The suitability of a piece of mechanism for a given job depended both on the nature of the job and on the solution offered. In aviation they had to consider performance, time of development, cost in production and serviceability in its widest sense. It was proposed to review these different aspects as they applied to the compressors for aircraft gas turbines.

Metal adhesives have been known to the Aircraft Industry for at least ten years, the Chrysler Cycle Weld process being among the earliest. Since then metal-to-metal bonding has been the subject of many papers, but no member of a firm of aircraft constructors is known to have lectured on the subject.

It is hoped, therefore, that this paper may prove a useful contribution to the workshop aspects of the method. The fundamentals of adhesion will be avoided and only brief reference will be made to the strengths of structures assembled by that means; those are matters for the physicist and aircraft designer.

The contraction of a wind tunnel should be free from adverse pressure gradients, since this might cause boundary layer separation.

A wall contour has been designed for a circular cross-section contraction using incompressible flow theory. This gave a favourable pressure gradient at the beginning of the contraction where separation is likely to occur.

Appendix I compares the theory with experimental results obtained from a model of a proposed supersonic tunnel of which the contraction is rectangular in cross-section and which has been based on the results obtained in this report.

Invariably the texts in elasticity and strength of materials derive the stability criteria for struts by first setting up the beam bending moment equation. Together with suitable boundary conditions this equation is then solved as an eigenvalue problem for non-zero solutions. It is indicated here that in general this procedure is too limited, both physically and mathematically, and that in some cases the correct approach yields additional results which normally would not become evident by employing the classical method.