The material herein presented was gathered as part of a research project for the Bureau of Aeronautics (Structures Branch) of the U.S. Navy on “Evaluation of High Strength Aluminium Alloys.” The Bureau has released this material for independent publication.

In this paper the physical constants determined are limited to elastic limit, yield stress, ultimate stress, modulus of elasticity, weight and ductility. The materials tested are primarily the new aluminium alloys 75 ST, R 301 T, and R 303 T.

To offer an immediate basis of comparison for aluminium alloys, the aluminium alloy at present in common use, namely 24 ST, was also tested. To extend the scope of the project still further, a few tests on magnesium alloy and stainless steel were included.

The following investigations were made primarily in order to determine the manner of transmission of concentrated loads from the frames to the skin of a circular fuselage. The usual assumption, that the shear distribution in the skin adjacent to the frame is given by the simple “ beam theory,” was considered to be of doubtful validity, and for some time past the writer had suspected that a critical examination of the problem would show a very considerable variation from the ordinary theory in the immediate vicinity of the loaded frame. The writer's attention was first drawn to the problem by the work of Wignot, Combs and Ensrud in N.A.C.A. Technical Note No. 929, and the present investigations were made because a more fundamental approach to the subject was considered to be desirable.

The purpose of this paper is to present the case that can be made for the tailless aircraft on the grounds of improved performance and operational suitability.

The whole field of possible investigation is not treated here with uniform thoroughness and the main reason for this is that I have only quoted detailed results for those cases which I have actually considered myself, so that in some instances the general qualitative arguments can be backed up by actual figures, whereas in others the argument has had to be confined to generalities.

Consider the growth of the boundary layer over an aerofoil placed at high incidence, the potential flow pressure distribution of which is shown in Fig. 1. In the region AB, the flow will normally remain laminar because of the large favourable gradient, but after reaching the peak B, instability will begin. Depending on the Reynold's number and the actual adverse gradient, the boundary layer will do one of three things:

1. 1. It will separate from the surface while still remaining laminar;

2. 2. It will become turbulent (transition) and will remain on the surface, or;

3. 3. It will become turbulent and will separate from the surface a little later.

In the design of gas turbines, the most important limitation is imposed by the materials of which the combustion chambers, guide vanes, and, most important, the turbine blading are made. Any improvement in the heat resisting properties of the materials used in the construction of these parts will immediately show as an increase in power output.

As Major Halford stated before the Royal Society of Arts in a recent lecture on the gas turbine, a gas temperature of 850°C. at the turbine blade will allow a maximum take-off thrust of 15,000 lb. for one unit, running at 6,200 r.p.m.

The present temperature reached is around 750°C, this being attained after six years of war-time development. From this it will be seen that unless the metallurgist produces a new alloy, the limit with metal blades will soon be reached. Of course, cooling of the blades could be resorted to, but this brings with it the attendant difficulties.