The 999th Lecture to be given before the Royal Aeronautical Society “ The Importance of Time in Aircraft Manufacture ” by Air Commodore F. R. Banks, C.B., O.B.E., F.R.Ae.S. was given on 17th October 1956 at the Institution of Mechanical Engineers, Great George St., London, S.W.I. Mr. E. T. Jones, C.B., O.B.E., F.R.Ae.S., President of the Society, was in the Chair. Opening the meeting, Mr. Jones said:—

This evening marked the opening of the Society's 1956-57 Lecture season in so far as the London district was concerned. Actually, two Main Lectures had already been given at Branches; the first at Derby and the second at Henlow and at both there was a large and appreciative audience. It was gratifying that these early Main Lectures at the Branches had been received so well. He mentioned this because out of nine Main Lectures this session four were planned to take place at Branches, and that was quite an innovation. It was, he thought in 1948 that Council thought it would be a good thing if a few of the Main Lectures each session were held at the Branches and, so to speak, take the Society now and again to the Branches. He was sure they would agree that that was a good thing to do. There might be some present from the Branches and he had no doubt there would be reciprocal response in the Branches' members coming to lectures in London.

Now it was his pleasant duty to introduce their Lecturer. Actually of course he did not require any introduction. Air Commodore Banks, as they well knew, was a Lecturer of some importance. He had lectured many times to this Society and, indeed, to other Societies in other countries. He was a Fellow of their Society, a Companion of the Bath, an Officer of the Order of the British Empire and, what was a little more unusual in their Lecturers, he was a Commander of the French Legion d'Honneur and a Commander of the United States Legion of Merit. He had a particular distinction in respect of the subject he was speaking on tonight. He started life as an engineer. He then became an aviation fuels specialist. Then he became Director-General of Engine Production in the Ministry of Aircraft Production, and later changed from Production to Development and became Director of Engine Development in the same Ministry. He then went back to his first love, fuels, and returned again for sixteen months to the post of Principal Director of Engine Research and Development at the Ministry of Supply, when at that point of time this Ministry was rather hard put to get the right man in the right job. He was now a Director of The Bristol Aeroplane Company and was also on the Boards of Bristol Aero Engines Ltd. and Bristol Aircraft Ltd.

This report presents an abbreviated summary of theoretical studies made by a group at the Research Laboratory of Electronics, Massachusetts Institute of Technology, under contract with the Air Navigation Development Board of the Department of Commerce. The details of the analysis and the results have been treated more comprehensively in two technical reports of the Research Laboratory of Electronics.

All of us who are intimately connected with aviation appreciate that the introduction of a new era of air transportation—the jet age—will not be accomplished without a tremendous effort in almost every field of the Industry.

There are current problems for which solutions are available but not implemented, current problems requiring new solutions, and new problems associated with the unique characteristics of the jet aeroplane.

There has been much discussion of late on the nature of the noise from aircraft travelling with velocities greater than that of sound. It is possible that these phenomena can largely be explained in terms of the Doppler effect. For a source of sound travelling with a velocity greater than that of sound relative to the observer, the Doppler effect takes a very interesting form. It is discussed mathematically in Ref. 1.