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Aviation History
1918
1918 - 0944.PDF
AUGUST 22, 1918. the majority of the more important members are stressedas beams. The wing spars are subjected to bending moments, and are generally regarded as continuous beams with thenumber of supports according to the number of interplane struts, while the fuselage is usually considered as a cantilever.It would therefore seem reasonable to suppose that the material which, as a beam, is stronger for the same weightper foot run can be built up into a machine which shall itself be lighter for the same strength than the orthodoxconstruction. With this object in view it is proposed to compare two wing spar sections, one of Californian spruceand one of Duralumin. Fig. 1 represents a section of typical proportions, the weight per foot run in Californian spruce,being .425 lb. Fig. 2 represents a section built up in Duralumin to the same depth limit, viz., 2 ins.; its weightper foot run is .417 lb., which is slightly less than that of the spruce section. For Fig. 1 / can be taken as 12,000, andusing a factor of safety of 10, reduces to 1,200. For Fig. 2, /can be taken as 56,000, and using a factor of safety of 6 (whichis not too small), reduces to 9,333. M for Fig. 1 comes out to 1,157, a^d for Fig. 2, 1,940. This shows a gain of 40 percent, of strength for the same weight, while the Duralumin spar is actually not quite so heavy as the spruce one. Theweight of the flanged recesses shown dotted has been taken into account, but they have not been considered when: calcu-lating the moment of inertia. The rivets have not been taken into account in either case ; this is probably more than balancedby the extra weight of fittings, &c, and portions of the spar where the spindling is not carried through, in the case of thespruce spar. This construction of Duralumin spar shown is patented. Having proved that metal is superior as far as strength forweight goes, and taking into account the advantages outlined above, it would seem that the case for the all-metal machineis well founded from the point of view of the designer, and also from that of the user. We have now to consider the(Jaestion of comparative cost of, and incidentally the speed of production. The operations required to produce thelongerons, such as planing up and spindling, would probably be just about balanced by the operations necessary for rollingthe longitudinal members of a metal fuselage, and though fuselage struts are quickly and easily made, we must alsoconsider the relatively large number of them, and their accom- panying wires, turnbuckles, shackles, &c.; against all thesewe probably have the production of a few flanged transverse members in most cases blanked out in one operation. Sometime would no doubt be gained here by the metal con- struction. In the case of the orthodox machine by far thebiggest proportion of time and labour is spent in assembling the sides of, and erecting, and trueing the fuselage itself. The fuselage of an average up-to-date machine of the scouttype can be completed in approximately 550 to 660 man hours. These may be divided up somewhat as follows :— Man hours.1. Assembling sides alone (in jig).. .. .. 60 to 80 2. Erecting sides 130 to 1603. Fitting and trueing engine bearers or plates .. 60 to 100 4. Fitting and trueing undercarriage .. .. 12 to 155. Fitting fairing, decking, &c .. * .. .. 80 to 90 6. Installation of tanks and pressure and petrolsystem .. .. .. .. .. ,. Approx.40 7. Installation of engine, guns and gun gear .. „ 808. Assembling and fitting controls and control cables 309. Installation of water pipes (if water cooled) and Radiators .. .. .. .. .. „ 4010. Painting and finishing and fitting cowling .. 20 to 25 From the above figures it may be seen that approximately50 per cent, of the total man hours are spent in erecting and trueing the fuselage itself. Considering the metal fuselage,against these 330 man hours we should have to put the time for erecting the transverse members in the longitudinalsand fitting the shell complete and riveting up. Assuming a fair output per week, this would probably amountto 100 man hours in the best cases, and not more than 200 in the worst. This, of course, is only an estimated figure,but it would seem obvious that the metal fuselage would score heavily on erection times. With regard to times forinstalling engine, petrol tank, piping, &c, it is probable that these would work out about the same for each construction.As in the metal machine there is no fabric, more time and money would be saved here by the non-existence of the dopeshop. The point might be raised that press tools, dies, &c., would prove a large item in the costs, but actually the numberof dies and punches involved would probably be less than for the average present-day machine, with its numberless smallfuselage clips and fittings, very often all of different sizes and shapes. The shell itself and similar parts could in most casesbe made in wooden dies, while the longitudinals would be rolled. Summing up the case for production, it is very difficultto compare with accuracy the relative costs of the two constructions, as all figures for an entirely new type of machinecan of necessity only be estimated, but with the saving which could be effected on fuselage erection, and the fact thatthe " trueing " of the fuselage and doping would no longer be necessary, it would seem reasonable to regard the all-metal machine favourably from a manufacturing point of view as well. AIR RAIDS ON GERMANY IN JULY. DURING the month of July no fewer than 100 raids werecarried out by the R.A.F. Independent Force, of which 96 were into Germany itself. In all 81 tons of bombs weredropped upon important military objectives during these raids. It is a significant fact that, notwithstanding thefrequent periods of bad weather, the month's work con- stitutes a record, both as regards the number of raids under-taken and the weight of bombs dropped. The previous best month was June last., when 74 raids were made into Germanterritory, and 61J tons of bombs dropped. The following is a list showing the towns raided, the precisemilitary objectives upon which the bombs were discharged, and the number of separate occasions upon which each placewas raided. This list covers only the work of the R.A.F. Independent Force, apart altogether from the immenseweight of bombs dropped by Royal Air Force airmen through- out the Western Front, and upon such'coastal objectives asOstend, Zeebrugge, Bruges, &c, or the formidable work of the French Air Service:— TimesPlace. Military objectives. raided. Baden .. .. Station .. .. .. .. 1Balan-Se^an .. Factory .. .. .. .. 1 Boulay .. .. Aerodrome .. .>' .. • • 13Brulange.. .. Station .. i. .. .. I Buhl .. .. Aerodrome .. 3Burbach .. .. Blast furnaces and works .. .. 3 Coblentz .. .. Station, sidings, factories, barracks 3Courcelles • .. Junction .. .. .. .. 1 Dieuze .. .. Aerodrome .. .. .. .. 1Falkenberg .. Station .. .. .. .. 1 Freisdorf.. .. Aerodrome .. .4 '.. .. 5 Hagenau..Hagondange HanHeidelberg KaiserslauternKarthaus LahrLumes LuxembourgMalmy .. MannheimMarville Metz-SablonsMorhange OberndorfOffenburg PforzheimRastatt .. Remilly ..Rottwell St. AvoidSaarbruck Saarburg..Sollingen.. Speyer ..Stuttgart ThionvilleTreves Vahl EbersingVergaville WargassenZweibrucken .. Station and barracks _.. Blast furnaces .. .. • .. Railway junction .. .^ . .. Station.. Station and factorites .. Railway,.enginesheds, workshops.. .. Station and sidings.. .. .. v Rail way junction.. Station, workshops, sidings .. Aerodrome .... Factories, docks, railways .. .. Aerodrome .. .. ..... Railway •• •. .. .-^ .. Aerodrome .. .". .... Powder factory and munition works .. Station, sidings, engine sheds.. Station and factories .. Station.. Junction .. Powder factory.. Aerodrome .. Factories and station .. Junction and sidings .. Wharves.. Station .. Factories and station.. Railway and sidings .. Station • .... Aerodrome .. Aerodrome.. Blast furnaces .. Factory .. . .. i I I i 2 2 2 2 I I 4 i 56 2 7 I I 4 I I 3 2 I I 2 5 2 I X I I 942
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