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Aviation History
1931
1931 - 0386.PDF
FLIGHT, APEIL 24, 1931 AN ALL-METAL TENDER FOR SEAPLANES OK a number of years the Bir-mingham Aluminium Casting Co. Ltd. have teen develop-ing a special corrosion-resist- ing aluminium alloy, to which hasbeen given the trade name " Birma- bright." This material, which isnow obtainable in all the usual forms, such as sheet, extrusions and cast-ings, has not hitherto come into general use in aircraft construction,but it is believed that in the near future its properties will be founduseful for a variety of purposes. " Birmabright " can, as alreadymentioned, be obtained in the form of castings, extrusions and sheets,and its mechanical properties, need- less to say, vary according to theform. In the case of castings the yield point lies between 5 and 7 tonsper sq. in., according to whether the bars are chill cast or sand cast. Theultimate stress lies between 9 and 15 tons per sq. in., while the elongation is 4|-5| per cent, for sand cast barsfind 14-20 per cent, for chill cast bars. The corresponding Brinell figures are 54 and 58. Extruded sections in" Birmabright " have a yield point of 10-12 tons per sq. in., an ultimate stress of 16-19 tons, and an elongationof 15-24 per cent. The Brinell hardness figure is in the neighbourhood of 60. In sheet form, the figures for " Birmabright" varyaccording to gauge, and cover the following ranges: Yield point, 7-20 tons per sq. in.; ultimate stress, 15-24 tonsper sq. in. The elongation varies between the figures 4 per cent, in light gauges and 26 per cent, in heavy gauges.The Brinell figures lie between 58 and 86. The composition of " Birmabright " has not been dis-closed, but considerable corrosion-resisting properties are claimed for it. It is not, of course, claimed that thematerial is corrosion-proof, but it is fundamentally a film- forming alloy, so that when the surface is scratched ittends to " heal up." The usual anti-corrosion treatments can be applied to it, such as the anodic treatment. Some time ago the Birmingham Aluminium Casting Co.produced a general utility launch built entirely of " Birmabright " alloy. This launch, which has now beenstandardised and is on the market, will, the makers believe, prove very serviceable as a tender for seaplanes, moreespecially for use in tropical climates where wooden con- struction may cause trouble owing to warping, shrinkageand consequent leaking, etc. As the launch has a speed of about 20 m.p.h. when fitted with the Morris 18/50 h.p." Commodore " engine, it should be fast enough to be able to get to the aid of a seaplane quickly, while the seating .MANCEUVRABILITY : " Miss Birmabright " turns in not much more thanher own length. The engine is a Morris " Commodore." (FLIGHT Photo.) accommodation (10, including driver) is such thatpassengers can be taken to and from a flying boat with a minimum of delay.Last week " Miss Birmabright " was giving demon- strations on the Thames between Putney and Hammer-smith, and the launch certainly appears to handle remark- ably well. Short turns can be made at high speed, thelaunch banking automatically when the rudder is put over. While going astern, the launch answers the rudder well. The " Neptune " model, of which " Miss Birmabright "is an example, is a hard-chine craft without steps. All three forms of the " Birmabright " alloy are used in theconstruction. The frames are in the form of castings, while extruded sections are used, sparingly, for various minorpurposes, and the planking is, of course, in the form of bheet. The thickness of the planking is 3 mm. In order togive the " Birmabright " alloy a really thorough test in this particular launch, no protection whatever has beenapplied to the planking, although normally the anodic treatment is used. " Miss Birmabright " has, we areinformed, been in commission for some 6 months, and certainly there were no signs anywhere of serious corrosion,so that when anodically treated the material should stand up well even in continuous service in sea water, so longas the anodic treatment film is not scratched, during beach ing operations, for example. The launch has a length of 22 ft., a beam of 6 ft., adepth of 3 ft., and a draught of 1 ft. 9 in. With complete equipment the price of the launch is £650.For further particulars application should be made to Birmal Boats, Birmid Works, Smethwick, near Bir-mingham. CRUISING : " Miss Birmabright " running very comfortably at some 15 m.p.h. The hull is of the hard-chine, non-stepped type, constructed throughout of " Birmabright " corrosion- resisting aluminium alloy. (FLIGHT Photo.) 362 v ""•;;•;
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