VII. The aerodynamics of a spinning shell.—Part II

In a previous paper the authors, with others, have described observations of the angular oscillations of the axis of a 3-inch shell over the first 600 feet from the muzzle of the gun, and from an analysis of the observations have obtained information about the forces due to the air. In the experiments, shells were fired from two guns giving different degrees of axial spin to the shell. While the shells fired from the gun giving the more rapid spin were all stable, most of the shells from the other gun were slightly unstable, this condition being shown by the much larger maximum yaw developed. These unstable rounds were not analysed in (A) as no suitable method of doing so had then been devised. The analysis of these rounds, about one-third of the number fired, forms the subject of the present paper; the results confirm those of (A) and provide some additional information. The information as to the force system obtained from the stable rounds was confined to yaws up to 7 degrees or perhaps 10 degrees; by analysis of the unstable rounds this information is extended, though in a fragmentary manner, over the region up to 35 degrees of yaw. On the other hand, no information has been derived from the observed damping of the unstable rounds. The observations are, in respect of the damping, clearly in qualitative agreement with the theory and results of (A), but no method has been devised of making a quantitative analysis of the damping.