In January, 1926, Major Buchanan gave a lecture before this Society on the Schneider Trophy Race for 1925. He then gave a very complete history of the race and full information about the machines up to that period. I propose to give a brief description of the development which has taken place since then in the design of British high–speed seaplanes.

After the failure of the British team to win the race in America in 1925 it was brought home to all interested that our machines were a long way inferior to the American machines, and that if we wished to again hold our own in this important field of aviation we should have to treat the matter much more seriously. Furthermore, it became obvious to all that machines could no longer be entered for these races by private enterprise. It is true that the Air Ministry had loaned the machines for the race, but very little opportunity had been given for research and experimental work, and the engine designers and aircraft designers had been working independently.

Racing airscrews differ essentially from Service or commercial types by reason of the extreme values of engine horse-power, revolutions and forward speed which enter into the specified requirements.

These three variables, associated with the condition that the thrust–horsepower shall be a maximum, determine the airscrew completely, but the exceptional values which they assume for racing aircraft have various important reactions on the efficiency obtainable.

Thus high power and revolutions, especially the latter, have a distinctly detrimental effect, whereas high forward speed contributes to a large extent to restore the position.

I propose to examine very briefly the relative importance of these factors and to indicate how they influenced the process of selection and design in the particular conditions of last year's race.

Let us first consider a typical power curve (Fig. I). As it is not permissible at this stage to publish actual figures in detail I have made use of relative scales which should be sufficient for our purpose.

When considering the engine programme for the 1927 Schneider Trophy Race, a study was made of the machines used in the race held in 1925.

There appeared to be a considerable divergence of opinion between experts as to the best form of engine to adopt. Some thought it would be essential to have a Vee type of engine. Some thought the “Lion” or “Broad Arrow” type to be suitable. This view was supported by Mr. Mitchell in the discussion on the paper on the 1925 race read before the Society by Major Buchanan in January, 1926. Others seriously considered the radial type of engine.

We of the Napier Company were, perhaps, a little biassed, but we thought the “Broad Arrow” type of engine would be best under all the circumstances, and in view of the accumulated experience we had of that type, it could be developed to a very high standard of mechanical performance and power output.

In a previous issue the equations of motion were obtained of a piston operated by an auxiliary connecting rod. together with the stresses in such a rod and its effect on the master rod stresses. In the following article the problem of the balance and the torque due to inertia forces has been examined and equations derived which may be applied to any multi–cylinder engine.

The following equations show that all balance and inertia torque equations for a single cylinder may be reduced to the form of Σ[f1 (sin θ) +f2 (cos θ)]. These functions are combined vectorially for the multi–cylinder engine as shown in Appendix II. of the previous article.

The full equations of motion for the flow of a viscous fluid have proved too complicated for any general solution to be obtained. It is to be doubted if, in. the near future, the problem of fluid motion will be solved in a general manner, although solutions for a few special cases may be found. In view of this it is of some value to investigate experimentally certain cases which are likely to prove of mathematical interest at a later date; this paper deals with such a problem. By means of the results obtained experimentally the mathematical analysis may be guided along the right lines and a satisfactory analytical solutioa of the problem be obtained.

The instrument used in exploring the fluid motion has a special interest of its own as it may prove of use in further aerodynamical investigations where the flow is of three–dimensional character. The development of this instrument, and its performance when tested, are described in Part I.

The experiments for the measurement of the forces on the spinning sphere are described in Part II.