During the past few years a new series of low drag aerofoils has been developed which represents a radical departure from earlier practice. The changes envisaged are much greater than those which accompanied the general change-over from the biplane to the monoplane, and give rise to many problems whose solution requires considerable theoretical and experimental work. An important feature of the new sections is the precision in design and manufacture which is essential for their success. This has given renewed interest to the investigation of many of the detailed problems of air flow and calls for parallel improvements in manufacturing technique so as to achieve the high standard of surface finish required.

The purpose of this paper is to give a brief account of the theoretical basis of the design and application of the modified profiles as aircraft wing sections. It deals with the design of aerofoils for the subsonic range only, or, to be more precise, for flight at speeds below the critical Mach Number at which shock waves are first formed. The critical value usually lies in the range 0.6 to 0.8, depending on the wing shape and incidence, as will be described in more detail later.

The strengths of the metals at present available to industry are of especial importance to the aeronautical engineer who is also in a position to appreciate the need for greatly improved materials, the absence of which often places restriction on much needed developments. Although the materials of the future may become available by the somewhat fortuitous development methods at present employed, it is undeniable that greatly accelerated developments would result if a correct understanding was obtained of the fundamental characteristics of the cohesion and fracture of metals, of which the former belongs to the field of the atomic physicist.

It has been found possible, for the first time, to show that failure under static and fatigue stressing is associated with changes in the crystalline structure which are identical. These changes are (1) a dislocation of the initially perfect grains into large components which vary in orientation from that of the internal grain by amounts up to about 2°,(2) the formation of “crystallites,” approximately 10-4 to 10-5 cm. in size, whose orientation varies widely from that of the original grains, and (3) the presence of severe internal stresses in the crystallites. At fracture, whatever the type of applied stressing, the whole of the specimen behaves to the X-ray beam as a medium of crystallites showing marked lattice distortion and oriented completely at random. X-ray diffraction methods are shown to distinguish clearly between the effects of the application of safe and unsafe ranges of stress; the first method that has been successful in this respect.

In order to show the relationship between the new work described and previous work dealing with the use of X-rays in studying the deformation characteristics of metals, a preliminary section of the paper deals with cold-rolling and drawing. A survey is also presented of the present position regarding strength and atomic structure, together with references to various theories regarding the imperfections of crystals as encountered in practice. An introductory section describes briefly the atomic structure of metals, as revealed by X-rays.

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.

Wartime experience with aircraft steels emphasised the desirability of a complete revision of specifications for aircraft steels from both the technical and inspectional points of view. This was undertaken in association with the steel makers and the Society of British Aircraft Constructors under the aegis of the British Standards Institution. The aims were

1. (i) To reduce the number of basic types of steels to a minimum, consistent with satisfying the demands of aircraft engineers.

2. (ii) To transfer as many materials from the D.T.D. series of specifications to the B.S. Aircraft series.

3. (iii) To prepare an Inspection and Testing Schedule, which would exist separately from the Materials Specifications, but applicable to all steels in whatever form they may be required.

4. (iv) To achieve a degree of economy in alloying elements, again without detriment to the satisfying of designer's requirements.

The Inspection and testing schedule was issued as British Standard S100 in January 1949, but significant difficulties in its full application appeared in practice and it was not until the second half of 1952 that agreement was reached to put into practice the current standard 2 S100.

Petroleum as it occurs in Nature is a very complex mixture of hydrocarbons. Imagine a mixture of petrol, paraffin, gas oil, fuel oil and lubricating oil, together with a certain amount of water and other foreign matter, and you have an idea of crude petroleum as it is found in Nature.

It is interesting to note that practically the sole use of petroleum for some time after the first well was drilled was as a burning oil. The object of the refiner was therefore to produce as large as possible a percentage of paraffin from his crude. The lighter fractions were regarded as a necessary evil, and it became a very difficult problem to dispose of them satisfactorily. It was, of course, necessary to keep the flash point of the paraffin high enough to avoid the danger of explosion of the lamps in which it was used. Petroleum inspectors were employed to ensure that the paraffin on sale was not “adulterated” with the then valueless light petroleum spirit. No market other than as a source for lighting gas was found for this light spirit until the advent of the motor car.