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Aviation History
1925
1925 - 0570.PDF
SEPTEMBER 3, 1925 AERONAUTICAL RESEARCH COMMITTEE REPORTS FROM the number of enquiries we receive it appears that there is a desire in aircraft circles to know approximately the contents of the various technical publications of the Aeronautical Research Committee. All the aircraft firms probably receive these reports regularly, whether or not they contain anything of immediate interest or utility. In the case of draughtsmen, however, and others interested in aeronautics, who can hardly be expected to purchase all the reports, the problem of deciding whether any publication interests him is often a difficult one. As it is obviously desirable that the knowledge of aeronautics should be made available to all who take an interest in the subject, we have arranged with the Air Ministry to publish in FLIGHT summaries of all the technical publications as soon as these are issued, or shortly before they are published. All A.R.C. publications can be purchased from H.M. Stationery Offices at Adastral House, Kingsway, London, W.C.2 ; 28, Abingdon Street, London, S.W.I ; York Street, Manchester ; 1, St. Andrew's Crescent, Cardiff ; 120, George Street, Edinburgh, and through any bookseller. The Effect of Keyways upon the Strength and Stiffness of Shafts subjected to Torsional Stresses. By H. J. Gough, M.B.E., B.Sc. R. & M. No. 864. 20 pages and 6 diagrams. April, 1925. Price Is. 3d. net. Keyways are extensively used in engineering practice, and their effect on the strength and stiffness of a shaft is important. A previous paper on this subject by Dr. A. A. Griffith has been published in the Reports & Memoranda Series (R. & M. No. 334, " Determination of the torsional stiffness and strength of cylindrical bars of any shape.") The main object of the present enquiry was to determine the relative limiting ranges of torque under reversals of load for a solid shaft, a shaft with a standard keyway, and a shaft with a keyway of equal depth and half the width of a standard keyway. The limiting ranges of torque were determined by endurance tests. Two materials were employed in the tests, Armco Iron— as representing materials of great ductility, and 0-65 per cent. C. steel, as typical of harder metals. Endurance tests were also made upon a keyed drive in Which the torque was transmitted through a shaft, via a key, to a keyed member. The elastic stiffness and strength of each type of shaft under statical torsional straining have also been determined. These results have been compared with those calculated from empirical formulae derived from soap-film experiments by Dr. A. A. Griffith (R. & M. 334). Under reversed torsional stresses the limiting ranges of torque for shafts with full width and half-width keyways were identical for any one material. The reduction in strength due to the presence of the keyway amounted to 21 per cent. and 12 per cent, for 0-65 per cent. C. Steel and Armco Iron respectively. In the keyed shafts (of Armco Iron) a total reduction of 33 per cent, was observed. The effect of the presence of the keyway was to reduce the elastic stiffness by 6 per cent, and 10 per cent., respectively, for shafts containing the narrow and wide keyways. The reduction in elastic strength for each type of keyway had the same value of 23 per cent. Agreement was found in comparing these results with those predicted by the formulae of Griffith, the maximum divergence being 4-7 per cent. A Continuous Rotation Balance for the Measurement of Pitching and Yawing Moments due to Angular Velocity of Roll (Mp and N,,). By T. Lavender. Reports and Memoranda, No. 936. (Ae. 157.) (3 pages and 2 diagrams). February, 1925. Summary.-—For the complete analysis of the stability of an aeroplane a knowledge is required of various so-called rotary derivatives, which are the rates of change of the moments about three mutually perpendicular axes caused by angular motions about these axes. Some of these deriv- atives for model aeroplanes can be measured in the wind tunnel by oscillation experiments only, but three of them, viz., the rates of change of rolling, pitching, and yawing moment due to an angular velocity of roll (L,,, M,, and Np) can conveniently be determined by causing the model to roll continuously about an axis parallel to the wind direction and measuring the appropriate couple. In a previous report (R. & M. 828) a description was given of a continuous rotation balance for the measurement of L,, at small rates of roll ; the present report describes the modifications which have been made to this piece of apparatus to enable it to be used for the measurement of Mp and Np as well. The apparatus has proved satisfactory, the general order of accuracy of the measurements being found to be at least as great as, and probably greater than, that usually obtained in experiments involving measurements of pitching and yawing moments on a stationary mcdel. Reports and Memoranda of the Aeronautical Research Committee Published between April 1, 1923, and December 31,1924. Reports and Memoranda, No. 950. April, 1925. Summary.—It has been customary in the Reports of this series to make every hundredth report (starting from R. & M. 650) take the form of an index. In accordance with this practice, the present R. & M. 950 gives a list of the Reports and Memoranda published by the Aeronautical Research Committee between April 1, 1923, and December 31, 1924. In the section dealing with the aerodynamic loading, reference is made to a number of reports containing the results of wind tunnel observations on model airships. The Report of the Airship Stressing Panel (R. & M. 800) is taken as the basis for recommendations for strength calculations, with the addition of certain more recent material tabulated in Appendix III of the present report. Attention is drawn to various points which the Panel considered important in the application of the methods of R. & M. 800. In section (3) is given a schedule of factors of safety for various conditions of loading and aerodynamic trim of the airship. In section (4) consideration is given to the questions of fire prevention ; protection from electrical discharges ; the utilisation of about 4 per cent, of the full engine power for moving the ship astern ard for controlling the angular movement of the ship at lower speeds ; and to the questions of instruments, guy ropes, ballast and the inspection of the material and workmanship. Three appendices are attached to the report, of which the first contains calculations relative to the effect of deflated gas bags, the second contains a note on the possible gradual deterioration of duralumin, and the third contains a list of papers relating to airships. The Measurement of Airflow Round an Airscrew. By C. N. H. Lock, M.A., and H. Bateman, B.Sc, D.I.C. R. and M., No. 955. (Ae. 174.) (15 pages and 8diagrams.) November, 1925. Price Is. net. This paper gives the results of observations of airflow near to an airscrew made with the siandard N.P.L. type of yawmeter, from which values of the axial, radial and circumferential components of the velocity were deduced on the assumption that the flow was symmetrical about the axis of the airscrew. The experiments were undertaken partly with a view tp supplementing some previous work on overall performance of airscrews (see R. and M., No. 892, " Experiments with the Family of Airscrews, Part III," Lock and Bateman), and partly with the object of comparing the velocities of the airscrew with those predicted by the newly advanced vortex theory of airscrews (R. and M., No. 786, " An Aerodynamic Theory of the Airscrew," Glauert). This theory has already been substantially verified on the basis of overall force measurements, but the comparison of the measured axial and circumferential velocities with the interference flow from the vortex theory provides a more critical test of the theory. Fair agreement between observa- tions and the results predicted by the theory was obtained in most cases, and the results may, therefore, be considered as encouraging to the use of measured interference flow for analysing airscrew performance in cases where the vortex theory does not apply. Notes on Stalled Flying. By R. M. Hill ard H. L. Stevens, of the Royal Aircraft Establishment. R. and M., No. S63. (Ae. 179.") (9 pages and 1 diagram.) October, 1922. Price Qd. net. The subject of the control of aeroplanes at and beyond the stall is one that is receiving considerable attention at the present time, and this report is of interest in that it describes full-scale experiments conducted on a standard 570
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