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Aviation History
1938
1938 - 0520.PDF
SUPPLEMENT TO FLIGHT d FEBRUARY 24, THE AIRCRAFT ENGINEER After leaving tht drying kilns the wood is impregnated with synthetic resin by being passed between rollers, as 'jhown in one ol the photographs. Stacks of these impreg- nated sheets are then passed on to the hydraulic press in which heat is administered at the same time as pressure. A total of eight of these stacks of wood can be placed in the press at the same tune, so that eight compressed blocks are " manufactured " in one operation. The period necessary is less than one hour, depending upon the thickness of the blocks being made, the wood used, and similar considera- tions. During the compression process the wood is pre- vented from expanding laterally. After leaving the press the compressed wood panels are cut up into standard size planks or boards, the ends cham- fered and glued to the similarly chamfered ends of the natural wood boards When the scarfed joints are dry these composite planks are glued into complete blocks, ready for shaping. The process of shaping the blades is similar to that used for ordinary fixed-pitch wooden blades, with the exception that for the blade roots wood-working tools cannot be used, metal-working tools being employed instead. The root of the blades are inserted into metal sleeves, a very coarse thread being cut on the blade root to corre- spond with an internal thread in the sleeve. To prevent any possibility ol " play " between the blade hub and the steel sleeve a cement is forced into the space between the two. This cement has the peculiar quality of expanding as it sets, so that any minute gaps between the steel and the wood are effectively filled. At the ends of the rleeve rubber rings are inserted, and the joint made perfectly weatherproof by spinning over the edge of the sleeve. In Germany the Schwarz Company uses mostly beech for the compressed blade roots. That is because beech is indigenous to Germany. In this country birch is more plentiful and may possibly be used. The weights and mechanical properties of these two woods are so nearly identical that the substitution of one wood for the other will have no appreciable effect on the quality of the finished article. \ •;- ; Sleeved blade blanks for a De Havilland v.p. airscrew (inthe foreground) and for a Rotol airscrew. Mention nas already been made of the weight saving upon which Dr. Watts counts, a matter of some 200 lb. per airscrew in the case of the Bristol Pegasus engine. Actual figures are not available for typically British-built wooden-bladed v.p. airscrews for British engines, but the following figures for similar airscrews built in Germany will give an indication 01 the sort of weights obtained with the Schwarz v.p. airscrews: Engin? As 10'' BMW IX RR Kestrel Sam 22 B BMW VI U B.H.P. 240 900 575 660 730 No. ot Blades. 2 2 2 3 3 Dia. tt 7.85 10.25 11.5 11.8 12.K Weightm. 45.3 102 137 166 180 Distance ot eg. iroin root it •0.7« 1.07 1.23 1.21 1.37 Weight perh.p. (ID. 0.1" 0.11a.24 o.2;>0.24; United Steets at Birmingham THE Birmingham Office oi the United Steel Companies,Ltd., has been moved from the old Martino Steel Works in Princip Street to a more accessible spot in the centre of the citv—Union Chambers, Temple Row, Birmingham (Midland 6231). Chains in AircraftM OST people know of the proverbial Tommy Rose telegram,sent home on one of the rare occasions when that famous pilot failed to break an air record—" Sorry, chain came oflbicycle." Actually, and more seriously, quite a large amount ot chainis used on a number of modern aircraft. It is all small- gauge—up to the size of cycle chain—and is used chiefly foicontrols, for operating starter magnetos, and for emergency hand operation of undercarriages. In their large and well-laid out works at Didsbury, Man-chester, the Reynolds and Coventry Chain Co. make every type of chaiu, from the smallest to large flat-link conveyorchain The type used in aircraft is assembled by very in- genious machines which have links, rollers and pins auto-matically fed to them. Inspection and testing of the finished product is an exceptionally thorough process. The links arevisually scrutinised by works inspectors and approved inspec- tors: they are tried over standard teeth, stretched, run in, re-inspected and tested for amount ol stretch. The limits allowed are an extremely small percentage of the total lengthof a chain. The firm are now building a large new stores department,tor, although their premises are already big, much room must be found for the designing, servicing and assembling of mostof the specialised machine tools ; for a pattern shop; for cut- ting of teeth and finishing of wheels; and for large numbers ofpress tools. The careful baling and disposal of scrap and swarf is charac-teristic of the systematic methods noticeable from the now overflowing material stores throughout the works to the finaldespatch. Laminated Wood in Torsion TV/TR. E. REISSNER has asked us to publish the accom- panying revised version of Fig. 7 of his article on " Improved Laminated Wood in Torsion," which appeared in the January 27, 1938, issue, as the original contained some errors. We would take this opportunity to point out, what most readers who studied the article will already have under- stood, that in the formulae (1) to (8a) cases occurred of the factors x and y being erroneously printed as suffixes to instead of as factors. ]—C — / c __2. f-Qf-" * Breaking and accom panying sheer stress:
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