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Aviation History
1928
1928 - 1014.PDF
SUPPLEMENT TO FLIGHT 82 OCTOBER 26, 1928 THE AIRCRAFT ENGINEER THE BEHAVIOUR OF A SINGLE CRYSTAL, OF «-IRON SUB- JECTED TO ALTERNATING TORSIONAL STRESSES. By H. J. Gough, M.B.E., D.Sc, Ph.D. Work performed for the Engi- neering Research Board of the Department of Scientific and Industrial Research. R. & M. No. 1148 (M. 54). Oetobsr, 1927. (34 pages 40 photographs, 15 diagrams.) Price 2*. 3d. net. A general research is in hand at the National Physical Laboratory on theproperties of the fatigue of materials and the present experiments, which are a part of this research, relate to a series of tests on large metallic singlecrystals. In previous experiments single crystals of aluminium • were used ani it is balieved that the present fatigue tests on a single crystal of a-ironare tte first of their kiud. The changes in microstructure of u-iron and the method of failure produced by alternating torsional couples have been studiedin relation to the crystal structure and to the stress system employed and the results of the experiments are consistent with a new theory of the mechanismof distortion, which is here outlined. Slip is determined by shear stress considerations and the direction of slipcoincides with that of the moat highly stressed principal line of atoms (greatest) linear atomic density). Deformation of the specimen under test usuallyoccurs by slip on two of the crystailographie planes. Further experiments are contemplated to repeat the present experiments ona crystal P333e35itig a different relative orientation of the crystallography- and straining axes. Other experiment* will be directed to repeated strainingactions and to the study of single crystals of iron under repeated impact stresses, thus continuing earlier work.'t • " Expsriments on the behaviour of single crystals of aluminium."—Gough, Wright and Han3on. Jour. last. Metals, vol. xxxvi. No. 2, 1926, p. 187. t -;The Resistance of Materials to Impact."—Stanton and Bafrstow. Proc. Inst. Mech. Engra., Nov. 1908. REPORTS AND MEMORANDA OF THE AERONAUTICAL RE- SEARCH COMMITTEE PUBLISHED BETWEEN MARCH 1ST, 1927, AND JUNE 30TH, 1928. R. & M. No. 1150. July. 1928. (8 pages.) Pries 4rf. net. The Aeronautical Research Committee issue at intervals lists of Reportsand Memoranda published hetween given dates. The complete lists are given in R. & M. NO3. 650, 750. 850. 950, 10J0. and the present issue, which lastcovers the period up to June 30. 1928. For a classified list under subjects of the reports on sale by His Majesty's Stationery Office, application shouldbe made to that office for their free issue, known as " List B " (revised to February 21, 1928). EXPERIMENTS WITH THE FAMILY OF AIRSCREWS IN FREE AIR A.T ZERO ADVANCE, By H. C. H. Townend. B.Sc, W. S. Walker and J. H. Warsap. R. & M. No. 1153. (Ae. 318). April, 1928. (10 pages and 6 diagrams). Price Is. net. It has always been somewhat uncertain how nearly the performance of anairscrew rotating at a fixed point in free air can be estimated from the usual " static " tests in which the screw is tested in a wind tunnel with the tunnelfan at rest. The screw itself induces a general flow along the tunnel which may be quite appreciable so that the condition of zero advance is not actuallyobtainable. In order to overcome this difficulty and so obtain more reliable results with which to compare the theory in this region, the tests describedin this report were made, under conditions closely approximating those of free air. As no measurements of velocity had been made in the originalstatic test of the Family* it was decided to repeat them in the tunnel and to observe the tunnel velocity by means of a sensitive vane anemometer, aswell as on the tunnel gauge. It was found not to be possible to estimate accurately the thrust at staticfrom test3 in a tunnel ma4e with the wind off unless the velocity induced by the screw is measured with a sensitive anemometer, in which case a reliablevalue of V/nD can be found which corresponds to the measured thrust. For a 3 ft. screw tested in a 7 ft. tunnel this value may also be derived empiricallyfrom a curve (Fig. 6) in terms of the P/D ratio of the screw. By either method the resulting value of V/nD will be sufficiently near zero to permit of extra-polation to zero, except for screws of high pitch, which are usually critical near static. *R & M. 829. Experiments with a family of airscrews, including the effectof tractor and pusher bodies. Part I—Experiments with the family of airscrewa mounted la front of a small body.—By A. Fage, A.R.C.Sc.C. N. H. Lock. M.A.. R. G. Howard. B.9r. and H. Bateman. B.Sc. ON THE HOPJZONTAL FLIGHT OF A HELICOPTER. By H. Glauert, M.A. Presented by the Director of Scientific Research, Air Ministry. R. &' M. No. 1157. (Ae. 322). (12 pages and 2 diagrams). March, 1928. Price 9rf. net. In a previous report (R. * M. 1132)*, a theory has been developed for thevertical ascent of a helicopter, and this has now been extended to cover the case of horizontal flight also. The analysis is confined to the case when the helicopter is in horizontalflight with its axis vertical. The effect of variation of the blade angle is considered, and also the effect of the periodic motion on the behaviour ofairscrews mounted on the blades. Ths effect of the horizontal motion of the helicopter is to reduce the powerrequired for smtentation. The drag force is not high and the helicopter should thsrefore be able to attain a satisfactory horizontal speed. *R. & M. 1132. " On the vertical ascent of a helicopter," H. Glauert. THE RESISTANCE OF THE INTERNATIONAL AIRSHTP MODELS MEASURED IN THE WIND TUNNEL OF THE ROYAL COLLEGE OF