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National Resources Planning Board 



been abrupt, bill apparent periods of stngnntion merely 

 indicate times when research results are accumulating 

 while application is blocked at some point. At any one 

 time there is no lack of good ideas but the ideas may be 

 impractical imtil advances have been nuule in related 

 fields of science and teclmology. A tecluiical advance 

 comes only when the time is ripe. High-compression 

 engines could not be adopted until high-octane fuel 

 was commercially available. Landing gears could not be 

 retraced \mtil thick cantilever wings were in use, and 

 it was not worth-while to retract them until the speed 

 of flight became gi'eat enough to put a premium on 

 saving the drag of such exposed jiarls in spite of the 

 increased weight and cost of the retracting mechanism. 



The airplane flies in accordance with aerodynamic 

 piinciples which govern the phenomena of air flow. 

 Advances in aerodynamic knowledge set the trend of 

 design and stimulate the adoption of nonaerodynamic 

 features, which in themselves may load to further im- 

 provements in performance. Likewise, the engine and 

 propeller are fimdamental to the mechanics of flight 

 and improvements in the power plant are reflected in 

 improved airplane performance. Pilotmg is also an 

 essential element, and improvements in aids to naviga- 

 tion, in weather forecasting, and in radio have been 

 important stimulants to the growth of the industry. 



The effect of improvements arising as a result of 

 research is easily traced in the growth of air transport 

 from a daytime air-mail service in 1924 to the overnight 

 transcontinental sleeper service we have today. For 

 the year 1939 the air-transport planes, on domestic air 

 routes only, flew approximately 80,000,000 miles. 

 This development in only 15 years could never have 

 happened unless the public patronized the planes with 

 increasing confidence as the service improved. 



Dr. Edward Warner, in his Cabot Lectme of 1938 at 

 Norwich University, noted five major steps in air trans- 

 port's technical development: 



1925-29, increased wing loading; 

 1925-26, multiengined airplanes; 

 1929-33, N. A. C. A. cowling; 

 1930-36, high-octane fuel; 

 1933-34, controllable-pitch propeller. 



Each of these steps was marked by the general 

 adoption of a specific design feature wliich had a great 

 effect in improving the performance of the airplane and 

 consefjuently the service offered by the common carriers. 

 None of these features appeared at a single stroke, but 

 resulted from years of research and experiment with a 

 few false starts and failures. 



To consider these five steps in order, let us inquire as 

 to increased wing loading. The weight per sciuarc foot 

 carried by the wing increased only from about 8 pounds 

 in 1918 to 10 pounds by 1925. Smaller wings for the 

 same weight of airjjlanc mean more sj)eed, less dead 



weight, and a smoother ride. The wing loading for a 

 given safe landing speed increased after 1925 very 

 slowly, but in 1929 the Guggenheim prize was won by 

 a macliine using wing flaps temporarily to increase the 

 lift when landing. By 1933 such flaps were in general 

 use on air transports, permitting a wing loading of 15 

 pounds per square foot. Research had, in the mean- 

 time, shown how to design them and to ])redict their 

 effect. Wing loading has since doubled with a corre- 

 sponding reduction in wing area. 



The second major improvement in air transport 

 planes came with the introduction about 1925 of Ford, 

 Fokker, and Jimkei's midtiengined planes. Multien- 

 gined bombers had been used in the First World War 

 but were notoriouslj' inefficient, and needed all of their 

 engines to l;ee]) in the air. By 1935, however, inii)roved 

 engines and aerodj'uamie qualities permitted these new 

 transports to fly with one engine stopped. Results of 

 research allowed the use of this design feature that 

 greatly increased safety and, at the same time, made it 

 possible to build larger airplanes to carry greater loads 

 with lower cost. With the general adoption of multi- 

 engined transports, the industry expanded to handle the 

 increased traffic that resulted from reduced fear of a 

 forced landing. No passengers arc now carried on our 

 air hiu's in singlc-engincd machines. 



The third major step in improvement and in the 

 industry's growth had its origin in the construction in 

 1927 by the N. A. C. A. of a wind timnel large enough 

 to test a fuU-scale airplane with its regular engine and 

 propeller. AVith this equipment, it was discovered that 

 a very large part of the head resistance of the airplane 

 was due to the radial air-cooled engine. The engine 

 had to be exposed to the wind to keep it eool, but in 

 such a position, the air flow was spoiled for part of the 

 airplane behind it. Systematic research disclosed 

 means to smooth ovit the flow by means of a cowling to 

 lead air to and away from the cooling fins of the engine. 

 The cowl devised bj' Fred E. Weick, now known as the 

 N. A. C. A. cowl, reduced engine drag 75 percent. This 

 important saving permitted a sharp increase in speed 

 and economy of transport planes. By 1933 the N. A. 

 C. A. cowl and radial engines were standard on all 

 United States air lines, as well as in militarj' service, 

 ft is estimated that the fuel bill in 1939 for United 

 States domestic air lines was about $5,r00,000 and for 

 the Army and Navy at least $f),250,nC0. Ken oving 

 the N. A. C. A. cowls from a typical transport plane or 

 bomber would increase the drag approxin'ately 30 

 percent or reduce the speed 10 percent. To maintain 

 the same speed, the national fuel bill would be increased 

 $3,375,000. This sum represents an aimunl recovery 

 of many times the cost of the research. 



The N. A. C. A. cowl when first applied to single- 

 engine airplanes increased speed approximately 15 per- 



