As technical progress has improved the airborne performance of aircraft, so the difficulties associated with their take-off and landing have increased.

The grass airfields which were still commonplace at the end of the Second World War have now developed into complex arrangements of concrete runways of up to three kilometres (two miles) long, taxiways, dispersal areas, and so on. The main disadvantages of these large airfields, both for military and for civil aviation, soon become obvious: —

1. (i) The enormous expenditure in either case; for military aviation this expenditure has to be approved, but it is at the expense of the production of actual aircraft—like Ugolin who ate his children so that they would not be fatherless;

   for civil aviation, the high cost of airfield construction has hampered the development of aviation in the remote areas where it would be of particular use in raising the standard of living.

2. (ii) The lack of flexibility of air forces operating from fixed bases, thus reducing their efficiency.

3. (iii) The increase in vulnerability as destructive weapons become more highly perfected.

This paper is concerned with the problem of the skin–and–stringer–covered conical fuselage of circular cross section, having flexible frames and being subjected to an arbitrary distribution of loads applied in the planes of these frames or on the end cross sections. The skin thickness and stringer cross section may vary from bay to bay but are assumed to be constant in a bay, i.e. between any two consecutive frames. The stringers are assumed to be uniformly spaced round the circumference. The frames are assumed to be of uniform cross section (circumferentially) but their stiffnesses are arbitrary, as is also their spacing along the fuselage.

This paper is a sequel to one previously published in the Journal, but the method of analysis is now by minimum strain energy instead of by deflections. Owing to the generality of the investigation it is impossible to present the solution—in terms of the known loads and stiffnesses—in any explicit form, and attention has therefore been concentrated on the technique of numerical computation. A scheme of tabulation has been evolved, and its use is illustrated by a fully–worked numerical example of a moderately complex type.

The problem of analysing the behaviour of a structure as a combination of members joined together, may be stated in the form of a question—What system of loads must be applied to a single member of the combination so that its behaviour as an isolated member is identical to its behaviour as an integral part of the structure? The question becomes clearer upon defining some of the terms used in stating the question.

Seven years ago a paper on this same subject was read before the Main Society. This has been used as a basis from which to start.

It will be seen that great strides have been made in performance, and the projects in the Design Office and on the drawing boards particularly, would even satisfy parliamentary critics. In Derby, however, where jet lift was conceived, such things are well known. From the fuel system standpoint in general the changes in requirements have been routine, merely much greater fuel demands, greater altitudes and air speeds and hence, a greater range of fuel flow, and it is this which gives the fuel system engineer his greatest worries. Beyond this there is always the need for smaller and lighter units in fancy shapes.

This paper is the first of a series of three which are concerned with the subject of “ hysteretic damping.” This type of damping, in a simple system with one degree of freedom, is like the familiar “ viscous damping ” in that it implies a resisting force which is in phase with velocity; but it is unlike viscous damping in that the magnitude of the force is not proportional to the velocity but to the displacement. When a system has n degrees of freedom, hysteretic damping implies that damping forces exist which are proportional to relative displacement but which are in phase with relative velocity.

From a physical standpoint, hysteretic damping may give a better representation of the facts when the damping arises from the internal friction of solid materials. On the side of theory, it raises considerations which it is the purpose of these three papers to elucidate. It may be said, at the outset, that the notion of hysteretic damping raises no great mathematical difficulty; on the contrary, a main reason for presenting the theory is that it appears to allow of a much simpler discussion (than does viscous damping) of the nature of steady damped oscillation of systems having n degrees of freedom.

In the first paper, the purpose is discussed of mathematical theories of damping in vibration theory. It is concluded that the theory of “ hysteretic damping ” is a useful one since it provides an alternative to the fiction of “ viscous ” damping while retaining the mathematical linearity of equations of motion. The word “ hysteretic” is proposed for use in this sense instead of the previously used adjective, namely “ structural.” “ Complex damping ” is related to hysteretic damping in a way which is explained.

The theory is given for forced oscillations of a system with one degree of freedom. It is shown that free vibration cannot be treated satisfactorily unless the definition of hysteretic damping is widened in some way to cover non-harmonic motion.

