PRINCIPLES OP GUNNERY. 
367 
“ that the derivation of cylindrical or flat-headed projectiles* is in the 
opposite direction to that of projectiles with conoidal or pointed heads, 
fired with similar rotation. For instance, if a cylindro-conoidal and a 
flat-headed shot be both fired with right-handed rotation, the deri¬ 
vation of the former will be to the right and the latter to the left.” 
There seems to be no doubt that flat-headed projectiles, for direct 
fire under service conditions with right-handed rotation, drift to the 
left; but for indirect and high-angle fire they may be driven to the 
right. It depends upon the direction of the rotation impressed on the 
projectile by the resultant of the resistance of the air. 
All possible conditions may be stated thus (supposing right-handed 
rotation of the projectile) :—-The resistance of the air, according to the 
shape of the head of the projectile, and the angle between its axis and 
the tangent to the trajectory, tends 
Either to raise the head, (1), or to depress the head, .(2) 
according as C is before or behind G- (Eig. 1). 
If the 1st, the axis of the projectile commences to gyrate to the right;.(3) 
if the 2nd, the axis commences to gyrate to the left. .(4) 
In the case of (3), if the resultant of the resistance makes a greater 
angle with the axis of the projectile than the axis of the projectile 
makes with the tangent to the trajectory (as in Fig. 1), the projectile 
will drift for the first half-gyration to the right, in the second half** 
gyration to the left, but the drift on the whole will be to the 
right , for reasons before mentioned ; but if the resultant makes a 
smaller angle, the projectile will drift for the first half-gyration to 
the left , in the second half-gyration to the right, but the drift on the 
whole will be to the left. 
In the case of (4), if the resultant makes a greater angle with the axis 
of the projectile than the axis of the projectile makes with the tangent 
to the trajectory, the projectile will drift for the first half-gyration to 
the left , in the second half-gyration to the right, but the drift on 
the whole will be to the left; but if the resultant makes a smaller 
angle, the projectile will drift for the first half-gyration to the right , 
in the second half-gyration to the left, but the drift on the whole 
will be to the right. 
It will be seen from the above how very complicated the question of 
the drift of elongated projectiles becomes, on account of the varying 
conditions of shape of head, steadiness of the projectile, &c. 
The practical conclusions with regard to drift are 
(1) With service ogival-headed projectiles and right-handed rota¬ 
tion, the drift is to the right. 
* By “flat-headed projectiles” are meant cylindrical-shaped projectiles |_ 
shoulder is rounded off, the centre of resistance may he in front of the centre of gravity | 
and the drift would be to the right. 
If the 
Varying 
conditions 
which af¬ 
fect the 
drift. 
Practical 
conclu¬ 
sions! 
