AIRPLANE PERFORMANCES — HAMLIN AND SPENCELEY 451 



Turning to the ram-jet airplane, it is astonishing to note that its 

 speed for best climb considerably exceeds the turbo] et's maximum 

 speeds at all altitudes up to 33,000 feet, but that its ceiling is quite low. 

 Maximum speed, 650 miles per hour, occurs at sea level, and the Mach 

 Number limitation on speed is obvious in the figure. Climbing speeds 

 aie about 90 percent of the maximum speeds. 



Although the ram-jet engine is hypothetical, and is undoubtedly 

 optimistic, it is interesting to note that 270 percent of the actual 

 thrust at 650 miles per hour at sea level is required to reach a Mach 

 Number of 1.0. Because of the fact that thrust increases greatly 

 with sjDeed, this represents an engine of 190 percent greater power. 

 Because of the impracticability of such high air speeds at high air 

 densities, sonic speeds may be regarded with considerable pessimism 

 in this case also. Nevertheless, from the standpoint of maximum 

 speed alone, the ram- jet excels the turbojet by as good a margin as 

 the latter excels the propeller. 



The rocket airplane excels in speeds at all altitudes by a wide margin. 

 At sea level the ram-jet is capable of competing for high speed, and 

 at altitudes up to 30,000 feet it also is similar in speed for best climb. 

 Since the rocket thrust remains constant, the rocket airplane is capable 

 of increasing its Mach Number with increase in altitude until it reaches 

 sonic velocity at about 24,000 feet. Thereafter maximum air speed 

 increases rapidly with altitude, the maximum limitation being imposed 

 purely by the available fuel. 



Speed for best climb is of interest, showing a best climbing speed 

 at approximately constant Mach Number up to the tropopause. Be- 

 yond this altitude the lower drag resulting from lower air densities 

 enables the best climbing speed to increase until at about 57,000 feet 

 Mach Number 1.0 is reached. Beyond this altitude, of course, per- 

 formance is dictated entirely by the available fuel consideration. 



3. Rates of climb and ceilings (fig. 19). — Maximum rates of climb 

 for both the propeller and turbojet airplanes are similar. The latter, 

 however, climbs at a much higher air speed, giving it a considerable 

 advantage in combat in that it therefore can determine the conditions 

 of engagement in combat or terminate it at will. The absolute ceiling 

 of 47,000 feet, compared with 41,500 feet, also adds to this advantage. 

 Climb and speed calculations for the propeller airplane are practically 

 independent of the small fuel consumption, while in the case of the 

 other three airplanes gross weight has necessarily been reduced ac- 

 cording to the rate of fuel consumption. It should be noted that the 

 larger fuel load in percent of gross weight for the turbojet will result 

 in appreciable improvement in climb performance during tactical 

 operation. 



Again, the excellence of low-altitude performance is noted for the 

 ram-jet airplane. Since its thrust falls oflf with air density, its ceiling 



