When designing an aircraft structure, the structural engineer has to achieve given standards of airworthiness in respect of strength, stiffness and fatigue life while ensuring that the final weight is as low as possible to give operating economy or flexibility. At the same time he must ensure that a minimum of design effort is used, manufacture is as easy as possible, the serviceability is good, the aerodynamic shape is retained, aeroelastic effects minimised and so on. The structural engineer of today has to ensure that the fatigue life is satisfactory, together with the older concept of purely static strength, and if he has resorted to the use of fail safe principles he has to establish those characteristics as well.

A brief survey is made of the way the flow develops about wings with leading edges swept at about 50° as the stream Mach number rises from a subsonic to a supersonic value. The shock pattern which occurs may be complex. Three aspects of the wing flow are discussed in more detail, including the possible conditions for shock-induced separation of the surface boundary layer. The effect of the changing flow pattern on the overall wing lift, drag and pitching moment is commented upon.

The 48th Wilbur Wright Memorial Lecture, “Mathematics and Aeronautics” was given by Mr. M. J. Lighthill, F.R.S., before a large and distinguished audience at the Institution of Mechanical Engineers, 1 Birdcage Walk, on 19th May 1960. Dr. E. S. Moult, C.B.E., B.Sc, F.R.Ae.S., M.I.Mech.E., President of the Society, presided.

As has become the custom, before the lecture was delivered the President presented the awards made by the Council for 1960 for outstanding contributions to aeronautics. In the unavoidable absence of the Secretary he was assisted by Miss E. C. Pike, M.A., A.F.R.Ae.S., Secretary of the Medals and Awards Committee and Editor of The Aeronautical Quarterly. The list of the awards presented on this occasion was published in the June 1960 Journal—(p. XXXII).

The President, introducing the lecturer, reminded the audience that the Wilbur Wright Lecture commemorated the first manned, powered controlled flight by Wilbur Wright at Kitty Hawk, North Carolina on 17th December 1903. The first Wilbur Wright Memorial Lecture was held in 1913 and they had been held each year ever since, through two World Wars; in itself a wonderful record. The custom had been, and would continue to be, to have alternately a lecturer from the United Kingdom and a lecturer from the United States; last year the lecture had been by Mr. McCarthy of Chance Vought and next year again it would be by an American.

The Wilbur Wright Lectures had been a most distinguished series by distinguished lecturers, and he was sure that the lecture that night would be in keeping. His pleasant duty was to introduce Professor Lighthill—or as they had to call him Mr. Lighthill now that he was Director of the Royal Aircraft Establishment, which was an even greater distinction. Mr. Lighthill was the youngest Director that the R.A.E. had ever had—that alone was a tribute to Mr. Lighthill's ability and his high standing in the profession. Before joining the Royal Aircraft Establishment Mr. Lighthill was Professor of Applied Mathematics at Manchester University, and for a time, after leaving Cambridge, had worked at the National Physical Laboratory where he applied the mathematics of Cambridge to the problems of aerodynamics. His lecture was on “Mathematics and Aeronautics” he would ask Mr. Lighthill to deliver the 48th Wilbur Wright Memorial Lecture.

The 1,158th lecture to be given before the Society, “Engines for Supersonic Air Liners” by Dr. R. R. Jamison, B.Sc., F.R.Ae.S., A.R.I.C. and Mr. R. J. Lane, Diploma of Graduate Studies (Birmingham), G.I.Mech.E., of Bristol Siddeley Engines Ltd., was given on 24th March 1960, at the Institution of Mechanical Engineers, 1 Birdcage Walk, London, S.W.I. The Chair was taken by Air Commodore F. R. Banks, C.B., O.B.E., C.G.I.A., F.R.Ae.S., Hon.F.I.A.S., M.I.Mech.E., M.Inst.Pet., Vice-President of the Society.

Introducing the lecturers, Air Commodore Banks said that after receiving his education at the South African College and the University of Cape Town, Dr. Jamison joined Rolls-Royce in 1937 and had remained with that Company until 1950, when he joined Bristol Aero-Engines Ltd.–now Bristol Siddeley Engines Ltd. He was Assistant Chief Engineer and Head of the Ram-jet Department and since 1950 had been working on ram-jet development. He and his team were regarded as the specialists in this country–and probably in Europe– on controllable ram-jets. Mr. Lane, joint author with Dr. Jamison of the lecture, had graduated from the University of Birmingham and had served his apprenticeship at the Royal Ordnance Factory before joining Bristols. He was now working on ram-jet dynamics and gas-dynamics of ram-jets with Bristol Siddeley Engines Ltd.

The paper gives a précis account of studies made at the Rocket Propulsion Establishment of the Ministry of Aviation to determine the relationship between the specific weight and thrust of a liquid bi-propellent rocket engine.

Although the need for a better understanding of basic phenomena is established, the conclusion is reached that, within the selected premises, the minimum specific weight is achieved at a thrust level near 50,000 lb. The difference in specific weight between engines of 200,000 lb. thrust and 50,000 lb. thrust is only about 10 per cent and this is shown to be equivalent to only one per cent in propellent specific impulse. Although small, it is considered significant that a minimum has been established and this fact is used as an argument to justify the use of clusters of engines (generally four) to provide levels of thrust greater than 100,000 lb.

The object of this paper is to set down an overall picture of the practical aspects of compressor blade vibration. In doing so it is inevitable that a certain content is effectively a repeat of other people's contributions to the subject. The authors make no apology for this and offer the paper as a "state of the art" as practised at Bristol Siddeley Engines Ltd. In bringing together the many relevant issues of this problem, it is hoped that a useful presentation is obtained.

There is little hesitation in indicating the most obvious and important practical aspect of blade vibration as that of the inherent danger of blade failure and it is known that the axial flow compressor is susceptible to complete failure caused by the fatigue of one blade.

The multi-stage axial flow compressor is a highly complex aerodynamic machine with, its early and late stages required to operate over wide ranges of incidence and Mach number conditions. To some extent, of course, use of variable geometry can reduce this to less taxing proportions. The aerodynamic environment of front stages has broad boundaries somewhat wider than those relating to rear stages, while middle blade rows generally operate under sensibly constant conditions. This diminishing “severity” of operation, front, rear to middle stage blading is not unrelated to the incidence of blade vibration problems which shows a similar pattern.