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Aviation History
1927
1927 - 0058.PDF
12 SUPPLEMENT TO FLIGHT JANUARY 27, 1927 THE AIRCRAFT ENGINEER considerable progress has been made in determining the general velocity field and mean velocity through the airscrew disc (see especially R. & M. 786*). For extreme values of the thrust where the same methods break down, an attempt has recently been made to obtain an empirical relation to determine the velocity through the airscrew disc by analysing some experiments on model airscrews in a wind tunnel (see B. & M. Nos. 1014f and 1026J) : in addition, the actual velocity field has been photographed under extreme conditions, including the windmill brake state. The photographs given in this report show a considerable turbulence around the screw, but the actual degree of turbu- lence can best be judged by visual observations. The photographs suggest that most of the fluid which actually passes through the screw circulates continually in a closed path, but visual observations indicate that this is not the case ; on watching individual oil drops it appears that few of them pass through the screw a second time, and very few a third time. Owing to the small scale of the experiments, it is obvious that the constraint of the boundaries of the stream exerts a considerable influence on the velocity distribution. * E. & Jl. 786. Ail aerodynamic theory of the airscrew.—H. Giauert.t K. & M. 1014. An extension of tho'vorte-x Theory of Airscrews with applications to airscrews of small pitch and including experimental results.t E..I& M. 1026. The analjslsof experimental results in the windmill brake and vortex ring states of an airscrew. SOME PHYSICO-CHEMICAL STUDIES ON THE EFFECT OF SUNLIGHT ON COTTON. By GUY BARK, B.A., D.Sc. and ISABEL H. HADFIELD. M.Se. R. & M. No. 1016 (M. 36). (22 pages and <l figures.) July. 1926.* Price Is. net.) Fabrics after exposure to sunlk'ht of periods from 3 days to 5 weeks and from 6 hours to 42 hours h.ive been compared b\* the viscosity of their solutions in euprammonium hydroxide solution. The determination of the viscosity of a solution of cotton in cuprammonium hydroxide solvent has proved to be an extremely sensitive method of following the deterioration due to sunlight, particularly in the early stages. An exposure of six hours' duration to bright sunlight was found to produce a significant reduction in viscosity. Cellulose modified by exposure to sunlight and air for short periods show increased reducing properties and an initial decrease in absorption of methylene blue. It is evident that chemical and not merely physical change has taken place, but to what extent the change can be regarded simply as oxidation is doubtful from the results on fabric after such short exposures. It is probable that Harrison solution would be valuable for measuring the reducing power of a modified cellulose when only small samples of material are available. The viscosity method appears to be suitable for investigating the effect on cotton of light of different wave-lengths. In the past attempts to find the region in the spectrum, which has the most deleterious effect have not met with much success, owing to the fact that the deterioration was measured by a relatively insensitive method, namely, the change in tensile strength. The authors hope to get more satisfactory results by using the viscosity method. Tests, similar to those used in this paper, on fabric exposed in the absence of oxygen would show to what extent the change in the fabric, due to sunlight and air. is an oxidation process. Further work, however, on the quantitative use of Harrison's solution is necessary before it can be regarded as an entirely satisfactory method. * Rewritten for publication. These Reports are published by His Majesty's Stationery Office, London, and may be purchased directly from H.M. Stationery Office at the following addresses : Adastral House, Kingsway, W.C. 2; 28, Abingdon Street, London, S.W.I ; York Street, Manchester ; 1, St. Andrew's Crescent, Cardiff ; or 120, George Street, Edinburgh ; or through any book- seller. AMERICAN NATIONAL ADVISORY COMMITTEE REPORTS. The .National Advisory Committee for Aeronautics in the United States of America corresponds to our own Aero- nautical Research Committee. Two distinct classes of reports are issued, the first being known as Technical Reports. These Technical Reports are printed, and are illustrated by photo- graphs and /or drawings. The second class are known as Technical Notes, and are issued in mimeographed form so as to enable them to bo rapidly distributed to a somewhat smaller, but directly interested, circle of readers. Copies of the Reports and Notes may be obtained from the Superin- tendent of Documents. Government Printing Office, Wash- ington. D.C., U.S.A., but the American N.A.C.A. have a Technical Assistant in Europe, whose office is at 18, Rue Tilsitt, Paris, from whom copies can usually be obtained, thus saving a certain amount of time. The average price of the Technical Reports is 10 cents, which is, of course, remarkably cheap in view of the informa- tion contained, and in some instances the price is as low as 5 cents. Summaries of Technical Reports Published in 1926. TESTS ON AIRPLANE FUSELAGES, FLOATS AND HULLS. —REPORT No. 236. By WALTER S. DIEHL. Bureau of Aeronautics, Navy Department. This report is a compilation of test data on airplane fuselages, nacelles, airship cars, seaplane floats, and seaplane hulls, prepared by the Bureau of Aeronautics at the request of the National Advisory Committee for Aeronautics. The dis- cussion of the data includes the derivation of a scale correction curve to be used in obtaining the full-scale drag. Composite curves of drag and L/D for floats and hulls arc also given. THE EFFECT OF FLIGHT PATH INCLINATION ON AIR- PLANE VELOCITY.—REPORT No. 238. By WALTER S. DIEHL, Bureau of Aeronautics. This report was prepared at the request of the National Advisory Committee for Aeronautics in order to supply a systematic study of the relations between the flight velocity V and its horizontal component VH in power glides. Curves of V and YH plotted against the inclination of the flight path 6 are, given, together with curves which show the maximum values of VH and the corresponding values of 6. Curves are also given showing the effect of small departures from the horizontal in high speed performance testing. METEOROLOGICAL CONDITIONS ALONG AIRWAYS. REPORT No. 245. By W. R. GKEUU, Weather Bureau. This report was prepared at the suggestion of. and for publication by, the National Advisory Committee for Aero- nautics, and is an attempt to show the kind of meteorological information that is needed, and is in part available, for the purpose of determining operating conditions along airways. In general, the same factors affect these operating conditions along all airways though in varying degree, depending upon their topographic, geographic, and other characteristics ; but in order to bring out as clearly as possible the nature of the data available, a specific example is taken, that of the Chicago- Fort Worth Airway on which regular flying begins this year. TECHNICAL NOTES. PROPELLER DESIGN: PRACTICAL APPLICATION OF THE BLADE ELEMENT THEORY—I.—No. 235. By FRED E. WEICK, Langley Memorial Aeronautical Laboratory. This report is the first of a series of four on propeller design, and contains a description of the blade element or modified Drzewieckc theory as used in the Bureau of Aeronautics, U.S. Navy Department. Blade interference corrections are used which were taken from R. & M. No. 639 of the British Advisory Committee for Aeronautics. The airfoil character- istics used were obtained from tests of model propellers, not from tests of model wings. A short method is also shown in which the forces on only one blade element are considered in order to obtain the characteristics of the whole propeller. The methods described have proved satisfactory in use. 46/
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