Will a Projectile Fly True? 



The uniformity in the balance of the shell deter- 

 mines its accuracy and ultimate destructiveness 



By Reginald Trautschold, M. E. 



IF a projectile 

 is to strike its 

 mark miles 

 from the muzzle 

 of the gun from 

 which it is fired, 

 more is required 

 than accurate 

 range finding, ac- 

 cura e gaging of 

 the propelling 

 charge and ac- 

 curate aiming. 

 The projectile 

 must be well bal- 

 anced. Otherwise 

 it can not be 

 counted upon to 

 fly true. In other 

 words, the pro- 

 jectile must weigh 

 just so much; its 

 dimensions must 

 not vary; and it 

 must be properly balanced, both about its 

 axis and lengthwise. Accurate tests must 

 therefore be made to discover whether a 

 certain, very slight allowable variation 

 (human fallibility cannot be entirely over- 

 come) has been exceeded. 



In France, the shell to be tested for 

 balance about its axis is laid at right angles 

 across two level and 

 parallel steel bars. 

 Since the weight of the 

 projectile can never be 

 evenly distributed, the 

 shell will obviously roll 

 until it comes to rest, 

 heavy side down. • Is 

 it too unbalanced ? To 

 find out, a contrivance 

 known as an "eccen- 

 tricity weight" is 

 clamped to the base of 

 the shell. This eccen- 

 tricity weight, as its 

 name implies, is not 

 evenly balanced about 

 its center; one end is 

 heavier than the other. 



Testing the French 120 m.m. shell for weight and 

 ballistic properties. The man is holding a small 

 weight showing the allowable tolerance in weight 



A shell balanced 

 on the knife 

 edges of the 

 weighing appa- 

 ratus to ascer- 

 tain the point of 

 its length- 

 wise balance 



An eccentricity weight is attached to 

 the shell on the bars. If the 



weighted end points downward when 

 it comes to rest the shell is approved 



The exact weight of this fixture is known 

 and also the exact distance from its center 

 of the point at which it would balance if 

 laid across a knife-edge. The fixture is 

 clamped to the base of the shell, perpendic- 

 ularly, with its heavier end up, i. e., 

 opposite the heavier side of the shell. 



The shell, with attached eccentricity 

 weight, is rolled along the parallel! bars 

 until the fixture is horizontal, and then 

 released. Should the 

 shell and weight re- 

 main in this position, 

 the surplus weight on 

 the heavier side of the 

 shell exactly balances 

 the offset weight of the 

 fixture. Such a state 

 of equilibrium rarely 

 occurs. The shell usu- 

 ally rocks in one direc- 

 tion or the other until a 

 position of exact bal- 

 ance is found, when it 

 comes to rest. Should 

 the weighted end now 

 point toward the 



743 



