Mr. Haynes in his contribution to the Symposium, and also in previously published papers, has very adequately described the general development, advantages and characteristics of the maraging steels. However, as much of the information which he has given relates to the work done in the laboratories of International Nickel, and because we have only been able to find relatively little information available relating to production experience, we at Dowty Rotol set out to investigate the problems of steel making, forging, and resultant mechanical properties to be obtained under more normal production conditions. As landing gear manufacturers, our prime interest lies in the production of relatively large forgings of somewhat complex shape, and we were therefore particularly anxious to investigate first of all that our normal steel suppliers could produce material to the correct composition, that the material would forge as easily as conventional material, and that the subsequent forgings possessed adequate trans-verse properties, particularly insofar as ductility is concerned. In this latter connection, we had heard of certain difficulties encountered in the USA relating to inadequate ductility in large forgings, which they had concluded was related to the carbon and sulphur content of the steel: i.e. that it was essential to eliminate brittle intermetallic compounds such as titanium carbo-nitrides and titanium sulphides from the steel.

Inventors who work in secret, and whose vital creations never see the light of day until the world has passed them by, are mostly figures of romantic fiction. Most inventors take good care that their devices are brought to public notice, preferably after patents have been granted to them; and one of their main concerns in the 19th century was therefore the channels of communication open to them.

Sir George Cayley wrote, in 1837, that “the experiments that have been made, and the investigation which it (the subject) has undergone, lie almost unconnected in the periodical publications of the last thirty years; and hence, every new speculator on the possibility of steering balloons takes up the subject merely on his own view”.

Among my collection of aviation papers and souvenirs, a favourite item is the Art souvenir and programme of the 1909 Blackpool Meeting. There, as a young schoolboy, I saw for the first time an aeroplane flying in a strong, almost gale force, wind. Bleriot's successful Channel crossing and the great Aviation Week held at Rheims had stimulated organisation of the first aviation meetings to be held in England, at Blackpool and Doncaster. It was a great treat, and an exciting experience to be taken to this meeting by my father, to see the new heavier-than-air flying machines. When we arrived at the flying ground, it had turned out a wet morning, with a strong wind.

In terms of cost, BEA estimate this to be worth over £3 000 000 a year or, putting it another way, 7% of the revenue we receive has to pay for unreliability.

No specific allowance is made for the rectification of defects in the scheduling of aircraft during its turn-round time and to cover this we aim to schedule two stand-by Tridents, two Vanguards, one Comet and three Viscounts for their respective fleet sizes, so that if the snags are anything but minor, the stand-by aircraft take over while the defective one is rectified.

Unsuccessful attempts to obtain active service in the 1914-18 War led, in 1917, to my first serious job in aviation, in the D.O. at Handley Page, on the 0/400 and V 1500 bombers. As an eyewitness of the spectacular crash of the V prototype—just before my own first flight, on an 0400—I was sharply faced with the first essentials of air safety. Over the next 20 years, on design, strength, performance and stability investigations, flight-testing, etc. of many types of landplanes, flying-boats, autogyros and aero engines, where attainment of acceptable performance was the primary aim, the needs of safety were always much in my mind. Close involvement in various air accidents, near-drowning, frostbite, immersion in a glacial lake, mountaineering, etc., formed a valuable background to subsequent work on survival.

This paper defines Internal Aerodynamics and via similarity generalises the concept to include internal flows of fluids other than air.

Variable area ducted flows are considered distinguishing one, two and three-dimensional treatments and the difference between accelerating and diffusing flows is stressed. The design of variable area ducts using ideal inviscid fluid theory, ideal fluid plus boundary layer theory and inviscid but rotational fluid theory is discussed. The success and limitations of these theories with reference to contractions and diffusers is surveyed The particular difficulty of a diffusing flow as affected by entry velocity profile and turbulence is considered.

From the problem of simulating entry velocity profiles arises the need for the generation of required velocity profiles in duct systems. Examples of methods of generation and difficulties are discussed.

Next follows a series of examples of internal flow problems.

The radial flow diffuser is considered as an example of the interaction of viscous and inertia effects. An approximate theoretical treatment is given and the real flow, with the occurrence of reverse transition, is described.

The deliberate production of a reversed flow regime for flame stabilisation is described with reference to a marine boiler register Aspects of pressure drop and stability are considered.

Secondary flow is defined and the origin in the distortion of the upstream vorticity field is described. The case of a strut wall junction is given with details of the downstream flow where the secondary flow produces apparent multiple wakes from a single strut.

Air flow excited vibration of heat exchanger tubes is described. Different mechanisms resulting in transverse or streamwise oscillations and the coupled modes of tube rows are discussed.

Finally the paper emphasises the large available body of information in internal aerodynamics, largely of aeronautical origin, and considers its usefulness and limitations for the problems discussed.

I am going to restrict myself to consideration of those problems which arise from the natural wind, and I am going to begin—and perhaps also to continue—with what may be, to paraphrase one of our Chairman’s expressions, some offensively simple . considerations. I do this because, in our studies of industrial aerodynamics, we are increasingly applying the sophisticated techniques developed from years of aircraft aerodynamics; and there is always a danger that, unless we go back to fundamentals, we may invoke a theorem or technique from aircraft practice which is inappropriate for an industrial problem. First of all, therefore, I shall go back to square one.

Just after the turn of the century, after many struggles, the heavier-than-air flying machine first rose from the earth, part of the success being due to the development of the comparatively light internal combustion engine. The materials of the airframe being mainly wood, including bamboo, and a few pieces of mild steel plate.

