Until about ten years ago the highest speeds achieved by aircraft, even in dives, rarely exceeded half the speed of sound. Under these conditions the air round the aircraft behaved very much as if it were incompressible, and the forces acting on the aircraft could be derived on the basis of laws governing the aerodynamics of incompressible fluids.

During the 1939-45 War great advances were made in the performance of aircraft and eventually speeds of over three-quarters of the speed of sound were being reached, even in level flight. At these speeds the air no longer behaves as an incompressible fluid; the aerodynamic laws involved become much more complicated and the aircraft designer is faced with a mass of new problems, involving many strange and unexpected effects.

The purpose of this lecture is to discuss the contribution which research in flight can make towards the elucidation of these problems, with special reference to work done at the Royal Aircraft Establishment during the past few years.

My purpose is to try to place before you three broad main problems which cover numbers of subsidiary matters of great significance. Taking safety as read (and safety itself is not a problem but a necessity, begetting various problems in varying circumstances), my divisions of the subject are: —

1. 1. Reliability including regularity.

2. 2. Safety in the context of economy.

3. 3. Economy of operation.

The Thirty-Sixth Wilbur Wright Memorial Lecture was delivered before the Society by Mr. A. Gouge on Thursday, 27th May, 1948 at 6 p.m. at the Institution of Civil Engineers, Great George Street, London, S.W.I. The chair was taken by Dr. H. Roxbee Cox, President of the Society.

It is now a matter of history that the development of an efficient gas turbine for use in aircraft engines had to await the availability of materials with the properties which would give an adequate life under the conditions which have to be imposed for efficient and economic service. These conditions are, of their type, more severe than any so far imposed on materials in other mechanical equipment. For efficient operation the gases employed in the turbine must be at a high temperature and the flow of gas passing through must be large. In aircraft engines also, the turbine must operate at high speed, with the resulting accompaniment of high stresses. It was to the metallurgist that the engineer naturally turned first for materials to meet these conditions of high temperatures and high stresses and, although some attention has been given to non-metallic substances, the problem still remains essentially a metallurgical one.

Travellers by air to-day only too often can be heard to remark how good it is to be on the ground again. Even now flying is considered by many as an adventure and only those living near an airfield realise the regularity and reliability of air transport.

It is with the hope of removing this feeling of adventure and instilling a sense of security in air travel that this Paper has been written. An attempt has been made to reduce the power plant engineering to plain science and to show the care, knowledge and painstaking development that has gone into the design.

The second world war resulted in tremendous progress in aeronautics and while, during the war, the major factor was the aircraft efficiency as an offensive unit, that was not to say that reliability and passenger comfort were ignored.

On 6th January 1916 Lord Northcliffe, seconding a vote of thanks to Mr. Griffith Brewer for his lecture on the Life and Work of Wilbur Wright, said among other things : “The fact remains, however, that after more than one hundred years of experiment with aeroplanes, these two brothers were the first people in the world who made a machine to fly, and flew it. I make that remark emphatically, because there is one point to which Mr. Griffith Brewer did not call attention, and that is the attempt that has been made to rob the Wright brothers of the credit of their invention. We have not heard much of that in England, but ‘a prophet is not without honour save in his own country,’ and in the United States there have been long and persistent attempts to belittle the work of Wilbur and Orville Wright. I have closely read and followed the history of the hundred years of aeroplane experiments, and I am convinced that the credit of the first flying aeroplane is due to the Wright Brothers, and from the point of practical flying to nobody else. As an Englishman I am in an independent position, and I know that these words of mine will go across the Atlantic, and I believe they will assist in stopping the spread of the insidious suggestion that the Wrights did not invent the aeroplane.”

The Third British Commonwealth and Empire Lecture was delivered before the Society by Mr. James T. Bain on Thursday, 30th October 1947 at the Institution of Civil Engineers, Great George Street, London, S.W.1. The chair was taken by Dr. H. Roxbee Cox, F.R.Ae.S., President of the Society.

To commemorate the great French pioneer Louis Bleriot, who made the first crossing of the English Channel by aeroplane on 25th July 1909, the Association Franҫaise des Ingénieurs et Techniciens de l'Aéronautique, better known as A.F.I.T.A., has instituted a series of lectures to be known as The Louis Bleriot Lectures. The Lecture is to be given annually and the intention is that it should be given alternately, in Paris and London, by an Englishman and a Frenchman.

The first Louis Bleriot Lecture was given in Paris on 12th May 1948, in a lecture hall attached to the Hotel George V, by Air Commodore F. R. Banks, C.B., O.B.E., F.R.Ae.S., M.I.Mech.E., F.I.Pet. It was attended by the President of the Royal Aeronautical Society, Dr. H. Roxbee Cox, D.I.C., F.R.Ae.S., F.I.Ae.S., Sir Frederick Handley Page, C.B.E., F.R.Ae.S., Past-President, the Secretary, Captain J. L. Pritchard, Hon.F.R.Ae.S., F.I.Ae.S., and by a number of members of the Society and of the Aircraft Industry.

In the Realm of stability and control, we are at present travelling headlong into a region of new problems. Besides tidying up the outstanding items on the types of aircraft we are used to seeing flying about to-day, a not inconsiderable task when one considers the troubles we encounter when we undertake the design of a new so-called “conventional” aeroplane, we have to tackle two major lines of research and development. First, the peculiar problems associated with the stability and control of aircraft of large size, both military and civil, into which difficulties associated with high Mach numbers intrude themselves but little; and secondly, the even more extensive problems associated with the stability and control of aircraft, both large and small, which are to fly at very high Mach numbers, not only at their design cruising and diving speeds, but also in the extremely important slow speed conditions. Mr. M. B. Morgan of the R.A.E. has dealt with some aspects of the second series of problems, so I propose to concentrate on some of the problems involved in the first series, that is those primarily associated with the increase of aircraft size.

