. American engineer and railroad journal . rtificial flight, but experimentaldata, from which the relative efficiency of different types ofscrews could be determined, have hitherto been almost whollylacking. Even in the case of propellers working in the water, thoughused on so extensive a scale in steam navigation, the mathe-matical analysis is quite incomplete ; so that engine designersarc compelled to depend mainly on empirical formula; and therule of thumb. In the case of air screws, which work in a medium subjectto great variations in pressure as well as temperature, thetheoretical investi
. American engineer and railroad journal . rtificial flight, but experimentaldata, from which the relative efficiency of different types ofscrews could be determined, have hitherto been almost whollylacking. Even in the case of propellers working in the water, thoughused on so extensive a scale in steam navigation, the mathe-matical analysis is quite incomplete ; so that engine designersarc compelled to depend mainly on empirical formula; and therule of thumb. In the case of air screws, which work in a medium subjectto great variations in pressure as well as temperature, thetheoretical investigation is of course even more difficult. Forthis reason a series of experiments made during the past yearby Professor Georg Wellner, of Briinn, Austria, is of consider-able scientific interest apart from any special application toproblems in aeronautics. Z The following resume of his investigations has been preparedfrom a paper read by the author before the Austrian Society ofEngineers and Architects, and published in their transactions.*. Fig. 1 The task the author had set himself was to determine forsome half-dozen different forms of air screws the axial thrustexerted against the air and the amount of power required whenthe propellers revolve at different rates of speed. His apparatus consisted of three parts : 1. A Siemens-Halske electric motor rated at | whenmaking 1,500 revolutions per minute. * From the cles Oesterr. Ingenieur und Architekten , August 17 and 24, 1894. 2. Air screws of different shapes and sizes, which could be readily attached to the shaft of the motor. ::. Devices for measuring the power absorbed in turning thescrews as well as the actual thrust or reaction, The various forms of propellers used are shown in tigs. the purpose of comparing the different forms, the totulprojected area of the bladeson a plane normal to the axis wasin each case measured, and the reaction of the air was sup-posed to be concentrated at a
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
