Aero engines, whether in Service or Civil use, work under very different conditions from engines used in mechanical transport. It is absolutely necessary that a high standard of reliability should be constantly maintained, although long periods of full-throttle, or nearly full-throttle running militate against this, especially when it is considered that the weight of these engines has to be cut •down in every possible manner.

In general, the designer of an aeroplane has fixed for him the engine, the useful load, the strength factors, and the landing speed.

A weight estimate is prepared, in the process of which it would appear that the power loading, and the wing loading for the chosen section, fix themselves automatically; in practice, as we all know, the designer has a certain scope for variation of these, in addition to the choice of wing section.

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.

It is proposed to confine this paper entirely to the point of view of the propeller constructor.

More than 90 per cent, of the propellers now in use are constructed by shaping from a block formed by the glueing together of hardwood laminations. This type is cheap to produce either individually or in quantity, and has been proved by experience to be satisfactory for all types of aircraft, for tip speeds up to 1,000 feet per second, diameters up to 19 feet and for engines developing over 1,000 b.h.p., without showing any signs of having reached a structural limit.

This construction was standardised for production purposes by the Air Ministry during the War, and the official Handbook of Instructions is a most complete guide to the method of manufacture.

Other forms of construction are, to a certain extent, still in the experimental stage and will be considered chiefly by comparison with the standard type.

This paper should be regarded as a continuation of the one I read before you last session and is intended, primarily, to cater for those who wish to sit for a Ground Engineer's Licence.

My previous paper dealt with the alignment and checking of fuselages. I propose in this paper to deal with the alignment of certain other components, and also with the inspection of components.

Whilst carrying out various tests on radiators and airscrews in Iraq, it was necessary to take the air temperatures up to 10,000 feet, and the results of twenty-six flights are given in these notes as it is thought they may be of interest to aircraft designers requiring data to predict the performance of their aircraft in a tropical climate.

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.

I wish to give you to-night some idea of the computing work necessary between the receipt of the performance figures from the pilots and the issue of the complete report.