336 AIRCRAFT ENGINEERIN G November, 1940 Reviewe d by Major P . L. Teed, A.R.S.M., M.I.M.M. AN'S increasing power over the physical this book is no t unsatisfactory. Proof Stress is added to aluminium, reduces this property. A world has been largely due t o his ever explained reasonably, but some of what are further legitimate grievance on the par t of the growing knowledge of the chemistry called in the text stress/strain diagrams, arc engine designer is th e absence of an y information and physics of materials. From the end of th e not accurately described ; one is a load/elonga as to the change in mechanical properties of th e Stone Age until almost the present , this develop tion curve, while two of the others, through aluminium alloys with change in temperature. ing mastery has largely depended on th e metal neglect to mention the units in which strain is A warning should certainly have been given as lurgist, who first by empiricism and then by th e expressed, leave something to be desired. In t o the extreme sensitivity of the well-known same means, leavened to an increasing extent view of the very great importance of Young's casting alloy, B.S. L.5, to temperatures but b y Science, has found means of producing, with Modulus, Professor Hill's brief note is dis little above the atmospheric ; while on the bu t little regard to their specific gravity, sub appointing. He neglects to tell how this other hand, a t least something should have been stances possessing in greater or less degree propert y can be rapidly determined from a said of the notable hot strength of "Y " and those two outstandin g qualities, hardness and stress/strain diagram or from a load/elongation certain proprietary alloys of somewhat similar ductility, on which progress, prior to the flying one. One regrets that he does not mention how chemical composition. In view of these omis era, so muc h depended. In a world of ove r ninety little this vital quality can be changed by con sions, one almost resents the presence of some elements, three quarters of which arc metallic, siderable modification of chemical composition nineteen pages devoted to rubber, surely a the combinations and permutation s open to th e or of physical treatment ; further he does not substance of no grea t importance to th e aircraft experimentalist arc almost infinite. That these expose tha t ancient heresy, believed to this da y designer of to-day ? Indeed, there is a double possibilities have not been neglected when the in many drawing offices, to the effect that this cause of resentmen t in this chapter, for such oil- urge existed, is shown by a single example, modulus of a material is proportional to its resisting synthetic rubbers as neoprene, duo- aluminium. This metal, the discovery of which density—a few common engineering metals prene and buna are no t even mentioned, yet in dates back little over one hundred years, now seem to justify this belief, but when it is many contemporary aircraft they are ; with th e possesses over 600 alloys whose genesis dates mentioned that the moduli for gold and exception of the tyres, the only rubber from that of mechanical flight. aluminium are virtually the same, its inaccuracy substances used. will be apparent. While no doubt it is the metal group which When a considerable portion of th e structural provides b y far th e large r number of substances Of the qualities used by the engineer, weight of most civil and military aircraft is useful in aircraft construction, two others, one composed of solid light-alloy extrusions, it is ultimate shear stress is of comparable import of long history, timber, and the other, plastics, indeed remarkable to find that there is not a ance t o tha t of tensile, ye t as regard s the metals, of little over a generation in age, possess a Professor Hill has nothin g t o say of it ; indeed, single word as t o these, ye t much should have bewildering number of opportunities for useful except for a brief reference when dealing with been said. Good and bad sections from the employment. Professor F. T. Hill's " Materials plywood, this vital property receives no notice point of view of the manufacturer should have of Aircraft Construction," whose work whatever. This omission is indeed unfortunate been indicated. Emphasis should have been is now in its fourth edition,* purports to and will be so characterized by any designer laid on the superiority, from many points of give guidance to th e designer, user and student who not unreasonably consults this book for view, of drawn strip as opposed to extrusions of aircraft and aircraft engines through this for a wide variety of sections of a thickness not guidance as to such a fundamental matter. One almost perfect maze of varying possibilities. exceeding about 3/16 inches . The wide variation would have liked to have seen in th e chapte r on Such a task is formidable in a degree, even when mechanical testing a brief description of the in maximum speed of extrusion of different one bears in mind, not the great number of apparatu s generally used for the determination alloys of virtually the same mechanical proper materials which might be employed in aircraft of the ultimate shear stress of sheet and bar . ties should have been pointed out ; for example, construction, but merely those