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Aviation History
1927
1927 - 0368.PDF
40 SUPPLEMENT TO FLIGHT MAY 26, 1927 THE AIRCRAFT ENGINEER HEAT-RESISTING AND NON-CORRODIBLE STEEL. A most interesting paper on above subject was read on May 23 by Mr. S. A. Main. B.Sc. F.Inst.R, before the Institu- tion of Aeronautical Engineers. Mr. Main, it might be pointed out, is associated with Sir Robert Hadfield at the Hadfield Research Laboratory of Sheffield. The paper commenced with the following passage, which is worth noting and taking to heart: "In few branches of engineering is enterprise more necessary, and indeed more evident, than in aeronautical •engineering. Since all engineering progress is based upon the properties of the available materials, it is of first importance that the engineer should have up-to-date knowledge of the latest developments in this direction, and of the properties— and also the limitations—of the materials provided for his use. Without a knowledge of the latest progress of the metallurgist the engineer may perhaps be entirely ignorant that schemes, which are beyond the capacity of existing materials as he knows them, and therefore remain in abeyance, may be brought to fruition." Space does not permit of giving a summary of the paper, but it may be of interest to mention that the following alloy steels were referred to : "' Era " steels •of various classes in the heat-resisting steels, and " Era " Cr. (chromium steel) and " Hecla ATV " among the non-corrodible steels. The lecturer, while admitting the somewhat higher cost of these special steels, pointed out that there are many purposes which they are able to serve in which their higher cost is amply justified. The paper was one of very great interest to all aeronautical engineers, and should be read in full in the Institution's JOURNAL. ABHANDLUNGEN AUS DEM AERODYNAMISCHEN INSTITUT AN DER TECHNISCHEN HOCHSCHULE AACHEN It is a somewhat peculiar fact that although in Germany the aerodynamic design of aircraft has been studied very fully indeed, the structural side has not received anything like as much attention. German aerotechnical literature is full of articles on aerodynamic subjects, but to come across one dealing with the subject of aircraft structures and the stresses set up in them is the exception rather than the rule. We admit that of the two the aerodynamic side is the more interesting, and that German aircraft designers are probably as well posted on structural design as any others, but the subject has not, on the whole, received much general publicity in the German aviation press. During the last few years there has been a tendency towards giving greater attention to this side of aircraft design, and it is perhaps significant that Number 7 of the Abhandlungen aus dem Aerodynamischen Institut of Aachen, published by Julius Springer of Berlin, is devoted almost entirely to the subject of stresses in beams. Professor Th. von Karman contributes an article entitled " Uber die Grundlagen der Balkentheorie " (On the foundation •of beam theory), in which he attacks the problem of deriving systematically the foundations of beam theory from the laws of elasticity, confining himself to the transition from two- dimensional strips to beams, the two-dimensional strip •corresponding to a beam of rectangular section and small width. Friedrich Seewald contributes an article on " Die Spannun- gen und Formanderungen von Balken mit rechteckigem Quersehnitt " (Stresses and changes in form of beams of rectangular section), in which the author arrives at the •conclusion that the problem resolves itself into two parts, one which is identical with the elementary theory, and the other which can be calculated once and for all for any given load. An examination of the inaccuracies involved leads to the belief that the solution given is sufficiently accurate for all practical purposes. The only exception is the case, which rarely occurs, when the length of beam is small in proportion to the depth. " Stegbeanspruchung hoher Biegungstrager" is the title •of an article by Use Kober, dealing with the stresses in the vertical walls of deep beams of box section, such as those frequently used in the wing spars of cantilever monoplanes. The authoress points out that the usual formula; are suffi- ciently dependable for beams of normal proportions, but if the depth of the beam or spar is increased considerably, while the walls are reduced in thickness so as to save weight, a point is soon reached where the normal formulae become unsatisfactory owing to buckling of the walls. The subject is dealt with at considerable length, and examples of how to use the new formulae are given at the end of the article. The last article in the present volume is by Max Knein, and deals with the