It is only within recent years that the helicopter has emerged from the experimental aircraft category to a position in which it can be considered as an effective operational and commercial means of aerial transport. The development of the helicopter to its present stage is due to extensive work in many countries, particularly in America, and it is unfortunate, but unavoidable, that Britain was unable to take a larger share in this work.

Aerodynamics is naturally associated with the external air flow past aircraft, but with the advent of the gas turbine it has also become of the greatest importance for the internal flow through such engines. The efficiency and bulk of the compressor and turbine components in gas turbines are largely an aerodynamic matter, and their design is determined by a knowledge of the lift coefficients, drag coefficients, Mach numbers, and so on that can be used. The same fundamental laws, if they were fully known, would apply to both internal and external flows, but there are at present considerable differences in practice between the data obtained, and the detail methods used, for the two categories of flow. This lecture attempts to cover in a general way the internal aerodynamic flow through gas turbines.

What are the particular factors of the aeroplane of 1947, which have a special effect on landing gear technique?

1. (i) Increase in the speed of take-off and landing.

2. 1940: 65 to 90 m.p.h.

3. 1947: up to 130 m.p.h.

4. (ii) Increase in wing loading and the use of thin or laminar flow wing sections.

5. 1940: 301b. sq.ft.

6. 1947: more than 50 lb. sq. ft.

7. (iii) Increase in physical dimensions and all-up-weight of the aircraft.

8. 1940: 80,000 lb.

9. 1947: 300,000 1b.

10. (iv) Increase in operational altitude.

11. 1940: 10,000 to 15,000 ft.

12. 1947: 15,000 to 30,000 ft.

In preparing this lecture I found it necessary, when considering recent changes in aircraft design, constantly to ask myself the question “Is this particular change due to airworthiness requirements or does it arise from reasons other than airworthiness?” In fact, one must consider whether requirements have any influence at all on the development of trends in design. Should design be likened to a runaway horse with requirements following some way behind, or are requirements a strict rein by which the pace and direction of design is controlled?

My own answer to these questions is that the pace at which development takes place is not influenced at all by airworthiness requirements, but that requirements help to prevent design from running off the path of safety. To carry the analogy a little farther, the faster the development is, the more difficult it is to keep it running on the path of safety.

In the past few years, two problems in applied aerodynamics have received much attention. The first is the problem of low drag in which it is desired to reduce considerably the drag of aerofoils over a certain range of lift coefficient by suitable design and construction. The second is the problem of increasing the lift in which it is desired principally to obtain a higher maximum lift coefficient.

The rotary derivatives of a Delta wing pitching or rolling at supersonic speed are obtained in addition to the lift curve slope first given in an earlier investigation.

This paper discusses the elementary use of non-dimensional parameters for analysing the performance of a simple jet turbine engine. The coniponents of the engine—intake, compressor, combustion chamber, turbine and final nozzle—are linked together by means of the component characteristics. The possible running points are such that the characteristics are satisfied simultaneously when the whole of the engine is in equilibrium.

The components of the engine in general can be matched only at one point, called the design point. Performance af equilibrium points away from the design point may be predicted by the methods described, before the engine is built.

The paper also shows how the essential parameters governing the behaviour of the jet turbine engine are linked with the aircraft parameters.

The buckling of a round tube or curved A plate under axial compression is an example of that class of instability in which the initial buckled form becomes itself at once unstable. As a result the buckle immediately develops to a large amplitude, often with loud noise. This class of instability has been aptly termed “oil canning” from a familiar example.

Thorough investigation of oil canning problems must always be tedious. As for any buckling problem it is essential to use large deflection theory and, since the amplitude of buckle rapidly becomes large, it is necessary also to consider in detail the distribution of the membrane (or mid-plane) stresses due to the buckle. This necessity, in combination with peculiar buckled forms, renders the complete solution even for a tube extremely difficult and tedious. Moreover, since the buckled form for a complete tube does not accord at all well with the edge conditions for a curved plate, the full analysis for the latter is almost prohibitively difficult.

There are various possible interpretations of the title of this lecture and because of this and the fact that I have not had complete responsibility for the design of any one aeroplane, I regarded this lecture and title with some diffidence at first. Nevertheless in recent years no lecture has dealt with the general problem of how an aeroplane design progresses stage by stage, from the first ideas to the prototype flight trials and I have tried to make that the basis of my lecture.

A recent paper gave an elementary analysis of the effect of control procedures on the flow of air traffic. It was shown that the average delay experienced by aircraft landing at an airport increases rapidly as the arrival rate approaches the maximum handling capacity of the airport. It is the object of the present paper to give a more rigorous treatment of the problem and to derive the distribution of delays under different traffic conditions.

The maximum handling capacity of an airport is the greatest rate at which aircraft can enter the airport with absolute safety. It is determined by the safe minimum separation between successive landings. An aircraft arriving in the central zone with less than the safe minimum separation is withheld from landing until the minimum interval has elapsed.

In the following it is generally assumed that aircraft cross the boundaries of the control zone from random directions with random separations, the mean arrival rate being constant. Aircraft which follow their predecessors too closely are assumed to be delayed for a minimum period so that none lands with an interval less than the safe minimum. As a simplification it is assumed that no aircraft takes off from the airport.