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Aviation History
1914
1914 - 0451.PDF
CORRESPONDENCE. Climbing. £1854] After reading Mr. B. C. Hucks' excellent paper in your issue of April nth, I had expected to see some correspondence on the question raised by Mr. Mervyn O'Gorman as to whether a machine climbs better against than with a wind. But since there was none, perhaps some of your readers may find the following remarks of interest. Mr. Hucks considers that the custom of rising head to wind is merely due to an illusion; but it seems to me that it is all a question of propeller efficiency at high speeds. When a machine rises head to wind, it is still travelling at its proper air-speed ; but when it rises with the wind, the machine does not travel at its correct air-speed, and so the propeller is not so efficient as at the slower speed. For example, a machine whose normal flying speed is 60 m.p.h., when rising against a wind of 40 m.p.h., is still travelling at a speed of 60 m.p.h., relative to the air. But when rising with the wind, the machine will not reach 100 m.p.h., because at the higher air-speed the propeller is not working efficiently ; thus the machine will not climb as well as at the lower speed. Of course, the difference in efficiency would be scarcely noticeable with low winds, but in a high wind rising against the wind must be more rapid. Hoping that these few notes may be of interest to some of your readers. Luton. ALFRED M. COATE. Wood in Aircraft. [X8S5] The letter of Mr. Alexander L. Howard challenges comment. His main point or " theory " is, that timber in an air craft owing to " exposure to climatic change" and to " the intense speed at which it is driven through the air ... . suffers from exactly the same fatigue without the recuperative power which the human being possesses." He asks whether the aeroplane builders have considered the point. Your correspondent can be assured that aircraft builders have considered the possibility of fatigue, in the mechanical sense of the word, in all structural materials used in aeronautical engineering. The human-like fatigue in wood was not known to exist. The known superiority of seasoned wood over metals with respect to mechanical) fatigue is one reason why the general substitution of steel for timber in aircraft has been deferred. One does not need to be an aeronautical engineer to realise that Mr. Howard's apprehensions are practically baseless. First with regard to climatic change. The statement that "fresh timber " stowed in the hold of a hot ship may become affected with fungus is true and irrelevant. If one has to compare wood with human beings, one may point out that through exposure to glare from a furnace men may become afflicted with blindness; but such afflicted men will not be urged to become pilots. Aeronautical engineers do not use fresh timber showing fungus ; further, such defective timber if put aside to season is readily recognised at each of its stages towards decay by the experienced timber merchant; and if by accident it is sent in to aeronautical firms the defect is promptly discovered by experienced woodworkers. Fungus and woodworkers existed before aircraft. The smallnessof the sections used in aviation work is an additional help in discovering any defects in wood. Any aeronautical firm will agree that construction of aeroplanes does not suffer from lack of independent inspection. There is no'excuse for defective timber being used in aeroplanes. Discussion is thus narrowed to general properties of sound wood used. The assertion that thoroughly seasoned timber in a damp atmo sphere will absorb damp and expand does not carry us far. Aero nautical engineers require quantitative data. Amount of possible absorption depends on the kind of wood, but use of appropriate varnishes and " dope " covering the wood and filling the pores reduces the inconvenience to vanishing point. In any event the question to be answered would appear to be whether the varnished timber used in aircraft shows signs of being adversely affected by moisture to a degree importing danger to the structure. The answer is one for an engineer to make after verifiable and adequate tests, and not for suppliers of raw material to decide ex cathedra or •even in holy conclave. The statement that " timber placed in the heat of the sun will crack sometimes with a report like the firing of a gun " is misleading. Seasoned timber built into aircraft in this climate does not go •off pop. That imported timber (not of the kind used in aircraft) occasionally has suddenly cracked in our climate, in the process of seasoning, does not warrant any inference that there are dangers arising from the use of seasoned timber of a different kind appropriately varnished and built into aircraft. One might as well argue that because some young English soldiers have sunstroke in Hong Kong, acclimatised