In this first lecture upon the origin and development of the heavy oil aero engine to be delivered under the Akroyd—Stuart foundation, it is appropriate to devote some space to the early history of oil engines generally, for it is certain that the aero engine of the future will claim a direct descent from some terrestrial parent. The early history moreover, of the heavy oil engine is of quite exceolional interest, both technical and personal.

Herbert Akroyd—Stuart was born in 1864.His father, Charles Stuart, owned a small engineering works at Fenny Stratford, and it was here that the son gained his training as an engineer. Between 1885 and 1890 he took out several patents for the improvement of oil engines, which appear to have been the outcome of his experience with a “ Spiel ” petroleum engine used for power generation at his father's works.

When we consider the physical properties of the air, the most noticeable features are its low density and its compressibility, and a student new to the subject might be excused for doubting whether the air were not too light and yielding to support an aeroplane in flight. The air is indeed very compressible, but this property of the air becomes important only when the speed of motion becomes a fairly large fraction of the speed of sound, and in practice its influence is felt only in the behaviour of airscrews with high tip speeds.

A more important property of the air is its viscosity or internal friction, and this property is of fundamental importance in flight, either by its direct frictional action or by its indirect action in determining the type of flow round a body. As an example of this indirect action we may consider the lift of a wing.