AIR TRANSPORT — ^DURAI^D 523 



volume of air is drawn into a cylinder of an airplane engine for every 

 cycle of engine operation. Of this air about 23 percent is oxygen. 

 At sea-level pressure and density, this will provide for the burning 

 of a proportionate amount of fuel with the corresponding develop- 

 ment of power. The same volume of air drawn in at the density of 

 20,000 feet elevation would have only 45 percent of the weight of 

 oxygen at sea level with a corresponding reduction in power de- 

 veloped. The corresponding figures for altitudes of 30, 40, and 50 

 thousand feet would be respectively, 13, 18, and 11 percent of the 

 oxygen at sea level. 



It is, therefore, evident that if anything approaching full engine 

 power is to be maintained at high altitudes, the air going to the 

 engine must be precompressed to something approaching sea-level 

 pressure and density. Or, put otherwise, the more nearly these con- 

 ditions can be approached, the greater the power developed at alti- 

 tude and the higher the altitude ultimately reached. 



So then, combining this condition with those previously noted, it 

 works out that an altitude approaching 60,000 feet is within the 

 framework of possible achievement without trespassing on what might 

 be considered the fantastic. The present record is close to 53,000 

 feet (52,937) held by an English pilot. 



There are many difficulties and limitations against which the 

 struggle for high altitude must be made. Only a few of the more 

 serious can be here noted. 



1. Of the total power developed by the fuel burned, only a part 

 can be used for climbing, since a part must be made available for 

 the precompression of the air, a part which grows ever larger and 

 larger the higher the altitude achieved. 



2. No matter where it is in climbing flight, the weight of the 

 plane together with the vertical component of the drag must be 

 balanced by the reaction of the air on the plane together with the 

 vertical component of the pull of the propeller. But the weight of 

 the plane remains constant, except for the decrease by way of the 

 combustion of fuel, while the density of the air, on which lift de- 

 pends, grows less and less with increasing altitude, thus calling for 

 higher and higher speeds through the air. The resistance to motion, 

 for the same speed, is indeed correspondingly reduced, so that higher 

 speed becomes possible; but the actual relations are complex, and 

 it works out that there is difficulty at the propeller (even with the 

 modern variable-pitch forms) in transforming with high efficiency 

 such power as it receives from the engine into useful propulsive 

 work; and this difficulty increases the higher the altitude. Add to 

 these difficulties reliable oxygen equipment for the pilot with cloth- 

 ing for protection against temperatures somewhere about 67° below 

 zero, Fahrenheit, and it is seen that the attempt to scale the ultimate 



