438 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



The influence of part thrust S. F. C. variation from figure 6 is clearly 

 seen. For instance, the opposite cruising trends shown for the turbojet 

 and the propeller increase their relative specific fuel consumptions 

 from 2 or 3 to 1 at maximum continuous thrust to 5 to 8 to 1 at optimum 

 cruising thrust. 



Here again, the fact that an enormous sacrifice in economy accom- 

 panies premium performance, that is high cruising speeds, is empha- 

 sized. Ridiculous comparative S. F. C.'s and cruising speeds for the 

 rocket seem to eliminate this power plant from any consideration 

 involving economical operation. 



FiGTjBE 7. — Power plant plus fuel weight. 



9. Power plant plus fuel weight (fig. 7). — Figure 7 is a plot of 

 power-plant weight plus fuel weight, excluding fuel tanks, taken at 

 maximum continuous rating versus duration. Weights of power plant 

 are assumed as follows : 



Power-plant weights 



Motor + contr ols and pJumbiB; 



Cooling system + coolants 



Propeller 



Turbine and pumps 



Total pounds. 



Propeller 



1,000 



450 



600 







2,850 



Turbojet 



2,000 

 

 

 



2,000 



Ram-Jet 



550 

 

 



150 



Kocket 



450 

 

 



225 



675 



For the rocket motor the power plant plus fuel weight is startling, 

 being 10,000 pounds for less than 4 minutes duration, with no weight 

 allowance for fuel tankage. However, when the vastly superior thrust 

 rating is considered the picture improves somewhat. 



