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National Resources Planning Board 



tunnel experiments, but results were not of major 

 importance. In general, designers tested new ideas by 

 trial flights or by ad hoc wind-tunnel tests. 



During the First World War, experimental aerody- 

 namics expanded rapidlj', but the pressure for routine 

 testing of current designs side tracked systematic 

 research. The momentum of the war period carried 

 on for several 3'ears, but by 1925 the airplane, although 

 refined as a result of manj' minor improvements, 

 ceased to progress by customary cut-and-tr\- methods. 

 The airplane designer now needed fundamental guidance 

 in applied aerodjmamics. He received it in full measure 

 from the National Advisory Committee for Aero- 

 nautics whose laboratories at Langlcy Field, started 

 in 1917, had been steadily ])ublishing systematic wind 

 tunnel research data. Some of their more valuable 

 contributions are listed below: 



(1) The determination of the aerodynamic loadings on 

 wing, tail, and control surfaces in steady flight and in 

 maneuvers, and pressure-distribution data led to more 

 economical structural designs. Designers became con- 

 scious of the relative costs of drag and structural 

 weight. They were provided wnth criteria and methods 

 of analysis from which they could proceed with con- 

 fidence. The wired biplane was soon replaced by the 

 cantilever monoplane. 



(2) In the early years of the airplane, wing profiles 

 were drawn up arbitrarily by their designers. The 

 N. A. C. A. published characteristics for a codified and 

 classified series of systematic variations. Its 2,300 

 series has been notably successful and has had world 

 wide application. 



(3) High-lift devices: The trailing edge flap, the 

 slotted flap, and its variants were invented by indi- 

 viduals in the industry, but the N. A. C. A. has been 

 of great assistance in evaluating the effectiveness of 

 such devices and in publishing aerodynamic data 

 regarding their operation. Such devices are now in 

 general use. 



(4) Low-speed control: The N. A. C. A. data on 

 flow separation and stalling led to the design of im- 

 proved methods of control. 



(5) Spinning: Special laboratory and niathemalical 

 analyses by the N. A. C. A. of this dangerous fault in 

 an airplane have given a better understanding of the 

 mechanics of the motion and the cure for it. Practical 

 solutions are made by the airplane designer (vertical 

 tail-surface location). 



(6) Flutter: Again special laboratory and mathemat- 

 ical analyses by the N. A. C. A. have given a rational 

 theory of the mechanics of wing flutter as a foundation 

 for the designer's practical solution (mass balancing of 

 control surfaces). 



(7) Rotating wings: The N. A. C. A. has supplied 



the basic theory and the experimental coefficients for 

 designers of helicopters, autog3'ros, and other rotating 

 wing craft. The inventions have come from individ- 

 uals, the theory from the laboratorj-. 



(8) Full-scale testing: N. A. C A. work with air- 

 planes in flight, equipped with complete instrumenta- 

 tion to record behavior, has given an engineering foun- 

 dation to performance estimation. In particular, flight 

 check on spinning-tunnel results, full-scale measurement 

 of profile drag by the use of the wake comb, low- 

 friction laminar-flow wings, aileron-control studies, and 

 Reynolds Number effects have supplied fundamental 

 data and methods to designers. 



(9) Tank testing: The design of flying boats is based 

 on model tests in the towing tank. American flying 

 boats now enjoy a superiority that can be attril)iited in 

 large part to the research work of the tank at Langlev 

 Field. 



(10) Skin friction: The theoretical analysis of skin 

 friction (Prandtl and von Karman) has been develop- 

 ing for more than 30 years, but its practical applications 

 have not as yet been impressive. Langley Field wind- 

 tunnel work, however, has given important guidance to 

 designers by evaluating the cost in drag of roughness of 

 surface. Research conclusions have recently stimu- 

 lated designers to the introduction of flush riveting and 

 new standards of surface smoothness for high speed 

 airplanes. 



(11) Compressibility: Progress toward higher speeds, 

 approaching the velocity of sound where the compressi- 

 bility of the air changes the flow pattern, depends on 

 specialized wind tunnel equipment. Research of the 

 N. A. C. A. has given designers information as to sharp- 

 nosed wing and propeller profiles, easier body forms, and 

 other data vital to the design of high-speed airplanes. 



(12) Engine cooling: The N. A. C. A., by means of 

 tests in its large-scale wind tunnels, showed the industry 

 how to enclose air-cooled engines %vith minimum drag. 

 Progress in this avenue of research is continuing with 

 the promise of further substantial gains in speed and 

 economy. 



(13) Engine location: Systematic wind-tunnel re- 

 search by the N. A. C. A. on the best location for engines 

 of multiengined airplanes has had the efl"ect of stand- 

 ardizing the monoplane wing with two or four engines 

 in the leading edge. This contribution to practical 

 design originated in the laboratorj-. 



(14) Propellers: By means of systematic studies of 

 model propeller performance, the aerodynamic design 

 of airplane propellers has been standardized. The 

 mechanical design of propellers, notably the variable- 

 pitch constant-speed feature, was evolved by the in- 

 dustry. The N. A. C. A. contribution is to the predic- 

 tion of performance. 



