This paper presents the twenty or more principal problems encountered in the designing of aeroplanes for passenger service at altitudes of about 20,000 to 30,000 feet, together with a discussion of the recent attempts made in the United States to solve these problems. Particular attention is given tothe design features of pressure cabins for maintaining low altitude air pressure at high altitudes.

The author wishes to express his appreciation of the honour that has been paid him in being requested to present a paper before the Royal Aeronautical Society. Permission has been given by the Air Ministry for the publication of the paper, but the author is alone responsible for the views expressed.

The growing demand for aerodynamically advantageous forms, for smooth surfaces, and last but not least for a better ratio of useful cross section to total cross section of fuselages lead to an increasing application of monocoque structures in aircraft construction. Unlike ordinary beams the behaviour of such thin walled structures under loads and their ultimate failure is influenced a great deal by instability phenomena. In the present paper these problems are dealt with in some detail for the case of pure bending.

The problem of landing an aeroplane under conditions of low visibility hasbeen a subject for speculation for the last twenty years, but it is only withinthe last ten years that it has been given any serious practical attention. Thispractical attention has been forced by the necessity for aircraft to maintainschedule regardless of weather conditions in competition with other forms oftransport.

Although certain schemes involving radio were amongst the earliest proposalsfor a solution of the problem, the first practical work appears to have beenconcerned with methods of a more mechanical or optical nature, including aproposal to deposit the fog by high tension discharge.

To the practical designer the cumulative knowledge on airscrews seems at present to be in an unsatisfactory state of disorder. He wants to get reasonably accurate estimates reasonably quickly, without taking the time to become a specialist.

Several airscrew theories exist, but they either give wrong answers or take too long to work out, or both.

The great mass of test data that have been accumulated is so confused in a tangle of variables that the practical designer is often forced to select a test report almost at random and use it as if it applied to his particular problem; usually it does not and the calculation is seriously in error.

The present study attempts to clarify airscrew practical knowledge by coordinating data in a form suitable for use in performance calculations. It embraces the whole body of test data, but places particular reliance upon large scale wind tunnel results.

The arrangement of the analysis is such as to permit quick estimates to be made, the degree of accuracy obtained being a function of the amount of time available to the calculator. It is also designed to be as foolproof as possible so that it may be readily applied by inexperienced calculators.

It is especially adapted to calculations of the performance of aluminium alloy variable pitch airscrews.

One of the points brought out in the paper is the need for more data on certain subjects. They are specifically designated, and suggestions are made for carrying out research.

For many years there have been used in aircraft construction aluminium alloys to a steadily increasing extent, and particularly alloys of Al.-Cu.-, Mg. and Al.-Cu. capable of being improved by heat treatment. Among the different methods known for permanent connection of structural parts, the rivet is still to-day the most reliable and safest connecting element. According to the special quality of this light metal group, due to their natural material characteristics and owing to the fact that in most cases the connections of aircraft structural parts are very complicated and highly stressed, the rivets are always driven cold. Due to these conditions, the tools, machines and working methods for strengthening of riveting diverge essentially from the commonly known riveting methods of general machine construction. In the course of my lecture I shall give further details regarding these questions.

The Focke helicopter presents the first successful solution of a problem which has occupied aeronautical science for a considerable time. Details of the record flights carried out last year caused a world sensation and with further development it is not too much to hope that this new type will open up fresh fields which up to now remained closed to orthodox aircraft.

This lecture is an attempt to provide a general view of soaring, including the views of the pilot, the meteorologist, the engineer, and the club. If this can be done, it will be easier for each specialist to recognise how he can best contribute to the advance of the pastime.

I think that the technique to build a glider has been available for several hundred years, but the knowledge and desire have only recently grown. The present state of gliding is due to advance in two ways, in art and practice, and in organisation. Perhaps I should not leave out science which is the record of the practice and of the experiments which have been made to improve the practice.

The study of the problems connected with a successful racing sailing boat, like Gaul, can be divided into three parts. There is first of all the general configuration of the hull upon which lately much study has been directed. Anybody interested in this should look up the article, “Model Tests of Sailing Yachts,” by Kenneth S. M. Davidson, Director, Experimental Towing Tank, Stevens Institute of Technology, New Jersey, appearing in the August issue of “The Rudder,” in which it will be noted model hulls are pulled through the tank at an angle of heel, and with an angle of drift.

My lecture deals with the effect of the compressibility of air on bodies moving through it at speeds ranging from the velocity of sound (710 m.p.h. at high altitude) as an upper limit to a lower limit ranging roughly from half to threequarters the velocity of sound. Somewhere within this range will commence a very rapid increase of the drag coefficient of an aircraft as a result of the formation of local shock waves.

Before reading my paper I wish to express my thanks to the President and Council of the Society, and my great appreciation of the privilege accorded to me of speaking before this expert gathering.

My ambitions with regard to the subject of this paper were originally very farreaching, but I soon realised that it would be impossible to cover the enormous field falling under the heading of “ rotating wings,” and at the same time to advance sufficiently into detail to escape the criticism that this was merely a new collection of facts, already known and very general in terms, and therefore possibly only of interest to students of the history of aviation.