which, in fact, One would have been interested in a short a t least one relatively new aluminiu m alloy can are so employed. dissertation on th e similarity of th e shear/tensile be extruded at three times the speed of dura I t is not of course the author's purpose to ratios of alloys of the same type. Attention lumin and, since it possesses similar physical and urge the claims of a particular material or class might have been drawn to th e less known fact mechanical properties, should, from production considerations, always be used in place of the of materials, bu t rathe r to give useful particulars tha t while cold work raises the shear stress of latter. Further, it would not have been out of of those whose employment might be reasonably an alloy, its tensile is increased in even greater proportion ; consequently its shear/tensil e ratio place had a word of caution with regard to contemplated.' To-day, it is a matte r of common falls. Again, while in the section of the book extrusions been uttered, for there are certain knowledge that, excluding training aircraft, the dealing with the inter-crystalline corrosion, the differences between their longitudinal as airframe of the vast majority of both civil and influence of this most sinister form of attack opposed to their transverse mechanical pro military machines is abou t three quarters light alloy, yet in th e work under review twice as on the fatigue properties of alloys is rightly perties which may on occasion have to receive much space is devoted to ferrous materials as t o stated, the reassuring fact that their ultimate consideration from the designer. In conclusion, one feels that when Professor Hill's book first aluminous ones, while timber, the use of which shear stress is decreased to a lesser degree than appeared in 1933, it served its purpose far more is nowadays so markedly restricted, except in a any other property, is not mentioned. Bearing stress, often so crucial in present types of con adequately than it docs to-day. When, in partl y certain class of aircraft, receives only ten pages struction, is no t dealt with a t all. The question metallized biplanes, spruce was being replaced less space than the aluminium alloys—a of fatigue receives brief but not unsatisfactory b y drawn steel strip and ligh t alloys had neither criticism whose force is increased when it is notice, bu t one regrets the absence of reference their present field of application nor the mentioned that in the edition of 1934, when aircraft and th e materials of their construction to Gough's stimulating work on th e interpreta mechanical properties they now possess, such were distinctly different from to-day, the tion of Laue diagrams of fatigued metals; a work was no doubt useful, but in this world of light alloy monoplanes almost innocent of relative proportions of space devoted to these further, the failure to give examples of limiting carbon steels, it is frankly disappointing, for it different groups were substantially the same as fatigue ranges of common alloys and a caution in those cases where no known safe range exists, deals all to o briefly with the materials of which in the present work. is to say th e least, unfortunate. Neglected as h e aircraft and aero-engines arc in fact made and To a designer of aircraft, the physical pro is with regard to fatigue, the engine designer dilates at unnecessary length, not indeed on perties of material s in which he would be chiefly receives in the other fields in which he has " stick and string," but on almost as archaic interested, would be, density, Tensile Stress, special interest but little specific help from materials from the aircraft point of view—such 0•1 per cent Proof Stress, Young's Modulus, Professor Hill. In these days of light-alloy as streamline wires, ropes and cables, copper- Shear and Bearing Stresses, while in addition to pistons, and sometimes of similar cylinders, tin alloys and, above all, plantation rubber these, the engine designer would wish to know of shock absorbers. questions of co-efficients of expansion are of the fatigue limit, the co-efficient of expansion, immense consequence, ye t throughout this book- and of th e chang e of mechanical properties with no mention whatever is made of this property. variation of temperature. As regards the first Surely some reference to the great differences and second of the above important qualities, in co-efficients between most steels and alu BOOKS RECEIVED minium alloys would have been desirable ? In *The Materials of Aircraft Construction. such a work, one might , not unreasonably, have Fourt h Edition. By F. T. Hill. [Pitman. Strengt h of Materials . By A. Morley. expected to be told of those steels, the 20s.] Ninth Edition. 571 pp. , illustrated. [Long austenitic ones, which most closely approach Previous editions of this book were reviewed in mans. 15s.] aluminium as regards co-efficient of expansion ; AIRCRAFT ENGINEERING : First edition, Vol. V, one would have been grateful for some mention Structures . Fourth Edition. By J. D. August, 1933, p. 183 ; Third edition, Vol. IX, of the alloying element, silicon, which, when Haddon . [Pitman. 6s.] July, 1937, p . 186.
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Nov 1, 1940
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