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.

Thanks to the pioneer work of Lanchester and Prandtl everyone seriously interested in aeronautics has nowadays sufficiently clear ideas about the power and the associated drag which are essential for the support of an aeroplane in flight. This induced drag, as it is now called, can be calculated with an accuracy which is ample for most practical purposes, and even with the very clean aeroplanes of the present time it contributes, at and above cruising speed, a minor part only to the total drag. We are equally familiar with the idea that the remainder of the drag—the drag involved in getting the aeroplane through the air as opposed to holding it up—can be reduced, by careful design, nearly to the mere skin-friction of the air rubbing over exposed surfaces; the reason being, of course, that the pressures on the surface of a well streamlined aeroplane are so distributed that their horizontal components form an almost completely balanced system.

It is safe to say that in no branch of applied science have the difficulties been greater or the process of development more rapid than in aeronautics. By far. the largest factor in the triumph of the aeroplane has been the improved internal combustion engine, a class of prime mover which, generating a maximum of power for a minimum of weight from concentrated fuel, is to-day such an outstanding engineering achievement as to arouse one's curiosity regarding its origin and development.

I cannot find better words, adequately to express my meaning, than those of John Farey (I) in his remarkable book, “On the Steam Engine,” published in 1827. Applying Farey's statement also to internal combustion as we know it, we might well say that in common with the steam engine, “It is an invention highly creditable to human genius and industry for it exhibits the most valuable application of philosophical principles to the arts of life and has produced greater and more general changes in the practice of mechanics than has ever been effected by any one invention in history.”

Before reading this paper, I should like to make a brief explanation of my reason for changing the published title.

The original intention was to give a survey of civil flying boats in general, but after due consideration the subject appeared to me to cover far too much ground, unless it was restricted to merely a collection of already published data of past and present aircraft of this type.

Whilst a paper of this nature would, undoubtedly, prove to be of considerable interest, yet, personally, I feel more competent to review the three types of flying boats designed purely for civil use, which have come directly under my supervision during the past eight years.

During the last four or five years a remarkable evolution has taken place in the policy of aircraft design. Its ultimate aim is to reduce the aeroplane to the simplest possible form offering the least resistance to the air. This process of eliminating any structural members which are not necessary for the production of lift and the housing of passengers or military load has automatically led to the adaptation of the fully cantilever monoplane with retractable undercarriage (Fig. I). The final logical result of this evolution is, of course, the flying wing with the engines, passengers or military load housed inside, thus suppressing such components like the fuselage and the tail unit which at the moment are still causing a non-productive addition to the total drag. There are still certain difficulties which will prevent us from achieving the ideal of, say, a mere flying wing, and our present compromise solution consisting of a tapered cantilever wing, a streamlined fuselage and a cantilever tail unit will probably persist for some time to come. The next step in suppressing parasitic drag will, therefore, consist in a still greater refinement of fuselage design and in eliminating outside engine nacelles by using engines buried inside the wing.

The early work of Froude. Relation of skin-friction to resistance arising from other causes. The Langley fallacy. The Reynolds Number and the condition of laminar flow: expressed graphically. Resistance as a functionl of velocity. Ichthyoid or streamline bodies: exemplifield in the Graf Zeppelin airship, etc.

The more I think about the subject chosen for this Address, the rasher does it seem. To proclaim limits to human flight is to do two things. To say what can be done, and to suggest what cannot. Now, though there may be little rashness in the one, there is much in the other. If I say that such and such a thing can be done and someone in the distant years points out that actually it has not been done, my shade has the easy reply that achievement requires effort and that my critics should use their brains.

But if I suggest that certain boundaries cannot be crossed, what fun for the coming race of engineers who cross them (if they do), than to poke fun at the memory of your lecturer to-night! And when I use the word flight I mean flying with wings and not the flight of a projectile.

The author's experience in flying dates from before the war and includes a good many years as a naval test pilot, over 5,000 hours of actual flying time in the air in some 360 different types of aeroplanes, ranging from purely experimental to large modern passenger transports and the latest single-seater fighters, and the interest created by some of his experiences has prompted him to attempt some consideration of the complex problem of spinning.

The phrase “tail spin” was probably adopted by reason of the fact that when an aeroplane is in this manoeuvre, it appears, from the ground, as though the nose were pointed straight down and the tail was describing a circle, whereas a spin is a complicated manoeuvre and the nose is actually travelling in a helical flight path, the radius of this helix being relatively small.

During development of solid metal airscrews in the U.S.A. many vibration failures occurred and various investigations have been made there and elsewhere with a view to overcoming such troubles. The problem is to avoid airscrew failures while keeping weight as low as possible; its solution involves mathematical analysis, further development of experimental methods, and investigations in relation to particular combinations of engine and airscrew.

Automatic pilots are gradually coming into general use all over the world. Their usefulness has now been proved over a period of about ten years in this country and over a somewhat shorter period in other countries, notably the U.S.A., where the Sperry Automatic Pilot has been evolved after many years of pioneering work. Early pioneering work had also been done in this country by Mr. T. W. K. Clarke before the war.

