CHAPTER VI 



CONSTRUCTION OF SUPPORTING SURFACES 



. An examination of the wings of birds, whether those of soarers or of any- 

 other type, impresses one not only witli the general strength of the wing, but 

 also with the fact that, while it possesses considerable stiffness, there is also a 

 graduated pliability, not only of the whole wing, including the bones, but more 

 especially in the feathers, the rear tips being exceedingly pliable so that, when 

 the wing is held in a stiff breeze, they are seen to be easily deflected in a gentle 

 curve towards the rear and upper side. This lack of rigidity has several ad- 

 vantages, among the more notable of which is the lessening of the strains on 

 the wing caused by sudden wind gusts. Of great importance is the further fact 

 that a supporting surface having a graduated pliability, such as is possessed 

 b\ a bird's wing, does not experience a shifting of the center of pressure to 

 the same extent as a rigid surface of similar form. Furthermore, since any 

 bird, even the best soarer, must use its wings not only for soaring, but, when 

 starting to fly from a state of rest, for flapping, a rigid surface would not 

 furnish anything like the same universally available sustaining and propelling 

 means that the bird's wing does. 



In an inspection of the various wings or supporting surfaces which Mr. 

 Langley built, from the very earliest rubber-pull models up to the successful 

 steam machines Nos. 5 and 6, the point which is most impressed upon the ob- 

 server is the increasing strength and rigidity embodied in these wings. While 

 the success with the later models was due to many things, including the devel- 

 opment of a strong frame and a suitable power plant giving sufficient power 

 for the permissible weight, besides the very important development of effec- 

 tive ei|iii!ihr'mm mechanism, yet it is safe to say that even with the development 

 of all these other things to the state to which they had been brought in 1896, 

 success would not have been achieved had not the wings themselves been simul- 

 taneously changed from the very flimsy construction which was at first used to the 

 later type, using a verj strong and rigid wooden frame over which the cloth cover- 

 ing was tightly stretched, and which possessed only a small amount of pliability 

 at the extreme rear ends of the cross ribs. 



The development of this successful type of win.:;' for the models, it will be 

 remembered, had been achieved only after an extensive series of experiments ; 

 and it was realized thai the construction of suitable wings for the large aero- 

 drome, even with the knowledge gained in the early work, would be still more 



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