CHAPTER X 



CONSTRUCTION AND TESTS OF THE LARGE ENGINE 



The main requirement in an engine for an aerodrome — aside from relia- 

 bility and smoothness of operation, which are necessary in an engine for any 

 kind of locomotion — is that it shall develop the greatest amount of power for 

 the least weight. It is, therefore, desirable to reduce the weight and number 

 of parts of the engine to the very minimum, so far as this can be done with- 

 out sacrificing reliability and smoothness of running. Furthermore, since the 

 strongest metal for its weight is steel, and since the greatest strength of steel 

 is utilized when the stress acting on it is one of tension, it is advisable to de- 

 sign the engine so that the parts which sustain the greatest strains shall be 

 of steel and, as far as possible, meet with strains which are purely tensional 

 ones. 



In designing the new engine for the large aerodrome it was, therefore, 

 planned to make it entirely of steel, as far as this was possible. The only 

 parts which were not of steel were the bronze bushings for the bearings, the 

 cast-iron pistons, and cast-iron liners of the cylinders. Previous experience had 

 shown that, while it is possible to use a cast iron piston in a steel cylinder or 

 even a steel piston in a steel cylinder-, provided the lubrication be kept exactly 

 adjusted, yet the proper lubrication of the piston and cylinder of a gas engine 

 is difficult even under the most favorable conditions, owing to the fact that ex- 

 cessive lubrication causes trouble from the surplus oil interfering with the spark- 

 ing apparatus. It was, therefore, determined not to risk serious trouble by at- 

 tempting to have the pistons bear directly on the steel walls of the cylinders. 



While visiting the French engine builders in the summer of 1900 in the at- 

 tempt to find one willing to undertake the construction of a suitable engine for 

 the aerodrome, it was pointed out to them that the great amount of weight 

 which they claimed to be necessary for the cylinders, and which they staled 

 made it impossible for them to build an engine which would meet the require- 

 ments as to power and weight, could lie very greatly reduced by making the 

 cylinders in the form of thin steel shells having cast-iron Linings. All, how- 

 ever, to whom this suggestion was made declared that it was impossible to build 

 satisfactory cylinders in this way; some of them even stated that they had tried 

 it and found if impossible to keep Ihe thin liners tight in the steel shells. The 

 difficulty which they had encountered is due to the difference in expansion of 

 the steel and the iron when raised to a rather high temperature by the heat of 

 the explosions, if the cylinders are not well jacketed with water; and if the steel 



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