An invitation to address the Royal Aeronautical Society, the first Society of its kind ever founded, is indeed a signal honour and not without misgivings to a humble visitor who, in the land of Elizabethan English, finds himself embarrassed for words adequate to express his appreciation. The scientific contribution of the Society to the advancement of aeronautics and the meritorious achievements of its members are well known in the United States.

A sort of unselfish and patient willingness, which encourages men to depart from beaten paths and invade unknown realms to bring forth something new and beneficial to society, is indispensable to any new enterprise, and most characteristic of those who are pioneers in airship development. Certainly none so far have garnered any substantial profits.

The establishment of contact between aircraft in flight for the purpose of refuelling, has until recently been regarded as a somewhat hazardous procedure employed mainly during attempts to create endurance records.

It would appear, however, that if such contact between aircraft could be established safely and as a routine operation, considerable advantages could be obtained by the employment of such a scheme.

From the point of view of commercial aviation, not only would it make possible long distance non-stop flights over regular air routes, but it would enable a large increase in pay load to be carried, since the bulk of the aircraft's consumable load, i.e., fuel, would not be taken on board until the aircraft had left the ground and climbed to a reasonable height.

Even from the early days of 1860, when your countryman Wenham experimented with gliders, the development of aerodynamics has been a systematic search for facts. The well–directed efforts of Wilbur and Orville Wright to search out the fundamentals of flight gave a profound impetus to contemporary and later experimenting, and libraries have been filled with the orderly research of aeronautical science. The development of manufacturing practice, however, has been dictated by the immediate needs of the moment, largely without the benefit of methodical study.

I trust I shall not be suspected of pleading a case either for the art of manufacturing, or for aeronautical science, as in the early days it was not unusual for me to find myself designing with one hand, while, in a manner of speaking, manufacturing with the other.

The attainment of the mighty speed of 379 miles an hour by an officer of the Royal Air Force (Flight Lieutenant Stainforth) is fresh in our minds and we honour the pilots, the aircraft builders and the engine constructors who made this possible. We remember also, I hope, the scientific workers, whose investigations afforded the basis on which so much else was built. When one contemplates motion at such speeds as this, one cannot help speculating where such enterprise will lead. The power to move is not new; railways and roadways give abundant evidence of high speed, but motion along them is almost entirely in two dimensions. It is only when the freedom of the air makes three-dimensional motion possible that the problem appears in its greatest and most interesting aspect. In the air there is combined the greatest possible freedom with the highest possible speed, and it is this combination which makes the study of such intense scientific interest. Moreover, the flight path may be greatly curved and that curvature may be in any plane. Great forces may then arise and act upon the aircraft from any side. It is not for nothing that the pilot is strapped into his seat.

Confusion has arisen regarding just what is meant by adjustable variablepitch and controllable-pitch propellers, and the matter should Be more clearly defined in the following way:—Fixed-pitch propellers to apply to both (a) the ordinary fixed-pitch propeller, made up with the hub and blades integral, and the material the same throughout, and (b) the detachable-blade or ground-adjustable type that will usually have the hub and blades of different materials, and in which the blades will be clamped in the hubs on the ground to an angle that is assumed, usually by experiment, to give the best general or some specially desired performance results.

When we consider the physical properties of the air, the most noticeable features are its low density and its compressibility, and a student new to the subject might be excused for doubting whether the air were not too light and yielding to support an aeroplane in flight. The air is indeed very compressible, but this property of the air becomes important only when the speed of motion becomes a fairly large fraction of the speed of sound, and in practice its influence is felt only in the behaviour of airscrews with high tip speeds.

A more important property of the air is its viscosity or internal friction, and this property is of fundamental importance in flight, either by its direct frictional action or by its indirect action in determining the type of flow round a body. As an example of this indirect action we may consider the lift of a wing.

Apart from the subject of straight normal flight and all the problems of stability and performance concerned with it, more thought has been given to the spin than to any other form of motion of an aeroplane. The reasons for this are not far to seek. The spin is the evolution which, until the recent introduction of certain well known methods of lateral control and stabilisation, invariably followed the loss of control at speeds below the stall, and its occurrence near the ground has been responsible for the majority of fatal flying accidents.

It is the only form of stable uncontrolled motion which is exhibited by an aeroplane other than that which it may possess in straight flight. This stability has in a number of cases proved extremely dangerous, if not fatal, as in prolonged spins on certain aeroplanes it has been found impossible to recover.

