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Aviation History
1929
1929 - 0843.PDF
April 25, 1929 Supplement to FLIGHT ENGINEERING Edited by C. M. POULSEN April 25, 1929 CONTENTS PAGEDevelopment of Metal Construction. By H. J. Pollard, Wh.Ex. A.F.R.Ae.S 25 The Theory of Long-Distance Flight. By Robert J. Nebesar ... 28 In the Drawing Office 33 Technical Literature 5 EDITORIAL VIEWS. After a long absence Mr. Pollard returns to our columns this week with an article dealing with the calculation of moments of inertia, etc., of beams made up of corrugated strip of small thickness. Mr. Pollard points out that in the case of ordinary box sections, such as those in use when we still built aircraft with wooden spars, the draughtsman could easily remember the formula?, or else could look them up in almost any text book on structures. For the new corrugated strip sections used in the construction of metal wing spars in steel or Duralumin no information is yet included in text hooka, and we therefore feel that a large number of draughtsmen and designers will be very glad to have the friendly advice which Mr. Pollard has to offer. During some years with the Bristol Aeroplane Com- pany Mr. Pollard has had a very wide experience in the design, manufacture and use of metal aircraft structures, and at the present moment he is engaged upon work of extraordinary interest, some of the results of which we hope h< will share with us and our readers by giving an aeconnt in THE AIRCRAFT ENGINEER. For the present, however, this work ifl of a confidential nature, and we must await developments. In view of the impending attempt by the Fairey monoplane •with Napier " Lion " engine to beat the existing world's records for distance and duration without alighting, the article which we publish this week, by Mr. R. J. Nebesar, should be of considerable interest. Mr. Nebesar is on the technical staff of General Airplanes Corporation, of Buffalo, New York, and his treatment of the subject of range is somewhat unusual. For instance, we do not remember Previously having seen the theory advanced that for best results the sum of parasite and profile drags should equal the induced drag, at the angle of minimum resistance. This appears to lead to rather low aspect ration for machines "^•''ded to make long non-stop flights, and the views of British designers on the subject would be welcomed. "he use of the nomograph is far lese general than it de- H-rves, and as we rather share the views of Mr. Rodger that he average draughtsman "funks " it as being too difficult, we are glad to publish Mr. Rodger's explanation of its con- traction and use. DEVELOPMENT OF METAL CONSTRUCTION. By H. J. POLLAED, Wh.Ex., A.F.R.Ae.S. (Continued from December 27, 1928, issue.) One of the difficulties of the individual who has not learned a little very elementary calculus, and who wishes to be able to design beams, etc., from thin metal, lies in not being able to compute rapidly the constants of corrugated sections. For ordinary box or girder sections of timber there is no difficulty ; the draughtsman can remember the necessary formulae, or easily turn them up in almost any handbook bearing on engineering, but formula? for corrugated shapes are not as yet published in the usual handbooks, and it is fitting that we should discuss some of these. In the first instance, then, we will take a simple case and establish a formula for the moment of inertia of a circular arc or. more correctly, circular annulus, which is usually referred to as an arc, about any axis, which in this instance is t3'pified by the line SS as shown in Fig. 1. y FIG. 1. 0 s r \ ^ i s Let AB (Fig. 1) then be such a circular annulus of thickness ( which is small compared with r, the radius of the arc. The centre of the arc is taken as origin of co-ordinates, and the radii OA and OB drawn from the origin through A and B make angles a and |3 respectively with oy the axis of y. Any radius typified by OP makes an angle 6 with oy. The length of an element is rd%, its width t, and its distance from the axis SS is l+r cos 6, consequently its moment of inertia about SS is rt (I + r cos 6)2 <Z6, and we have for the whole annulus 338a
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