Industrial Research 



141 



Airplane Design 



(1) Multiengined airplanes; The desire to build 

 larger airplanes led the industry to undertake multi- 

 engined designs as soon as the state of the art permitted. 

 The initiative lay with the industry. 



(2) Steel construction: Beginning with Foldver's 

 weldcd-mild-steel-tube fuselage, the industry quiclvly 

 adopted alloy tubing when it became available in the 

 automotive industry. 



(3) Stressed-skin construction: When increased 

 speeds made fabric covered frameworks inadequate to 

 carry high local air loads, the industry adopted metal 

 coverings. Designers had to use this skin as a stress- 

 carrying element, but had no rules to guide them. 

 Research at the N. A. C. A., National Bureau of 

 Standards, Massachusetts Institute of Technology, and 

 California Institute of Technology provided criteria 

 for allowable stresses in thin structural elements. It 

 may be said that the heavy all-metal monoplane wings 

 would not have been used until high wing loadings, 

 cowled engines, retracted landing gears, and high speeds 

 were current. Also, such wings could not be designed 

 with confidence until research data were available. 



(4) Plastic construction: It is too early to evaluate 

 the effect of reinforced plastics in stressed-skin airplane 

 construction, but the advantages are obvious and re- 

 search in the industry is very active. One may predict 

 with confidence that a successful application will be 

 made. 



(5) Cantilever monoplane: This development was 

 stimidated by N. A. C. A. aerodynamic research which 

 showed its advantages and showed that a thick wing 

 need not be inefficient. The actual construction was 

 undertaken by the industry when duralumin became 

 available. 



(6) Retractable landing gear: Increased speed as a 

 result of aerodynamic refinement made a retracting 

 landing gear worth-while. The idea was embodied 

 in a racing airplane as early as 1922, but was then con- 

 sidered impractical. With thick cantilever monoplane 

 wings, retracting the wheels into the wings became 

 relatively simple. An important gain in speed resulted . 

 A further development by the industry is a mechanism 

 bj' which the landing wheels on cantilever struts are 

 rotated during retraction so as to fit into the thin wings 

 of a pursuit type airplane. 



(7) Tricycle landing gear: The placing of a castering 

 wheel in advance of the main landing wheels is not new 

 but has been revived for modern transports to avoid 

 instability when running on the ground and to facilitate 

 the use of the new "blind landing" system. The tri- 

 cycle gear is not in itself a research result, but its re- 

 adoption was the result of N. A. C. A. research indicat- 

 ing its fundamental advantages, and was necessary 



to take advantage of other advances in the art which 

 require a new landing technique. 



(S) Hydraulic retraction: Research in the industry 

 has developed a hydraulic shock strut that may also 

 be used to retract the landing wdieels. This device 

 has made it possible to build "amphibians" without 

 excessive weight penalty. 



(9) Retracting wing floats: Similarly the industry 

 has developed a retracting wing float for high-speed 

 flj'ing boats. 



(10) Wheel brakes: Wheel brakes independently 

 operable were experimented with and their advantages 

 for maneuvering airplanes on the ground and for 

 shortening the landing run weie presented by Porter 

 H. Adams in 1915. They were introduced in industry 

 in 1929. The gain in operation efficiency for air trans- 

 port service is important. 



Engines 



(1) Air-cooled radial: The greatest factor in the 

 improvement of American airplanes in the 1920's is 

 without doubt the air-cooled engine, originally devel- 

 oped by the industry with Navy backing. Such a 

 light, efficient, and reliable power plant could be pro- 

 duced only when research and development work in 

 many fields had progressed to the point of useful appli- 

 cation. In that connection may be mentioned light- 

 alloy castings, e.xhaust-valve steel, salt-cooled valve 

 design, special bearing metals and lubricants, light 

 reduction gears, special-precision machine tools, heat- 

 transfer data, high-output cylinder design, improved 

 spark plugs, improved steel forgings, etc. 



(2) Twin-row air-cooled radial: The output of the 

 air-cooled engine has recently been greatly increased 

 by tlie twin row without sensible increase of frontal 

 area. Such engines are made possible by more effective 

 baffling and cooling, vibi'ation elimination, better con- 

 trol of carburetion, and in general by an enormous 

 amount of research and testing by the industry. 



(3) Liquid-cooled engines: The successful develop- 

 ment in this country of high-output liquid-cooled en- 

 gines similar to those in use abroad for high-speed 

 pursuit airplanes is a notable achievement. This type 

 of engine has been produced bj' the automotive industry 

 through its own research, with Army backing. 



(4) Dynamic damping: The practice of djmamic 

 damping of crankshaft vibration has greatly improved 

 engine performance and safety. A widely used prac- 

 tical solution is based on theoretical work in a uni- 

 versity laboratory. 



(5) Dynamic suspension: The current method of 

 mounting engines, by so positioning the angular bracing 

 with relation to the center of mass of the engine that 

 engine vi])ration has little disturbing effect on the main 



