The wind tunnel has been the main instrument for experimental research in aeronautics since the turn of the century and its history is as brief as powered flight itself. It has always played a leading rdle in aeronautics right from the time of the Wright Brothers to the present day.

The early form of wind tunnels as developed at the National Physical Laboratory and other research establishments have been replaced over the years by larger and more elaborate facilities, each having a particular speed range and specific role in aeronautical research and development. Modern wind tunnels having continuous operation of the type installed at the Royal Aircraft Establishment involve powers of up to 100 000 h.p. and cost in the neighbourhood of £10 000 000. In spite of this cost it is a sobering thought that, if anything, the overall cost of each data point is less today than it was in the early days of aeronautics. Such tunnels are highly complex instruments for research and development and although they play a rôle similar in many respects to that of a computer, they have the advantage of always dealing with a real fluid. Indeed no known computer could cope with the range of problems that can be solved in a wind tunnel, ranging from such complex problems as the structure of turbulent flow to the pressures in separated flow regimes, to quote just two examples. This fact must always be kept in perspective when arguments are presented for more and more work on digital computers to solve basic fluid motion problems. Of course we cannot overlook the problems of interpretation of wind tunnel data and the difficulties encountered in extrapolating these data to flight conditions.

The development of theories for such problems together with answers is of ever increasing importance, especially as the problems in aeronautics are becoming more and more complex. These solutions have the important function not only of high-lighting certain aspects of the flow, but of pin-pointing the important parameters in a problem together with providing better than order of magnitude results. However, theories must be based on physical facts and these can only be determined in the final analysis from experiments.

The wind tunnel has three highly significant roles in modern aeronautics:

• (i) Experimental research as a forerunner to future theoretical research.

• (ii) Experimental research as a confirmation and extension of theory.

• (iii) Current research and development work on a given aircraft.

The current trend in bringing strong theoretical and experimental groups together, plus the employment of rapid measurement techniques in wind tunnels, promises the greatest possible productive utilisation of these highly important and expensive facilities. In most cases today they are playing a strong, if not the leading, role in aeronautical development.

Up to the present most of the methods used to calculate the flow over delta wings with leading edge separations have been based on slender wing theory. In this paper one of the simplest of these methods is carried over to linear theory and the overall lift calculated. In general the results are in agreement with experiment, in particular both show a fall in nonlinear lift as the leading edges of the wing approach the free stream Mach angles. The discrepancies which exist appear to arise mainly from the use of linear theory rather than from the mathematical model introduced to treat the separated flow.

Before I attempt to describe the various missiles which we have developed, I feel it useful to give a brief review of the evolution with time of our technical group, of the position of this group in France and finally of the criteria which guided its choice of a working programme.

Our technical team was formed in 1946 at the Arsenal de 1'Aéronautique, a government establishment. Its staff, at that time, comprised some ten engineers and specialists. In 1953, the Arsenal de 1'Aéronautique was turned into a company, the SFECMAS, which eventually merged with Nord-Aviation in 1955. The growth in manpower and facilities of the Nord missile group went on steadily during that entire period. The present staff amounts to some 900 engineers and specialists, who are employed only in laboratories, design, research and test facilities. This does not include the production side, which is dispersed among four plants outside the Paris Area.

I am honoured to have been invited to give this Third Cierva Memorial Lecture on a subject which has a general application to all forms of aircraft, and which is central to any consideration of the future of the helicopter.

Reliability is a problem, the extent and urgency of which can only be appreciated fully and at first hand by the operator of a large fleet of aircraft, but most of the discussions and documents which have helped to lay the basis for this paper are not for general publication. I believe that this has helped me to concentrate on the essentials of the problem, but there is a danger that the simple arguments on which the paper is based may not carry the emphasis needed to convey to my colleagues the critical attitude of the operators.

The A. & A.E.E. has been associated with rotorcraft in this country almost from their earliest days. For example, the records show that a C30A Autogiro was evaluated at Martlesham Heath in 1935. After the outbreak of war responsibility for development work in the rotary wing field was assumed by the Airborne Forces Establishment (later the Airborne Forces Experimental Establishment) and the accounts of such developments as the Rotachute and the airborne jeep have since become well known. In 1945 the A.F.E.E. was declared to be the official testing establishment for prototype helicopters and this responsibility has remained until the present time. The A.F.E.E. was merged in 1951 with the A. & A.E.E., becoming the Airborne and Helicopter Division of the latter Establishment.

The Minister of Aviation has expressed his interest in the work of the Air Law Group of the Royal Aeronautical Society, and has offered his best wishes for its success. One of the valuable things about the Group is that it will provide a forum where problems of air law can be discussed, quite unofficially, by those responsible for advising the manufacturers, operators and insurers of aircraft, by those who act for travellers, and shippers by air, and by those whose duty it is to advise the Government on matters of civil aviation law. All this under the watchful eye of technical experts, who will ensure that legal doctrine does not stray too far from the realities of actual flying.

My Talk will be Brief because Mr. Kean has covered the field extensively and extremely well.

What is Interchange? Mr. Kean indicated that it is not a very satisfactory description of what takes place because it is not a word which describes it accurately, and I think a good deal of confusion about interchange exists in the minds of many laymen because, unlike most air transport words which had their roots in surface transport, interchange so far as I know is peculiar to air transport; hence people are apt to think that it is something special, and that special rules must apply to it. In fact I suggest that it is nothing of the kind; all it is is a certain kind of charter, and the same rules apply to interchange of aircraft as to any other kind of charter, and the reason that it has been singled out as a special problem for lawyers is that its characteristics make it extremely difficult to work satisfactorily, internationally particularly, if the normal rules are applied.

This investigation has been concerned with heat transfer between a jet and the inside surface of a circular cylinder whose axis was normal to the jet axis. Such a jet system could be used to direct cold air on to the inside surface of a sheet metal nozzle guide vane in a gas turbine engine. As will be seen later high rates of heat transfer can be obtained in the vicinity of the point of impingement, so that this method of cooling could be particularly valuable for reducing the temperature of a “hot spot.”

For uniform-thickness, solid circular plates made of isotropic elastic material and elastically restrained at the edge, expressions are derived for the optimum support stiffness to minimise the following quantities:

1. 1. The largest effective stress based on several different strength theories.

2. 2. The largest effective stress per unit of maximum deflection or per unit volume displaced.

A Matrix Eigenvalue Calculation is rich in information content but expensive in computer time. This is why, in a typical vibration problem, there are many more elements than masses, or rather, many more elementary deflections than degrees of freedom for vibrations.

Mr. Wilkinson's paper (July 1963 Journal, pp. 421-6) will doubtless be universally applauded by airline management. One can only hope that it receives equal attention from those responsible for the education of Graduate Engineers.

His point about economic training is basic. It is extraordinary how, as professions evolve, certain fundamentals appear to be lost. From the earliest days of Engineering, an Engineer was denned at “a man who could do for a penny what any fool can do for twopence.” I think if the point were raised with most Engineers they would all admit that economy is at the very root of the profession. Nevertheless, how true Mr. Wilkinson is when he points how that Engineers receive little or no formal economic training in their basic education.

Recently some data from tests done on a cambered plate have been published. The shape of metal plate aerofoil tested matched that taken up by a flexible two-dimensional sail. The most striking result in the rneasurements was the waviness present near the leading edge in the upper surface pressure distribution. To find the theoretical conditions under which such a waviness would occur a parabolic skeleton aerofoil was investigated, as this shape differed little from the actual aerofoil tested.