No one who has the honour to serve on the Council of this Society, and can therefore be tackled in person once in every month, can long avoid the additional but more alarming honour of being called upon to lecture. When I in my turn was brought to bay, I cast about for a suitable subject, but could not satisfy myself that any of the work in which I happen personally to be engaged had a sufficiently general appeal. I therefore decided to take advantage of my association with the Aerodynamics Department of the National Physical Laboratory, and to base my lecture on the work of other men. I want to make this clear at the outset, because I may omit in some instances to attribute credit where credit is due, and at all events it must be understood that the credit does not belong to me.

‘The Aerodynamical Characteristics of the Airship as Deduced from Experiments on Models’ was the subject selected by Dr. R. Jones for his R.38 Memorial Prize Paper. The essay surveys the present-day state of knowledge in airship research from the standpoint of the wind-tunnel.

It has frequently been stated and written that in order to popularise light aircraft the first essential is the production of a reliable engine capable of being easily maintained and having a long life, at the same time selling at a low figure. In the first part of this lecture it is desired to point out the difficulties in the way of realising this ideal before remarking on the claims of the various types for adoption.

In the early days of the war the desirability of reducing the weight of areoplane engines to a minimum, consistent with reliability and efficiency, very soon led designers to consider the advisability of using alloys considerably lighter than cast iron or steel for all possible parts of aero engines. Aluminium alloy crank cases had been used for some years in connection with motor car engines, and it was natural, therefore, that such alloys should come into use for the crank cases of aeroplane engines.

The problems of aeroplane stability in flight have been studied very thoroughly, both practically and in theory. Extensive mathematical investigations have been carried out by such men as Bairstow, Bryan, etc., and it is largely due to this work that the numerous questions arising with regard to the stable flight and equilibrium of the aeroplane are so well understood.

Nevertheless, though the work of these investigators is undoubtedly of primary importance, a discussion of the more practical aspects of the subject will be more within the scope of the designer. It is proposed in the present paper to deal with but one form of stability, namely, longitudinal, and to discuss the requirements of practical design together with the methods of complying with these. The question, therefore, resolves itself into an investigation of the main points controlling the size and setting of the tailplane of the aeroplane.

Aeronautics now covers a large field. The bibliography alone, compiled and published annually by the United States National Advisory Committee for Aeronautics, requires something like two hundred pages of a book seven inches by ten inches. Needless to say, I am not undertaking to review the whole field.

Owing to the difficulties of conducting free flight tests of performance and the fact that we cannot afford to make many mistakes in an appliance whose operation involves the risk of human life, it is peculiarly desirable that we may be able to predict the performance of the completed airplane from small-scale experiments; and probably in no other branch of mechanical science have we at present so many research laboratories.

Before proceeding, I wish to say that I much appreciate the invitation to present this paper to your Society. The science of aeronautics has evolved at a great pace, and typifies what can be done with applied science, and the tangible results are so apparent that it would be superfluous to discuss them. It would appear to me that the rapidity with which the efficiency has increased is due to the whole-hearted collaboration of the different branches of applied science and engineering, the honours being shared after giving first place 10 the sportinginstinct of the early flyer, by the physicist, the engineer, and the metallurgist. You will notice that my modesty places the metallurgist last. It is quite a confession to make, but it is a fact, nevertheless, that I accepted with pleasure your invitation to give this paper, principally because I have always taken a keen interest in the metallurgical side of aeronautics.

At the request of the Secretary I have attempted to prepare some notes on the flying qualities of the light aeroplane as compared with those of its larger prototype.

I am indebted to the Air Ministry for the facilities granted me in preparing these notes, but at the same time it must be understood that in this paper I am expressing entirely my own personal views.

The air surveys undertaken in Burma in 1924 and the beginning of the present year originated in a suggestion by Mr. C. E. Hay, of the India Forest Service, that aerial methods would be best for surveying the Delta of the Irrawaddy. The suggestion was not taken up seriously until 1920, when Mr. Watson, now Chief Conservator of Forests in Burma, and then in charge of the Delta Circle, took up the idea with persistent enthusiasm. Mr. Watson visited England later in that year and carried his negotiations during the ensuing year so far that I remember when we returned from the survey of the Orinoco Delta and demonstration in British Guiana at the end of 1921 that we fully expected to be on our way to Burma in the next few months.

As a matter of fact it was not till January, 1924, that I found myself at Marseilles looking for the P. & O. liner “ Malwa ” to take me to India on the way to the Irrawaddy.

It became apparent after the light aeroplane competition at Lympne in October, 1923, that the popularisation of the light aeroplane from the civil point of view demanded something more than the single-seater, although, in many respects, the considerations already aimed at and generally achieved must still form a definite controlling factor in design.

The study of aerodynamics is still largely empirical, and there seems little hope at present that the gap between theory and practice will be sensibly diminished by any means at present known to the applied mathematician. Yet the light that would, in all likelihood, be thrown on a number of practical problems by the complete solution of even a single case of turbulent motion would be very great. Of the problems that can be attempted, that of the flow of a fluid past a circular cylinder is likely to prove the least intractable.

The early conception of a flying boat in the days before the war was due to the aeronautical rather than the marine community, and the whole problem was regarded in the light of aeronautical experience. It was thus inevitable that whilst the flying boat had a comparatively satisfactory aerostructure, its marine functions were given somewhat primitive treatment. As a result the hulls were fragile, unseaworthy, and of high resistance. During the war this attitude of mind became well entrenched and the constructional method it involved was highly developed. Nevertheless the more logical system of making a boat that would fly rather than an aeroplane that would float soon received the attention that was its due. By 1918 the flying boat was definitely recognised as an amphibious machine, and its marine and aeronautical functions were being given full and separate consideration.