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Aviation History
1918
1918 - 1234.PDF
OCTOBER 31, 1918. out undue heat. We are not in a position at the moment to giveany comparative figures of tests, but we should say that, from the standpoint of tensile strength, silver-soldering ishigher than soft-soldering, and very near to that of brazing. The heat necessary to perform the operation is lower thanfor brazing, and is not likely to weaken any members if reasonable care is used. It is, however, a longer process,and the material used is very costly. WeldingWe may well ask ourselves, in these days, where we should be without some form of autogenous welding. The thousandand one "articles that are built up ot sheet metal welded together speak for themselves, and make us wonder how weever got on without this useful engineering process. Still, welding has its limits of usefulness, and if exceededdanger may be near. In the early days of aeronautical engineering welding wasoften used in places and on parts where to-day it is " taboo," and such a method as welding tube to tube has dropped to agreat extent out of favour, having been superseded by the more costly, but better and safer engineering practice ofjointing by means of machined or built-up tubular sockets, previously referred to. Welding—by whatever means it is done—is always opento a certain amount of doubt, and chough there are innumer- able cases where this doubt as to the strength of a joint iswell covered for, yet, owing to the hidden nature of the defects of welding, and the possibility of burning and oxidisation,present-day designers avoid it in any important member of an aircraft structure. A most important rule introduced during recent yearshas been the suitable annealing of welded joints, and this rule should be adhered to whenever possible. Many will havenoticed the brittleness of a welded joint before annealing or normalising, and the malleability of the same after-wards. On this point the writers have discovered within the lastfew months a rather strange fact. We had occasion recently to make up some small lugs from which it will be seen that acertain amount of shortening took place as the result of the welding on of the arm. We have since noticed this shorten-ing in other tubes, some of quite considerable length, where various fittings have been welded on at" intervals,and so far we have not arrived at a satisfactory explana- tion. For the sake of any who may not have been able to carryout their own tests on welded joints, it may be helpful if we here give the results of some experiments we have made. The easiest method of welding is the butt joint, i.e., whentwo tubes are placed end to end and joined together to form one length or mitred together to form one piece. In such acase the surfaces to be welded are readily accessible, and the flame has freedom for doing its work. A more difficult type of welding is that necessary when onetube has to be mitred to the outside of another tube, as when forming a " T " lug. In this case ths easily-melted end ofthe one tube has to be united to the outside surface of the other, and anyone who has had experience with weldingwill know how much more difficult it is to attack the hard outside skin of a tube or sheet than it is the edge. In order to prove this point we carried out tests on tubesmeasuring r in. outside diameter by 20-gauge and 1 in. outside diameter by 16-gauge—some being butt-welded and othershaving an interposed tube of about the same diameter, to which the end of each tube was welded. Comparative tests were made on a cantilever tube joinedto the main member by welding, and a similar type of load- ing was also tested for a lug, with the tube fixed in place bywelding. The following were the results : Welded direct to tube,335 lbs. ; welded into socket, 365 lbs. Welding is often harshly criticised as regards its abilityto withstand vibration, but even in this respect we have mWt*£a£fr found striking instances where the tube has broken beforethe joint. Some time ago we tried an intermittent shock and vibratorytest on a machine which gave a series of vibrations to the tube, the blows due to the "peg-cam" being 1,400 perminute. In some cases the tube broke off without the welded joint suffering in any appreciable manner. As regards welding of any description to be done on tubing,we do not advocate the use of tubing made from steel too high in carbon. A low carbon steel gives the better result, and itis also most essential that the phosphorous content of both tube and welding wire shall be low. Wherever possible, we would suggest that the welding onof hinges and sockets to- a main spar or post be avoided. To slot a tube or soften it by welding is unwise, and in placeof any fixtures that at present demand such operations we recommend a sweated and pegged fitting. In support of this some experiments were carried out byour company, in order to convince some of our friends of the advisability of following the course we have suggested. Inone case a wiring lug is fixed on a main spar by welding, and in the other by sweating and pegging. Alternatingtests on these tubes gave the following results : Welded, 5,190 revs. ; soldered, 8,800 revs. Tubular Construction Work. A few illustrations of tubular constructional work withwhich we have had to deal during the last few years will probably be of interest. We produced, prior to the war, a streamline and taperedstrut (seamless). This idea is now being carried further, and we quite expect that these will soon be generally adoptedin lieu of wood. A large trussed girder was designed by us for use in experi-mental airship planes. This girder weighed (complete, as shown) 4J lbs., and a load of 5 cwt. at the centre of the 8 ft.span produced a deflection of only £ in. A similar girder, weighing 5 J lbs. with a depth of 7J ins., buckled and collapsedat a total load in the centre of the beam of 10 cwt., equal to one ton distributed evenly. The distance between supportswas 8 ft. 6 ins. Rust Prevention One further point remains to be mentioned. It is wellknown that a long life for any modern aeroplane is not ex- pected. The present necessary wastage in aircraft is suchthat the question of internal rust and corrosion of the steel work is not of serious moment. The time is coming, how-ever, when such matters will have to be se.iiously considered. For any post-war machines-—especially if designed for generalpassenger traffic—the question of the length of life of all parts will be one of primary importance. Many experimentshave been carried out in this country with this end in view, but nothing definite has been reached. We have experimented with two or three methods of pre-serving from rust and corrosion, with fairly satisfactory results, and in the case of airship frame-work, subject as itis to salt-water influence, we have used with fair success the " cosletising " process. For soldered works, such as rudder and fip frames,we have instituted at our works a thorough system of washing and brushing in hot soda water to remove all traces of thefluxite or the flux, and we think this is most essential. In conclusion, we would say that " the last word " intubes and tubular structures has not by any means yet been spoken. With the increase in the size of machines, theconstant and ever-increasing shortage of seasoned timber, the extended use of machines in future years in hot climates,with all the climatic effects on timber, the " all-steel " machine will undoubtedly soon become a reality and a necessity, andconsequently the subject of tubes and tubular construction assumes increasing importance. We all have much to learnon this subject, and we trust that this paper will prove of mutual benefit, and help forward in some way the science ofaeronautics and the good of the community at large. A Chance for Boys at the R.A.E.AN examination for the entry of Trade Lads (Appren- tices) in the Royal Aircraft Establishment will be held atFarnborough in December. Applications for admission to the examination must be made on the proper form beforeSaturday, November 16th. The regulations governing the entry and training of the lads and the necessary forms canbe obtained on application, either by post or personally, from the Superintendent, Royal Aircraft Establishment,South Farnborough, who will also be glad to give any information. - , American A.I.D. Methods SOME little time ago we noted the fact that orders had been issued in the United States to the effect that Govern- ment inspectors who passed machines as ready and safe for flight were to accompany the pilot on the first test flight, and we now learn that the same rule applies to mechanics engaged on the repair of machines. They will be required to take a trip aloft after they have pronounced the repair satisfactory. The plan, according to the Director of Aircraft Production, is to give inspectors and mechanics a proper appreciation of their responsibility. 1235
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