Ji; SMITHSONIAN CONTBIBUTIONS TO KNOWLEDGE VOL. 27 



If we suppose this to be used, by means of a proper reducing valve, at a 

 mean pressure of 100 pounds, for such an engine as that of Aerodrome No. 5, 

 which takes 60 cubic cm. of air at each stroke, we find that (if we take no account 

 of the loss by expansion) we have 18,329 foot-pounds of energy available, which 

 on the engine described will give 302 revolutions of the propellers. 



There are such limits of weight, and the engines must be driven at such high 

 speeds, that the increased economy that might be obtained by re-heating the 

 air would be out of the question. The principal object in using it would have 

 been the avoidance of fire upon the aerodrome, and the expansion of the unheated 

 air would probably liave caused trouble with freezing, while the use of hot (i. e. 

 superheated) water was impracticable. So when, after a careful computation, it 

 was found that, having regard to the weight of the containing vessel, only enough 

 compressed air could be stored at 72 atmospheres and used at 4, to run a pair 

 of engines with cylinders 0.9 inch in diameter by 1.6 inches stroke, at a speed of 

 1200 revolutions per minute for 20 seconds, all further consideration of its adap- 

 tation to the immediate purpose was definitely abandoned. This course, how- 

 ever, was not taken until after a model aerodrome for using compressed air had 

 been designed and partially built. Then, after due consideration, it was decided 

 to make the test with carbonic-acid gas instead. 



Gas 



The gas engine possesses great theoretical advantages. At the time of these 

 experiments, the gas engine most available for the special purposes of the models 

 was one driven by air drawn through gasoline. As the builders could not agree 

 to reduce the weiglrl of a one horse-power engine more than one-half of the then 

 usual model, and as the weight of the standard engine was 470 pounds, it was 

 obvious that to reduce this weight to the limit of less than 3 pounds was im- 

 practicable under the existing conditions, and all consideration of the use of gas 

 was abandoned provisionally, although a gasoline engine of elementary simplic- 

 ity was designed but never built. 1 purposed, however, to return to this at- 

 tractive form of power if I were ever able to realize its theoretical advantages 

 on the larger scale which would he desirable. 



Electricity 



A.s it was not intended to build the model aerodromes for a long flight, it 

 was thoughl that the electric motor driven by a primary or storage battery might. 

 possibly be utilized. Tt therefore occurred to me that a battery might be con- 

 structed to give great power in proportion to its weight on condition of being 

 short-lived, and that in this form a battery might perhaps advantageously take 

 the place of the dangerous compressed air tubes that were at the time (1893) 