stress distribution by in compression and plain change of form when lateral expansion is entirely prevented. Unfamiliarity with the German language is a stumbling block, but those fortunate enough to be able to read technical German will find in this book much of considerable technical value. The price is 7-50 gold marks. Previous numbers of the Abhandlungen also contained interesting articles. Thus Xo. 6 (Price 7-50 mark) includes an article on the calculation of pressure distribution over airship hulls, by Prof, von Karman; and another, by Dr. Ing. Hans. Ermisch, on the air flow and pressure distribution over various bodies at various Reynolds Numbers. This is illustrated by diagrams, drawings, graphs and photographs showing actual flow patterns. No. 5 of the Aachen Abhandlungen is devoted entirely to the subject of the theory of gliding and soaring flight, being a paper by Dr.-Ing. Klemperer. The price of No. 5 is 6 mark 90. All throe numbers can be obtained from the publishers, Julius Springer, Linkstr. 23-24, Berlin W9. SUMMARIES OF TECHNICAL REPORTS OF THE RIJKS- STUDIEDIENST V00R DE LUCHTVAART, AMSTERDAM. REPORT A. 98. AIR RESISTANCE OF TWO AEROPLANE RADIATORS. The resistance to motion of two radiators which have been comparedearlier* for cooling power has l>eeu determined, together with the influence of a yaw relative to the direction of the air stream.The radiatora differed only by the construction of the cooling surface. Xo. 1 was built along normal lilies (round tubes with hexagonal equilateralopenings), whereas No. 2 was of the Andre system (flat tubes with longi- tudinal grooves and flat hexagonal openings) (see also Figs. 2 and 3,Report A. 92). Tables 1 and II give the resistances of both radiators normally exposedto the air stream. Table III and Fig. 2 show the influence of a yaw on the resistance of No. 1 radiator. The coefficients have been calculated withthe formula given in the Report: they apply only to the resistance of the cooling core. • Report A. 92. Verslagen en Verhandelingen R. L. Deel III, p. 11 REPORT A. 130. DISCUSSION OF THE RE HJLTS OF THE TESTS ON THE BOUNDARY LAYER OF THE AEROFOIL WITH ROTATING CYLINDER. The results of the velocity measurements in the boundary layer describedin Report A. 129 are discussed in detail. Consideration is given separately to :—(a) The flow around an ordinary aerofoil (aerofoil with cylinder at rest and fllled-up slot: C, Figs. 5, 6 (1)). The area with a steep velocitygradient is restricted to the immediate proximity of the surface. Even at the small angle of incidence used in the tests there is probably adissolution of the flow on the after part of the upper surface (b) The influence of the rotating cylinder (aerofoil with rotating cylinder : A,Figs. 3, 6 for upper surface, Fig. 8 for lower surface). The velocity in the boundary layer on the upper surface is increased, this increase is perceptibleover the whole upper surface ; the dissolution at the after part is reduced. At a short distance of the lower surface of the cylinder there is probablya counter-current. (r.) The influence of the slot (aerofoil with stopped cylinder : B, Figs.4, 7). In the foremost measuring points the slot caused an important retardation in the lower part of the boundary layer, followed by a morevigorous dissolution on the after part. A programme for the continuation of the research is developed. Divisioninto separate parts appears to be necessary. In the first place experiments will be made on the flow around an ordinary aerofoil by measuring thepressure distribution on the surface and the velocity distribution in the boundary layer. REPORT M. 219. MECHANICAL PROPERTIES OF SOME MATERIALS THAT ARE USED FOR THE CONSTRUCTION OF AEROPLANES. Generally speaking, the stresses that are tolerated in aeronautical con-structions are greater than in other technical constructions. Therefore it is necessary to keep a better account of the greatest stressesthat may occur, and of the actual properties of the materials that are used. The Aeronautical Research Laboratories took the limit of permanentelongation (elastic limit) for base of the strength calculations. In order to investigate the actual properties of the materials used, many tests weretaken on different steels, woods, light aluminium alloys, and on covering fabrics. The results of these testa are shown in the tables, where also many data from other publications are given. It is possible to make a comparison between the properties of the different materials by use of the ratio -TrFr (tensile strength: specific gravity) or -J—- (compression strength : O.U. b.&. specific gravity). . Further particulars about the methods of testing and the results obtained will be given in following publications.330/
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