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Aviation History
1912
1912 - 0189.PDF
By LOOKING back over the list of fatalities that have occurred since the inception of the heavier-than-air machine, one cannot help being struck with the number that have been attributable to inexperience, false manoeuvres on the part of the pilots, equilibrium lost through severe wind gusts, steep vols piques, and falls occasioned by motor stoppage. These accidents^ and they still, unfortunately, continue to occur, indicate in a most striking manner the lack of consideration that has been given on the part of designers to that function of the most primary importance—the stability of the aeroplane. Take, for example, the contests of this closing year ; in almost every case the prizes have been awarded to the competitor that could show the greatest speed, the greatest ability at finding his way across country, and the one who could exhibit the greatest hardihood and ability in fighting against adverse conditions. In this quest for speed, itself an important feature in the light of future requirements, and one which has a direct bearing on stability, there is little doubt that the consideration of keeping the aeroplane on an even keel, in both a lateral and a longitudinal sense, has been left too much to the care of the pilot. As a means of defence in war, and as a sporting pastime, the success of the aeroplane is at present assured ; but can it be expected that the industry will be content to exist on the business it does with the War Office, the Admiralty, and those representatives of the monied section of the community who can afford to indulge in aeroplaning as a sport ? It is scarcely likely. It is on the success of the aeroplane as a commercial or a pleasure vehicle that the larger success of the industry depends, and it is difficult to see how this can be attained while such acrobatical movements on the part of the pilot at the expense of so much physical exertion are required to maintain an even balance in a wind. Again, in the development of the aero plane as a commercial vehicle, such engine powers and such large supporting surfaces are likely to be obtained that means of maintain ing balance other than by utilising the ever-variable human factor will have to be devised. It may be argued that lack of stability has not in any way inter fered with the success of the bicycle, and that intelligent control has all along superseded any attempt at furnishing it with a modicum of stability by the addition of a thiid wheel. This, in our opinion, is scarcely a fair example to cite, for the rider has only to give his attention to balancing in a lateral sense—his longitudinal stability is already assured—while, at high speeds, he is given a great deal of assistance in the former respect by the gyroscopic action of the wheels. Again, in comparison with the aeroplane, the consideration that he would not have so far to fall in the event of his equilibrium being destroyed is one that perhaps has an important bearing on the subject. In the case of the aeroplane, stability has to be maintained in every direction. A disturbing gust may have the effect of tilting the tail, of tilting the head, or of rocking the machine about its longitudinal axis. In the first two cases it is the longitudinal equilibrium that is at fault, and in the latter case its natural lateral equilibrium is weak. If the aeroplane becomes tilted in any other direction it involves both longitudinal and lateral stability and in this case both are at fault. The means of securing stability, i.e., maintaining equilibrium in aeroplanes other than by manual control fall under two classifi cations :— 1. Those in which stability is natural, being inherent in the design by virtue of the shape of the wings or because of some other peculiarity of form. 2. Those in which stability is automatic, being obtained by the use of some purely mechanical device, which may be considered as a "brain equivalent." Much space has already been devoted to the subject of natural stability, and as, perhaps, the latter method of obtaining stability has not enjoyed so much elaboration, and in view of the renewed interest aroused by the rumour that the Wright Bros, intend to carry out further experiments in automatic stability devices, the writer intends to briefly review some of the ideas that have from time to time been put forward under this head. Let us first consider those devices that ensure stability in a longitudinal direction. These automatic stabilizers can be classified into four divisions according to which of the following principles their operation applies: — 1. Gyroscopic action. 2. Pendulum action. 3. Velocity pressure action. 4. A combination of velocity pressure and inertia actions. 189 STABILITY. . C. S. Some diversity of opinion appeais to exist as to the values of the gyroscopic and pendulum systems as compared with those that employ the velocity pressure or inertia principles. It has been maintained by some authorities that while the former two systems of correcting longitudinal balance do not come into action until the attitude of the machine has already been changed by the effect of the disturbing gust, the latter two systems act before any alteration in the attitude of the machine is apparent, in that they are brought into operation at the same moment and by the same force that tends to upset the balance. The essential difference between the action of the two pairs of systems is that the gyroscope and pendulum devices are continually restoring the machine to an even keel by a direct method, while those stabilizers operating on the pressure vane or a combination of the velocity pressure and inertia principles maintain longitudinal stability by the indirect method of regulating the speed of the machine. 1. Gyroscopic Devices.—Although most people are familiar with the gyroscope in the form of a rapidly revolving fly-wheel, which, mounted on a wire frame, amused us in our younger days by its marvellous powers of balancing itself on the edge of a tumbler or on a piece of string stretched between two points, perhaps the property that enables it to so behave is not so well-known. When a wheel, in which as much of its weight as possible is disposed at its rim, is spun rapidly, its spindle exhibits a strong tendency to remain pointing in the same direction as that in which it reposed when the initial spin was given. Further, the strength of this tendency increases in a certain relation to the weight, the diameter, and the speed of the gyroscope. Thus it can be seen that a gyroscope of sufficient size, and revolving at a sufficient speed, could be so mounted in an aeroplane as to keep it in an even keel by sheer brute force. However, such a suggestion, while it has with more or less success been applied to sea-going vessels, is impossible of application in the case of aeroplanes, owing to the excessive weight of a gyroscope necessary to fulfil this condition, and the excessive power that would be needed to drive it. Again, viewed in the light of the strength of present-day aeroplanes, it would be difficult to produce a machine that would withstand the heavy strains thrown upon it by a poweiful gyroscope so mounted. Several suggestions have been put forward in which the com bination of the gyroscope and pendulum is made use of, an arrange ment which allows of a much smaller gyroscope being used. A pendulum, in which the bob is replaced by a gyroscope, is, theoretically, a dead-beat one, but in practice it has not quite lived up to its expected reputation on account of the mechanical friciional resistance opposed to its free movement. In a system of this description the elevator would be operated indirectly by the gyroscope- pendulum through the medium of some form of relay. As there is no relay whose action is absolutely frictionless it can be seen that a considerable and continual resistance will be offered to the free movement of the pendulum by the relay, and this feature will have the effect of altering the direction of the gyroscope spindle by degrees until it eventually assumes a position in which no effect will be produced on it by any longitudinal oscillation on the part of the machine. In this position the gyroscope will naturally be useless as a means of preserving equilibrium in a fore and aft direction. 1.—The gyroscopic stabilizing device conceived by M. Paul Regnard. C
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