Melanesians are peculiarly liable to suffer from heat. Having dealt with some of your correspondent's generalities as to timber (a subject in which generalities are peculiarly misleading), let us look into these terrible climatic conditions. His bugbear is change. Are aircraft exposed to much greater climatic changes than other important structures in which wood is used ? In the all-air route to Monaco from London is there greater fluctuation in temperature than in the sea and land route ? Are yachts and motor boats immune from exposure to damp and ohanges of temperature? If not, why are they built of wood ? Is it safe to risk the timber in a yacht in the heat of the sun going off " with a report like the firing of a gun " ? The air pilot can within limits regulate his temperature, the terrestrial scorcher has to pat up with what he finds. The fear—not resulting from experience—that extreme frost will have a sudden effect on wood does not seem well founded. It is presumably the moisture in the wood that is going to solidify and " bust." But why should extreme frost be worse than a uniform temperature of, say, zero ? No further expansion takes place. Seasoned and properly protected timber will stand at much climatic change as the seasoned and properly protected pilot. Next with regard to speed.—Your correspondent seems to assert " 'tis the pace that kills. ' His theory is that as the outcome of the "intense speed" "timber suffers from exactly the same fatigue without the recuperative power the human being possesses." What sympathy pilots should have for their dumb struts and spars who suffering equally with them the fatigue of each trip are hopelessly doomed to retain and accumulate fatigue while the lucky pilot recuperates, nay, becomes less liable to fatigue after each experience. Aviation is to bring forth unsuspected fruit—The I'sycho-Physics of wood. If it is pure speed which causes this new fatigue then the wooden pipe resting quietly in the passenger's pocket suffers this human-like fatigue equally with the main spar ; and the brace button if made of metal does not lire, but if made of wood each trip rushes it on to inevitable doom through accumulated fatigue. On this new theory of fatigue a pilot and his brother wood flying at 100 miles per hour in calm air is much fatigued while one just able to do 15 miles per hour against a mighty wind would keep fresh for a long time, and cause less fatigue to his wood. So long as this human-like fatigue does not manifest itself under the guise of diminished tensile strength or some other physical property with verifiable references engineers will be content to grant timber in warplanes the privilege of a true son of Mars " to suffer and be strong." The tip of a 9 ft. propeller at 1,200 r.p.m. is flying round at about the rate of 360 miles per hour independent of its forward movement, i.e., at a speed of three to four times as fast as the " intense speed " which causes such alarm. Now this vital wooden part of an aeroplane is shaped in such a way as to make it extremely sensitive to physical effects ; it is subject to all the ills the other wooden parts of the machine are liable to, and has a few special ones of its own. Here is a field of research for your correspondent without waiting for accidents. With regard to investigations of accidents, excellent and autho ritative committees already exist equipped with members who have no commercial axes to grind, some of whom combine a knowledge of engineering and aeronautical design, with practical experience in wood work and metal work. An aeroplane is not a collection of stores to be sorted over by merchants ; it should be a compact whole of mutually related parts, and the eftect of shock or accident obviously depends not simply on the magnitude of the shock and the virtues of the material but also on the disposition and bracing of the parts. A merchant supplying material from which parts are made cannot usefully decide questions of design and distribution of stresses. The function ot suppliers of raw material would seem to be to see that good material is supplied when they are fortunate enough to get orders. The periodical inspection of aeroplanes in being is already carried out, but far more frequently than at the interval recom mended by your coirespondent. Eastmearn Road, West Dulwich. JOHN E. HUSON. April 22nd. ® ® ® ® Armstrong, Whitworth and Co. and Aeronautics. SPEAKING at the annual meeting of Messrs. Sir W. G. Armstrong, Whitworth and Co., last week, Sir Andrew Noble said that the development of the aviation department was proceeding satisfactorily on the estate which the company had acquired at Selby. Aeroplanes were being built temporarily at Gosforth, until the directors could remove the manufacture to Selby, where the com pany had a fine flying ground. 451
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