In the early days of aero-engines the test equipment was limited to little more than a brake or dynamometer, a fuel flow meter and a few thermometers, and the development of these engines in the direction of better performance and reliability, to a large extent, was an art, built up of experience aided by instinct, of deducing the happenings inside an engine from the few meagre measurements obtainable.

Nevertheless, the aero-engine made healthy progress, became more complicated in the process, and introduced many more problems.

I have chosen to describe the methods employed by the Research Division of the United States Navy Bureau of Aeronautics with the hope that others engaged in a similar line of endeavour may be able to make profitable use of this information in the solution of their specific problems. The development of the material to be discussed arose directly from the need for quick, reasonably accurate and simple means for studying a broad series of aircraft designs leading toward fulfilling an overall military requirement. This process is carried out in the Bureau of Aeronautics by the Research Division prior to the issuing of a type specification with a request for proposal to the various manufacturers. Before these specifications are decided upon, many designs must be investigated and reported to those initially responsible for the issuing of military requirements. By this process intelligent compromises are arrived at and the best possible aeroplane chosen. These compromises reflect the performance, the ability of operation from carriers, and the effectiveness of the design as a military weapon.

When one is honoured by the invitation to deliver the Wilbur Wright Memorial Lecture one's immediate concern is to find a subject worthy of the occasion, which (in view of the wide coverage of the field of aeronautics that already has been made in these Lectures) is no easy task, at least to those of us who have no specialised knowledge wherewith to take advantage of the many new technical developments that continue to emerge.

In choosing my subject and in the attempt to draw, within a reasonable margin of error, an overall picture of the human effort that has been devoted to the cause of Aviation, I realise that I have bitten off a very large mouthful, and that some apology is due for the degree to which I may fail properly to masticate it.

On 17th December 1903 the Wright brothers started something, when by the achievement of human flight they opened the road to the tremendous developments in aviation that have taken place in this last half century. This vast and rapid progress in the technology of design, manufacture and operation of the aeroplane is today accepted as a commonplace, and its continuance taken for granted.

In accepting the invitation to address the Royal Aeronautical Society I am deeply conscious of the honour that has been paid to me and of the responsibility I have undertaken. My sense of responsibility flows from the realisation that I have been called upon to contribute from personal knowledge and experience to the great volume of recorded and authoritative opinion already contributed by these lectures.

I have chosen to address you on some international aspects of air transport because it is my firm belief that the lack of an enlightened multilateral code in an important field of international air transport is one of the more serious impediments to the full exploitation of the technical advances with which air transport has been presented in recent years.

The purpose of this paper is to describe a method for making repeated load tests and to illustrate several applications of the method.

The general characteristics of fatigue testing machines operating on the resonance principle are described, with particular reference to the mode of excitation. A method of excitation different from that in common use is described, and its advantages and disadvantages are explored. Four applications of the new method are instanced.

The new method proves particularly applicable to the repeated loading of complete structures and components, because it is readily adaptable to parts of awkward shapes loaded in special ways. Moreover, application of the method is not seriously restricted by large strains of the component under test, nor by moderately heavy absorption of energy by the component.

Several further applications of the method to the testing of complete structures are under consideration, and the development of types of fatigue testing machines based on the same method is being explored.

To fly farther, to fly higher, and to fly faster, have been the aims ever urging the aircraft designer on to further progress. Of all, the lust for high speed is the most compelling. While the past few years have seen spectacular increases in the World's High Speed Record (see Fig. 1) still higher performance in the supersonic region will be commonplace in the near future. To attain these speeds, largely made possible by the increased power and light weight of the turbo-jet unit, the designer must seek out means still further to reduce aerodynamic drag.

Much work has been done on compressible flow since the contribution of the Aerodynamics Division to research in this field was last described to the Society by the late C. N. H. Lock in 1937. At that time he was able to review many of the data which were available from other sources, whereas today such a task would be impossible in a paper of this length. We shall confine ourselves here, therefore, to a description of some of the experimental work that has been done during the past few years in the high-speed laboratory of the Division, and to an account of the lines along which it is intended to continue the work in the future.

There is nothing new in attempting to design an aircraft to give trouble-free service. This has always been one of the major parts of a designer's job. In recent years there has been a lot of talk about improving design from the maintenance point of view and suggestions for “maintenance cells” in drawing offices. I would suggest that if aircraft have become too difficult to maintain, it is not entirely due to lack of appreciation of the problem in the drawing office, but mainly to the great increase in complexity of the modern aircraft, particularly in the past 10 years.

