AIRPLANE PERFORMANCES — HAMLIN AND SPENCELEY 441 



Next in bulky space requirements is the turbojet, nearly one-quarter 

 of the volume of which is compressor entrance air supply ducting in 

 an average installation. This feature requires a relatively large nacelle 

 or, because of the weight and diameter, dictates the fuselage size and 

 arrangement in a single-engined airplane. 



Although the internal-combustion engine is small, the space require- 

 ments are nearly doubled by carburetor, oil cooler, and Prestone radia- 

 tor air scoops and ducting. Fortunately, the main component parts, 

 the engine, oil coolers, and Prestone coolers, may be disposed about 

 the airplane structure to best advantage. 



The rocket motor is by far the smallest and simplest from the design 

 standpoint. Air-intake ducts are always a problem, and at high flight 

 speeds considerable research is necessary before satisfactory solutions 

 will become available. In the case of the rocket, no air is taken aboard 

 for the power plant, thus eliminating this problem. Note that the 

 total rocket motor volume equals only the air ducting required for the 

 reciprocating engine and that the power plant consists of two simple 

 components that may be located at the designer's discretion. 



In the frontal area comparison both air-stream engines will dictate 

 the fuselage maximum cross section; the conventional engine and 

 cooling system will definitely have an influence upon this design 

 feature, but the rocket eliminates this problem. 



Referring to figure 8, the additional volume required by the fuel is 

 indicated by the slope of the curves. Here again, the rocket is criti- 

 cally limited in duration. Following in increasing order of prefer- 

 ence are the ram-jet, turbojet, and propeller. Fuels are gasoline at 

 6 pounds per gallon for the propeller, kerosene at 6.7 pounds per gal- 

 lon for both air-stream engines, and equivalent densities of the 

 combined fuel and oxidizer for the rocket of from 8.4 to 11.2 pounds 

 per gallon depending upon the fuels chosen. 



11. Engine air requirements (fig. 9) . — In designing air-intake ducts 

 the relative problems are indicated by the engine air requirements 

 shown in the figure for maximum thrust conditions, which would 

 represent take-off, climb, and high-speed operation. 



Since the ram- jet curves approximate a straight line through the 

 origin, the scoop entrance velocity will be a relatively constant per- 

 centage of airplane speed. Volume of airflow is extremely large, 

 indicating difficult problems to be solved. 



The turbojet evidences only a slight increase in air consumption 

 with air speed, indicating that the optinmm entrance duct efficiency 

 for a fixed entry will depend upon the conditions selected in the design. 

 Again, large airflows must be handled. In the case of both air-stream 

 engines the ram drag due to taking this air aboard has been subtracted 

 from gross jet thrust to arrive at the maximum thrust available as 

 shown in figures 1, 2, and 3. 



