No one who has the honour to serve on the Council of this Society, and can therefore be tackled in person once in every month, can long avoid the additional but more alarming honour of being called upon to lecture. When I in my turn was brought to bay, I cast about for a suitable subject, but could not satisfy myself that any of the work in which I happen personally to be engaged had a sufficiently general appeal. I therefore decided to take advantage of my association with the Aerodynamics Department of the National Physical Laboratory, and to base my lecture on the work of other men. I want to make this clear at the outset, because I may omit in some instances to attribute credit where credit is due, and at all events it must be understood that the credit does not belong to me.

Ladies and Gentlemen, I feel that an introduction to our lecturer this afternoon is hardly necessary, as I am sure he is well known to most of you, but perhaps one or two may not be so well acquainted either with his background, or his work in rotating wing aircraft

Mr Pullin is the Managing Director and Chief Designer of the Cierva Autogiro Co Ltd, a Founder Memb2r of our Association, a Fellow of the Royal Aeronautical Society, and a Member of the Institute of Mechanical Engineers He has been actively engaged in the research and development of rotary wing aircraft since 1932, but his interest in aviation goes back to pre-1914 when he learnt to fly at Brooklands in the good old days He has been engaged in engineering for about 30 years, covering in this time, several of its different branches

For the past few years there has been some interest in aerofoils with blunt trailing edges but most work has been associated with the investigation of the base pressure and the pressure distribution on the aerofoil has received little attention. Nash proposed a method of calculating the pressure distribution on aerofoils with blunt trailing edges in the absence of a vortex street, that is with the vortex street suppressed by means of a splitter plate or base bleed. He assumed that the wake of the aerofoil could be taken into account in the calculation by specifying a pressure distribution along the wake and then applying thin aerofoil theory to the aerofoil and wake. This leads to a mixed boundary problem with the aerofoil shape and the wake pressure distribution specified and the calculation is laborious.

A simple model is presented for an aerofoil with a recirculating Prandtl-Batchelor region behind a spoiler. Using thin aerofoil theory the model is posed as a pair of coupled nonlinear singular integrodifferential equations for the shape of the separating streamline and the distribution of vorticity along the aerofoil. These equations are solved numerically and results are presented. In particular, some conclusions are drawn regarding the lift on such aerofoils.

The paper outlines the existing procedures employed in the field of defence procurement and mentions some new ones which may be used in the near future. It will serve as a reminder of the way in which major aircraft and weapon and equipment projects are conducted and will lay the foundations for what is hoped will be a fruitful discussion.

The CHAIRMAN, in opening the meeting, said that the paper, which Mr Stallabrass had come over from Canada to present, dealt with a very important subject in the helicopter field, having as a practical objective the eventual achievement of all-weather helicopter operation The National Research Council of Canada had been studying the problem of aircraft icing long before it was necessary to devote attention to the special problems of helicopter de-icing, no doubt the climate in that part of the world having had something to do with this

Mr Stallabrass had served in the Royal Air Force from 1941 to 1947 and had experience as a pilot with Coastal Command in anti-submarine operations Later, he took an honours degree at London University in electrical engineering and worked for a year on guided missiles with the General Electric Company In 1952 he went over to Canada, where he worked on various aspects of icing research at the low temperature laboratory of the National Research Council

The world of hearing is made up of two types of sound— on the one hand, that which provides communication, be it in the form of speech, music or the noise of a car or dog; on the other hand, a noise which interferes with that message, or a sound consisting of an unwanted message, intruding upon a person's thought processes or sleep. It is always difficult to separate these two functions, since one man's noise is another man's message, and this is particularly so for quiet noises heard at night or occurring sharply to frighten and alarm. It is for this reason that the law regarding noise has been less specific than in other fields and it is for this reason that seldom have any clearly defined limits been specified.

The beam on elastic supports is often considered as a beam on a continuous elastic medium. This method can be applied only to a large number of equally spaced supports having equal rigidities. The method proposed by the author, giving the solution in the form of rapidly converging series, is not bound by this restriction, and when applied to the problem of beams supported by cross-girders reduces it to a system of linear equations, their number being equal to the number of cross-girders, while the existing approximate method leads to the same number of simultaneous differential equations.

During the past decade, the theory of optimal control associated with linear multivariable systems having state and output equations of the respective forms

and

has been applied extensively to the design of controllers for a variety of aerospace systems. Such applications of this theory have been mainly concerned with the design of controllers that generate optimal control vectors, ẑ, which minimise performance indices of the form.

where Q and R are positive-definite matrices.

Sir George Cayley was a great man, many years in advance of his time and with a grasp of fundamentals which must be the envy of many people, even today. Consider the mental prowess of a man who in the technical environment of 170 years ago, where a 12 hp engine was as shown in Fig. 1, could make the statement that, “The whole problem is confined within these limits, namely, to make a surface support a given weight by the application of power to the resistance of air”; it is truly remarkable. It seems to me that the phrase I have extracted from that statement as a title to this lecture epitomises both the man and the subject.

What do we mean by reliability? Mathematically, it is the probability that a piece of equipment will be capable of working when called upon to do so for the time required and under the environment specified, and, if we know the mean time between failures and make certain assumptions about the randomness of the failures, we can derive expressions that will give numerical values of inherent reliability.

In layman's terms, we can say that it is the ability of a piece of equipment, whether it be a small component or a complete aircraft, to be ready to work and to continue to work in the environment for which it has been designed, for as long as the specification requires it to do so and to do this with the minimum amount of maintenance.