THE AERODYNAMICS OF A SPINNING SHELL. 
355 
cusp at the fourth minimum, and the motion soon becomes indistinguishable from 
a precession at the slower rate. In the meantime, the maximum yaw a 1 (t) decreases 
steadily. 
Vertical 
Fig. 14 a. Path of nose of shell. Round 1.21. 
Path described, relative to the centre of gravity, by a point on the axis of the shell in front of the 
centre of gravity, shown on an enlarged scale. 
The total time taken from O to K is 02572 second. On the scale used, 1 cm. distance from O 
represents 1° yaw (very nearly), and corresponds to a linear displacement of O'118 inch for the nose 
of the shell from the. line of motion of the centre of gravity. 
The numerical results for the damping must be affected to some degree by the 
impacts on the cards, but the available data are not good enough for corrections to 
be worth making. There is, moreover, the curious phenomenon of an increasing 
maximum yaw shown by the rounds at 900 f.s. to be accounted for. 
The value of k is known from equation (4.121) and the values of f L in Table I., so 
that the damping results determine h and h + 2y or, more accurately, h + 2y —T 
(§ 3.62). It at once appears that 2y —T is negative and of much the same order as h. 
This is somewhat unexpected. Of course F (or — N'/N) is positive, but it is hardly 
likely that its numerical value is much larger than 0-03. It is natural to expect 
