The 890th Lecture to be given before the Royal Aeronautical Society was held at the Institution of Mechanical Engineers, Storey's Gate, London, S.W.I, on 12th November 1953, and was presided over by Sir William Farren, C.B., M.B.E., M.A., F.R.S., F.R.Ae.S., President of the Society. Introducing the lecturer, Sir William said that Mr. Wimpenny had been with the de Havilland Company throughout his career in aviation and had been responsible for some years for the design and development of stability and control of the de Havilland aircraft, including the Comet, so that clearly he spoke with a wide knowledge of his subject.

The structural problems introduced by the kinetic heating of high speed aircraft require a radical extension of what has hitherto been regarded as the normal domain of structural theory. Aerodynamics, for example, cannot be regarded as a self-contained subject which merely provides basic data for the structural worker. Certain aspects of aerodynamic theory, particularly the mode of heat generation, have to be considered simultaneously with the structural problem. Thermodynamics and metallurgy are still more closely integrated with structural theory. The laws of heat transfer, and the variation of material properties with temperature, are both essential factors in the structural analysis.

The general recognition of the importance of vibration study, as a specialised branch of engineering science, is clearly reflected in the fact that each year sees the publication of a great number of papers on all aspects of vibration theory and practice. The theoretical papers most commonly describe new methods of analysis and calculation, and it is becoming increasingly difficult for the general engineer, who has neither the time nor the inclination to follow in great detail the development of all the specialised subjects, of which vibration study is only one, to retain in his mind a clear picture of the general strategy applicable to the attack on vibration problems, and to fit into this strategical scheme the tactical operations represented by the new methods.

The 887th Lecture to be given before the Royal Aeronautical Society was held at the Institution of Mechanical Engineers, Storey's Gate, London, S.W.I, on 29th October 1953, and was presided over by Sir William Farren, C.B., M.B.E., M.A., F.R.S., F.R.Ae.S., President of the Society. Sir William said that this was the first main lecture of the session. In one paragraph of his paper Mr. Mercer said that those who were specialists in fields of a highly specialised kind should get together with their friends in other branches of aeronautics, otherwise they might all go on in ignorance of what was being done by others; he hoped therefore, that there were a number of specialists present who would join in the discussion.

Introducing the Lecturer, Sir William said that he had known Mr. Mercer for many years; Mr. Mercer had joined the Blind Landing Experimental Unit at Martlesham Heath when it was formed and it was there that he had done the work described in the paper. The President said he had always felt that one of the things most needed for the real development of aviation was a means of landing in bad weather. He hoped that Mr. Mercer's paper was a contribution towards that end; it was concerned with one phase only of blind landing—approach—but he hoped there would be other papers on the subject. He now called on Mr. Mercer to give his paper.

In a previous paper (Aircraft Engineering, November and December, 1938) the writer gave an account of proposed methods of calculating the stresses in tapered girders of a special type. The beam was assumed to have a web of constant thickness which could be dealt with as a two-dimensional stress system, while the booms were assumed to be concentrated lines of material having no flexural rigidity.

It was this latter assumption which appeared to represent one of the main limitations of the theory, so an attempt has been made to remove this limitation; a solution has been found, for the case of tapering booms at any rate, which puts the theory at least on the same level of rigour as the well known theory for parallel beams.

In addition to the usual aerodynamic and structural problems the seaplane designer has a number of problems to solve which are associated with the behaviour of the seaplane on the water. The operation of a seaplane on the water is well known and in these days accepted as a matter of course. However, behind these apparently easy operations there lies a background of continued effort and development.