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Aviation History
1909
1909 - 0282.PDF
MAY 15, 1909. PRESENT STATUS OF MILITARY AERONAUTICS. By GEORGE O. SQUIER, Ph Continued Stability and Control. The question of stability is a serious one in aviation, especially as increased wind velocities are encountered. In machines of the aeroplane type there must be some means provided to secure fore and aft stability and also lateral stability. A large number of plans have been proposed for the accomplish- ment of these ends, some based upon the skill of the aviator, others operated automatically, and still others employing a combination of both. At the present time no aeroplane has yet been publicly exhibited which is provided with automatic control. There is little difference of opinion as to the desirability of some form of auto- matic control. ' The Wright aeroplane does not attempt to accomplish this, but depends entirely upon the skill of the aviator to secure both lateral and longitudinal equilibrium, but it is understood that a FOOT SQUARE 30 SOARING PLANE WEIGHING ONE POUND 20 30 HO 50 80 70 80 90 VEL0CITY,-MILE3 PER HOUR ' ii Diagram C. :• .;•;.-, -.. device for this purpose is one of the next to be brought forward by them. Much of the success of the Wright Brothers has been due to their logical procedure in the development of the aeroplane, taking the essentials, step by step, rather than attempting everything at once, as is so often the practice with experienced inventors. * The aviator's task is much more difficult than that of the chauffeur. With the chauffeur, while it is true that it requires his constant FOOT SQUARE SOARING PLANE WEIGHING ONE POUND TOW-LINE H0RSE-LOAD,-LBS. so «o 10 eo VELOCITY,-M1LES PER HOUR. Diagram D. .D., Major, Signal Corps, U.S. Army. from page 270.) attention to guide his machine, yet he is travelling on a roadway where he can have due warning, through sight, of the turns and irregularities of the course. The fundamental difference between operating the aeroplane and the automobile, is that the former is travelling along an aerial high- way which has manifold humps and ridges, eddies and gusts, and, since the air is invisible, he cannot see these irregularities and inequalities of his path, and consequently cannot provide for them until he has actually encountered them. He must feel the road since he cannot see it. Some form of automatic control whereby the machine itself promptly corrects for the inequalities of its path is evidently very desirable. As stated above, a large number of plans for doing this have been proposed, many of them based on gyrostatic action, movable side planes, revolving surfaces, warped surfaces, &c. A solution of this problem may be considered as one of the next important steps forward in the development of the aeroplane. V ' ••':; Hi. HYDROMECHANIC RELATIONS. SOME GENERAL RELATIONS BETWEEN SHIPS IN AIR AND WATER. F • At the present moment so many minds are engaged upon the general problem of aerial navigation that any method by which a broad forecast of the subject can be made is particularly desirable. Each branch of the subject has its advocates, each believing implicitly in the superiority of his method. On the one hand the adherents of the dirigible balloon have little confidence in the future of the aeroplane, while another class have no energy to devote to the dirigible balloon, and still others prefer to work on the pure helicopter principle. As a matter of fact, each of these types is probably of permanent importance, and each particularly adapted to certain needs. Fortunately for the development of each type, the experiments made with one class are of value to the other classes, and these in turn bear close analogy to the types of boats used in marine navigation. The dynamical properties of water and air are very much alike, and the equations of motion are similar for the two fluids, so that the data obtained from experiments in water, which are very extensive, may with slight modification be applied to computations for aerial navigation. Helmholz' Theorem.—Von Helmholz, the master physicist of Germany, who illuminated everything he touched, has fortunately considered this subject, in a paper written in 1873. The title of his paper is "On a theorem relative to movements that are geome- trically similar in fluid bodies, together with an application to the problem of steering balloons." In this paper, Helmholz affirms that, although the differential equations of hydro-mechanics may be an exact expression of the laws controlling the motions of fluids, still, it is only for relatively few and simple experimental cases that we can obtain integrals appropriate to the given conditions, particularly if the cases involve viscosity and surfaces of discontinuity. Hence, in dealing practically with the motion of fluids, we must depend upon experiment almost entirely, often being able to predict very little from theory, and that usually with uncertainty. Without integrating, however, he applies the hydrodynamic equations to transfer the observations made on any one fluid with given models and speeds, over to a geometrically similar mass of another fluid involving other speeds, and models of different magnitudes. By this means he is able to compute the size, velocity, resistance, power, &c, of aerial craft from given, or observed, values for marine craft. He also deduces laws that must inevitably place a limit upon the possible size and velocity of aerial craft without, however, indi- cating what that limit may be with artificial power. Applying this mode of reasoning to large birds he concludes by saying that, " It therefore appears probable that in the model of the great vulture, nature has already reached the limit that can be attained with the muscles as working organs, and under the most favourable condi- tions of subsistence, for the magnitude of a creature that shall raise itself by its wings and remain a long time in the air." In comparing the behaviour of models in water and air, he takes account of the density and viscosity of the media, as these were well known at the date of his writing, 1873 ; but he could not take account of the sliding, or skin-friction, because in his day neither the magnitude of such friction for air, nor the law of its variation with velocity had been determined. 284
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