There are various possible interpretations of the title of this lecture and because of this and the fact that I have not had complete responsibility for the design of any one aeroplane, I regarded this lecture and title with some diffidence at first. Nevertheless in recent years no lecture has dealt with the general problem of how an aeroplane design progresses stage by stage, from the first ideas to the prototype flight trials and I have tried to make that the basis of my lecture.

The importance of the effects of compressibility on the performance and behaviour of high speed aircraft has been appreciated for a great many years, but in this country it was not until 1937 that serious attention was given to the design of a wind tunnel that would enable the study of compressibility to be undertaken by tests on models of reasonable scale. Prior to 1937 the work which had gone on had established the characteristics of a few aerofoils and simple shapes; at Farnborough the work mainly related to the testing of high tip speed propellers, while at the National Physical Laboratory tests had been made of a two-dimensional character on aerofoils, these tests being made in a small wind tunnel driven on the injector principle, by air discharged from a high pressure reservoir.

The purpose which Air Transport should be designed to serve is, I suspect, all too often confused or ignored. I think that the essential contribution which Air Transport has to make to modern civilisation can be expressed, quite simply, in two words:—

Improved communications lead to traffic—both traffic robbed from older and less convenient forms of transport, and new traffic created by the new medium. Carriage of traffic is the fundamental task of all forms of transport. Air Transport, alone unimpeded by geographical barriers, has traffic-carrying potentials which are still largely unexplored, whether that traffic be passengers, freight or mails—businessmen to Brussels, honeymooners to Honolulu, or coals to Berlin. In the same way, estimates of traffic must form the basis of all operational planning and set the scale against which airline fleets and frequencies should be projected in terms of date as well as numbers.

This paper describes some work, mainly of a theoretical nature, done at the Royal Aircraft Establishment, Farnborough, during the years 1946-1947. The immediate object of this work was to establish some general principles for the guidance of the Ministry of Civil Aviation Airfield Lighting Committee, which is the body charged with the task of deciding what visual aids shall be installed on the civil airports of this country. The work is far from completion and from the scientific point of view, this account of it must necessarily leave some loose ends, but it is felt that the method of attack and the underlying ideas may prove useful to other workers in this field. If this should prove to be the case, then international standardisation will have been brought a little nearer, and as will be made clear in this paper, this is almost as necessary for the visual aids as for the radio aids.

A Study of the evolution of the flight I faculty—and in particular its effects in I the realm of Nature and in human affairs—reveals analogies which are, perhaps, of more ithan technical interest. When due proportions have been established, it will be seen that the current period in the development of human locomotion is comparable to that very remote epoch during which Nature, having herself solved the problem of flight, exercised the faculty in accord with some inscrutable law. The analogy gains strength from the fact that changes of a profound kind in the conditions of life on this planet followed the evolution of flight in Nature; and that changes no less profound in character have taken, and are now taking, place as the result of man’s so-called ‘conquest of the air’ brought about by technological advancement.

I feel that it is now more necessary than ever before to present some unbiased views on the subject of aircraft accidents in general and of crash survival in particular. Discussion of the subject must surely be useful, although the outcome may not necessarily be wholly welcome to all sections of the Aircraft Industry.

The method of achieving efficient and economical servicing with the maximum rate of utilisation of aircraft, is a problem which always confronts the aircraft operator, either a private owner flying his modest machine or a national airline with a variety of large and expensive aircraft. From the point of view of safety, their problems are the same.

Efficient servicing is closely related to safety in so far as the airworthiness aspect is concerned and, under present servicing methods, the direct cost of providing this aspect of safety may well amount to some 20 per cent, of operating costs; to this must be added the delays inseparable from major maintenance work which can reduce earning capacity as a result of the time taken to rectify defects. Invariably the cost to the private owner is higher than he had expected and, unless his aircraft is maintained by a competent servicing organisation, it can be subjected to frequent bouts of unserviceability—usually when he needs it most.

From the correspondence columns of the JOURNAL it is obvious that there is a great deal of interest in the present-day standard of maintenance design and that the general consensus of opinion is that it is not up to a high enough standard.

In order to stimulate still further the interest in design for maintenance the following series of questions are asked. These questions are the thoughts that run through the mind of a maintenance engineer when he is introduced to a new item of equipment. The perfect maintenance design is extremely rare, i.e. when all the questions can be answered in a satisfactory manner.

It is easy to produce what seems to be an efficient design on paper but the conditions of a well-lit and well-heated drawing office are different from an unheated hangar early in the morning of a winter day.

The importance of maintenance being considered right through all the design stages is even more vital these days, when the number of aircraft being manufactured is less than during the war years and the economic side is just as important as the performance figures. In fact, the words “economy” and “maintenance” are bound together. It is not possible to issue modifications in order to correct faulty maintenance design and still keep a high percentage of aircraft flying.

This paper gives details of the first flights of the German, Italian and Japanese jet-propelled aircraft and engines during the last war. Only gas turbine jet propulsion has been covered.

The distortion of straight wings is simple and familiar; upward bending causes slight changes in dihedral angle and loads offset either fore or aft of the flexural axis cause twisting, which involves changes in incidence. When wings are heavily swept back, bending causes change of incidence as well as change of dihedral angle, while the changes of incidence due to twisting are no longer equal to the angles through which the wing structure twists.

It is becoming recognised that before civil aircraft can operate at high density, the most important problem to be solved is that of traffic control. Methods exist by which a single aircraft can navigate from a distant point to an airport and let down to a safe landing under bad weather conditions. Difficulties arise when several aircraft are involved at once and long delays can occur in the neighbourhood of airports carrying high density traffic. In this paper an analysis is made of the traffic problem in an attempt to clarify some of the factors involved.

Each time a new undercarriage design is laid down by an aeroplane or undercarriage designer, the geometry of the undercarriage retraction system nas to be investigated. This often involves a review of known solutions and since the designer cannot be expected to remember all these known solutions, the following notes have been prepared to put on record most of, and possibly all, the known solutions.

The basic linkage from which nearly all solutions are derived is the well-known fourbar linkage, as illustrated in Fig. 1. Links A and C rotate, link B is “floating,” while the airframe forms the fourth link.

At a section of a cantilever distant x from its tip, let the depth of section be h and the bending moment M. Then if all the resistance to bending is concentrated in the flanges the loads in the flanges are ±M/h. If the flanges are inclined at a small angle α these flange loads have a component transverse to the cantilever axis of magnitude Mα/h. Now α=dh/dx and the shear load at section x is dM/dx. Therefore the shear load on the web of the cantilever is dM/dx-(M/h)dh/dx, and, if h/M is constant, the web is not sheared at all.