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Aviation History
1913
1913 - 0134.PDF
Negative Angle Wing Tips. LI7ISJ In connection with this matter, perhaps it is well to draw attention to the point that, apart from any controversy on their merits, tests of negative wing tips would be well worth making with the object of getting information about what might be called the anatomy of gusts and eddies. If we tried two machines, weighing alike, and having the same air pressure per square foot of wing, one with and the other without, negative tips, the effect of variation of velocity across the span would be eliminated, and that of variation in angle of incidence, which I suppose may likewise vary, would be aggravated by the negative tips, and by the larger wings required in the same aircraft. In fact, negative tips which extinguished the influence of variation of velocity will leave the influence of angle-variation outstanding ; such tips cannot balance it, because on the side where the greater angle of incidence on the main wing increases the upward pressure, the angle of incidence on the negative tip is diminished, and downward pressure reduced and vice versa at the other tip. With regard to Mr. Hume-Rothery's investigation, the inclusion of variation of angle of incidence, along with that of velocity might be described technically as making both U and /, or g and /, functions of z, instead of U alone. If I understand him aright, Mr. Hume-Rothery points out that the derivative moments which occur in Bryan's work can be balanced by others introduced by the negative tips if these be suitably designed. If, however, variation of angle be introduced, other derivatives come in, which cannot, I think, be balanced by permanent adjustments, because they depend on independent factors, namely the rates of variation along s of the velocity and angle respectively. I think I am right in assuming that difference in angle of incidence at opposite ends of the span is generally believed to occur in practice, as well as difference of velocity. MAURICE F. FITZGERALD. Monkstown, Co. Dublin. [The condition laid down in Mr. Berriman's article is that the downward pressure on the negative tips shall balance the up pressure on the positive part of the wing for a motion of spin about the vertical axis. If the pressures are balanced at one speed of spin, then they will presumably be balanced for any other angular velocity within the range at which the lift coefficient remains constant. Considering each wing i.e., each half of the span) separately, the entire lift due to angular movement is supposed to be obliterated and a gust being denned as a relative spin of the wind is regarded as equivalent to an angular rotation of the wings, which by the hypothesis is not a movement that produces lift.—ED.] Monoplane Wings. [1716] In the January nth issue of your esteemed journal you published an article by Mr. Brewer entitled "The Collapse of Monoplane Wings," and I feel myself called upon in my own interests as well as those of the industry generally, to offer some criticism and point out the fallacy of Mr. Brewer's theories and arguments. There is no doubt that there have been certain genuine cases of collapse in the air, but so far, nobody seems to have been able to discriminate between one accident of this sort and another, nor to take into account the characteristics of design and construction of the machines in question. Mr. Brewer commences his article by referring to M. Bleriot's well-known report on the subject, wherein he blamed the upper supports of the wings. Now, admitting for the moment that it is possible for a machine in flight to sustain a downward reaction on the top surface of the wings, it is obvious that would be more in the nature of a blow than a continued pressure. Now even if the top wires fall under this strain, there would be no tendency for the wings to drop further than four or five degrees at the most before they would have to return to their natural position and take up their load again. The load would naturally be taken up with a seven; jerk which would impose serious strains on (1) the main wires, (2) the wing spars and 3) the compression member between the two wings. If these parts were not designed and constructed with an ample margin of strength, one or more of them might fail; in the first case the wings would just fold up, as in the case of M. Wachter's machine at Rheims. The wing spars would probably break in compression between the innermost stay wires and the fuselage, upwards, causing the tips of the wings to drop momentarily before the wing went to pieces completely. In the last case (3) the butts of the spars