NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 22] 



new sparking arrangement for the engine on the juuip-spark principle, ^fter 

 introducing this change in the engine il was found to run very much inure 

 smoothly and to require a minimum amount of care in adjusting il. 



At the time that this engine was being developed it was practically im 

 possible to obtain any outside information regarding the proper way of con 

 structing it. The little that was then known had been learned through laborious 

 experience and at great cost by the experimenters who were attempting to 

 build automobiles, and was zealously guarded in the hope of preventing their 

 rivals from utilizing the results of their labors. It was the known custom, 

 however, of all engine builders at this time to use a separate spark coil and a 

 separate contact maker for each cylinder of an engine, no matter how many 

 cylinders there were. This multiplication of the spark coils, which at that time 

 were very heavy, not only added greatly to the weight but also had the same de- 

 fect that the wipe-spark type of sparking arrangement had of being exceed- 

 ingly difficult to so adjust that all of the contact makers would perform their 

 functions at exactly the same point in the cycle for each cylinder. To obviate 

 these difficulties, both of adjustment and of excessive weight, the writer devised 

 what is supposed to have been at that time a new and valuable multiple-spark- 

 ing arrangement whereby only one battery, one coil and one contact maker were 

 utilized for causing the spark in all five cylinders, a small commutating ar- 

 rangement in the high-tension circuit distributing i'Uo sparks to the proper cyl- 

 inders at the proper time. This form of sparking arrangement was found upon 

 test to work so satisfactorily that it was afterwards adopted for the small en- 

 gine of the quarter-size model, and also for the new and larger engine which 

 was afterwards built and which will be described further on. It is needless 

 to describe in detail the many and perplexing difficulties which were experienced 

 in procuring suitable spark coils, spark plugs and other appurtenances of the 

 sparking apparatus, all of which at this time were in a very crude state of 

 development, there being only a few different makes on the market, ami most 

 of these being very unsatisfactory. One important minor improvement con- 

 nected with the spark plugs may be described, as the beneficial effect produced 

 by it was so very great that its use was continued in all future spark plugs for 

 all of the engines. This improvement, however, is now incorporated in many 

 of the plugs which are on the market, and in some cases patents, covering the 

 particular form in which the improvement is incorporated, are exploited by the 

 manufacturer. Considerable difficulty was at first experienced with the spark 

 plugs from a coating of soot (resulting from the incomplete combustion ol'thc 

 gas and oil in the cylinder at the time of explosion) which formed on the por- 

 celain and thereby caused a short-circuit, preventing the plug from working 

 properly. This was overcome by extending the metal portion of the plug for 

 some distance into the cylinder, and for something like three-quarters of an 



