I wish first to express my deep appreciation for having been invited by the Council of the Royal Aeronautical Society to present a lecture on aeronautical research in Sweden. As the subject is a very broad one, it was necessary for me to consider rather thoroughly what would be expected from this paper and thus, which limitations in its scope should preferably be made.

Before the 1939-45 War it was possible to design new, successful aeroplanes mainly on the basis of experience from previous types in combination with generally available design information, such as aerofoil data. The success was, in fact, often more dependent on the skill of the designer than on the amount of research and detailed aerodynamic and structural testing done. After the advent of jet propulsion and transonic and supersonic speeds this situation changed radically. Nowadays a substantial amount of basic and applied research, as well as scientifically performed development work, is a necessity for any country, regardless of size, attempting to produce its own designs of efficient and safe aircraft.

The purpose of this paper is to attempt a broad review of some of the factors that influence the economic development of a country and to illustrate in general terms the importance and the application of airborne survey techniques, as a means of collecting the information on which any sound development must be based.

The industrial and agricultural revolution that is now taking place on a world-wide scale demands a completely new approach to the problem of economic development. When economic development was slow and confined to small areas it was sufficient perhaps to base that development on limited information. Today, however, the pace is quickening every year, but the speed with which we are obtaining the information, on which such development must be based, is lagging behind.

Why is the present position different from any other epoch in world history? The main cause is the industrial revolution, which has produced rapid means of communication, by air and by radio. The Twentieth Century now lives literally as neighbour to the Stone Age.

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.

The slender–body solution for the flow about low aspect–ratio wings of non–zero thickness yields a pressure distribution which is valid in the vicinity of the leading edge and therefore suitable for comparison with measured distributions. In this note an expression is derived for the theoretical pressure distribution, due to small incidence, on a slender elliptic half–cone in uniform motion. It is shown that this distribution is additive to the zero incidence pressure distribution. A comparison with some low speed measurements shows qualitative agreement.

The method can be simply extended to other bodies of elliptic cross section.

A structure with cut–outs or other discontinuities is generally considered to be more difficult to analyse than a similar structure without such features, although it is in fact less redundant. This is largely due to the special conditions which have to be introduced to allow for these discontinuities, tending to make the calculations less adaptable to routine computation . Another and very practical reason is that it is sometimes fairly easy to—dare we say it?—make a reasonable guess at the load distribution in a structure without cut–outs, whereas a much more critical approach is necessary for the treatment of structural discontinuities. Be that as it may, it will be assumed here that the structure without discontinuities, which will henceforth be termed the “original” structure, can be analysed exactly, in the sense that all the effective redundancies are taken into account. It will now be shown how these calculations may be modified to deal with the corresponding structure with discontinuities, which for this reason will be referred to as the “modified” structure.

Boundary layer problems may be divided into two classes: (a) those for which similar solutions can be found, i.e. where the boundary conditions are such that similar profiles differing only in scale factor exist at different sections; and (b) those where the boundary conditions do not effect similarity, so that the development of the boundary layer must be calculated in stages. The latter class are known as “continuation problems,” and very few numerical solutions have been obtained because of the labour involved.

Approximate methods of solving continuation problems are known, using the Karman momentum integral method (e.g. Ref. 1) or variants. Some of these methods make use of velocity profiles calculated for “similar” boundary layers. This note presents a new approximate method which uses “similar” profiles but avoids using the momentum integral. Instead of characterising the boundary layer thickness by the “momentum thickness,” which needs to be calculated yet is of less direct interest, the wall shear stress is used; this stress usually has to be calculated in any case and the present method is therefore comparatively simple.

In a recent article in the Journal Dr. Syed Yusuff complains of a lack of “analytical work on compression panels of integral construction … . to provide an insight into the mechanism of the various instabilities involved and also to enable the designer to evaluate its advantages more precisely.” It may therefore be pertinent to point out that there is no fundamental difference between the modes of instability of integral panels and those of conventional panels with riveted or bonded stringers, except in so far as certain modes such as inter–rivet buckling cannot arise. Consequently the analyses discussed by Argyris and Dunne in the Handbook of Aeronautics and the more recent paper by Argyris on flexure-torsion panel failure are immediately applicable to integral panels; indeed with an enhanced degree of accuracy due to the monolithic character of the integral panel. Thus, such uncertain factors as the rivet stiffness need no longer be considered. In fact, in the last mentioned paper the analysis is illustrated by application to an integral panel with flanged stiffeners.

The Journal in which Mr. W. Tye's Second Barnwell Lecture has been published (“ The Outlook on Airframe Fatigue,” May 1955 Journal) has now reached Australia. I felt that some comment was called for when I discovered that Mr. Tye had not mentioned the work done in Australia on the life of aircraft structures.

What I believe to be the facts are as follows. Australian concern regarding fatigue was awakened in January 1945, when a Stinson air liner VH-UYY crashed with the loss of ten lives. The analysis made by the C.S.I.R. Aeronautical Research Laboratory confirmed that it was caused by a fatigue failure in the welded tube of the primary wing structure.

Mr. H. A. Wills, in charge of structural and metallurgical research at the Laboratory, initiated a programme of fatigue tests on actual aircraft wings, designed to give factual answers to the problem of determining the safe life of aircraft structures. The basic idea that this could be done had been suggested in a paper by Bland and Sandorf0, and the Stinson accident provided the necessary urge.