would move inwards, and then either upwards or downwards according to the position of the centre of pressure of each wing in relation to its supporting stay wires, and the wings would appear to break up or down according to the circumstances. Now in some of the earlier monoplanes the back spars did not even have a compression member between them, but were simply housed. in sockets against the vertical struts of a wire-strung FEBRUARY I, 1913. fuselage ; and it is not at all unlikely that these verticals, subjected as they were to a severs bending strain, should have failed under any increased load. In the above cases we have supposed that the top wires of the wings failed in the first instance, but in the event of a machine being subjected to a considerable overload, as for instance being flattened out suddenly after a steep volplane', it is still possible for the wings to appear to break downwards owing to failure of the fuselage struts, should the spars be butted against them as explained above. I am afraid that Mr. Brewer's theories about the movement of the centre of pressure will not bear a very close examination. He starts by assuming that monoplane wings are set up with the wires slack enough to allow the wing tips to twist appreciably. I wonder what particular monoplane he is familiar with ? Then, supposing it possible for this to happen, the twist could surely never equal the twist caused by full warp. If Mr. Brewer's " very small and imperceptible" twist is going to cause the complete reversal of pressure on the wing, I should fancy that full warp would turn the machine upside down in the twinkling of an eye. Further, Mr. Weiss, in his experiments with large models and man-carrying gliders, found that his wing tips still lifted appreciably, even though they were set at an angle of between 12 and 15 degrees less than the wings at the fuselage. Again, if the "theory "were correct the "swivelling" wings of the Breguet would perform the most marvellous antics in flight. Perhaps it is not generally known that these wings "twist" so easily that making a proper sand test is practically impossible, as the wings turn and allow the load to slide off them. Lastly, is the Nieuport which flies at a smaller angle of incidence than, perhaps, any other machine, more troubled by this phenomenon than, for instance, the Bleriot, which uses a coarse angle ? It is curious that, because a few monoplanes have failed through causes and weaknesses which after all are not so very difficult to determine, almost every accident, from whatever cause is put down to wing failure. It must be the old principle of " Give a dog a bad name and hang him," and it is certainly not worthy of those who profess to have studied the subject. In point of mere strength, and apart from aerodynamic proper ties, wherein the monoplane has proved itself over and over again to be vastly superior to the biplane, there can be no difference between a properly designed machine of either type, It is a comparatively simple calculation of strains and stresses, wherein an engineer is far more at home than a man who gives all his attention to the theories of flight. Brooklands. H. P. MARTIN. ® ® ® ® A French Prize for Safety Devices. THE Committee of the French Union for the safety of aero planes has decided to offer a prize of 400,000 francs for the best arrangement for securing the safety of aeroplanes. The tests will be very severe, and include practical trials on a machine having a speed of over 100 k.p.h. Other prizes of 20,000 francs will also be awarded. The judges will include representatives of the Ministers of War, Marine, and Public Works. ® ® ® ® Aeronautical Patents Published. Applied for In i»n, Published January 30th, 1913. 22,025. W. H. NOSWORTHY AND S. J. PRESCOTT. Aerial machines. Applied for In ISIS. Published January 30M, 1913. 200. J. G. PARSONS. Aerial propellers. 559. G. H. SHORT. Wings or main supporting planes. 3,588. V. K. VYVYAN. Control and propulsion of flying machines. 13,855. E. A. DANDKIEUX. Aeroplane with automatic longitudinal balancing. FLIGHT. 44, ST. MARTIN'S LANE, LONDON, W.C. Telegraphic address: Truditur, London. Telephone: l828Gerrard. SUBSCRIPTION RATES. FLIGHT will be forwarded, post free, at the following rates :— UNITED KINGDOM. ABROAD. .vaa) s. d. s. d. 3 Months, Post Free ... 3 9 3 Months, Post Free ... 5 o 6 ,, ,, ... 76 b „ ,, ... 10 o 12 „ ,, ... 15 o 12 ,, „ ... 20 o Chegues and Post Office Orders should be made payable to the Proprietors of FLIGHT, 44, St. Martin's Lane, W.C., and crossed London County and Westminster Bank, otherwise no responsibility will be accepted. 134
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