The co-ordinate system used is shown in Fig. i.

The axis coincides with the axis of rotation and the plane is chosen parallel to the plane of rotation.

The plane serves as a longitudinal datum plane for the airscrew blade, and is perpendicular to the planes of the cross-sections of the blade. The axis OX is drawn in the direction of the radius from root to tip.

In my article Wing-Beats, which appeared in this Journal, in the issue of October, 1930, I recorded a series of experiments demonstrating the strength and lightness of a spring formed by twisting skeins of natural silk.

My hope is that silk torses of this kind will fulfil, in human flight, the postural function of a bird's pectoral muscles, leaving to human effort the phasic function of these muscles, that is to say, the activity induced by rapid nerve impulses from the brain.

The ratio that may subsist between these two functions cannot, I think, be determined otherwise than by full-scale flight experiments, but the experiments already recorded give reasonable ground for the belief that the requisite human phasic output will be small in relation to the total weight movement.

The idea of using the reaction of a jet of water pumped sternwards from a ship is endowed with a respectable antiquity, but tests on the efficiency of such propellers, whether model or full-scale, have not been extensive. Perhaps the most thorough tests were those of S. W. Barnaby (Thornycroft and Co.) in 1880, described by him in the Proceedings of the Institute of Civil Engineers, Vol. LXXVII, page 1, 1883. This investigator measured the reaction on a nozzle delivering water under pressure into still water by a force balance connected to the nozzle itself. As a result, the “ Waterwitch,” a vessel of 1,160 tons, was constructed to work on this principle, the jet being supplied by a centrifugal pump which took water from a scoop amidships. The efficiency of the jet itself worked out at .71, but with the pump the combined efficiency was only .38.

Monday July 28TH, 1930.—At Cardington—having spent Sunday morning on the ship after the last trial flight. A few eyelets damaged on that flight—nothing serious. One petrol tank leaking at the centre joint, to be changed on Monday. With so many tanks it would be odd if one was not leaking.

To the ship early this morning by taxi; worried about the sealing strip repair which carried away on Saturday. Saw Both and Meager about this on board.Prospects good for start at dawn on Tuesday. Back to the Bridge Hotel, and on to station, buying rubber shoes and overall on the way. To London on 10.23,first to the Club and then to London Office. No confirmation of flight. At about 7.30 two calls, Bamber and Burney—flight confirmed for start 3.30 Tuesday.

If the amount of printed matter published on a technical subject is any guide to the general state of knowledge on that subject, then neither the turbo-compressor nor the general problem of the supercharging of aircraft engines can be very well understood at present, much less the combination of the two. Apart from the brief treatment accorded to the behaviour of engines at high altitudes, and supercharging in the well-known text-books on engines, the only printed matter available on the subject is contained in papers published in technical journals (so far as one knows), viz.:—

“ Supercharged Aero Engines,” R. F. R. Pierce, the Journal of October, 1926.

Although there is one successful high–speed heavy-oil engine employing aif injection, it will not be disputed that the present rapid development of this type of internal combustion engine would not have taken place if a high-pressure air-compressor were an essential accessory. It is perhaps well to emphasise that from the beginning designers of engines of the pure “compression-ignition” type have striven after airless injection of the fuel, the first successful application in this connection being that of Sir James McKechnie, of Vickers, Ltd., in 1910. Subsequent development work by Professor Hawkes and others under the Admiralty brought this method to practical success on submarine engines, and it is interesting to note that as late as 1920 almost all experience with airless injection had been gained in this country.

Engines which are the lineal descendants of these early engines, namely, those in which the fuel is injected directly into a combustion chamber of simple form, and known conveniently as the “direct–injection” type, constitute an important section of those engines working successfully at high speeds.

The problem of the helicopter is one which has intrigued inventors for centuries, and which has perhaps attracted more attention and effort than any other phase of design of heavier-than-air craft.

Even as far back as the fifteenth century we find Leonardo da Vinci devoting several years of his life to studying- bird and mechanical flight, and he has left many sketches showing- flying machines. Of particular interest to us is a design showing- an aircraft consisting of a sustaining screw driven about a vertical axis.

The first helicopter actually to fly was a small model, little more than a toy, which was shown before the French Academie des Sciences in 1784 by Launay and Bienvenue, and since that time literally thousands of schemes have been proposed by inventors all over the world. The patent files of all countries are full of helicopter specifications, the greater part of them being based on faulty physical principles, and obviously impracticable.