Prior to the war, experience in this country in the production of successful rigid airships may be counted to be practically negligible. The war period, however, produced an intensive programme of rigid airship building in which the early designers were seriously handicapped owing to this lack of previous experience, and owing to the insufficient time and opportunities for research and experiment, a state of affairs which persisted to the end of the war.

The foundation of the modern theory of sustentation is the recognition of a cyclic or circulation component in the fluid motion surrounding the aerofoil.

But the “ circulation ” is of a somewhat abstract character. To the non-mathematical, and more generally to those who like to be positively assured that they are dealing with physical realities, the truth of the “ circulation ” is not altogether easy to demonstrate; in fact, it must be admitted that the word is used in a special sense.

Thus, when we talk of circulation we naturally expect to be able to track a particle in its path till it returns to’ some starting point or datum; such, for instance, as the underground trains on the inner circle, or as in the circulation of the blood from the heart through arteries, capillaries and veins, etc., and its return to the heart.

Students of Nature have come to believe that the sum total of energy cannot be changed; that is, in the principle of the conservation of energy. Bernoulli's theorem is a simple expression of the application of the principle to fluid motion and in this form the principle is probably one of the most useful conceptions that the engineer has as a guide in a subject which presents many difficult problems.

Stalled flying is a subject which at the present time is occupying the thought and time of aerodynamic experts all over the world. It is still more or less in the experimental stages, but its value to flying, and more especially commercial aeronautics, is now almost universally recognised.

It has hitherto been possible to fly an aeroplane at all angles of incidence from the no-lift angle up to the burble point of the aerofoil section employed for the wings. The burble point on the lift curve marks the change-over from streamline to turbulent critical airflow, and at this angle the aeroplane will stall. The machine sinks, and what is more dangerous, becomes unstable laterally so that the pilot loses power over its orientation. A spin then usually ensues.

It may be as well to state here that the only way of defining the change-over point from normal to stalled conditions is by means of the stalling angle.

The main object of this paper is to show the importance of supercharging, the desirable results brought about by the process, and a consideration of the difficulties.

Supercharging, as understood by aeronautic engineers, is the process whereby the output of an engine at sea level is maintained at altitudes. Forced induction, by means of a rotary blower, has however been tried on automobile engines. Only one maker, Mercedes, has so far incorporated this feature in the standard design. This practice has much to be said for it, as a small engine may be made to give a large output without running abnormally fast, or resorting to special fuel.

It would be interesting to consider the application of superchargers to aero engines with this idea of obtaining large outputs from small engines. Given good design, an actual increase in horse-power for a given weight would result.