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Aviation History
1936
1936 - 1601.PDF
SUPPLEMENT TO FLIGHT 652^ 44 THE AIRCRAFT ENGINEER JUNE 18, 1936 The first point on which one is inclined to quarrel with the author is in his treatment of spinning. He gives the conclu sions reached by his colleague, J. M. Gwinn, with the admis sion that other authorities disagree with Gwinn on a number of points. The influence of the inertia characteristics on spin ning is so completely accepted, at any rate in this country, that it seems unwise to condemn it. Special flight problems, including calculation of take-off and landing runs, and of range and endurance, are the subject of a special chapter. Another chapter deals iff an inadequate fashion with the important subjects ci model testing and flight testing. Early in the chapter appears the remarkable statement that airplane design by building, testing, changing and re-testing models is essentially a confession of ignoran-e. It is clear, from the author's later remarks, that he does not really mean to claim that we know all there is to know about the aerodrynamic side of aircraft design, but model tests have played, and can play, a very valuable part in aerodynamic progress, provided that their limitations are recognised and their interpretation is properly and carefully carried out. The parts of this chapter which deal with flight testing are also open to criticism. One does not feel that possible cus tomers, or even senior executives, will place the same faith in calculated rates of climb made by assuming the propeller characteristics and using level flight tests only, as they would do in actual climbing trials, even though these have to be sub ject to correction to standard atmosphere. The most serious fault in the whole book, however, comes at the end of this chapter on model testing and flight testing. In a stability test of an unspecified aeroplane with an unspeci fied initial position of centre of gravity it is stated that 60 to 100 lb. of ballast will be necessary to cause instability when flying at 1,800 lb. gross weight. When one adds that the posi tion of the ballast likewise is not specified it is astonishing that such a statement should have been allowed to creep into a book of such a generally high standard as this one. The book closes with a chapter on hull and float character istics, containing much useful data, and followed by eight Appendices. Of these, IV, V and VII have already been men tioned, while Appendix VI gives a very comprehensive collec tion of performance data of current American engines and air planes. This is very useful now, but it is the sort of informa tion that rapidly becomes out of date. This is a definitely useful book, worthy of recommendation to all who have to deal with aerodynamic design. As a book for students its value is enhanced by the large number of numerical examples given in each chapter, but these will not interest the older reader. The production is excellent, except for the small size of the illustrations, but it is, of course, real ised that this fault could only be remedied by giving fewer of them, which would be a pity. H. A. M. TECHNICAL LITERATURE SUMMARIES OF AERONAUTICAL RESEARCH COMMITTEE REPORTS REPORTS published by His Majesty's Stationery Office, London, which may be purchased directly from H.M. Stationery Office at the following addresses: Adastral House, Kingsway, W.C.2 ; 120, George Street, Edinburgh; York Street, Manchester, 1 ; St. Andrew's Crescent, Cardiff; 15, Donegall Square West, Belfast; or through any ordinary bookseller. STRESS-CALCULATION IN FRAMEWORKS BV THE METHOD OF " SYSTE MATIC RELAXATION OF CONSTRAINTS."—I AND II. By R. V. South well, F.R.S. R. & M. No. 1668. (1 page.) May, 1935. Price 2d. net. Abstract only of paper published in Royal Society Proc. A, Vol. 151,1935. SOME FEATURES OF THE BEHAVIOUR IN BENDING OF THIN-WALLED TUBES AND CHANNELS. By D. Williams, B.Sc, A.M.I.Mech.E. Communicated by the Director of Scientific Research, Air Ministry. R. & M. No. 1669. (13 pages and 15 diagrams.) February 28, 1935. Price is. net. Stressed skin components and structural elements of the tubular or light channel type are becoming increasingly popular in aircraft structures. As in certain respects the commonly accepted theory of bending is in these cases not applicable, it was considered desirable to examine the bending characteristics of such structures with particular reference to shear stresses and the position of the flexural axis. This report, therefore, deals primarily with the two closely related problems of finding— (a) the bending shear stresses induced when a beam of thin-walled section is laterally loaded at its flexural axis, (b) the flexural axis for thin-walled sections. For the case of thin-walled sections, simple and readily applicable solutions to both problems are possible. It is shown that the shear stresses in the flanges of either closed tubular sections or open channel sections, where the flange of the section is wide and its thickness is comparable with, or less than, the thickness of the web, may be important. It is also demonstrated that for the average open section the flexural axis is completely outside the section. A SUCCESSIVE APPROXIMATION METHOD OF SOLVING THE CONTINUOUS