454 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



As seen from the table, the gross weight change for the propeller is 

 small and for practical purposes may be neglected. Fuel expenditure 

 for the ram-jet is not comparable with the others in that take-off and 

 acceleration to 350 miles per hour is accomplished by auxiliary means, 

 for which no allowance has been made. Both the ram- jet and rocket 

 are extremely uneconomical. The rocket necessarily suffers in climb- 

 ing to higher altitudes where it becomes most efficient, while the ram- 

 jet is essentially a low-altitude airplane. Although the turbojet burns 



FiGUEE 21. — Range vs. altitude. 



more fuel in climb than the propeller, a greater percentage of fuel 

 remains after the climb, owing merely to the fact that fuel is a much 

 larger percentage of the gross weight. 



Referring to figure 20, the range versus air speed at sea level and 

 at 20,000 feet is shown, which does not include the distance traveled in 

 climb. Although the propeller has greatly superior maximum range, 

 it obtains at an extremely low air speed (200 miles per hour), and a 

 limited range of speeds. At 20,000 feet and the same air speed (350 

 miles per hour), the propeller and turbojet are equal in range. 



