew both French and foreign aircraft. He next became Engineer at the Technical Department of Aeronautics at the Air Ministry and then Director of the Department. While a professor at the Ecole Nationale Supérieure de I'Aéronautique he had published a book on the construction of aeroplanes, a copy of which was in the Library of the Society. Upon being attached to civil aviation at the Ministry of Public Works and Transport, he founded and directed for two years the National School of Civil Aviation at Orly. General du Merle was then appointed Director of Navigation and Air Transport at the same Ministry, and represented France at a number of international meetings on Civil Aviation. Appointed Ingénieur Général de l'Air, he had regained for a short time his original Ministry, which he now represented on the Interim Committee of E.D.C. He had been on missions to England a number of times since the end of the war, and in 1947 had flown several British aeroplanes, including the Sea Fury, the Meteor and the Vampire. He was a Fellow of the Royal Aeronautical Society, and was also an Officer of the Legion d'Honneur and held the Medaille de l'Aéronautique. General du Merle was at present Commandant des Ecoles et Stages at the Ministere des Travaux Publics et des Transports (Officer in charge of Schools and Courses).