I want this evening to present some reasons for believing- that we can build successful aeroplanes of enormous size, and, what is more important, that they will not be merely monuments to a desire for the gigantic.

In the past, bold computers have defined upper limits to the size of aeroplanes. Their prophecies have varied, and most of them have been belied by practical achievement. Their arguments were usually based on what has been called the “ Cube Law ” or the “ Square-Cube Rule.” This rule, though it has apparently proved misleading, is indeed correct when properly applied, and it forms a convenient point from which to begin an enquiry into the feasibility of the giant aeroplane.

Squadron Leader Buxton has pointed out the lack of basic design data for sailplanes available in English. To alleviate this condition to a certain extent, the following data are presented. All the data arc from German sources and the Society is indebted to Alexander Lippisch, A.F.R.Ae.S., and to the Deutsche Forschungsanstalt fuer Segelflug for much of the information.

In the usual Berry (I) expression of the generalised theorem of three moments (i.e., generalised in the sense that end load deflection effects are taken into account) the lateral loading on a continuous beam is regarded as uniformly distributed over each bay into which the beam length may be divided (either naturally by supports or artificially for convenience of analysis). In this paper the lateral loading is taken as distributed parabolically so that the resulting equations may be used as a sort of Simpson's rule for dealing with any arbitrary loading. By taking into account the “ sinking “ of supports any particular beam can be divided up into a convenient number of bays over each of which the lateral loading may be assumed to be parabolic. We may thus obtain reasonably accurate solutions for the bending moments, etc., in a continuous beam under almost any type of lateral loading.

In certain problems such as the vibration of airscrews or gyroplane rotor blades, account must be taken of the effect of the imposed rotation on the frequencies of vibration. A direct solution of the appropriate equation of motion is usually impracticable and in consequence recourse is had to the application of Rayleigh's Principle. But even this powerful device may involve increasing labour as ascending overtones are considered. In this note an empirical rule is indicated whereby the effect of rotation may be assessed. For a uniform rod the empirical rule is shown to be a very close approximation, particularly with ascending overtones. In other cases such as a tapered rod the rule is shown to apply, but the approximation is not so close.

It is indeed a very great honour for so new a member to be accorded the privilege of reading a paper before the Royal Aeronautical Society, and I would like to express my sincere thanks to the President and the Council of the Society for the invitation extended to me.

We have heard from designers and experts in all branches of aeronautics what problems confront them and how they propose to solve them. I am going to discuss, from the point of view of a pilot, some of the problems that seem to me to arise from high performance and increased wing loadings, and to indicate what appear to me to be possible solutions. I propose to consider these problems under five headings :—

1. (1) Take-off.

2. (2) Irreversible Aileron Control.

3. (3) The Approach.

4. (4) Flattening Out

5. (5) Touching Down.

The Wilbur Wright Lectures not only commemorate that pioneer flight on which the art of practical aviation was founded but also offer homage to the brilliant research and invention which made that flight possible. It is, therefore, natural and fitting that such a large proportion of the preceding 25 lectures have dealt specifically with the application of research to matters aeronautical. The materials of aeronautical construction can also justly be classed as the outcome of much research into many fields of pure and applied science, with practical results that have made some contribution towards the advancement of aviation and, hence, fittingly form the subject of a Wilbur Wright Lecture. Accordingly, when the Council of the Royal Aeronautical Society honoured me with the invitation to deliver the 1938 lecture on this subject, I naturally read up the preceding lectures and was somewhat surprised to find that materials, as such, had not previously been dealt with in this connection. The task of making the first survey of a field of such alarming scope, in a necessarily limited space and time, involved some anxious reflection regarding a suitable method of treatment; it appeared that a detailed discussion of personal research, or even of a selected group of materials, must have such a limited scope as to be incompatible with what is implied in the allotted title. To the casual observer, the really wide range of the more familiar materials of construction that have been available for some years, allied to the normal steady improvements that have been effected and those that may be expected, may appear to offer all that is required for the aeronautical requirements of the next decade or so, so that reviews of the materials of, say, 1924, 1931, 1938 and 1945 would mainly represent a story of development rather than change ; actually, this is not the position. A relatively few years has seen the relinquishment, temporary or permanent, of the position held by steel as a structural material; the use of light alloys has become very general, an improved form of wood is definitely in the field while it may be that the entire structure of moulded plastics will become a practical proposition in the fairly near future. Then, the accomplishment of the aims of the engine builder with regard to units of much greater powers are retarded to a certain extent by the fact that a number of materials appear to have reached the visible peak of their development; new materials are urgently required. Again, who would care to prophesy that the airscrew of the future 2,000-4,000 h.p. engine will even be made of any kind of metal, although the present aluminium alloy propellers give such good performance.

In certain types of aeroplane the empennage is carried on two tail booms emanating from the main body. In some cases the booms and tail plane form what is virtually a portal and in these circumstances a fairly simple approximation may be found for the stresses resulting from fin and rudder side loads. The method adopted follows the treatment given in the author’s paper, “The Stressing of Rigid Jointed Frames.”