The aerodynamic characteristics of airframes are expressed as aerodynamic transfer functions, giving the relationships between input and output for each of the three separate planes of motion, roll, pitch, and yaw. By assuming no cross-coupling between planes and linear aerodynamics, and by making certain other assumptions, which apply particularly to conventional airframes with fixed wings and rear controls, relatively simple approximate algebraic transfer functions giving the relationships between the control surface deflection (the input) and any airframe motion (the output), are obtained.

The open loop aerodynamic transfer functions thus obtained are used as part of the auto-pilot block diagram, in which the performance of other components, such as actuators, instruments and electrical networks, are also expressed in transfer function form. The aerodynamic transfer functions are useful in auto-pilot evolution and synthesis in that they aid selection of the airframe motions to be measured, modified, and fed back to close the auto-pilot loop.

For mathematical assessment of closed loop performance and stability, open loop transient and frequency responses are used, and curves of airframe responses are plotted in linear, logarithmic and polar form by standard methods from the aerodynamic transfer functions. Some methods of using these curves, which follow the general lines adopted in servo-mechanism and electronic amplifier design, are explained briefly.

Analogue computers are frequently used when the computations to be made are so complicated as to need the use of a computing machine. The aerodynamic transfer functions then form one block of the simulator set-up, and on larger computers the more exact form, including any non-linearities and cross-coupling effects, can be used.

I greatly appreciated the invitation of your Society to give this lecture on recent progress of aeronautical science in France; and if I hesitated a moment to accept it was only because I feared the difficulty of the task.

As a matter of fact, aeronautical science covers such a wide field that it is difficult to give an exact idea of the progress made in the different branches. Many results are obtained by the improvement of various details, and it is not easy to see clearly the influence of every one of them. I shall endeavour to be as clear as possible, and to describe to you the main purposes of. the French engineers and the results they have obtained in the way of their realisation.

The main objectives of French aeronautical progress have been safety in flight, development of commercial aviation, and metal construction. In every part of aeronautical science we shall find progress along those lines. They concern aerodynamics, building of aircraft, flying boats, motors and aerial navigation.

The field covered by the title of this paper is a very comprehensive one, and is too large to be dealt with in a single lecture. Only certain aspects of the subject, therefore, will be dealt with, and very brief reference made to such tests as have been described in other papers.

The subject naturally falls into three divisions:—Ground tests, tests on the water, and aerial tests, and it will be convenient to deal with them in this order. The methods of test described are those in use at the Marine Aircraft Experimental Establishment, Felixstowe, the official seaplane testing station, and, as far as is known, these methods are as up to date as those in use in other countries.

If it is felt that gaps exist on which information is desired, the inquirer is referred to Squadron Leader England's lecture on “ The Practical Side of Performance Testing of Aircraft,” which was published in the Aeronautical Society's Journal of January 1928, and to other papers which are mentioned.

The blow-down type of intermittent, supersonic tunnel is attractive because of its simplicity and because relatively high Reynolds numbers can be obtained for a given size of test section. An adverse characteristic, however, is the fall of stagnation temperature during runs, which can affect experiments in several ways. The Reynolds number varies and the absolute velocity is not constant, even if the Mach number and pressure are; heat-transfer cannot be studied under controlled conditions and the experimental errors arising from the effect of heat-transfer on the boundary layer vary in time. These effects can become significant in quantitative experiments if the tunnel is large and the variation of temperature very rapid; the expense required to eliminate them might then be justified.

In July, 1935, I had the honour of reading a paper before a joint conference of the Royal Aeronautical Society and the Society of British Aircraft Constructors, entitled, “ Future Research on Air-Cooled Aero Engines.” Much water has flowed under the bridges since that date, and we have entered on a period of intensive activity and development in aeronautical matters not fully envisaged 18 months ago.

A number of the suggestions put forward in my previous paper, as being suitable subject matter for research or investigation, have been, or are in course of being, investigated by various Government departments, or interested firms in this country, so that, when I received an invitation from the Royal Aeronautical Society to read another paper during the present Session, I thought it might prove useful to endeavour to write an addendum to the original paper, and try to outline the trend of a future air-cooled power plant for aircraft which would be built during the next five years, it being presumed that these engines would be designed as a result of the experimental work which had already been completed, or is being carried out at the present time, and with the object of meeting the more searching requirements demanded by this increased activity.

From Mr. A. M. Dobson's Note (July 1955 Journal, page 506) which dealt with the stability of an axially loaded continuous beam, and other contacts we have had with the Aircraft Industry, it would appear that the very considerable developments of structural theory which have taken place in relation to continuous beams subjected to axial load, as employed in normal structural steel work, are not well known in aircraft stress offices. The list of references appended may then be found helpful.

When I accepted the invitation to give a lecture on “The Uses of the ACE Computor” my first thought was to ask for the title to be corrected. The “ACE” as such has yet to be built and the machine that has been in use in the Mathematics Division of the National Physical Laboratory is a pilot model. However, to an audience whose chief interest is in aeronautics, the ambiguity of a title including the phrase “Pilot ACE” probably outweighs the advantage of its accuracy.

As its name implies, the Pilot Ace was built,at the N.P.L., with the intention of testing out the practicability of various ideas in the design of a full scale automatic computing engine, or ACE as it was called. The over-riding consideration was economy of equipment but, despite the rudimentary nature of the facilities provided on the machine, it was found to be a fast and powerful computor and has been fully and successfully employed for the past three years on a 13 hour basis.

Before the Second World War there were few airfields in Great Britain with paved runways.

The grassed flight strips of the pre-war years could carry the wheel loads of the aircraft then in use with little maintenance, other than grass cutting and rolling clinker or stone into local soft patches. From 1939 onwards, the increasing weight of aircraft, and more intensive flying, made it necessary to construct airfields with paved runways to permit operation in all weathers.

From 1939 to 1945, 444 airfields were constructed with paved runways for the Royal Air Force at a cost of £200,000,000, excluding the cost of building construction. Since 1945 the emphasis has been upon airfields for civil use, and the great airfields at Idlewild, Boston, Johannesburg and London Airport have been built.

The Gliding and Soaring Flight movement is as old as History. The observation of bird flight must have shown the men of former centuries in the same way as our own generation, that apart from power flight with wing beats there must be another flight possibility, enabling the use of the energy in the movement of air masses for flight without the expenditure of other power. The experiments undertaken in these times on the solution of the flight problem have come down to us only through myths and sagas, and we cannot differentiate between truth and imagination in these stories.

Experimental research, which can certainly be considered as the foundation of modern physics, has also in the realm of aerodynamics laid the basis for modernaeronautics. In this gliding and soaring flight plays the rôle of full–scale experiments, not as an end in itself, but as a proving-ground and last station before the invention of power flight.

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.