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Aviation History
1932
1932 - 1256.PDF
FLIGHT, DECEMBER 8, 1932 may, however, be increased to 3,300 lb. Fitted with a Kinner engine of 170/200 h.p., the machine has a top speed of 118 m.p.h. and a cruising speed- of about 100 m.p.h. In general outline design the BB.l is a typical Savoia flying boat, with flat-sided hull and straight-line vee bottom of the ;ingle-step type. The engine is housed in a streamline nacelle in the top plane and drives a tractor airscrew. The undercarriage can be raised clear of the water when the machine is used as a flying boat, but is not buried inside the hull or wings. A tail wheel is used instead of a skid, and as it moves with the air rudder it serves as a water rudder for taxy- ing on the water. The hull of the BB.l is built entirely of stainless steel, and consists of an internal skeleton of frames and light longitudinal stringers of U-section, to which the stainless-steel sheet planking is attached by shot-welding. The fact that the hull is of the straight-line type, i.e., with flat sides and a straight-vee as distinct from curved-vee bottom, facilitated manufac ture very greatly, as the sides could be welded up "in the flat " on the bench, and later attached to the frames and stringers as complete units. Similarly with the two halves of the vee bottom. These were first welded to gether as flat sheets on the bench, and afterwards welded to keel and chines. The whole manufacture of the hull must have been very rapid, but whether or not the Budd shot-welding process would be as readily applicable to the construction of a typical British hull with curved lines is, perhaps, open to doubt. Water-tightness is achieved by running solder into the gaps between welds. The biplane wings are of perfectly orthodox type, with two main spars, Frise ailerons, and the usual interplane struts and streamline wire bracing. Formed as a Warren girder, each spar is composed of top and bottom flanges of U-section, to which the short ties are joined by shot-welding. The material is, like that used in the hull, stainless steel. It is likely that a wing spar built up in the form of a Warren girder is slightly less efficient than the corrugated box spars habitually used by British constructors, at least for a machine as small as THE HULL OF THE BB.l : Sides and bottom were assembled as units and then welded to the frames and stringers. The latter are of U-section. Watertight joints were obtained by running solder into the gaps between welds. the BB.l, but the difference in weight cannot amount to many pounds, and the facility with which such a spar can be manufactured should be worth a slight sacrifice in structure weight. The wing ribs are also of stainless steel, and are assembled on the bench by shot-welding, being " slid " into place on the spars afterwards. The leading edge is covered with thin stainless sheet, up to the front spar. Wing-tip floats of usual type are used, and are bolted direct to the lower wing spars by four bolts each. Struc turally they are of similar construction to the main hull. The internal stringers of the hull, by the way, are U- section stainless strips similar to those used in the wing spars in order to reduce to a minimum the number of different sections used. In this way, and as a result of the rapidity of shot-welding, the higher cost of stainless steel is somewhat offset, in addition to the other advan tages regarded purely as a welding process. When, shortly, the BB.l comes to this country, it will be taken on a tour by Mr. Rex Stocken, when doubtless a large number of FLIGHT readers will take the oppor tunity to examine this very interesting piece of aeronauti cal engineering. 5S S5 Ss5 S 513 STAINLESS STEEL TUBES FOR AIRCRAFT Accles and Pollock, Ltd. Solve Some Difficult Problems THAT the all-stainless metal aeroplane and seaplane have " arrived," and arrived to stay, admits of no doubt ; and since British aircraft, at any rate, have latterly been based to a greater or less ex tent (chiefly according to size) upon a tubular construc tion, the history, production and characteristics of the stainless-steel tube are matters which interest and deeply concern aircraft manufacturers. The production of stainless-steel castings, forgings, strip, etc., were at one time considered difficult, but the produc tion of stainless-steel tubes has been a great deal more difficult. In fact, it is quite safe to say that, if Accles & Pollock, Ltd., had not interested themselves and under taken the production of stainless-steel tubes for aircraft, no such tubes might have been available to the aircraft industry for a long time. In the first place, the piercing and rolling of the stain less-steel billets present technical difficulties owing to the narrow range of temperature and the strength of stainless steels at high temperatures at which these operations can be performed without introducing forging faults. Even to-day, such faults are not uncommon in the blooms as they reach the actual tube manufacturers. Rigid inspec tion and a careful cleaning up of all visible faults at every stage are therefore absolutely necessary. In the next stage—the making of light and high-tensile aircraft tubes—the tube manufacturer finds that his ordi nary methods of drawing, lubricating and heat-treating must be revised. In short, the production of stainless- steel aircraft tubes requires a new and more skilful tech nique all along the line, and it is not altogether surpris ing to find practically only one tube manufacturer in this country producing these aircraft tubes. The following data, compiled by Accles & Pollock, Ltd., from their own experience, should be of great value to designers of aircraft: — As is well known, the general term " stainless steel," comprises two very different classes of steel—the austenitic, with a high nickel content, and the martensitic, with either a low nickel content or no nickel at all. Austenitic stainless steel can be cold-worked up to a very high tensile strength, but it is not so corrosion-proof in the hard worked conditions as when softened and de scaled, or polished. On the other hand, the tensile limit of proportionality is so low in the fully softened condition as to render it of no value to the aircraft constructor except for exhaust pipes and pipe lines, in this state. Austenitic stainless steel is comparatively easy to weld, and as it is also easy to manipulate in the softened condi tion, it is almost ideal for exhaust systems, but only since 1170
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