6:o 



NA TURE 



[October 29, 1908 



longitudinal stability of the aerostat or aeroplane, de- 

 pends, we believe, on the roots of a biquadratic equa- 

 tion, but in this case there appear to be two critical 

 velocities, one an inferior and the other a superior 

 limit to the speed. Of these the superior limit has 

 been reached in bicycling in the wake of an express 

 train. But bicycles are frequently ridden at speeds 

 below the inferior limit, being' kept upright by careful 

 balancing involving no conscious effort on the part 

 of the rider. It is highly probable that in many 

 circumstances longitudinal instability may be equally 

 well counteracted by the unconscious efforts of the 

 .•iviator. Regarding the recent successes, evidence is 

 far too conflicting to en.able judgment to be passed in 

 this review as to whether the machines were really 

 stable, though there is equally no evidence to show 

 that thev were not. 



" Now M. Leon Delagrange, after making quite a 

 number of short flights (the longest about 200 feet) with 

 his motor llying-machine, has found it advisable to go 

 with M. Voisin, the cleverest of the French flying- 

 machine pilots, to experiment with a gliding machine 

 on Ihe sand-hills near Le Touquet." ' 



However probable it may be that a man-carrying 

 machine is automatically stable, the performanc? of a 

 successful directed flight can never definitely answer 

 the question how far the success is due to automatic 

 stability and how far to the skill of the operator. 

 It may be that with a little experience something short 

 of truly automatic stability is sufficient for all prac- 

 tical purposes ; on the other hand, a great many writers 

 who place their views before the public insist on auto- 

 matic stability as a sine qua non. The evidence de- 

 rived from uncontrolled aerodromes such as th'ise 



rAR>\AN(«n«»flJ») S*NTOSDllMONT fORNU d,UV*ULX 



KAPPERER. 



BLCR^OT (^tPHRFtfJ 



Plans of the principal A-iroplane^. From " Le Probleme de l'.\viation," with slight modification. 



Chanute long ago experimented on automatic 

 stability, and stated that his gliding machines had 

 special appliances for securing it.' It is scarcely pos- 

 sible that Chanute's methods have not been utilised 

 b)- the Wrights. Vet according to the papers the French 

 aviators, while expressing great admiration for the 

 Wriijht performances, are of opinion that the successful 

 balancing of the Wright machine is mainly a feat of 

 skill on the part of the aviator, and that their object 

 has been to construct machines with which anyone can 

 fly. In support of this view we read that " neither 

 M. Delagrange nor Mr. Farman had ever driven an 

 .-leroplane before the last eight months."- On the 

 other hand, we were told more than a year ago that 



1 See, tf.^., Casstfrs Magazine, June, 1901. 

 - AcfonautkSy Augus*, igo8, t>. 61. 



used by Langley enables the question of automatic 

 stability to be tested much more definitely. The recent 

 reprint of Langley's researches will always prove a 

 valuable contribution to the literature of aviation. - 

 But in employing results of experiments with small 

 models to draw conclusions about larger machines, 

 everything depends on a correct appreciation of the 

 theory of dimensions, and who is there that is suffi- 

 cient of a mathematician that he can be absolutely 

 trusted not to drop into one of the innumerable pitfalls 

 that beset this elusive but valuable method of general- 

 isation ? 



Even to make a machine flv steadily in a horizontal 



1 Aniet-ican Magazine of Acrottnutks, July. 1907, p. 8. 



2 "Researches and Experiirents in Aerial Navigation." Bj'.S. P. Langley. 

 Reprinted from the Smithsonian Re;}orts. (Washington ; Government 

 Printiii.;; Office, 190S.) 



vn. 2 



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