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Aviation History
1926
1926 - 0534.PDF
72 SUPPLEMENT TOFLIGHT JULY 29, 1926 THE AIRCRAFT ENGINEER power = 15 lbs. ; top speed, — 115 m.p.li. ; useful load, 28 per cent. ; structure, 32J per cent. ; power plant, fuel and crew, 39| per cent. Its general proportions are otherwise similar to those of the D.H.9A. All the calculations refer to standard ground-level density, in view of the fact that (at present, at any rate) commercial flying is done at a height of two or three thousand feet. The general conclusion is that for an aeroplane of the type chosen (which is representative of the modern commercial machine of moderate size) there is little reason to adopt a loading higher than about 10 lbs./sq. ft. when the speed at which the service operates is 90 m.p.h. For higher operat- ing speeds useful load must be sacrificed (20 per cent, at 100 m.p.h. and 30 per cent, at 110 m.p.h. for a reduction of loading from 14 to 10 lbs./sq. ft.). At all operating speeds there is a large gain (of the order of 50 per cent.) in the angle of climb for the same reduction in loading. Although these conclusions apply strictly only to aeroplanes of the type chosen as a basis, there seems no reason to suppose that there would be any important difference if another type, or size, were selected for investigation. The main effect is due to the way in which the drag of the wings depends on their lift, and this (the induced drag of the Prandtl theory) depends only on the speed and loading so long as the general proportions of the aeroplane are unchanged. Note.—Formulae are developed which enable the direction and rate of change for several of the more important charac- teristics to be obtained for small variation in wing loading from any desired starting point. ON THE CONCENTRATION OF STRESS IN THE NEIGH- BOURHOOD OF A SMALL SPHERICAL FLAW ; AND ON THE PROPAGATION OF FATIGUE FRACTURES IN " STATISTICALLY IS0TR0PIC " MATERIALS. By R. V. SOUTHWELL. M.A., F.R.S., and H. J. GOUGH, M.B.E., B.Sc. R. and M. No. 1003 (M. 33). (22 pages and 12 diagrams.) January. 1921. Price Is. 3d. net. The presence of flaws in materials results in structural weakness, and this matter is discussed in the present paper both from the general standpoint of elasticity and on theoretical grounds. References are made to other workers on the subject, including Dr. A. A. Griffith, in his paper to the Royal Society. Vol. 221, 1920, and Prof. Jenkin's presidential address to Section G at the 1920 meeting of the British Association. It appears not to be possible to say in advance how the planes of greatest weakness will lie in a given region of con- centrated stress, nor why, when a shaft fails, the crack should develop usually in a spiral direction. Equations are developed for the stress concentration produced by a small spherical flaw in materials subjected to uniform tension, and it is found that the intensification is not dependent on the actual magni- tude of the flaw. It is concluded that a fatigue fracture once started follows that surface on which the greatest principal tensile stress occurs, and the directions of special weakness must, in the author's opinion, have been established by the time the first flaw was formed. The paper is illustrated by a number of excellent examples of fatigue failures in steel specimens. NOTES ON " DETONATION " TEMPERATURES IN CLOSED- VESSEL EXPLOSIONS. By R. W. FENNING, M.B.E., B.Sc., D.I.C. Work performed at the National Physical Laboratory for the Engineering Research Board of the Department of Scientific and Industrial Research. R. and M. No. 1005 (E. 17). (4 pages, 1 diagram.) March,1926. Price 6d. net. A large number of experiments have been carried out at the National Physical Laboratory on the occurrence of detonation in closed vessels, and the present note is supplementary to a previously published paper entitled " Closed-Vessel Explosions of Mixtures of Air and Liquid Fuel (Petrol, Hexane and Benzene) over a Wide Range of Mixture Strength, Initial Temperature and Initial Pressure " (R. and M. 979). The discussion is continued of the effect of temperature and pressure of the unburnt residue of the charge at the start of '' knock " or " detonation " on various mixtures of air-petrol, air-hexane, air-pentane and air-heptane. In closed-vessel explosions of normal mixtures of air and liquid fuel the temperature of the unburnt residue appears to be a much greater factor in the production of detonation than the pressure, the latter seeming to have little, if any, effect. These Reports are published by His Majesty's Stationery Office, London, and r>ay be purchased directly from H.M- Stationery Office, at the following addresses : Adastral House, Kingsway, W-C. 2 ; 28, Abingdon Street, London, S.W. 1 ; York Street, Manchester; 1, St. Andrew's Crescent, Cardiff ; and 120, George Street, Edinburgh ; or through any book- seller. YEAR BOOK OF THE GERMAN SCIENTIFIC AERO NAUTICAL SOCIETY. Issued as a special supplement to the " Z.F.M.," the Berichte vnd Abhandlungen der W.G.L. No. 13, of May 1926, contains the yearly report of the German Wissenschaftliche Gesellschaft fur Luftfahrt. The first part of this year-book is mainly devoted to the business of the society, but the second part contains a number of illustrated lectures given on the occasion of the nineteenth general meeting of the society, held at Munich. The first is a paper entitled " Some recent experiences in the construction and operation of metal air- craft," the author of which is Claudius Dornier, and which deals with such subjects as the influence of weather and water upon Duralumin aircraft parts, the proportion of spar length to spar depth if flexibility is to be avoided (for steel this is found to be less than or equal to 17 and for Duralumin the figure is 15), and the technical development of Dornier machines up to the present time. Particulars and photo- graphs are given of a number of Dornier machines, which should be of considerable value. A. Behm delivered a lecture on " The Behm Sounder and its development as an acoustic- altimeter for Aircraft." and H. Herrmann, chief designer and engineer to the Udet Aircraft Work* of Munich, contri- butes a paper on " Topical technical problems in German Aircraft Construction." This paper deals with the. details of the slotted wing machine built by the Udet firm, with the problems of undercarriage design, and with multiengined aeroplanes, and is full of interesting information. It is well illustrated. Dr. Ing. G. Lachmann is represented by a lecture on " Non-stalling aeroplanes," in which he goes into the subject of the slotted wing. The legal side of aviation is dealt with in a lecture by Otto Schreiber, and the insurance side by Hermann Doring. Those interested in the Flettner rotor will discover much valuable information in the well-illustrated article on " Cinematographic pictures of the stream lines past rotary and stationary cylinders." An article by F. N. Scheubel, of Aachen, dealing with some peculiar longitudinal oscillations of the Aachen glider " Rheinland," with cinematograph films of the oscillations of a model in the wind tunnel, contri- butes to our knowledge of stability, and is well worth studying. The book concludes with a lecture by Bruno Eck on " Hydro- dynamic methods in the turbine theory " and an account of the " Lilienthal Competition " by Georg Madelung. Altogether, this year- book is one well worth perusing, The publisher is R. Oldenbourg Verlag, Gliickstrasse, 8, Munich, and the price is 14 Mark, nett. TO CONTRIBUTORS The attention of contributors is called to the fact that, in the case of those not known personally to the Editor, it is essential that an undertaking be given that the work is original. Contributors employed by aircraft firms should, before sending in articles for publication, submit them to the chief designer of the firm for his approval.—Ed. 464A
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