Progressively less information becomes available from the Soviet Union about the development of its aircraft industry. In examining the material that has been released during the past five decades, much confusion arises in the initial attempts to piece this material together chronologically and to show realistically the development of the aircraft industry in the Union of Soviet Socialist Republics. It seems that much time would be spent before a somewhat realistic picture might be obtained. Therefore, it appears appropriate that a definitive analysis be presented at this time.

The industrial development under the Communists in the Soviet Union is, and has been, a direct result of a bureaucratic state-planned economy. Voznesensky points out that the balance of the national economy, which lies in the hands of the State, includes the production and allocation of the social product, the production and allocation of fixed capital, the balance and distribution of man-power, the production and allocation of national income, the balance of money incomes and outlays of the population, and the balance and allocation of material resources.

Two types of intermittent wind tunnel drives, the pressure storage drive(with atmospheric exhaust) and the vacuum storage drive (with atmospheric inlet), are examined and found to match well the tunnel pressure ratio-mass flow characteristics over a wide Mach number range (0 to 4). The design of components of intermittent wind tunnel installations, their operation and instrumentation are then considered in some detail. In order to increase the output of intermittent wind tunnels to a level comparable to that of continuously running tunnels, it is proposed to drive the models during each tunnel run through a range of incidence. This technique is at present under development in the National Aeronautical Establishment's High Speed Aerodynamics Laboratory and results so far obtained are discussed. Two tunnels are considered as examples of large intermittent installations: a 4 ft. square pressure-driven tunnel and a 6 ft. square vacuum-driven tunnel. The former is found to be a more compact and economical installation. Relative merits of continuous and intermittent installations are discussed.

The present preoccupation of aircraft designers and users with fatigue problems, brought to a head by the Comet disasters, has rendered the notion of the finite life of an aeroplane a commonplace to the man in the street, and has made the assessment of probabilities of failure and the collection of statistics regarding loads and structural properties a matter of detailed concern for all designers. This was not always so. In 1939, when Fairthorne and I essayed a first paper on airworthiness statistics it received practically no attention and publication was delayed for years until after the 1939–45 War. Even in 1942, an exploratory “ Philosophy of Aeroplane Strength ” brought smiles to the faces of practical designers rather than the real interest that the “new slant,” as some said, of its probability approach raised in a few scientists.

The local instability of a simple type of integral panel under uniform end compression is discussed firstly as a problem of interconnected flat plates, and secondly in terms of the torsional stability of the stiffeners. It is found that the second method under–estimates the “true” local buckling stress. This conclusion is in conflict with earlier work by Yusuff on closer study it is found that Yusuff's analysis involves two important assumptions which are generally unjustifiable. It is suggested that the collapse strength of a short compressed panel may be estimated with reasonable accuracy from a knowledge of the initial local buckling stress and the proof stress of the material of the panel.

During the past few years numerous developments in the hydrodynamic design of flying-boats have been brought about mainly by systematic model research. Although Germany deserves the credit for initiating research on the forces on planing plates and Vee wedges, we are indebted to various estabhshments in the U.S.A. for the multiplicity of data on both flying-boats and simple planing surfaces, which are now available.

Today there is growing interest on the part of aeronautical engineers in forgings of large size, for three main reasons. Certain types of forgings will naturally need to be bigger as the aircraft itself becomes bigger; more composite structures are being replaced by single components made as forgings; and there is an increasing use of complex units machined directly from blocks of metal which are too big in at least one dimension to be made as extrusions or rolled plate. It is with these larger forgings that we are mainly concerned. Their production presents many serious problems. It is reasonable to hope that some of these will be overcome as experience grows and techniques are improved but others seem to be inherent in the materials used and must be appreciated at the design stage of the component if fully satisfactory service is to be obtained.

