220 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27 



payment for the money which had been advanced, as it was hoped that some 

 of the parts of the engines might prove of use in experimental work. 



Immediately after the writer's return to Washington he began work on the 

 development of an engine. Taking some of the parts of the engine which had 

 been condemned and constructing others, he was able by September 18 to have 

 an experimental engine at work which, while not water-jacketed, but provision- 

 ally cooled by wrapping wet cloths around the cylinders, developed 18^ horse- 

 power on the Prony brake at 715 E. P. M., the engine, including these wet 

 cloths, weighing 108 pounds. Of course these wet cloths sufficed to keep the 

 engine cool for only a short time — three to four minutes being the maximum. 

 This was only a temporary expedient for enabling the engine to run for a suf- 

 ficient time to make brake tests and determine the power it developed, but the 

 results obtained were so very encouraging that it was decided to make water 

 jackets for the cylinders of this engine and see what power it would then de- 

 velop for more extended periods. 



This experimental engine, which was merely a " patched-up " affair, was 

 first equipped with a sparking arrangement built on the wiping-contact prin- 

 ciple. With this sparking arrangement several important difficulties presenled 

 themselves, among which may be particularly mentioned the great difficulty of 

 so adjusting the sparking arrangements that the explosion in each cylinder oc- 

 curred at exactly the same point in its cycle that the explosions occurred in all 

 the other cylinders, it being necessary to secure this result to a reasonably 

 accurate degree in order to cause the engine to run smoothly enough to be 

 used in the aerodrome. Where an engine has a large and heavy fly-wheel run- 

 ning at a high rate of speed, the nicety of adjustment of the sparking arrange- 

 ment is not so essential, for the fly-wheel acts as a reservoir of energy and 

 tends to smooth out the rough and jerky impulses which would be otherwise 

 introduced by slight variations in the force of the explosions in the cylinders. 

 In constructing an engine for an aerodrome, however, the permissible weight 

 of the engine is so very small that the use of a fly-wheel having sufficient 

 weight to act as an energy reservoir is practically prohibited. Another seri- 

 ous difficulty which was encountered with the wiping-contact type of sparking 

 arrangement was that of keeping the stuffing boxes around the rotating con- 

 tact rods tight enough to prevent leakage, without at the same time binding 

 and causing excessive friction. Although it seemed probable that the difficul- 

 ties which have been mentioned, and other minor ones which were apparent, 

 could be remedied by further experiment, yet the high tension or " jump-spark " 

 type of sparking apparatus seemed to offer much greater advantages. Since 

 it had fewer moving parts, and furthermore since the wiping-contact sparking ar- 

 rangemenl would have to be considerably modified in order to permit the con- 

 struction of water jackets around the cylinders, it was decided to construct a 



