Automatic pilots are gradually coming into general use all over the world. Their usefulness has now been proved over a period of about ten years in this country and over a somewhat shorter period in other countries, notably the U.S.A., where the Sperry Automatic Pilot has been evolved after many years of pioneering work. Early pioneering work had also been done in this country by Mr. T. W. K. Clarke before the war.

The world's patent literature shows that inventors have been interested in the problem for at least a quarter of a century. Indeed, this was inevitable since the automatic helmsman or “Iron Mike” for marine craft was a proved success and the vagaries of their younger sisters of the air clearly indicated the need for firmer handling in their case also.

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.

The general idea of making aircraft of single-shell or monocoque construction is not new. In the middle ages, the great English philosopher and man of science, Roger Bacon, “conceived of a large hollow globe made of very thin metal and filled with ethereal air or liquid fire, which would float on the atmosphere like a ship on water,” and ever since the inception of the aeroplane, suggestions have been made to construct aircraft wings and fuselages in the form of shells like those of crabs, lobsters or other popular crustacea.

There is at present, a marked trend in aeroplane construction towards the increasing use of metal covering both for wings and fuselages. The water loads on the hulls and floats of various aircraft have always necessitated the use of a robust skin, and although at first wood was commonly used, this was at an early stage of development, replaced by metal.