In March of last year I had the privilege of reading a paper on the airscrew before the Society, “The Screw Propeller in Air.” The object of this paper was to extend what is usually known as the aerofoil theory of the airscrew, so as to include to some extent the phenomena of slip essential to propulsion in a fluid. This method has since, I believe, been fairly widely adopted both in experimental research work on airscrews and for purposes of designing and analysis.

The present contribution is the outcome of an attempt to modify the previous theory outlined in my paper, “The Screw Propeller in Air,” which theory cannot be considered as being complete although at the time it was written nothing of a similar theoretical nature had been published with the exception of Mr. Lanchester's paper on “The Screw Propeller,” this work being of a purely theoretical nature throughout and not directly based on model aerofoil data obtained from the wind channel.

The previous method of estimating the quantity of fluid, air in the case under consideration, dealt with by the propeller was to assume some constant fraction f say of each annular ring element along the blade, the limiting possible value of f being taken to be unity.