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Aviation History
1915
1915 - 0561.PDF
TULY I9IS. [/JJGHT] THE INTERNAL WORK THERE has, perhaps, been no more important set of observations carried out in what may possibly be termed the environs of the subject of flight, than those made by Professor Langley on the normal state of the atmosphere, which resulted in the publication of his famous treatise entitled " The Internal Work of the Wind." His first public communication of the result of his researches was embodied in a paper read by title to the American National Academy of Sciences in 1893, and delivered in full by the author before the Chicago Conference on Aerial Navigation of the same year. It has been now for some time available in a book published by the Smithsonian Institute. At that conference, the subject of soaring flight /.«., continued flight without power, was one of those most seriously discussed by the delegates, and it was in relation to this aspect of flight that Professor Langley's investiga tions at that time appeared to have their most important bearing. Wind Fluctuations. Professor Langley's arguments were based on the results of experiments which resulted in his discovery that there is no such thing as a steady wind. He made observations on the state of the atmosphere, and as the result of many carefully conducted experiments, he found that the changes which took place in what had hitherto been regarded as a steady wind were phenomenally abrupt, of frequent occurrence, and of altogether greater magnitude than he would have believed possible. As an example, a case is cited in which a wind, commencing at 23 miles an hour as measured by an Ordinary standard anemometer, such as is used by the Weather Bureau, fell during the course of the first mile to a little over 20 miles an hour in a perfectly even manner such as would be represented by a straight line on paper. With records made simultaneously by Professor Langley's special instrument, however, this same wind was shown to be anything but steady for even an instant of time during the same period. Starting at 23 miles an hour, the wind rose within 10 seconds to a velocity of 33 miles an hour, and within 10 seconds more fell to its initial i,peed. In the subsequent 30 seconds it bounded up by three stages to 36 miles an hour, and then fell in 10 seconds to a little over 24 miles an hour, at which speed it remained with only a relatively slight increase for the next period of 10 seconds, when it fell to 18 miles an hour, bounded up to 27 miles an hour and down again to 19 miles an hour in the space of about half a minute. Midway during the course of this particular strip of record, which all told only includes a period of 13 minutes, the wind OF THE WIND. actually fell to zero from a speed of 24 miles an hour, and then as suddenly jumped to 22 miles an hour, after which it zigzagged about between 5 and 20 miles an hour, for the remainder of the period. Langley's Theory of Soaring Flight. This is merely an example of a very short record, but Professor I^angley stated that it was a very typical example 40 tier Wind fluctuations as Langley found them to exist by means of his delicate instruments. The horizontal divisions each represent only one minute of time, the vertical scale represents wind velocity, and the zig-zag line indicates the wind fluctuation. of what he found to be the case on every occasion, and it was on the assumption that this incessant change repre sented the true state of the atmosphere at all times that GUST _ 1 MlN. W/rvj) VCL. Diagrams Illustrating the application of Langley's theory of the "internal" work of the wind to the soaring flight cf birds.—The diagram on the left indicates a bird's wing extracting energy while moving with the wind, by inclining first one way and then the other. The diagram on the right illustrates how a bird might make head'.vay against the wind. 561
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