464 



NA TURE 



[March 16, 1905 



noteworthy performances, the former having failed 

 to stem a wind of six to eight miles an hour, and 

 the latter having made progress at the rate of three 

 rniles an hour. We have before us a brief descrip- 

 tion of the machine with which Mr. Beedle made a 

 successful preliminary trial in November, 1903, and 

 further trials were promised for last spring. Mr. 

 Beedle proposed to dispense with rudders and steer 

 by means of a screw fan in front which could be 

 turned in any desired direction, an arrangement 

 calculated to leave much to be desired in the matter 

 of steadiness. The particulars are : — Length qo feet, 

 diameter 24 feet, horse-power 12. Of the Deutsch 

 " swimmer " only a model was exhibited at St. Louis. 

 A cornparison of the figures of several of these air- 

 .ships gives the impression that the Lebaudy balloon 

 is far ahead of most of its rivals in its welf designed 

 proportions. The only questionable feature is the 

 presence of horizontal 'rudders at the back of the car, 

 in a place where they might prevent the stream lines 

 pf air from closing round the balloon, and thus 

 increase the resistance. About this point MM. 

 Lebaudy are best able to judge. 



The limits of speed of the aerial swimmer attain- 

 able by existing methods are now pretty well known, 

 and fall far short of the amount necessary to travel 

 in the teeth of a high wind. Still, the navigable 

 balloon offers the most promising field of experiment 

 for those who are not prepared to devote themselves 

 to a long course of purely mathematical and experi- 

 mental researches, or to run blindfold into the 

 dangers which such a course of study would enable 

 them to predict. 



For the successful realisation of mechanical flight 

 proper, what is most wanted is a complete and ex- 

 haustive investigation, both by mathematical and 

 experimental methods, of the longitudinal stability 

 of various forms of machine gliding at various angles 

 either under gravity alone or when mechanically pro- 

 pelled. 



The small fluctuations of a gliding machine about 

 steady motion are determined by exponential functions 

 of the time the coeflicients of which are the roots of 

 an equation of the fourth degree. If these roots 

 determine oscillatory motions there will be, not one, 

 but two different oscillations of the machine in a 

 vertical plane. Either of these oscillations may 

 increase or decrease with the time, and unless they 

 both tend to decrease the pitching will become 

 dangerous and the machine will overturn. Photo- 

 graphs of the paths of gliders taken bv Mr. Williams 

 some time ago with magnesium light distinctly 

 showed the two oscillations, and in several cases the 

 final overturning in a manner perfectlv consistent 

 with theory. 



Now it is possible to determine experimentally for 

 any given machine the coefificients of stability when 

 gliding at every different angle. To do this it would 

 be necessary to measure, by means of dynamometers, 

 the fprce and couple components acting on either a 

 full-sized rnachine or a model when moved through 

 the air in different directions in its plane of symmetrv. 

 It is necessary also to take account of the small 

 changes in these forces and couples when the machine 

 has a small rotational motion, such as occurs when 

 it is turning upwards or downwards in the course of 

 Us oscillations. These small changes mav, and in all 

 probability do, play an important part in affecting the 

 stability. A whiriing table gives exactly the kind of 

 small rotation required in addition to 'the necessary 

 translatory motion. By reversing the model experf- 

 mented on, the direction of this rotation may be 

 reversed, and the differences of the two sets of 

 dynamometer readings will give three of the coefficients 

 ■-' - :.b;iity. 



XO. 1846, VOL. 7 l] 



If observations of this kind were made it would 

 be possible to work out on paper the oscillations, and 

 to ascertain the lowest velocity at which a machine 

 would glide safely. 



But experimenters have hitherto confined their 

 attention to measurements of the air resistance, and 

 very few have up to the present given much atten- 

 tion even to the variations in the position of the 

 centre of pressure except for a few cases such as a 

 square lamina. The object in most cases has been 

 merely to find out the speed at which a flying machine 

 would travel under favourable conditions, and not its 

 powers of extricating itself from the most unfavour- 

 able positions which it might assume on a gusty day. 

 " Stability of motion " is a phenomenon which rarely 

 enters into practical problems. In the flying 

 machine it is of paramount importance. 



A similar mathematical investigation has been 

 made by Signor G. A. Crocco in Italy, in connection 

 with stability of airships, but the author obtains 

 an equation of the third instead of the fourth degree. 

 He, however, takes no account of the fluctuations in 

 the horizontal motion, which are certainly of 

 importance in the case of gliders. 



Meanwhile the artificial balancing of gliders under 

 gravity has been the subject of a considerable number 

 of experiments in America, and more recently in 

 France, and the initial success of Mr. Orville Wright 

 in rising from the ground on a motor-driven machine 

 in the face of a wind^ and landing safely constitutes 

 the first achievement of an actual flight. It is a 

 matter of congratulation that Mr. Wright was not so 

 emboldened by his success that he became reckless, 

 and pushed the experiments on to a premature 

 end. 



The large curved surfaces of the disastrous 

 Lilienthal and Pilcher experiments have now given 

 place to a pair of narrow superposed rectangles, first 

 introduced by Chanute and Herring. The tail has 

 since, in the hands of Messrs. Wilbur and Orville 

 Wright, been replaced by a front rudder, and the 

 adoption of a horizontal position " k plat ventre " 

 shows that the maintenance of balance has been 

 reduced to a matter of steering. 



These types of gliders have been taken up in 

 France by Captain Ferber, of the Artillery, and 

 subsequently by Mr. Ernest Archdeacon, both of whom 

 have become enthusiastic "aviators," and have in 

 their turn brought gliding experiments into consider- 

 able popularity in that country. As Captain F"erber 

 remarks, a sloping hillside with a wind blowing 

 straight up it are necessary, and a convenient experi- 

 menting ground has been found at Meudon. With 

 the object of experimenting on larger motor-driven 

 models Captain Ferber constructed an aerodrome 

 consisting of a column eighteen metres high, support- 

 ing a rotating beam thirty metres across. This 

 apparatus would be very useful for determining the 

 stability coeflicients of an actual machine firmly 

 attached to its beam, but it must not be forgotten 

 that any kind of suspension may seriously modify 

 the longitudinal oscillations. So, too, may the rota- 

 tion about the vertical axis ; it is much easier to make 

 a glider describe a corkscrew path than glide in a 

 straight line. A kite illustrates the same properties. 

 Its oscillations also depend on a biquadratic equa- 

 tion, but the supporting string modifies their 

 character, and Mr. Cody claims that a man has 

 been lifted 1600 feet by kites, though how the (>hoto. 

 graph of " the Cody man-lifting kite 800 feet high " 

 was taken, which appears in the Aeronautical ]our\ial, 

 is not explained. The use of kites for saving 

 life at sea might well receive more attention than 

 has been bestowed on this question up to the present. 

 The clumsy plan of sending up rockets in the teeth 



