About twenty years ago I was invited by the Council to read a paper before the Society, the title suggested being "The Use of Steel in Aircraft Structures." At that time steel, as the material for important parts of main structural members, was giving place to the then new and stronger aluminium alloys, and I decided that the lecture should be on something of growing, and not diminishing, importance; therefore in a paper entitled “ Some Developments in Aircraft Construction ” (March 1934) stiffened sheeted structure in aluminium alloy was chosen as the theme of the subject. The paper was as up-to-date as possible, but it contained no pictures or descriptions of British aeroplane structure of that type because in this country no aeroplanes (except the odd one in which fabric had simply been replaced by aluminium alloy) designed basically in that way had been built.

Air Traffic Control is an all-embracing term and on occasion there is some doubt about its scope. For the present purpose it will be as defined within the internationally agreed principles set out in Annex 11 to the International Civil Aviation Convention. Here it is set out that the Air Traffic Control service is for:–

1. (i) Expediting and maintaining an orderly flow of air traffic.

2. (ii) Preventing collision between aircraft.

3. (iii) Providing advice and information useful for the sake of efficient conduct of flights.

4. (iv) Preventing collision on the manoeuvring area between aircraft and obstructions.

5. (v) Notifying the appropriate organisations regarding aircraft in need of search and rescue and to assist such organisations as required.

After two years research work in the Universities of this country and elsewhere, there is need for a comprehensive review of the present position on the suppression of aerodynamic noise from jet engines. This report outlines the fundamental understanding of the problem that has been achieved, the basic experimental work done, and the noise suppression techniques which have been suggested.

A study is made of measured noise levels on advanced types of engines and an analysis is made of reductions required and so far achieved with the proposed noise suppression devices. While the basic principles underlying noise formation, both in subsonic and supersonic jet streams are beginning to be understood, the noise reductions so far achieved are still insufficient and warrant an extended programme of research.

The report includes helicopter noise analyses with pressure and pulse jets, and touches on the problem of structural fatigue in the vicinity of a jet stream.

In an interesting Technical Note in the January 1953 Journal, Messrs. Dickinson and Hadley reported some results from tests made to check a proposed extension to the Royal Aeronautical Society Data Sheets on stresses and deflections in flat panels subjected to normal pressure. The test rig was originally too weak and did not provide the edge conditions which were assumed when calculating the curves of Data Sheet 02.09.02. This explains the discrepancy with regard to the deflections, but it is remarkable that the measured membrane stresses f3 were so low. It is a well-known fact that the membrane tension at the centre of a square plate with large deflections is not influenced very much by different edge conditions. This can be seen in Data Sheet 02.09.05 where the two extremes, free edges and edges held apart, are represented for a square plate with edges free to rotate. The membrane tension at the edge is, of course, much more sensitive for an edge displacement, but we suppose that f3, is the membrane stress at the centre of the plate (as in Data Sheet 02.09.05).

Frame analysis problems in general involve the determination of the values of three redundancies, which can become somewhat laborious. By applying the redundancies at the elastic centre of the frame the amount of work is much reduced and the solving of simultaneous equations is avoided. The method does not seem to be very widely used and it is considered that this may be due partly to the way in which the proof has usually been presented. The following proof is given in the hope that it may assist in clarifying the method.

It is often supposed that the flow of gas from a compressor is, or should be, stable if the pressure-flow characteristic has a negative slope. It is shown here that this is only true if the Mach number is zero, i.e. if the machine is pumping a liquid. As the Mach number is increased towards one, a third regime becomes more and more important, wherein disturbances give rise to damped oscillations. The flow in this regime is stable in the mathematical, but not in the physical sense, since disturbances can occur all the time.

Two conclusions can be drawn. First, although compressors with “flat” pressure-flow characteristics have a wide range of stable flow at low speeds, they are poor at high Mach numbers, where the flat part cannot be used. Next, the actual points on the characteristics at which the flow becomes unstable are not fixed, but depend to a large extent on the steadiness of the entry flow.