The Materials Engineer should provide materials of proven integrity with the highest possible strength to weight ratio. This paper discusses the potentialities with the basic materials used for airframes. Attention is directed mainly to materials for subsonic aircraft.

It will be helpful to consider the distribution of materials in present day aircraft, and Fig. 1 shows clearly that the basic airframe materials at present are aluminium alloys and steels.

The objective of Structural Design is to provide the structure that will permit the aircraft, whether military or civil, to do its job most effectively, that is with the least total effort, spread over the whole life of the aircraft from initial design until the aircraft is thrown on the scrap heap. There is thus no all-embracing simple criterion by which the success of the structural design can be judged. It is not sufficient to believe that percentage structure weight is of itself an adequate measure of effective design, either of the complete vehicle or of the structure itself; a well-known example is the provision of increased aspect ratio at the expense of structure weight, which may give increased fuel economy in the cruise and reduction in the total aircraft weight. Nevertheless, percentage structure weight is a useful measure, provided its limitations are recognised.

The contribution of the production engineer to the improvement of aircraft structures lies in producing better and cheaper aircraft more quickly.

In the first place he must advise the structural engineers as to what methods of construction are practicable within the timescale of a particular project. He must also ensure that full weight is given to the economics of production in determining the type of structure to be employed. In this respect he must guard against a tendency to conservatism. It is always easier, and usually cheaper, to do a thing the way it has been done before than to develop something new, but in the long term some structural developments which appeared almost impossible have become routine economic processes.

Before looking forward, the structural significance of the trend towards the rear-mounted engine must be considered. The reason for this trend stems from the need to obtain increased overall efficiency. The advent of the jet engine first of all made it possible to bring the engines inboard into the root, as on the Comet and Vulcan aircraft, and now, in the interest of obtaining higher aerodynamic efficiency, they have been moved aft towards the tail end of the fuselage. This allows a reduction of wing area, a consequent reduction in tailplane area, an overall reduction in drag and a consequent decrease in fuel consumption for a given performance.

The emergence of electronic computers has brought about a revolution in the analysis of aircraft structures in the past decade which is now generally accepted throughout the Industry. But the major impact of computers on design has, in my opinion, not yet been realised and I hope, in this short paper, to show how powerful a tool they can become in the hands of imaginative design engineers. The direct benefits to the designer lie in the ability of the computers to perform large amounts of routine arithmetic in a short space of time. This capability enables us to obtain an insight into structural behaviour and to consider the influence of the aircraft environment and design alternatives from the earliest stages of design. By the development of general purpose computer programmes for handling routine calculations the structural designer can be freed from much of the laborious calculation associated with complex structures and he is able to devote more time to creative work. An even more important indirect benefit is the basic re-thinking of design processes which is necessary in order to reduce them to routine arithmetic. We begin to realise that many aspects of efficient design such as continuity, cost and weight can be introduced as quantitative parameters instead of relying on intuitive compromise.

In this article a magnetic suspension and balance system suitable for wind tunnel application is discussed. General considerations are presented that illustrate the nature of the problems to be solved as well as one solution of these problems.Finally some initial wind tunnel data are presented.

Rather more than twenty years ago the writer published a report on the design of wind tunnel fans: a single fan was implied. The report assumed that the pressure increment appropriate to a given axial wind velocity was known, having been either measured (e.g. on a model), or estimated from data such as the power factor of the wind tunnel. A preliminary calculation to determine rotational speed and solidity was followed by a detailed calculation of the appropriate blade angles; the detailed calculation involved the evaluation of the rotational inflow factor (here called a: in Ref. 1 it was denoted a2). Now most of the quantities involved are functions, implicit or explicit, of the rotational inflow factor, and it is not possible to evaluate it in closed form: some method such as cross-plotting for ranges of a at each radius, or successive approximation by a convergent process, is required. Ref. 1 advocated the latter method.

If it is assumed that the effect of radial flow can be neglected, then the vortices which are shed from the trailing edge of a propeller blade can be said to lie approximately on helical lines. These vortices form a vortex sheet which for practical purposes is assumed to extend unaltered downstream to infinity. If the propeller blade is approximated by a lifting-line of bound vorticity, then the velocities at the blade induced by the trailing vortex system can be derived from the simple flow conditions in the hypothetical far wake where the vortex sheets extend equally to infinity in both directions. Results are already well-known for the case where the vortex sheets exist in free space. It is the purpose here to examine the effect of adjacent boundaries, such as the hub and the duct wall of a ducted propeller. The results also relate to a test propeller in a tunnel.

Cockrell and Markland have found that the static-pressure recovery coefficient of a conical diffuser, which is well known to decrease as the (turbulent) boundary layer thickness at entry increases, actually rises again when the inlet boundary layer is so thick as to approximate to fully-developed pipe flow. It may be noted that this is not a consequence of the definition of the pressure coefficient because, for typical pipe flow velocity profiles, the pressure coefficient based on mean velocity, , is very nearly the same as that based on momentum flux .

The Evaluation of buckling loads of columns presents a difficult problem whose rigorous solution may be very difficult particularly when the variation of moment of inertia or the axial load does not follow a simple law. Hence approximate methods such as the variational and numerical methods will have to be employed. An approximate method is suggested in this note which offers a convenient method for the calculation of buckling loads of bars with any type of end conditions.

All too often, points dealing with some aspect or other of the thermodynamics of powerplants are made which are incomplete, ambiguous, erroneous, or a mixture of all three! The purpose of this note is to try to give a limited, but logical, theoretical analysis of one type of propulsion powerplant, namely the by-pass engine with the possibility of heat exchange between the by-pass air stream and the main gas stream before expansion through the propulsion nozzles. This is a problem to which the solution is not obvious, and which would probably present difficulties to the average student. Heat exchangers are perhaps more of hypothetical rather than practical interest at present, but it is important that a correct thermodynamic approach be made in every case. Nothing is less likely to be engineered than a Carnot engine, and the general line of argument should be of wider appeal than the particular example to which it is applied.