The employment of aircraft for surveying has become so usual, and so much has been written about it from one aspect or another, that perhaps the time is appropriate to define exactly what is meant by Air Survey; what the surveyor is trying to achieve, and how he is dependent upon the airman to obtain his objectives. To achieve good results from an air survey, closely integrated team work is required. The airman, photographer, instrument specialist, meteorologist and the surveyor each depend upon the other, any weakness in the chain making results more expensive and less effective. The author, as a surveyor, has worked in harmony for a good many years with the “air” side, and it is proposed in this paper to summarise the surveyor's approach and his requirements, and to explain why he seems never to be satisfied with the accuracy achieved. The greater the accuracy of photography, the simpler, quicker and cheaper become methods of using the results to fulfil the desired specification.

In this paper an attempt is made to analyse the overall gains that have been obtained in aerodynamic cleanness in the past, to review the overall performance improvement that can be expected in the immediate future from increased cleanness along orthodox lines, and to survey critically certain more advanced concepts aimed at giving still lower drag coefficients and better performance characteristics.

The principle of the ram-jet or athodyd has been understood for a number of years. It has been applied in many ways, the most prominent being the flying bomb and, rather less spectacularly, the ducted radiator. The principle is to. convert the velocity energy of a high speed air stream to pressure energy by means of a suitable duct, to apply heat energy to the compressed air, and then to expand this heated air in the form of a high velocity jet. The advantage of such a mechanism is an increase in thrust given by the product of the mass flow of air, and the difference in velocities between entry and exit; the disadvantages are, the necessity to project the duct at high forward speed before any thrust is obtained and, except at very high speeds indeed, the low thermal efficiency.

To the aircraft designer and contractor, those of us responsible for equipment may appear as arch-perpetrators of complex, bulky and weighty “ gadgets,” impossible to install and the source of all unsightly excrescences on the aircraft's skin.

Any aircraft, from its inception should be designed for some specific role, and its usefulness may well depend upon the availability or simultaneous development of equipment.

This lecture does not set out any new method or offer any ideas to enable the design office to start cutting down the weights of new projects.

The last lecture dealing with the weight of aircraft was given by Major T. M. Barlow, M.Sc, M.Inst.C.E., M.I.Mech.E., F.R.Ae.S., in 1929.

The principal materials employed in modern aircraft structures are aluminium-rich alloys which the aircraft manufacturer will normally buy in the semi-finished (cast or wrought) state. Wrought materials fall into the four main classes of tubes, sheets, extrusions, and forgings; eacri of these forms inherently exhibits distinctive mechanical strength characteristics. In this paper the relation of the mechanical properties of medium and high strength wrought light alloy materials to the grain direction, and the implications of this relation in aircraft design, will be discussed.

That synthetic glues for wood were used extensively for making Mosquito and Hornet aircraft during the 1939-45 War, and are now used for making Vampires in many European countries, is well known to aeronautical engineers, but not so well known is the fact that, since 1944, synthetic glues for metals have been used in the production of many hundreds of military and civil aircraft. A glue for metals, which gives joints stronger than can be obtained by riveting and which is also resistant to the severe conditions to which aircraft are exposed in service, offers the possibilities of savings in structure weight and of aerodynamically cleaner wing and fuselage surfaces. Such a glue may also be expected to be of value in the manufacture of pressurised fuselages, because it will avoid the large number of small leaks occurring at the rivet heads and may also help to solve the difficult problem of making integral fuel tanks in aircraft wings.

The title of Prototype Testing is taken here to refer to the flight tests carried out on a new aircraft by its constructor. It embraces a wide field of subjects and in a short paper, it cannot be covered in any way comprehensively. I propose therefore to deal mainly with very general aspects of the subject.

The paper does not attempt to embrace out of the ordinary types with special problems peculiar to themselves—an extreme example of which is probably the Brabazon I. Most of my experience on this subject has been concerned with small aircraft, many of them single-seaters, and consequently some of my statements may apply more particularly to this type of aircraft, although many will probably apply equally to other types of aircraft.

Sources of noise in aircraft are discussed briefly with particular reference to the introduction of the turbo-jet engine.

An account is given of a particular investigation made in a Lancastrian aircraft fitted with both turbo-jet and reciprocating engines. The equipment by which the noise spectrum was analysed over, an extended frequency band is described.

The results are examined and the effects of the two types of engine on the noise spectrum are compared, under different representative conditions, in the forward and rear sections of the fuselage.

A general approach and tentative solution has been indicated to the problem of estimating wing skin thickness from preliminary design data. The solution is presented in a form that permits calculations to be made quickly and with a minimum of effort.

In deriving the empirical formula relating perimeter and area of the aerofoil section, only symmetrical sections were considered. The amount of camber normally employed, however, should not alter the results appreciably.

While the problem has been dealt with only partially and as yet only tentative empirical coefficients have been suggested, it is hoped that the author’s considerations of the problem will be of some interest and use at this stage.

Introducing the paper Air Commodore Merer pointed out that the Americans, the French and the British were concerned in a close partnership in the Air Lift, but the Americans carried by far the larger portion of the load delivered into Berlin. The spirit of comradeship and endeavour which that joint task engendered was one of the heartening experiences of the operation and beyond all praise.