138 ELECTRIC PROPULSION OF SHIPS. 



vened and over-stressed the material at the surface of the teeth, causing pitting and peening 

 and early destruction of the gear. The thrashing soon causes them to rim so roughly as to be- 

 come impossible. Examination indicates that not only the positive side, but also the negative 

 faces of the teeth are pitted and peened and receive serious vjear. After years in which the 

 struggle was practically given up, it has suddenly reached a complete solution in the en- 

 deavor to secure extreme lightness in very large aircraft engines of 1,000 horse-power or 

 more, where engine speeds have had to be pushed considerably beyond the economic speed 

 of the air propeller. 



At this juncture an Italian engineer, Pomellio, found a very complete solution. He 

 divorces the pinion from the mass moments of the crank and allows the latter to "run wild," 

 the pinion being driven through an elastic link (see Fig. 1, Plate 26). This is found to com- 

 pletely smooth out the action so as to make the gear drive perfectly successful. The elastic link 

 does not require highly organized gears, simply spiral toothed spur gears of rather coarse pitch 

 which are found to show no wear, contact on the positive side only, the negative faces not 

 even indicating contact. 



Fig. 1 shows the crank shaft of a heavy airplane motor below and the short, hollow pro- 

 peller shaft above. The engine shaft operates a broad-faced pinion driving the gear, 

 plainly to be seen on the upper shaft. The peculiarity of this drive is that, rigidly moimted 

 on the conical end of the engine shaft is a slender hub terminating at the extreme right in 

 a thin disc with deep gear teeth of pecuhar shape cut in its broadened periphery, shown also 

 in elevation in the detailed quadrant in the little view below and to the left. The pinion is 

 mounted independently of the crank shaft on heavy ball bearings, plainly to be seen in the 

 lower part of the figure, and the only connection between them are 172 broad, highly tem- 

 pered steel springs entering the teeth in the shape of radial hairpins, each held on two pintles. 

 The thrash of the crank shaft is taken up completely by the springing back and forth on the 

 part of the 172 sheet steel leaves, allowing the pinion full freedom to accommodate 

 itself entirely to its master gear on the upper shaft. The smoothness of the operation of 

 this arrangement leaves little to be desired. 



There are two forms of the elastic link available for this purpose — the magnetic and the 

 mechanical. The latter, though extremely highly organized and made up from a great many 

 pieces, is lighter and better suited for aeronautical work. So entirely successful are these 

 geared reciprocating sets in the larger geared engines that one is now coming forward of 

 1,600 horse-power, all rendered possible by a complete separation of the crank shaft and the 

 pinion teeth, which are thus safeguarded completely from the thrashing of the crank shaft. 



The above method is not the one used in power plants of ships, because we have a better 

 and more complete elastic link in the magnetic air-gap drive. Besides, this drive makes a 

 number of other important contributions in connection with ships' plants, but I have dwelt 

 in some detail upon the above hairpin drive to emphasize the point that whenever the pinion 

 is given full freedom, gears operated by reciprocating oil engines are perfectly successful and 

 are now available, this having received complete demonstration under service conditions. 



The magnetic form of the elastic link is much simpler, having two as compared to some 

 260 parts in the mechanical drive. It also gives more complete and smoother operation. This 

 is quite outside its important two-fold contribution in case of oil-engine ship propulsion, be- 

 cause, while for the first time it renders comparatively inexpensive gearing entirely success- 

 ful with reciprocating engines, it goes still farther and takes care of all fractional speeds in 

 the lower range, where the Diesels are found to draw too heavily on the starting air re- 

 serves. They run with good reliability at, say, one-quarter speed or below. Why go lower 



