The purpose of this paper is to outline the “operational angle” of the hijacking problem and of the measures which might be taken to combat it.

Before considering what can be done on the aircraft itself to prevent or deter the hijacker from achieving his or her objective, I think it important to first review the likely circumstances of a hijack incident. By this I hope to ensure that my conclusions are seen against an essentially practical background.

Aeroplanes are often noisy, and sometimes smelly. Some of them also produce smoke. The purpose of this paper is to attempt an assessment of these and other forms of environmental pollution, also to consider the engineering and administrative measures which are being taken to control them. But before embarking on the subject one must try to put the matter in perspective. As I see it, the threat to the environment does not just come from aeroplanes, transport systems, factories or advancing technology. It comes from man.

Under the Civil Aviation Act there is a responsibility on the Airways Corporations to establish machinery for the determination of terms and conditions of employment and consultation with the staff they employ. There is, equally, a responsibility upon the Boards of the Corporations to recognise those unions who are appropriate to the grades of staff they employ.

The machinery, which was created in 1949, was based on the concept of Whitleyism but its application had to be rather wider than was the case in other industries because:

• (i) Civil aviation was in its infancy at the time

• (ii) The formidable task of bringing together a wide variety of skills

• (iii) The problems of adjusting to the varying practices and philosophies of unions catering for a wide variety of occupational groups.

This invitation to lecture to the Swindon Branch of the Society coincided with a period of crisis and change in the air transport industry where events stemming from growth, new technology, commercial challenge and political action were bringing about unprecedented ferment. Admittedly it could be said that the manufacturing industry has known this condition continuously for 20 years. But whereas the manufacturing industry has run into problems arising from retrenchment in military procurement, there is no sign that commercial air transport will do other in the long term than continue to expand. The main question is, what is the most beneficial nature of the expansion? A correct analysis of the present situation is important to the transport industry and also to the design and manufacturing organisations that are interested in building aircraft to meet the needs of the expansion ahead.

One of the great challenges of our time lies in the exploration of space. Part of this challenge has already been fulfilled but, up to this date, the transport of men and materials has been accomplished by means of expendable booster systems. In order to meet this challenge effectively, a new, fully reusable transportation system has been conceived which will be dramatically lower in overall cost than present-day launch systems. The proposed space shuttle is a fully reusable spacecraft consisting of a booster and an orbiter. A key factor in the design of the space shuttle is the selection and development of materials. Many current materials which have been widely and successfully used in space vehicles were developed for the most part with only a single short-time use requirement. The reusable, long-life requirements of the shuttle vehicle necessitates re-evaluation of the suitability of existing materials for this distinctly more demanding task for materials.

In the first Henry Tizard Memorial Lecture presentee here at Boscombe Down on the 28th October 1964, Professor R. V. Jones gave a masterly survey of the life and times of Sir Henry, as one who knew him well and it will be no part of my plan to retrace the story of this great man tonight.

While re-reading Jones’ paper I was reminded of the men of stature who were around in the aviation business in the years immediately before the Second World War. It was one of Henry Tizard's great tasks to harness these giants at a time when this country led the world in scientific research.

I, personally, had little to do with Tizard as in those days my job was to carry the bags for those who had the message to convey. This in no way detracts from my admiration of him as a quite outstanding person and a rare example of a real scientist who understood the practical problems associated with the interpretation of new ideas.

It is a great honour for me to be asked to give this, the Sixth Henry Tizard Memorial Lecture.

There is little published work on the flow past a sphere. Some experiments were carried out in the 1930s (see Fage), and other measurements have been made more recently (Cometta and Kendall). Much of the work has been restricted to flow visualisation and to measurements of drag and surface pressure distribution. Very few measurements have been made in the near wake.

In the present paper, measurements of vortex shedding frequency, wake dimensions and static pressure up to three diameters downstream are reported. The experiments were carried out in the Aerodynamics Laboratory of the Cambridge University Engineering Department, under the supervision of Professor W. A. Mair.

When one attempts to define “advances in helicopter avionics” it is possible to do one of two things:

• (a) either describe in some depth the development of one particular aspect of helicopter avionics, or

• (b) illustrate the broader impact of avionics on the increased use of helicopters in general.

In the present context the latter appears to be the more important because otherwise it is possible to give the misleading impression that helicopter avionics is a limited or narrow field, as it was in the past, whereas it is very wide and covers the whole spectrum of helicopter operations. The importance of avionics can hardly be over emphasised because in many ways avionics transforms the basic helicopter attributes of vertical flight and flexibility, and the continued development of helicopter avionics will be inevitable. It will also be inevitable because, in order to survive, our forces must continually improve their operational capabilities and avionics developments can allow them to do so. Now the most rapid advances in helicopter avionics may be achieved by adapting fixedwing aircraft technology although there are situations where entirely new techniques are called for. In any event the primary task is one of defining and tailoring equipment to the helicopter and its environment.

A favourite device of lecturers is to take a key word in the title of their speech and quote its definition from the pages of Webster's dictionary. Even though this may be mildly insulting to the audience—especially if the word being defined is something simple like “aviation”—it immediately gets the listeners onto the same track with the speaker. If nothing else, it proves the speaker at least knows how to spellthe key word in his speech and establishes his credentials as an expert in the field being discussed.

