246 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27 



self, bul makes it very much less liable to damage; long crank shafts with sev- 

 eral crank pins being frequently twisted by improper explosions in the cylio 

 ders. The supporting drum or crank chamber is likewise reduced to the very 

 minimum, both in weighi and simplicity, the drums being perfectly symmetrica] 

 with no lost space either inside of them or on their exteriors. The cam mech- 

 anism for operating the valves is reduced to a simple ring carrying (for a five- 

 cylinder engine) a double pointed cam and journaled on the exterior of the hub 

 of one of the drums, the cam being driven by a train of gears journaled on studs 

 mounted on the drum, and co-acting with a gear fastened to the crank shaft 

 against t he crank arm. 



The radial arrangement of the cylinders is thus seen to give not only an 

 engine with the smallest number of parts, each of which is as far as possible 

 worked to a uniform amount during each complete revolution of the crank shaft, 

 but it also gives a very compact and readily accessible mechanism with its ecu 

 ter of gravity coincident with its center of figure, and with the liability of dam- 

 age tn it, in case of a smash of the vehicle on which it is used, reduced to the 

 minimum from the fact that the greatest weight is located at the strongesl part. 



Fourth, and of almost as great importance as the reduction in weighi which 

 the five-cylinder radial arrangement permits, is its unusual qualities as regards 

 vibration. Since these five-cylinder engines were built by the writer a very 

 thorough treatment of their properties as regards balancing has been given in 

 a treatise on the balancing of engines,' so no discussion of the mathematical 

 formula' involved in a study of the question of the inherent balancing proper- 

 ties of these engines will be here given. It is sufficient to call attention to the 

 fact that in an engine having five cylinders arranged radially, all of the recip 

 rocating parts are balanced for all forces of the first, second and third orders. 

 As it is only the reciprocating parts which give any trouble in balancing any 

 engine, the unbalanced rotating parts being readily balanced by placing an equal 

 weight at an equal distance from the center of rotation, and on the opposite 

 side thereof, it is readily seen that the properties of balancing which are in- 

 herent in this type of engine are unusual. A six cylinder engine having a six 

 throw crank shaft is not nearly so thoroughly balanced as this type having its 

 live cylinders radially arranged, for in the latter case all the moving parts are 

 in one plane, while in the former case the moving parts are in six separate and 

 parallel planes, and there is consequently considerable longitudinal vibration 



which can never I vercome. While this is true as regards the vibration due 



to moving masses, it is still more impressively true as regards vibration due 

 to reaction arising from the force of the explosions in the engine cylinders, espe 

 cially when the engine is running slowly and having heavy explosions. 



The usual practice in balancing the rotating parts of an engine is to attach 



' See Balancing of Engines, by Archibald Sharpe. 



