[ 227 ] 
VII. The Aerodynamics of a Spinning Shell.—Part II. 
By R. H. Fowler and C. N. H. Lock. 
Communicated by H. W. Richmond, F.R.S. 
Received August 17, 1921,—Read February 9, 1922. 
§ 1. Introduction. 
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 yawf developed. 
These unstable rounds were not analysed in (A) as no suitable method of doing so had 
then been devised.t 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. 
The force system on a model shell was also determined at low velocity in the wind 
channels of the National Physical Laboratory. The results are shown in fig. 2 of (A) 
* “ The Aerodynamics of a Spinning Shell,’' ‘ Phil. Trans.,’ A, vol. 221, p. 295 (1920). This paper 
will be cited as (A). The experiments analysed here and in (A) were carried out for the Ordnance 
Committee, and the. results are published with their sanction. 
f The “ yaw ” is the angle between the axis of the shell and the direction of motion of its centre of 
gravity. 
t As will appear later, the ordinary solution in elliptic functions of the equations of motion of a top 
is not adequate for this purpose in the case of large yaws. 
VOL CCXXII.—A 600. 2 K 
[Published March 15, 1922. 
