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Aviation History
1959
1959 - 2364.PDF
FLIGHT, 18 September 1959 Round the Stands . . . 255 argon metal shows a marked superiority in the vacuum-cast alloy.Incidentally, Nimocast 713C is a new investment casting alloy for high temperature service, and forms a possible alternative towrought alloys for gas turbine rotor blades. Henry Wiggin over the eighteen years since the first Nimonicalloys were introduced, have produced so many notable advances in the heat-resisting alloys that there is a danger that their latestproduct, Nimonic 105, might fail to draw the attention it deserves. It is difficult to convey by a few figures the properties of amaterial, when the three variables of life-to-rupture, temperature, and stress are involved, but Nimonic 105 when stressed at 7 tonsper sq in at 940 deg C has a life-to-rupture of 50 hr, as well as considerable resistance to corrosion at this temperature. Under the influence of missile development, and high speedaircraft where the "heat-barrier" poses its own peculiar problems, heat-resisting and stain' ss steels featured strongly with manyexhibitors. Firth-Vickers Stainless Steels were showing a new steel, FV520,which has potential uses for the skinning of high speed aircraft and missiles, since it combines heat resistance with lightness,while Firth-Derihon Stampings featured nickel-based alloys for gas turbine discs in addition to the more usual ferritic alloy steels. In the more moderate temperature range of 400 deg C—500 deg C, Titanium 679, developed by I.C.I. Metals Division, shows superior resistance to creep, while another new alloy,Titanium 230, combines the easier working of softer material with the strength of titanium alloy. Turning now to methods of shaping metals and alloys, thecastings shown by many exhibitors had a finish and dimensional accuracy that was really surprising. Noteworthy was a casting madeby Sterling Metals in a magnesium-base alloy which showed a thin section and a degree of finish that would not have been seena year ago, and which may therefore be classed as a new develop- ment. "Centrispinnings" shown by Firth-Vickers Stainless Steelsrevealed a freedom from defects which made them indistinguish- able from wrought metal. Mere size may mean nothing or be very significant, but in thecase of aluminium alloy plate it is significant to both the aircraft engineer and to the plate manufacturer; Northern Aluminiumcan now offer plate up to 50ft long and 7ft wide, though since length, width and thickness, as well as the size of ingot, are inter-related, these extraordinary dimensions may not all be realised simultaneously. Since the plate is stress-relieved by a processinvolving stretching, this means a plate stretcher capable of dealing with a cross-sectional area of plate of 200 sq in! Another shaping problem has been solved by Reynolds TJ.Aluminium. In a striking exhibit they show stepped tube of aluminium alloy; not only may the outside diameter be raised inone and the same tube, but the wall thickness may be varied also. This makes possible the threading of thickened ends, with-out wasteful machining of the rest of the tube. What is flow turning? It is a combination of spinning andextrusion whereby a circular metal blank is fabricated into a spun shape, but in which the wall thickness may be varied from theoriginal blank thickness down to very thin sections. This was shown by Wilmot Breeden on cones and Venturis, but wouldappear to have many other applications. Plastics, synthetic rubbers, and resins generally, tend tobewilder by the sheer number of types available, by their difficult chemical names, and by virtue of the fact that they may appearsuperficially to be indistinguishable one from the other. It is a help then to have a short and distinctive trade name, and one ofwhich a great deal more will be heard is "Viton," a fluoro-carbon synthetic rubber for high temperature service (approx. 250 deg Cmax.). Viton has also a resistance to a wide range of fluids. It is manufactured by the Avon India Rubber Co. and is offered ascomponent parts by George Spencer Moultoo and also by Ronald Trist, who are specialists in many varieties of high-performancerubbers. "Propathene," which as its name suggests is a member of thepolythene family, is resistant to temperatures up to 150 deg C, while showing the same chemical inertness as polythene. Thisand a new material "Kralastic" are made by I.CI. Plastics Division. In a class of its own is a new material "Astrasil" which com-prises woven silica cloth laminates bonded with a resin. This is resistant to the really high temperature of the oxy-acetylene flame,the "burn-through" time being considerably greater than a similar thickness of a stainless steel or of glass-cloth laminate, which itresembles in appearance only. British Refrasil market "Astrasil" which is of great interest to missile engineers, and others con-cerned with the "heat-barrier." The problems of fastening structures together has evidentlybeen intensively studied recently from the aspects of security, ingenuity of method, and weight-saving. Ingenious methods oflocking and weight saving were shown by C. J. Fox & SODS Precision castings by Sterling Metals. The dark-coloured impeller, cost in magnesium, has an exceptionally high finish (Aviation), who are the sole distributors in this country for theKaynar Company of America. Weight is saved by the ruthless paring away of unnecessary nut material, strength being retainedby the use of high tensile steel. The locking is affected by a slight elastic distortion of the nut. Guest, Keen & Nettiefoldsachieve locking by the well-known method of a nylon insert in the nut, or in the bolt. Both systems have the advantage of beingcapable of re-use after dismantling. Logically, it is but a step to save weight further by dispensingwith separate fasteners altogether, where this is possible. This may be achieved by spot-welding or by flux-less vacuum brazing.Sciaky Electric Welding Machines showed a light sandwich con- struction in austenitic stainless steel, assembled with manythousands of tiny spot welds, whereas Centrax achieve a similar result by vacuum brazing with an 80 per cent nickel alloy, result-ing in a flux-free assembly capable of a working temperature of 800 deg C. Centrax also had a tip-shroud ring for turbine bladeswhich allows for blade creep, the tip of the blade burring over the open ends of a very thin honeycomb brazed to the inner face ofthe shroud ring, the effectiveness of the gas seal thus being retained. Among the exhibits which defied classification under any hardand fast heading were a stainless steel, convoluted, fully flexible tube which could be bent by hand to follow the most tortuous pathin engine bays and airframes. This was shown by Accles & Pollock and its advantages over rigid pipes would be evident to thoseresponsible for mock-ups and trial installations. An interesting new method of applying "marking-out ink" wasshown by Brent Chemical Products. Ardrox 381 is an Aerosol consisting of a blue ink which is sprayed on and is removable bytrichlorethelyne. A useful adjunct for non-destructive testing was a white strippable paint, also sprayed on, which may be applied tosteel parts on which it is desired to use black 'magnetic crack detection "ink." FLIGHT CONTROL Powered Flying: Controls The tremendous develop-ment that has gone into powered flying controls in recent years has now undoubtedly slackened. Of flying control hardware it-self, little that was revolutionary was to be seen at Farnborough; in fact, each manufacturer has settled more-or-less firmly on oneline of development and is offering that in any new system. Boulton Paul continue to show their rotary valve (applied to theNA.39 flying controls), Dowty use their licence-built Moog valve in a new 4,000 lb thrust aileron control with integrated auto-stabilization, Fairey have continued work on the sliding-plate valve and Hobson again offer controls with spool-type valves. Where the interest lies is in the type of system into which thepowered flying control unit—which must now be considered as the straightforward element in the system—is installed, and themanner in which provision is made for autostabilization, for the autopilot, and for a completely fail-safe system. During the first (Continued on. p. 258, after double page of aircraft pictures) In tests under identical conditions, British Kefrasits Astrasil (extreme right) took three times longer to burn through than did stainless steel, and many times longer than the two other materials shown
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