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Aviation History
1913
1913 - 0259.PDF
STABILITY DEVICES. By MERVYN O'GORMAN (Continued from t>ag? 238.) 37. The pendulum shaft does not now remain vertical. The thrust of the propeller is now less than before, the bob is pushed backwards by the head iesistance plane till the pendulum shaft is at right angles to the trajectory. Thus eliminating the objection above. Such a pendulum device is only very partially " stabilising," it has nothing to do with lateral balance, but it has a tendency to correct variations in the angle of attack of the wind since we still get the corrective action for an up.gust or a down-gust. Whether or not this or any device is "worth while" is another and a very subtle question not to be answered by the simple negative suggested by weariness of the subject. 38. Category C. Bob>weigbt Devices.—Perhaps the next most popular of the pendulum devices is the one which causes a ST*>A/Gssr *>sir~ Fig- 9. centrally suspended weight to pull down directly, or through a relay, the wing flap on the side towards which the weight has moved (see Fig. 9, in which only one wing control is shown for simplicity). This gives rise to an air reaction, tending to restore the wing which is too low to its old level, and this so far is a good intention ; indeed, it is good in effect if quick enough. Moreover it will be seen that in this case, were the aeroplane to be yawed without banking towards the left hand, the weight would fly out towards the right (Fig. 10), and so cause the right flap to be pulled down until <rovw<r.^ s*yirff~ £>/*?ercr'0/v os ^ 3/£>£ *rof^Af£,vr, Fig. 10. the banking was sufficient to allow the bob-weight's line to hang more or less perpendicularly to the wing spar (Fig. 9). At this an approximation to the proper condition for a banked turn would have been achieved. 39. A criticism of this method is that it is either sluggish or calls for another device, " the fin," to do its works. Any finless aeroplane when ruddered without banking, necessarily yaws and side-slips outwards (Fig. 11), and the more the sideslipping move- cisx-y^t, /*,irM ment, the less the pendulum swings out, so that the more the aeroplane side-slips, the less the device acts. In the case where the aeroplane side-slips without proper relation to the turn, e.g., if it were not following a curved path, but commencing to side-slip in any sideways direction, with an increasing side velocity, the bob- weight would act as an accelerometer, i.e., it would lag back, due to its inertia and therefore would not introduce any useful pull on the warp wire which banks the aeroplane in the manner for Safety, 4a This last is the beginning of the typical dangerous sideslip • and failure of the device here is failure indeed. Moreover, since no change of course on to a circular path is usually effected unless the aeroplane offered some tin, or fin equivalent, it appears necessary to show that some special merit over the prompter fin method or banking by hand is obtained by pendulum control for lateral balance. No such proof is available at present but it does not follow that no conceivable pendulum method will be of use here also. 4«. Pendulum and Relay— Gawlet's device 101S4, April, 1910) is an example of an elaboration in which the pendulum is in vacuo and operates electric switches which, in turn, actuate the elevator and warp through a compressed air device. No mention is made of how to overcome the difficulty that the same correction is given to the elevator in the two cases :— (1) when the aeroplane engine stops pulling and gives loss of air speed and (2) when a gust strikes the aeroplane and slows it as a whole, but giving increased air speed : while these two occurrences require opposite elevator cotreclion for speed maintenance. Laterally similar conundrums are introduced since similar pendulum action results from side movement due respectively to a side gust and due to a side-slip although lateral control movements desirable in the two events are opposite to one another. o 42. Such devices as these if they were worked out would not be devoid of interest in spite of their inutility. There is a vast gulf fixed between the theory of a mechanism which tells the control what to do, and the production of that mechanism within the weight limits needed for aero purposes. The evolution of an electric, a pneumatic, or a mechanical relay device for aeroplanes are exceedingly difficult problems, and may well be utilised in the near future. It is unfortunately usual for the inventor to set out a theory and stop there—after the easy part is done. The theory of a watch is quite simple, it has taken centuries to evolve the reliable thing we use, hence real workers in this field are as welcome as they are rare. 43. Wendtland (8326, April 4th, 1910) balances laterally by causing a pendulum to deflect a blast of air under one wing or under the other. 44. Pendulum without Relay.—Schmitt's scheme is a curious example of the opposite kind when the sensitive relay and its troubles are evaded by introducing others in cidental to the hingeing of all the fundamental parts, so that they shall constitute a heavy pen dulum (Fig. 12). His patent (11355, May, 1909) claims that it entitles him to dispense with the tail. He hangs the weights of pilot, engine, Sue., in a frame below a hinge which is parallel to the main wing spar and arranges thai when the wings are given a greater angle of incidence by the flyer the movement of the centre of pressure (which he mistakenly assumes to be backwards under these circumstances) is attended by such a movement backwards of the chief weights that these remain always underneath the centre of pressure, and thereby the upsetting couple which the tail corrects for is not introduced. He forgets that the wind moves and varies the centre of lift independently of his intentions and very quickly, and he is misinformed as to the direction of movement of the c.p. of cambered aerofoils. This type of device has benefited the patent offices of France, England and U.S.A. in various forms, and it seems a pity the money should not have been spent on aviation. 45.' Planes, Ltd., and Thompson (April 19th, 1910) suspend the car flexibly from the wings and the adjustments of the planes for steering and balancing are effected by movement of the car. This car movement is abo controlled by a lever. 46. Mitchell (4249, February 20th, 1911) causes his suspended car to bend down two balancing flaps which extend beyond the wing tips. The flaps are cross- connected. 47. Adam and Stamkort (4408, February 21st, 1911) balance an aeroplane by running electrically a carriage of considerable weight, and bearing two accumulators and motors, the pendulum consists of a mercury switch in which the liquid flows over the appropriate contacts. To be continued.) Fig. 12. 265
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