The world's patent literature shows that inventors have been interested in the problem for at least a quarter of a century. Indeed, this was inevitable since the automatic helmsman or “Iron Mike” for marine craft was a proved success and the vagaries of their younger sisters of the air clearly indicated the need for firmer handling in their case also.

An account that is to be of any value of a subject in such an early stage of development as the use of synthetic resin materials in aircraft construction, must necessarily contain a great many first thoughts and rough guesses, and anyone writing such an account must be prepared to take the risk of having to eat his words at a later date. But I believe it is better to have blundered than never to have thought at all, and it is my hope that what I have to say will at least arouse interest enough among those with special knowledge to contribute to the discussion at the end of the lecture.

This paper seeks to draw from current research work on flutter and related problems results of general design significance; and, avoiding mathematics, endeavours to set these results out in relation to past and present problems.

A preliminary section of the paper indicates the main stability and allied troubles concerned and draws attention to the general similarity between wings and tailplanes in relation to these troubles. The remainder of the paper is then devoted to a discussion of the problems involved in terms of wings and ailerons.

For this purpose a “ stiffness diagram ” is constructed for a typical wing, indicating the relative stiffnesses, etc., required to prevent wing-aileron flutter, wing flutter, aileron reversal, and wing divergence. By means of this diagram the course of recent history in relation to wing-aileron flutter and aileron reversal is illustrated, and attention is then given to present and future tendencies and problems. The current tendency to employ wings of high density—arisingly largely from high wing loadings—is making wing flutter the problem of immediate importance, and ways of avoiding the provision of increased stiffness as usually adopted to prevent this trouble, as well as to prevent aileron reversal and wing divergence, are discussed.

Appendices are given commenting on the variation of wing flutter speed with altitude and on the modern tendency to usa wings of low flexural stiffness.

Almost the first thing anyone thinks of, when confronted with a type of aeroplane which he has not seen before, is its performance. He thinks, “ What will she do?” This paper is an attempt to set out the methods by which the performance is estimated for a new design.

The subject has considerable scope, and only a certain portion of it will be covered here: Level speed and climb, range (at constant r.p.m.) and the take-off run.

Before anything can be done at all, something must be known about lift and drag, and something about airscrews. These will therefore be considered first.

Recent contributions to the theory of structures with particular reference to the design of aeroplanes have dealt with the theory of frames in which the members are rigidly connected together at the joints; the object being to ascertain the degree of increase in strength of the individual members due to the restraint at their ends supplied by the contiguous members.

Briefly, when a member forms part of a rigid-jointed structure it acquires a rigidity arising from the rest of the structure. The amount of rigidity given by the rest of the structure may vary from zero end fixation to full encastreing.

The basis for the calculation of wing vibration has been laid by the work of Küssner (I). The present paper describes a comparatively simple and yet accurate method of solving the two-dimensional problem in a manner suitable for the aircraft designer. In addition some of the results obtained by the new method are discussed.

The present paper is confined to matters concerned with the requirements for landing and take-off of aircraft at land aerodromes, that is to the landing area.

In the selection of sites the questions that arise are size and over-all gradients. In development of a selected site account must be taken of directions of landing, dimensions of flightways or runways, local gradients or undulations, nature of surface. Finally, to ensure safety of flight the site must be protected by zoning.

The subsequent problems of detailed layout, of civil engineering in construction, of control and equipment, and of design of administrative and terminal buildings, though susceptible of more popular treatment, come later in sequence. My first more detailed study is therefore devoted to what may be termed the aircraft's point of view as to what it would like in order to bring in and take out its load in the most economical manner.

In the present paper (Part II) the engine, and more broadly the power plant, is considered in its relation to altitude. The discussion hinges mainly on the question of supercharge. After a brief reference to the various types of supercharger the author opens the discussion on an ideal basis, in which the supercharger is supposed to be 100 per cent, efficient, and the atmosphere is treated as adiabatic, as was at one time supposed. Then the “International Standard Atmosphere” is introduced as modifying the conditions, and after that the question of supercharger efficiency is dealt with. The author treats this on the basis of a law of adiabatic type but with a different index, and shows that this treatment gives an efficiency varying from approximately 60 to 70 per cent, as a function of altitude.

The difficulties connected with supercharge as affecting temperature, having been made clear, the subject of inter-cooling between compressor and engine is dealt with at length with the aid of thermodynamic diagrams. Then the propeller is discussed, and the case for variable pitch made clear.

Finally, the subject of surface cooling is dealt with, applied both to the engine and to the inter-cooler.

An account is given of developments during the last three years in the production of light magnesium alloys suitable for aircraft construction. The heat-treatment of castings and the hardening by ageing of forged alloys are considered as well as the copditions affecting forging at various temperatures. The connection between these properties and the crystalline structure of magnesium is discussed.