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.

During the early stages of the development of aircraft in the pre-war days it was realised that wireless communication would provide the only satisfactory means of maintaining contact between an aeroplane and the ground. Although the technique of wireless was in its infancy at the time, it must be remembered that the needs of aviation in this respect were correspondingly limited; pilots of early types of aircraft had their time fully occupied in keeping their machines in the air at all, and had no energy to spare for communicating with persons on the ground.

The amount of information on the effect of accelerations on human beings is scanty and somewhat rudimentary with the single exception of observations made on aeroplanes. Aircraft in general have to be built to certain factors of safety so as to keep the total flying weight as small as possible, and for this reason accelerometers have been carried to measure the resultant forces experienced in flight. In this way a measure has been obtained of the forces likewise impressed on the human pilot directing the craft. The practice of flying has gradually developed by the careful training of the pilots so that undue stress is not placed on the aircraft structure and as a corollary this has been made possible by the pilot using his physical sensations to limit the violence of any aerobatic manœuvre. But the practice in this respect differs in various countries and so an attempt is here made to collate what information exists on the effect of accelerations on the human body and to consider whether the stresses experienced in flight can be increased with safety. It is, however, realised that the subject is a very open one and that the experimental data are very scanty.

Sources of noise in aircraft are discussed briefly with particular reference to the introduction of the turbo-jet engine.

An account is given of a particular investigation made in a Lancastrian aircraft fitted with both turbo-jet and reciprocating engines. The equipment by which the noise spectrum was analysed over, an extended frequency band is described.

The results are examined and the effects of the two types of engine on the noise spectrum are compared, under different representative conditions, in the forward and rear sections of the fuselage.

There is nothing new in attempting to design an aircraft to give trouble-free service. This has always been one of the major parts of a designer's job. In recent years there has been a lot of talk about improving design from the maintenance point of view and suggestions for “maintenance cells” in drawing offices. I would suggest that if aircraft have become too difficult to maintain, it is not entirely due to lack of appreciation of the problem in the drawing office, but mainly to the great increase in complexity of the modern aircraft, particularly in the past 10 years.

In accepting the invitation to address the Royal Aeronautical Society I am deeply conscious of the honour that has been paid to me and of the responsibility I have undertaken. My sense of responsibility flows from the realisation that I have been called upon to contribute from personal knowledge and experience to the great volume of recorded and authoritative opinion already contributed by these lectures.

I have chosen to address you on some international aspects of air transport because it is my firm belief that the lack of an enlightened multilateral code in an important field of international air transport is one of the more serious impediments to the full exploitation of the technical advances with which air transport has been presented in recent years.