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Aviation History
1926
1926 - 0127.PDF
FEBRUARY 25, 1926 21 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT The Aeronautical Research Committee have, however, put their money on the Slot-cum-Aileron lateral control as a useful means of preventing the worst effects of the stalled crash. I have tried this gadget, and my impression is that, firstly, it does not do what is claimed for it, and, secondly, as my remarks above are intended to show, it would be of no use if it did. It is true that, beyond the stall, this control provides a powerful rolling effect, so powerful as to throw the machine over the other way if hastily used. It also has a very powerful positive yawing effect, which, I understand, was one of the things it was particularly designed to avoid. On the machine to which this gadget is fitted for test—a standard Avro—it is true that during the use of the aileron the nose tends to come up, but this is Avro, and has nothing to do with control. So far as this control may claim to raise the nose of the machine, it is true that the use of the slot on one side provides an addition to the total lift. This, however, has nothing to do with the control aspect of the matter. The whole stall could be avoided by the use of a complete slotted wing system, which, however, is apparently not proposed. The mechanism is obviously heavy and expensive, and would undoubtedly be difficult to maintain in truth. It would not apply, probably, more than once in fifty thousand flights, and when it did it would be at the best of very doubtful value. Hence it seems difficult to understand that the control should have been recommended seriously to aircraft constructors as a means of achieving some useful object. As a help for stalling crashes, it seems about as useful as handing a cup of hot tea to a drowning man because the water happens to be cold. The sponsors of this strange and elaborate gubbins do not seem to have noticed that a powerful rudder control will do the same thing, but will do it rather better. For example, if a stalled machine starts a spinning motion to the left, the application of a powerful rudder control to the right will stop the spin, will check the yaw. will bring the machine to a laterally-horizontal position, and. owing to the downward movement of the tail unit, to a temporarily horizontal position fore and aft. The stunt known as the " falling leaf " is an excellent example of this, since it reproduces many times consecutively the actual conditions in question; rudder alone is used in alternate directions under the " stick back " condition. Having dealt at painful length with destructive criticism what about something constructive '' The stall being (until the advent of the Autogiro) an indelible feature of the aeroplane, must be dealt with as it is in working practice. I suggest that the practical way of ameliorating the dangerous conditions of the stall is two-fold : (1) Making the stalled-crash subject a definite and important part of flying instruction : (2) Providing powerful control right down to stalling speed. The only point on this subject on which the scientists are, nearly right is that a pilot in difficulties may easily instinctively do the wrong thing. Only, as a matter of fact, it is not instinctive—though the word is good enough—it is purely a matter of training. For example again, a pilot with an engine failure tries to reach a field the machine cannot reach, or to clear a tree that it cannot clear. His training—or instinct—is that if you pull the stick back you go up. He knows perfectly well, subconsciously, that he cannot reach the field, but another part of his brain, reacting to that training, pulls that stick back. This is most decidedly the state of affairs governing the stalled crash, and, regarded as such, is most definitely easy to deal with in training. If the trouble is " instinctive," the cure must also be " instinctive." and my own instructional methods used to be to try and instil a definite and separate emergency instinct into the pupil. This instinct, being mainly based on the necessity of avoiding stalling, can be formed on a sort of Coue idea of " When in trouble, bang your stick up against the dashboard, and think afterwards." By making a habit of switching off the engine (during dual instruction) at all sorts of unexpected moments, I found it very easy to induce pupils to push the nose hard down, without thinking, in the most unfavourable of situations. It is an almost infallible method of instilling the avoidance of the stall into a pupil, and though the violent push on the stick that I used to insist on became modified to a more reasonable push, the " instinct " for maintaining flying speed definitely overcame the " instinct " to hold the nose up. As I claimed at the start, the stalled crash is almost entirely psychological, and must be cured psychologically. On the mechanical side I claim definitely that control beyond the stall as a serious study is of greatly exaggerated importance. But, control right down to the stall has more importance than might appear. For supposing, as frequently happens, control becomes feeble some ten miles an hour before the stall, then, if the pilot wishes, to glide at his very lowest speed he definitely risks passing stalling speed for lack of control. Further, should he then get into some of that panic state which inevitably means the " stick back " policy, this will be increased by the knowledge that, if he does push the stick forward, he must not only come unstalled, but must gain a further 10 m.p.h. before he has full control. If, on the other hand, full control exists down to the stall, a mere forward flick on the stick restores both normal flight and full control. The perfect, or nearly perfect, low speed control is a fairly simple matter, yet it seems to have had very little practical examination. The result is that the two most popular forms of lateral control at the moment are ones in which the main principles militate against perfect low speed control. But in any case, the stall provides fundamental difficulties, not to be cured by any such methods as a clumsy lateral control, whose principles only operate on rare occasions. IN THE DRAWING OFFICE. STREAMLINE STRUTS. Areas and Moments of Inertia. By Lieut.-Col. J. D. BLYTH, late R.A.F. IN the process of calculating the dimensions of a stream-line strut to take a given load, it becomes necessary to find the area and the least moment of inertia of its cross-section. Doubtless designers and draughtsmen have their own abbre- viated ways of so doing ; but the great majority of those whose experience of aeroplane design is small, and whose interest in the subject is growing, have to adopt the various methods given in text books, most of which are somewhat laborious. A method of considerably simplifying the work and of obtaining the required results from one set of measure- ments may be of interest to the latter. Given the shape of the cross-section as in the figure, draw the longer axis XY, and complete the rectangle XABY so that AB is a tangent to the curve. Then I --= XY = length of section. t = 2AX — thickness of section. _ = F = fineness ratio.t Since the section is symmetrical about XY, XY is the neutral axis. Xow divide XY into 10 equal parts, and draw the ordinates !li, «/2. V& • • • !/e- -Measure the lengths of these ordinates. 110*
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