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.

The purpose of this paper is to review briefly some means of reducing the normal-pressure drag at transonic speeds of wings and wing-body combinations without lift. By transonic speeds is meant here not only the range of main stream Mach numbers around unity but, more generally, that speed range where a transonic type of flow around the body may exist. Thick non-lifting bodies as are considered here cause a displacement flow and it may be recalled that at least three different types of flow are involved: a subsonic, a transonic, and a supersonic type of flow, all of which are here assumed to have one attachment line along the leading edge and one separation line along the trailing edge. This excludes types of flow where separations occur elsewhere, such as shock-induced separations along some line within the wing chord.

In parallel with the work undertaken at the University of Southampton on the study of the noise from subsonic jets, a further investigation has been made into the noise from supersonic or choked jets. Whereas in the former case the noise is due to the turbulent velocity fluctuations and thus contains a wide spectrum of random frequencies, the latter case contains, in addition to this wide spectrum, noise caused by turbulence-shock wave inter-action.

Once the critical pressure ratio of a jet has been attained, i.e. that pressure ratio which produces sonic or supersonic flow in the jet pipe just before the orifice, the structure of the jet depends crucially upon the nozzle shape.

The solution of a set of m ordinary linear differential equations of the nth order having variable coefficients can be provided by the use of a set of m2 indicial admittances and the solution is derived from that given by the use of impulsive admittances. The indicial admittances are easily derived from the impulsive admittances and vice versa.

An “indicial admittance” is a function representing the response of a system to an applied “input” in the form of a “unit step function” and the concept is due to Heaviside. When the indicial admittance is known, the response to an input which varies with time in an arbitrary manner can easily be found. Similarly, the response can easily be found when the “impulsive admittance” is known, where this is the response to a unit instantaneous impulsive input.

The evaporation rate of a liquid spray in a turbulent gas stream is of interest in connection with direct contact heat transfer and combustion equipment. Any fundamental approach to this problem has usually dealt with single drops evaporating in an “infinite” atmosphere. The evaporation of sprays from actual atomisers is obviously a more complicated process and few attempts have been made to find in how far single drop data may be applied, or to measure the evaporation from a whole spray.

The main difficulties lie in devising a satisfactory method of measuring the evaporation rate. Selden and Spencer, injected the liquid into a bomb filled with hot gas under pressure and measured the decrease in pressure with time on a special indicator.

There are two types of shock loading to which aircraft components are subjected, namely: medium shock loads which can heavily damage equipment; and shocks of high impact, such as those imposed during crash landing, causing the equipment to be torn loose from its mounting, with danger of injury or even death to aircraft personnel.

An impact shock machine has been installed recently in a laboratory for studying this important problem. The machine is capable of providing calibrated shock tests up to a maximum peak acceleration of llg, and of simulating the shock loads normally experienced under everyday operating conditions. Apparatus being tested is mounted on a frame bolted rigidly to the table of the impact testing machine, which has been designed to take specimens up to a maximum weight of 400 lb., with maximum overall dimension equivalent to a cube of 30 inches side. A specimen under test is dropped from a maximum height of 5 ft., falling freely.

In the early stages of preliminary design, it is essential to have a method for the comparison of aircraft on an operating cost basis. The standard S.B.A.C. method is too lengthy and, in any case, demands a greater amount of data than is usually available in the early design stages.

The formulae presented in this note were evolved by the author some years ago and the general method was quoted in a paper entitled “The helicopter—has it a future?” which was read to the Belfast Branch in January 1955. (See Journal, November 1955.)