Sir William Hildred, C.B., O.B.E., Director-General of I.A.T.A., in his Annual Report, which he presented at the I.A.T.A. Conference in Paris in the middle of September 1954, pointed out that there was an urgent need for a drive for greater efficiency to obtain a balanced airline economy. He quoted some interesting I.C.A.O. figures. These covered all the world's scheduled operators, both the profit-making and the loss-making companies. In 1951, the world's airlines showed that total operating revenues were 6 per cent, higher than total costs. In 1952, this figure was down to 3·6 per cent, and in 1953, down to 1·1 per cent., which represented $27-million profit on a total business of $2,500-million. It should be noted that this $27-million profit is arrived at after the pay-out of direct taxation by the profit-making companies to the tune of $69-million.

I intend in this lecture to discuss tlie ways in which I think analogue computing can be of assistance to aeronautics in the future. I shall therefore be less concerned with how they are built, than with how they are used, and in fact, what circumstances justify using them at all. Up to a few years ago the only large computors were analogue ones, so the user had no choice, but when the automatic digital computor became established as a practical machine (and even before) there were many people to suggest that the analogue was obsolete. This view is now less widely held, even by makers and designers of digital machines, and reviews of aeronautical computing aids have usually found some place for the analogue computor, without establishing any general principles on which the choice has been made, except, perhaps, to suggest that the accuracy required is the criterion.

I shall start by describing three of the types of computor most commonly used in aeronautics, the “ response simulator,” the “ electrolytic tank” and the “network analyser” and use these to illustrate the particular properties of analogue computing.

It is a very great honour indeed to find myself addressing the Royal Aeronautical Society. If, as I am often told, “a little learning is a dangerous thing” then you are in for a very dangerous address. For much as I would like to say that I know nothing about aviation it would not be altogether true. My knowledge is of the picked-up rather than the learned variety. During the war I was either at the receiving end of enemy aviation or under a friendly and comforting umbrella, which counts as passive experience. I started flying as a passenger in about 1935, and in common with many others 1 have put up with all the frustrations and delays of airline travel, particularly getting to and from the airfields—this I put down to semi–active experience! The active part of my experience began two short years ago when I started to learn to fly.

From this you will gather that any views I express this evening must be treated with caution if nothing else.

The theory of stress concentration is such a fascinating study that the whole of this lecture could be most happily devoted to discussion of the stress distribution round all sorts of special boundaries. At the same time the most detailed knowledge of elastic stress distribution is of little value unless we can be sure how the stresses computed will be reflected in the actual strength of the part. For that reason this paper is divided into three sections: the first deals with certain moderately simple cases of stress and load concentration and shows how the stress analysis is confirmed by static and fatigue tests: the second describes some investigations of special two–dimensional boundaries and indicates, some fairly general theoretical conclusions which can be drawn: in the third I shall try to review the possible reasons why, in practice, the best found conclusions are not always borne out.

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.

The first idea about unsteady motion in the atmosphere seems to have been the vague notion of “ Air Pockets”—areas or gaps, wherein the air just does not generate lift, and an aeroplane falls in consequence. It is astonishing how widely this view is still held.

Those engaged in aviation soon learned that unsteady flight was due to turbulence and two sorts, friction and orographical, were quickly recognised. Friction turbulence, which affects only the lower layers of the atmosphere, can best be observed by watching a soaring sea-bird in a breeze. The friction of the water surface creates a velocity gradient or variation of windspeed with altitude, and the bird will probably be diving down-wind, and climbing into wind, with no effort— from the bird's point of view a fair approach to perpetual motion. However, the air is really a mass of tiny eddies where friction is at work and close observation of the bird's wings and feathers will show them to be constantly in motion as they yield to each puff.

The minimum weight approach to structural design was introduced by F. R. Shanley with reference to narrow and wide columns and shells subjected to bending, and was later dealt with more comprehensively in a book by the same author. This was further extended to structures like tapered round thin-walled columns and frames. In this paper expressions giving optimum sectional dimensions for long thin walled cells of circular, semi–circular, rectangular and triangular shapes and uniform wall thickness have been derived. The design criteria used to obtain the minimum necessary conditions are (1) failure by local buckling and (2) a limit on the twisting deformation of the cells. Working curves from which the optimum sectional dimensions can be read for given torque and limiting twist have been plotted. And finally, a method of approach to the problem of combined bending and torsion has also been indicated.