The Science of Aviation.
(By L. J. Lesh, the "Boy Aviator.")
There is probably no problem in engineering mechanics which boasts such a scarcity of reliable data as the new-found science of aviation. Countless experiments and calculations have established the art of hydrogen ballooning on a fairly stable mathematical basis, but the design of gasless or " heavier-than-air " flying machines still involves a dangerous amount of guesswork. Aeronautical engineers who have had experience in the design of aeroplanes realise the inadequacy of the formulae and tables at our disposal to cope with new developments, and we feel seriously hampered thereby in our ambition to work out original plans which do not permit of exact calculation and verification of principles before the machine is put into the air. However, with a fair knowledge of the general principles of flight and the design of machines, a builder should be able to construct an aeroplane (employing a high factor of safety) and to carry on his experiments safely without going into the deeper mechanics of flight, which are rather complicated and had best be left to the scientists who are perfecting these formulae and tables by means of laboratory experiments. As this paper is to deal exclusively with aeroplanes, I will not consider other types of flyer such as the gyro-plane, helicopter, and ornithopter. After constructing and testing many different types of aeroplane, experimenters have produced three general types of machine which can prove their ability to take to the air under favourable conditions and
stay aloft until the motor gives out or an accident occurs to the wings or rudders These types are the monoplane, invented by Lilienthal and reach ins 1 its highest development to date in the Bleriot and R. E P. machines ; the following surface flyer invented bv Professor Langley and copied by Bleriot; the Chanute types (two-deck, three-deck, and multiple wing) invented by Octave Chanute, perfected in part by the Wright Brothers, and imitated by Santos Dumont and the Voison Freres, constructors of the Delagrange and Farman flyers. The monoplane flyer has met with considerable favour among designers because of its similarity to the soaring birds which give us daily proof that flying can be accomplished on wings of the monoplane plan. The simplicity of this type also makes it comparatively easy to calculate beforehand the exact values of the wings and the power required for propulsion, thus giving the engineer who adopts this design something of an advantage over the experimenter who plans a machine of the Langley or Chanute types The principal disadvantage of the sin-gle-plane fiver is its lack of inherent stability during flight, since it is quite out of the question to devise artificial surfaces whHi duplicate + he complicated balancing movements of the soaring bird's wing Experimenters have attempted to balance monoplanes by shifting weights and by various vertical and horizontal rudders, but these methods of control are seldom resorted to by the birds, and in adopting them for their machines, inventors have imitated Nature's design without following her excellent example as to principles of operation In this connection it might be well to call attention to the fact that one experimenter at least attempted to build a machine that would duplicate the soaring of birds as he explained the phenomenon after thirty years of observation, but he did not live to realise his ambition. This man was Louis Pierre Mouillard, a wonderfully patient and accurate observer, who was unfortunate, however, in his methods of experiment and finally became despondent through his failure to launch a machine which was probably quite capable of soaring had it been skilfully manipulated He was enabled to carry on his work through the generosity of O. Chanute and it now seems that if he had adopted that excellent engineer's methods of experiment he would have excelled the performance of Lilienthal and probably equaled the flights of the Wright glider. The monoplane in its simplest form, as devised by Lilienthal, was intended merely for experiments in gliding flight, and since the whole weight carried through the air was not very great, It was a comparatively simple matter for the aviator to balance the wing's during Avind gusts by shifting his weight. Such an apparatus, spreading some 200 square feet of supporting surface, can be made of wood, wire, and cloth so as to weigh about fifty pounds; but when the surfaces are enlarged and a motor added, the disturbing forces cannot be met bv shifting the centre of gravity and new controlling influences must be utilised to maintain the equilibrium. If the mam supporting surfaces are rigid and shaped to the plan, curvature, and attitude of the soaring or sailing birds (wings tilted upward at a dihedral angle as the buzzard or arched downward in the attitude of the sea gull), then the main dis-
turbances to be overcome are, first, fore-and-aft oscillation resulting in dangerous downward plunges ; second, lateral oscillation during changes in direction and velocity of the wind. Fore-and-Aft Stability. — This problem may be solved by hinging the sustaining wings in such a way as to permit their flexing backward and forward, adjusting the < outre of pressure to the variations in velocity of the wind and to changes in the angle of incidence of the machine to the air current. This is the way of the birds and it was adopted by Mouillard and later by Chanute, who utilised the principle to good effect in his multiple wing glider, but the device has never to my knowledge been tested on a motor-driven flyer. Presentday experimenters prefer to maintain fore-and-aft balance by means of horizontal rudders and shifting weights or merely by accelerating and retarding the motor. Any one of these methods might be sufficient for ordinary conditions but they are certainly inferior to the way of Nature, which is positive under all conditions and has the advantage of automatic action which leaves the aviator free to attend to other things connected with the machine's management. Lateral Stability. — The second problem constitutes the principal drawback to the development of aeroplanes whether they be of the monoplane, multi-plane, Langley, or Chanute type and as yet no satisfactory solution of the problem has ever been made public. Some few experimenters have made indifferent attempts to maintain lateral balance by means of some special attitude of the wings, shifting weights, or vertical keels, but the greater proportion of designers are either entirely ignorant of the importance of this feature, or they purposely ignore it for reasons that reflect no credit on their inventive ability. The writer made a careful stoidy of the problem of lateral balance during experiments with ten different aeroplanes, but this work had to be supplemented by several months of concentrated theoritical investigation before a satisfactory plan was found.
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Bibliographic details
Progress, Volume IV, Issue 5, 1 March 1909, Page 156
Word Count
1,130The Science of Aviation. Progress, Volume IV, Issue 5, 1 March 1909, Page 156
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