In 1909 Monsieur Louis Blériot forged a link between our two countries, one might say an aeronautical link. He did so in an aeroplane which by today's standards took only a short take-off run and a short landing.

Today there are signs of new links being forged between the two countries and among them is co-operation in the development of vertical take-off and landing aircraft. There can, therefore, be no more suitable subject for a lecture in commemoration of Louis Blériot than one on “The Role of Jet Lift.”

The lecture illustrates, by typical examples, the standard of mobility which can be achieved by present military vehicles. An outline is then given of the mobility improvements which might be obtained by the use of military ground-effect vehicles but, in the concluding section, emphasis is given to a number of generalised problems in the military operation of such vehicles which require detailed consideration before an adequate specification of ground-effect vehicles for military use is possible. The lecture deals only with overland vehicles —although capable of water crossing—which are designed specifically to exploit the ground-effect principle and whose capabilities for sustained airborne movement are limited to the ground cushion.

The significance of joining flow regions with moving waves is discussed and a generalised treatment of simple, one dimensional, moving shock waves is presented analytically and in chart form. The problem is next considered with the shock wave replaced by different types of non-steep waves and their corresponding charts given.

Possible and impossible flow configurations are examined and the results presented in the form of a diagrammatic table. An alternative shock wave chart is described in an appendix and worked examples, showing the use of the charts, are presented.

I feel that the title of this lecture needs clarification, because it would appear from it that aircraft reliability is necessary only in the interests of Flight Safety. Although safety is vital, the operational capability of the aircraft must also be considered because, as in a missile system, operational reliability is of paramount importance. An aircraft may be completely reliable from the Flight Safety aspect without necessarily having a reliable weapons system.

In the past few years, of course, much has been said about the need for reliability. Conventions have been held in this country and in other countries and it might be thought that the lesson has been so often and so well propounded that to discuss it again is hardly necessary. However, I hope to show that we still have some way to go before we even begin to approach the ideal.

Two-dimensional photoelastic tests have been carried out on uni-axially loaded flat-plate specimens with two collinear edge slits, to investigate the effect of finite plate width on the elastic stress distribution. It was found that the effect of slitlength/ plate-width ratio on the elastic stress concentration at the end of the edge slit of length l was virtually the same as that for a central slit of length 2l in a plate of the same width, and could be adequately expressed by existing theories.

Using the Argyris matrix formulation a concise and definite justification for the correctness of the use of groups of unknowns in the analysis of redundant structures is given. It is shown also that to consider groups of unknowns is equivalent to changing the basic system. These two intimately related concepts are applied to the force as well as to the displacement method.

Using relations derived by Dixon and Inglis, the values of the elastic stress concentration factor for a fixed length notch in a finite width tensile strip with a varying notch end radius have been obtained in the form:

Photoelastic tests on internally notched tensile strip models showed excellent agreement with the analytical results.

In some recent tests we have successfully used the smoke from smouldering paper to indicate the flow of air in the vortices above slender wings at speeds in the region of 200 f.p.s. Smokes of this kind are particularly suitable for the production of the large volume flows required because in certain conditions they do not lose density by condensation in long supply tubes.