This paper attempts a view of the development of civil aviation in a rather broad and fundamental way, deliberately avoiding any detailed discussion of the many technical aspects of this large and complex industry.

Anyone who is associated in any way with the design and production of aircraft and with the administration and operation of airlines and airports will be only too well aware of the immensity of the technological and organisational effort involved. And looking back over the past 50 years, the development of civil aviation into a major world industry can be viewed, rightly, as a major technological achievement. However, any technological development and the successful evolution of any transport system or industry must be initiated and sustained by some form of social demand. Frequently the demand is difficult or impossible to identify, indeed the idea of a demand may be less useful than the idea of a welcoming response to supply: technical advance frequentiy seems to generate a new market rather than to satisfy an existing one. Nevertheless aviation has during its development passed through a number of phases and been subject to shifts of objective, sometimes gradual, sometimes very rapid, reflecting changes in the response of individuals, companies, nations, and now perhaps even of the world community at large. These changes in demand may be expressed as changes in priorities and we have tried, in Fig. 1, to give some indication of how the balance of demand appears to have shifted as aviation (in this case, both civil and military aviation) jhas progressed from its early status as a sporting pastime to its present position as a world-wide transport system.

Today we speak of the quality of life and the need to improve the quality of the environment. The removal of all kinds of pollution from our environment is a laudable aim and for some types of pollution positive action and an awareness of the problem can make improvements with a minimum of cost. However, in the case of most forms of pollution, and this includes noise, improvement in the quality of the environment can only proceed at a price. Thus there is considerable need for phased reductions in pollution and future planning with imposed realistic targets is paramount. In this region of social planning the problem of cost benefit analysis cannot always be applied and pressures are exerted to directing funds for economic gains and combating other pressures in national and international life in directions which lead away from pollution control. Nevertheless improvements to the environment dependent on the supply of finance can only be achieved, all other things being equal, when the economic state of a country is stable and attention of governments is directed with a willingness to achieve what at first sight is a downright impossibility.

The basic building block of a filamentary-composite laminate is a ply or a lamina consisting of a larger number of stiff filaments (e.g. glass) embedded in a compatible material (e.g. epoxy). The laminate or multi-directional composite is considered to comprise a number of perfectly bonded laminas with different fibre orientations. The deformation response of a laminate to an applied force is calculated by means of its material constants. One of the common methods of determining these constants is by means of a micro-macro mechanical analysis in which the characteristics of the composite are found in terms of the constituent material properties, geometry, and volume percentage of fibre content. Numerous papers have been published to investigate the micro-macro mechanical approach. Some of these works are based on the mechanics of materials approach and on the variational principle of minimum potential energy, as well as on the classical theory of elasticity.

Several recent theoretical advances have been incorporated in computer programs which find the initial buckling loads of prismatic assemblies of thin plates “exactly”. Any such assembly of plates which are connected together and/or supported along their longitudinal edges, while being simply supported at their ends, can be analysed. Furthermore, curved plates and anistropic materials are allowed. Thus plate assemblies with many practically important types of cross-section can be analysed. Consequently, published results mainly relate to a few crosssections of each of several possible types. However, the designer needs comprehensive design curves, like those in the Structures Data Sheets of the Royal Aeronautical Society, for as many common cross-section types as possible. Unfortunately, production of such curves using the programs mentioned is unlikely to be achieved for all desired types of cross-section, at least for some time, because each type involves plotting curves as several parameters are varied. Nevertheless, a range of results for one type of cross-section is obviously valuable. Thus the lipped channel strut made from isotropic material is considered in this Note (see Fig. 1).

There is much current interest in numerical methods of solution of the laminar boundary-layer equations. Methods used to date may generally be classified as

• (i) explicit finite-difference methods (e.g. Refs. 1, 2, 3);

• (ii) implicit finite-difference methods (e.g. Refs. 4, 5, 6, 7);

• (iii) difference-differential methods (e.g. Ref. 8).

A method based on converting the boundary-layer problem into an integral equation and solving the latter by iteration has been developed by one of the present authors.