For a few years the materials of construction altered only a little and the knowledge of those materials and their behaviour was limited and confined to that which had been established during the course of mechanical engineering.

The mechanical engineers had been able to include fairly substantial factors of safety in their calculations which covered many variations and possible errors in materials, loads and workmanship and also—probably unknowingly —problems which could arise from fatigue.

The present re-look at compressible flow graphs arose during extensive testing of jet blowing models in low speed tunnels. In these tests, it is often necessary to calculate such quantities as jet thrusts, mass flow rates and velocities assuming isentropic expansion to the tunnel static pressure from the measured values of the stagnation pressure and temperature. These jet flows are usually compressible but subsonic and, in order to make these calculations, use has to be made either of Bernoulli's compressible flow equation or, alternatively, the extensive compressible flow graphs that are now available.

I joined the scientific staff at Farnborough in the summer of 1915, in a very minor capacity under R. McKinnon Wood, who was in charge of the Wind Channel and Whirling Arm sections.

Now looking back to a time 50 years ago, the following names come instantly to mind: Glauert, Grinstead, Hoare, B. M. Jones, G. I. Taylor, and McKinnon Wood, and of course Miss Gilford, who sat behind glass in the office of the head of B.A. Department, always busy and helpful.

For some time Glauert and I lodged in the same house in Church Circle, and if he joined in a conversation his remarks were always worth listening to, even if he was not familiar with the subject. His comment too was always stimulating, and in spite of his brilliant intellect, he could explain in simple terms something that one had had difficulty in following.

The past few years have evidenced a remarkable increase in the use of helicopters in agriculture. There are any number of individual reasons for this: helicopters are more plentiful, for example, but the primary reason is one of simple economics combined with a capability to meet new demands. The demands have been generated by the overwhelming population explosion. Sometimes hard to imagine and even more difficult to cope with, but the facts remain that:

1. 1. 25 % of all the people that ever existed on earth are living on it today,

2. 2. The world population increases at a rate of 5400 people every hour; and

3. 3. This staggering number of people will double again within the next 40 years.

The origin of the Society's Stressed Skin Data Sheets was certainly my own paper, R and M No. 1553; it embarrasses me not at all to put it so. In 1930 the Structures Sub-committee of the ARC asked for a summary of the present state of knowledge regarding sheet metal construction, and the chairman, (Sir) William Farren, directed me as secretary to prepare a draft. I did so—the draft was discussed by the Sub-committee, revised and amended and finally in 1933 published over my name. To me the paper was a chore, albeit a welcome one, and all I myself really got out of it in the end was the realisation that I could do with a little more Anglo-Saxon: “What we know about …” would now be my title.

By integration of the pressure distributions of Part I of this paper values for the normal force and centre of pressure position (or moment) are obtained herein for the three effects; interference on the body, interference on the wing, and overall body-wing. In order to estimate overall body-wing characteristics the net wing alone and body alone normal forces and centre of pressure positions are also required, methods of estimating these quantities are readily available in the literature (e.g. ref. 2). The present method gives an estimate of overall body-wing normal force which is usually accurate to within 10 per cent and an estimate tor overall cp position which is usually accurate to half a calibre. Comparison of the present method with the method of Nielsen, Kaatari and Pitts shows that there is little to choose between the two so tar as overall estimates are concerned; the present method has the advantage of an associated pressure field.

The intention in presenting this paper is to outline the main trends in recent alloy development and to indicate the current state of the art as far as the user is concerned, particularly on the behaviour of the new products in the problem areas so designated by the engineering metallurgists and materials specialists in the industry.

In reviewing recent alloy development it is convenient to identify two main lines in terms of the metallurgical structures involved, since these tend to define the more appropriate areas for design interest.

The production of required velocity profiles in a duct or wind tunnel is a necessary part of much research aimed at understanding fluid behaviour. Perhaps the most obvious application is the simulation of wind gradients for the study of wind effects on structures, but equally important is the study of diffuser and duct behaviour when subjected to a variety of known and convenient velocity profiles. Furthermore, the effects of the variation in turbulence characteristics within a range of identical velocity profiles produced by different methods are not clearly understood.

An immediate requirement within the aerospace industry appears to be the development of a practical system for the evaluation and control of complex projects. No amount of qualitative evaluation will present management with the answer to the problem of making complex decisions. The Generalised System for Project Control and Evaluation presents an approach towards evaluation of quantitative indices of “value” and “cost effectiveness” that can be optimised, possibly by operational research methods, to produce information that can be used by management in the making of realistic decisions.

No one present can be complacent about the standard of aircraft reliability and his contribution to it. This applies to all concerned, to those responsible for the requirement, those responsible for the specification, all those concerned in the design and manufacture of airframes, engines, equipments and components and finally, the user and his servicing organisation. Significant improvement in reliability will result only from a contribution by everyone involved. It seems that in recent years the attention given to reliability has been out of balance with that given to all the other desired qualities. Those responsible for the requirement must be prepared to sacrifice performance or perhaps time, or variety, or pay more, for a gain in reliability; they must be given some indication of the rate of exchange to help them in this judgment. The designer must have this problem of balance and compromise clearly in mind and must play his part in clarifying the issue. Generally we have striven after the best performance possible and because weapons systems take so long to develop this tendency is probably more pronounced. But if you cast your minds back, systems which were regarded as being designed somewhat conservatively have often, overall, given the best service. Thus my first point is that there must be a conscious compromise between performance and reliability, associated of course with the time-scale and cost of the project. The designer must give equal consideration to reliability and to maintainability (the two go together of course) as to performance and other qualities.