SCIENCE, SOUTH KENSINGTON, S.W.7. By Professor F. T. Hill and T. Tanner, A.C.G.I., D.I.C. Communicated by Professor L. Bairstow. R. & M. No. 1160. (Ae. 325). (9 pages and 9 diagrams). March, 1928. Price Qd. net. The two models here described were tested over a range of wind speeds upto 75 ft. per second to find the resistance at different Reynolds numbera. The report contains a careful description of tlir method of test and discussesthe effect of various supports for the model. The resistance coefficient of the short model decreased with increase of theReynolds number over most of the experimental range, and the coefficient of the' long model increased slightly. REPORT ON THE DROP OF STRESS AT YIELD IN ARMCO IRON. By A. Robertson. D.Sc, and A. J. Newport, B.Sc. Work performed for the Engineering Research Board of the Depart- ment of Scientific and Industrial Research. R. & M. No. 1161. (M.56.) (7 pages and 25 diagrams.) November, 1927. Price 9rf. net. One of the authors had previously investigated the drop of stress at yieldin ductile material in compression and in conjunction with Professor G. Cook in tension alone. The apparatus used in these investigations did not permitof tension and compression tests being carried out on the same specimen. It appeared desirable to investigate the phenomenon further and apparatuswas constructed with the help of a grant from the Engineering Board to test hot rolled Armco iron.It was observed in the preliminary tests on this material that the yield stress was affected by the rate at which the straining was made. In order toobtain consistent results it was found necessary to adopt a low rate of straining. When the time from zero load to yield load was about half-au-hour, quiteconsistent results were obtained. Small scale tension and compression stress-strain diagrams for " as received"material are shown in Figs. 4 and 5 and large-scale diagrams in Figs. 6 and 7. Tension and compression diagrams for normalised material are shown inFigs. 8. 9 and 10. The tension and compression diagrams were found to be of glightly differenttypes. In tension, immediately after the drop of stress at yield, there is no increase in stress until the strain is about twelve times the yield strain. Incompression, however, thia region of constant stress is absent, the stress rising immediately after the drop of stress at yield has taken place. Theexact shape of the stress-strain diagram immediately after yield can also be varied slightly by the manner in which the test is carried out. With this material the yield does not take place so suddenly as with anordinary mild Bteel. For " as received " material the yield stress was 9-35 tons/sq. in. in tension and 9 • 61 tons/sq. in. in compression, and for normalisedmaterial 8-63 tons'sq. in. and 10 0 tons/sq. in. respectively. The drop of stress at yield for " as received " material was 20 per cent, intension and 24 per cent, in compression, and for normalised material \~> per cent, in tension and 23 per cent, in compression. The "drop " stress, orstress immediately after yield, for the " as received " material was 7 -5 tons/ sq. in. in tension and 7-3ton?,sq. in. in compression. For the normalisedmaterial it was 7-3 tons/sq. in. in tension and 7-7 tons/sq. in. in compression. A SUMMARY OF THE EXPERIMENTAL AND THEORETICAL INVESTIGATIONS OF THE CHARACTERISTICS OF AN AUTOGYRO. By H. Glauert, M.A.. and C. N. H. Lock, M.A. Presented by the Director of Scientific Research. Air Ministry. R. & M. No. 1162 (Ae. 326.) April, 1928 (5 pages.) Price 4rf. net. Several reports on the autogyro have been published by the AeronauticalResearch Committee, and a list is given below. The present paper was written at the request of the Committee to summarise the results of theexperimental and theoretical Investigations on the autoeyro's characteristic*. The exjwrimental and theoretical results of the paper are in satisfactoryagreement on all essential points, it would appear that the performance of a gyroplane is inferior to that of a correspondiiiK aeroplane, bnt the gyroplanepossesses valuable qualities of stability at largt angles of incidence and of ease of landinc. LIST or REPORTS Ref. Report. Author. Title.So. 1 R. * M. 1111 .. H. Glauert .. A general theory of the autogyro.2 R. <fc M. 1116 .. L. K. Cayeill Wind tunnel and dropping tests of and A. K. W. autogyro models.Nutt s RAM. till .. H. Glauert .. An analysis of the energy losses ofan autogyro. 4 R A-M 1127 .. C. X.H.Lock Further development of autogyrotheory. h RAM. 1154 .. C. N. H. Lock Wind tunnel experiments on aand H. C. H. G-foot model autogyro. Townend.6 R. &. M. 1108 .. H. E. Wimperig The rotating wing in aircraft. NOTE OK THE FORCES EXPERIENCED BY ELLIPSOIDAL BODIES PLACED UNSYMMETRICALLY IN A CONVERGING OR DIVERGING STREAM.—By Dr. H. Lamb, F.R.S. R. & M. No. 1164 (Ae. 328). May, 1928. (4 pages and 3 diagrams.) Price 4rf. net. The forces on ellipsoidal bodies placed obliquely in a converging ordiverging stream can be found direct by calculation of the pressures on the surfaces. This has been done in the present report for the two-dimensionalHow past an elliptic cylinder and for an ellipsoid of revolution. The|resultp agree with those of the indirect but more general investigation by G. 1.Taylor.* • The force acting on a body placed in a curved and converging streamof fluid—G I. Taylor. (R. & M. 1166.) TO CONTRIBUTORS. The Editor will always be phased to consider for publication articles on any subject relating to aircraft engineering, and partictdarly articles dealing with design and constructional problems in seaplanes and flying-boats. Articles published will be paid for at our usual rates. •
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