582 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 8 



is, I think, most easily seen by drawing a single curve showing for a 

 representative design the amount of engine power necessary at all 

 heights in order to produce a specific level air speed. With such a 

 curve sheet (kindly drawn for me by Mr. A. R. Collins) it is simple to 

 add a graph showing the power which would be given atjeach height 

 by the engine; then when the engine is shown by the curve sheet to 



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' brake Horse Power . 



Figure 2.— Power against altitude for constant speed. 



be giving more power than is required for the basic speed chosen, it is 

 clear that a higher speed is attainable. A glance at this illustrative 

 diagram shows that this increase of speed is at its maximum at the 

 rated height of , the engine (i. e., the height at which the supercharger 

 just maintains the^power at its sea-level value), and that afterward 

 the surplus power, and. therefore the additional speed, will fail off till 

 the two curves cross, which they do at the altitude at which the speed 