I would like to show you how informed I am by starting with a Webster's dictionary definition of “general aviation”, the key element in my speech title. Unfortunately, I cannot find it in my dictionary, and I doubt if you can find it in your Oxford dictionary. In the eyes of the lexicographers, “general aviation” simply does not exist. But you and I know it doesexist, and I would still like to start with a definition of it.

Eight years ago, Dr. S. G. Hooker and M. Michel Garnier gave the 17th Louis Blériot Lecture on the same subject under the title “Power for Supersonic Flight”. Between then and now the airlines and the manufacturers have jointly evolved the new practices of health monitoring and modular maintenance, and have also made significant advances in both the basic safety of the design and the safety-monitoring of the functioning engine. More important still, the operators and manufacturers have become fully conscious of, and determined to respond constructively to, the growing public pressure to reduce pollution and technological nuisances of all kinds. Within the same eight years a complete new generation of civil engines, the large high bypass ratio turbofan, has been conceived, developed and has begun to operate in airline service. It incorporates many of the new concepts mentioned above, as well as reflecting the general progress in technology that has taken place in that time.

May I thank the Society for the immense compliment it has paid me tonight by the award of the Society's Gold Medal. Earlier this year I was prevailed upon by Council to prepare the Wright Brothers Lecture. This is an occupational hazard of the Director, RAE, and has led to a situation—unique in my experience—in which the Society has presented the Medal and then within a few minutes asked the recipient to stand up and earn it. I am not at all optimistic about the outcome—but will do my best.

It is suggested that those wishing to familiarise themselves with the general history of Pitcher's work consult “Aviation” by C. H. Gibbs-Smith, HMSO, 1970, pages 85-90, and items 1 and 2 in the references at the end of this paper, although it should be remembered that this paper amends some of the information contained in these sources.

When dealing with famous men in history, perhaps one of the most persistent and difficult questions is that of their relative importance. It is very easy, in a bout of enthusiasm or contempt, to over- or underestimate the influence that a person may have had upon his contemporaries. This applies no less in aeronautics than elsewhere. The example of Percy Sinclair Pilcher (Fig. 1), the British gliding pioneer, is a case in point.

Any assessment of industrial relations must start with consideration of the character of the industry in question. It would be, for example, impossible to understand the behaviour of the modern miner without some knowledge of the history of the coal industry. Aviation has only a brief history. It nevertheless has a flavour of its own.

Three distinctive features are of note. To the outsider it is clear that the aviation industry brings with it the sort of challenge which appeals to the enterprising and the romantic. It is therefore no surprise that the industry has more than its fair share of strong character. There exists an independence of outlook on both sides of the industry which is not always easy to control within the normal industrial relations framework.

The object of this paper is to assess the efficacy of various measures, legal and physical, for the prevention of hijacking. I limit myself to examining the inherent limit-ations of different measures; and I propose to elaborate certain proposals, already made, for closing the ring. First, it is desirable to see what conclusions can be drawn from past events.

Reports from the airlines on hijacking incidents, during a period of three years from July 1968 to August 1971, have been recorded by IATA. Summaries of these reports have been made available to us, by courtesy of the Director General, through Sir William Hildred. I base my analysis in Tables A to D (see Appendix) on these records, for they are the only source of information available on the course of events and the consequences of each incident.

Although the concepts of “efficiency” or “coefficient of performance” are useful in relating the output to input energies of a system, they do not give any indication of the manner in which this input energy varies within the system.

This shortcoming may be overcome by using “energy flow diagrams” which have the great advantage of providing a pictorial, yet mathematically accurate, representation of the energy balance of the system, from which an overall appreciation of the energy variations can be obtained at a glance.

Involvement with the development of an aircraft engine can create deep mental scars. There seems to be an almost infinite variety of ways to encourage failure when considered in detail, and at the same time, there is no rule that will ensure success, except “Don't make any mistakes!”, a rather absurd bit of guidance. There is a small number of basic resources necessary for success, but only proper application of these resources can permit success. The basic resources are money, manpower, facilities, and knowledge. This paper provides, on the basis of one man's scar tissue, some guidance in creating an environment to encourage success. This introduction defines the general size and importance of the problem and the resources applied to the paper. The problems of organisation are outlined, followed by a definition of the game rules. The problems line people must overcome are discussed, followed by what to expect and where to inspect for problems. The paper ends with a suggested approach to the technical portion of the problem.

Smoothing screens are frequently used in wind tunnels and other ducts to minimise irregularities in velocity profiles and reduce turbulence.

There is an optimum value for the screen pressure drop coefficient which, for wire gauzes, corresponds to an open area ratio less than 0·5 if only one screen is used. However, screens with open area ratios of about 0·5 or lower, produce lateral non-uniformities in the downstream flow due to jet coalescence. To avoid coalescence, two or more relatively open screens may be used in succession, either so close as to behave more or less as a single screen or more spaced out with each screen operating independently. It is the latter situation which is considered in detail in this note.

Because of inevitable manufacturing tolerances there will always be errors in the characteristic screen parameters, which will make the screen impose its own irregularities on the downstream flow.

It is a great privilege for me to give the Twelfth Cierva Memorial Lecture. The title, which was suggested by the Society, might imply a mere recitation of past deeds. This would hardly be a fitting tribute to a great inventor like Cierva. Such men are usually impatient with the past and eager to explore the future. Accordingly I will deal with Bell's history as briefly as possible, and then discuss some aspects of helicopter rotor systems which have recently come to light.