BEAM PROBLEM. By D. Williams, B.Sc., A.M.I.Mech.E. Communi cated by the Director of Scientific Research, Air Ministry. R. & M. No. 1670. (21 pages and 13 diagrams.) May 31, 1935. Price is. 3d. net. The solving of a continuous beam problem by existing methods, especially when the loading system is complicated and when there are several bays, is rather tedious and lengthy. The method described in this report seeks to reduce this labour. It is based on the general notion, due to Professor Hardy Cross, of considering a structure one joint at a time, the other joints meanwhile being considered fixed. The general problem is considered in relation to continuous,beams under the following conditions : (a) cross section and lateral loading constant over each bay and no end loads, (6) as for (a) but with end loads, (c) constant cross section and end load, but arbitrary lateral loads, over each bay. (d) cross section and lateral loads arbitrary but end load constant for each bay. Detailed numerical examples are given for cases (a), (b) and (d). The method provides a simple and rapid means of solving the general problem of the continuous beam, offers advantages over other methods in many cases and is capable of dealing with any number of bays. FLEXURAL AND SHEAR DEFLECTIONS OF METAL SPARS. By I. J. Gerard, M.Sc, A.M.I.C.E., and H. Boden, B.Sc. (Eng.). Communi cated by the Director of Scientific Research, Air Ministry. R. & M. No. 1671. (14 pages.) June 7, 1935. Price 9d. net. Five typical spars which were kindly supplied by aircraft firms were tested within the elastic limit as simply supported beams carrying one or more concentrated lateral loads. They were also tested with combined end loading and lateral loading, with various ratios of bending stress to end load direct stress ; at a selected ratio each spar was tested to destruction. The apparent values of the effective flexural stiff ness EI and the elastic shear constant " r " were determined. The results of these tests have been compared with a large number of similar routine tests. It is concluded that spars may, in general, be divided into three categories according to the material of manufacture, i.e., (1) hardened and tempered steels, (2) relatively softer steels, and (3) duralumin. There is no appreciable varia tion in El in category (1), but there is an appreciable reduction in the value of EI towards failure in categories (2) and (3) and this still leaves the problem of how to allow for this reduction when calculating the failing load of the whole spar, as built into an aeroplane, from tests on a relatively short specimen. As, however, most spars at present belong to category (1), further research is not warranted. It will be possible to make assumptions, when dealing with spars in categories (2) and (3), sufficiently conservative to cover the uncertainty introduced by variations in EI when bridging the gap between the test specimen and the spar as built into the aeroplane. THE CALCULATION OF THE LOADS AND BENDING MOMENTS IN THE MEMBERS OF A PLANE BRACED FRAME WITH RIGID JOINTS. By J. Morris, B.A., A.F R.Ae.S. Communicated by the Director of Scientific Research, Air Ministry. R. & M. No. 1672. (42 pages and 12 diagrams.) March 23, 1935. Price 2s. net. A rapid successive approximation process for determining the bending moments in the members of unbraced frames of the portal type has recently been given by Professor Hardy Cross. The possibility of extending this process to the general case of a plane braced frame with rigid joints is here considered. By taking account of the deflections of the members of a braced frame, a general successive approximation process is developed for determining the end toads and bending moments in the members of any plane frame with rigid joints. In addition, a method is given for obtaining the angular as well as linear deflections of the joints from the results of this process. Several fully worked examples illustrate the applica tion of the process. For plane frames under practical conditions the process provides a rapid and accurate method of determining the internal loading actions and thus represents a considerable advance upon existing methods. The examples given indicate the importance of end-load-deflection effects in frames' under the conditions obtaining in aeronautical structures. ICE FORMATION IN CARBURETTORS. By W. C Clothier, M.S., Wh.Sch. Corrmunicated by the Director of Scientific Research, Air Ministry. R. & M. No. 1676. (2 pages.) September, 1935. Price 2d. net. The phenomena associated with ice formation caused by the evaporation of the fuel have been studied both theoretically and experimentally. Consideration has been given to the prevention of ice formation, by the application of heat either to the intake air or to the surfaces on which ice may form, and by the use of ice in hibitors. An automatic device has been developed whereby an ice inhibitor may be added to the fuel whenever ice commences to build up in the induction system. The general results of the investigation are given in this abstract of the original paper which has been published in the Journal of the Royal Aeronautical Society, Vol. XXXIX, No. 297, page 761 (September, 1935). (Other Summaries on page 39)
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