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Aviation History
1931
1931 - 0193.PDF
February 27, 1931 Supplement to FLIGHT ENGINEERING Edited by C. M. POULSEN February 27,1931 CONTENTS PAGE The Paris Aero Show, 1930. By H. J. Pollard, Wh.Ex., A.F.R.Ae.Soc. 9 Technical Features of the Air Mail. By Frank Rartclifle, B.Sc, A.M.I.A.E., A.R.Ae.S 12 Technical Literature ... ... ... ... ... ... ... ... 14 THE PARIS AERO SHOW, 1930. By H. J. POLLARD, Wh.Ex., A.F.R.Ae.S. (Conchided from p. 4). We now pass on to discuss some of the details of con- struction of the Junkers Junior machine. The low cantilever wings are of two-spar construction, the spars having upper and lower tubular booms. Some weight economy is obtained by telescoping one tube inside another along the span, the joint between two tubes being made by the well-known Junkers method of inserting and " holding up " a rivet in a hole several feet away from the open end of the tube, the operation of ingfirtion and " holding-up " being carried out at the end of this 1^ in. (?) diameter tube. Similar methods are used for securing the vertically corrugated web, see Fig. 11. This is attached to one side of the spar only, while on the other side are placed at about 2 ft. pitch pieces of web, consisting of a double corrugation only. Providing the rivets are tightly clinched (and in examination qf bits of Junkers structure made in this country, this has^invariably been found to be the case), the only criticism relates to the stresses set up in the "ooms due to the offset shear members. Our own more symmetrical methods of spar construction do not lead us to simple methods of stress computation, the Junkers method still less so, but one would imagine that mechanical testing takes care of the safety phase of the subject. A remarkable feature of the wing construction is the termination of the rear spar in the wings at a distance of from 65 to 70 per cent, of the wing span measured from the root. The aileron is continued nearly to the wing tip attached to the trailing edge, this member being merely a light channel on the sides of which the wing covering terminates. There can w- no question but that the coverings on these wings, besides contributing very largely to their torsional strength, also does8ll Ppryiopart, an(j an appreciable part, of the moment of resistance against direct bending. This was easily provedb Y applying a hand load to the complete port wing and then repeating the operation to the partly uncovered starboard *ujg; the difference in deflection was startling. Since the corn.gations lie across the wing, it has been assumed that their1L =ance to eompressive forces applied at right angles to them must be negligible. Actually in the case of the Junkers it would not be surprising to know that the covering supplies at least 30 per cent, of the moment of resistance of the wing, probably much more. The body was on straightforward Junkers lines, the structure consisting of transverse hoops and the skin. In all-metal construction one of the chief problems is the joining of one part to another in a light, safe and cheap way, and this usually requires special attention to accessibility of rivets. The Junkers firm have a liking for round tubes, and with great ingenuity, as we have already seen, have devised a means of using rivets working from one end of the tube. In the case of the fuselage, tubes again have largely been utilised for oval formers, the ends of one length of tube abutting to make a complete former. In this case it is impossible to operate from one end of the tube, and in con- sequence holes are made at intervals in the wall of the tube, thus enabling the satisfactory riveting of the tube to the skin. The tube is certainly weakened, but there is a minimum size for these members and undoubtedly adequate strength is retained. A simitar method of joining fittings to tubeswas observed on the ailerons of the Vickers machine exhibited at the last show at Olympia. In spite of this, and other aids towards cost-reduction on this light aeroplane, the cost is higher than one would anticipate, this being £795 for a land- plane, and £975 for the same machine on floats, the price of a 184a
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