1919.] Jenkinson.—Engine-balancing : The Connecting-rod. 
75 
l cc 
W* j dx must be con- 
It is therefore plain that no single division of the whole weight of the 
rod into revolving and reciprocating parts can give exact results for com¬ 
puting the inertia forces, for by (1) the part J 
sidered revolving when calculating the horizontal components, and by (2) 
ri x 2 
the part j W r y dx must be considered revolving when calculating 
the vertical components. If, however, the horizontal and vertical 
components of all the inertia forces are evaluated separately for 
the whole engine, as indicated in a previous paper,* equations (1) and 
(2) can be used to calculate exact values of these components for the 
connecting-rod. 
The calculations necessary are really simple, since the greater part of the 
work has to be done in any case in the designing office in order to obtain the 
/ l QQ 
Wa- ~ L dx 
will be recognized as the part supported by the crar. k-pin when the rod 
ri x 2 W k 2 
is horizontal, while the part J W x dx is equal to —p~ where k is the 
distance of the centre of gyration from the crosshead-pin. Simple tests 
can therefore be carried out on the finished rod to check the results of 
the calculations. To check the first integration each end of the rod is 
A B CD 
F G H J 
weighed in turn while supported on the scales by a narrow packing-piece 
under the centre of the pin-hole. The weight supported by the crank- 
pin is thus directly ascertained and data obtained for calculating m, 
the distance of the centre of gravity of the rod from the crosshead-pin. 
To check the second the rod must be swung as a pendulum while sup¬ 
ported on knife-edges (or other frictionless device) at the centre of the 
crosshead-hole. Then if t is the time in seconds of one swing (or 
single oscillation) we have 
W k 2 
IT 
3915 
W t 2 m 
Z 2 
where all dimensions are expressed in inches. Great care must be taken 
to minimize friction at the sunports or the value of t will be much too 
small. 
* S. H. Jenkinson, Balancing of Locomotives, this Journal , vol. 2, p. 19. 
