94 Miracles Ahead! 



celerated through a tunnel toward the rear by an engine- 

 driven compressor or blower. Fuel is burned in the air stream 

 just before ejection at the nozzle. Since the oxygen used by 

 the plane must be obtained from the air in which the plane 

 flies, it, like other planes, is limited by the atmospheric pres- 

 sure at high altitudes. 



A rocket-propelled craft of the future, which carries its 

 own fuel and oxygen, would become more and more efficient 

 as it gained speed. In a perfect vacuum the plane would, the- 

 oretically, be 100 per cent efficient because the forward veloc- 

 ity of the plane would equal the velocity of the propulsion 

 jet. 



Radio Aids 



Numerous other wartime devices will be on hand to aid 

 postwar commercial aviation. David Sarnoff, president of 

 Radio Corporation of America, predicts a great advance in 

 the science of radio, in which radio instruments will emerge 

 from the war "almost human in their capabilities." 



He pointed out that "the radio direction finder, which here- 

 tofore had only an ear, now also has an eye. The safety of avi- 

 ation will be greatly enhanced, for the aviator will be able 

 to see the ground through clouds or darkness. By the scien- 

 tific application of the radio echo, the radio 'eye' will avert 

 collisions, while the radio altimeter will measure the altitude 

 and warn of mountains ahead or structures below." 



The radio altimeter (or absolute altimeter) is a great im- 

 provement over the instrument used in past years. This altim- 

 eter is operated by the change in air pressure, and it gives only 

 the altitude above sea level. A pilot flying at five thousand 

 feet might pass over a peak at an altitude of only fifty feet, 

 but the altimeter would show the altitude as five thousand 

 feet. 



