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Aviation History
1926
1926 - 0789.PDF
OCTOBER 28, 1926 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT •3 •E5 .2 -15 UJ .1 s 1- o 1I 1 ii > * U 5 ' 25 £ •15 -1 •05 o 1 i i i ; : C ; - _: A f I \ I c ; ni l - MM ASE MM . Jw 1 V II 1 El§_ = jASE2^-5 = MM < y MM •mi 0-8^ •^ ^\ MM WE w y 11 I t 1 M Ml 1 1 1 1 1 2000 4000 6000 IMI ^~ **> -—- II 1 1 i ! I I MM —' -—" —- iiii ' ^1 ^1 **^ _,—— 111 > 1111 --^ . ^— ^—— ^* ^* ^- ^-— IMI 1 II 1 ^—' , in .. " Fig. 17. •^•^ Fig. 18 MM Mil MM ,— -—«• ^-- ' — MM MM , — ^—— . • --^ . . -^ ——- MM . 8000 10000 12000 14000 TOTAL WEIGHT MM . , ' i Mil , H IMI ^ ^ . — — — 1 II 1 - - IMI —«= i — — w l+C.FWt St V ^^ ^-—• — 1111 ^-= L—-*-^ — P ——" -. _ — IDI & 3th ^—-' . - — — KIP Mil I I I MM —— • i II i ' ^. — — — - 1—-" ^-— ——— .—^ IMI ——— _ _ — , II- _— .—^-H Mil , • — — -—•— " ——— Wmq Loaaing 8:5lbs./s(i Ft IIII 1 i M i II i 16000 18000 20000 22000 MIL - ; : III I Mi l ~_ ——• II III I ; \ l 1 1 l 1 1 1 T 1 i 1 L F«7 F-6 F-4 F-7 F-6 F-3 F--4- 24000 Span-correspond approximately to a value for —-— of loading of 8'5 lb. per square foot. The effect of varying the loading on similar wines can also be illustrated. For example, take a machine of gross weight 10,000 lb., load factor 5, — = 0-6, loading 8-5 lb. per square foot. Change to — 0-5, loading 10-2 lb. per square foot. W In the first case the weight of the wings is 15-8 per cent, of the gross weight. Multiply the gross weight by the ratio of Span2 5the -^—- figures, i.e., 10,000 x - lb. W 6 That is. 8,333. Multiply the load factor by the inverse ratio, 6i.e., 5 x - = 6. 5 The value of —f for 8,300 with load factor 6 is 0-168;w multiply this by the ratio - to express it as a fraction of the actual weight, •fi and a 0-168 X - = 0-14; hence structure weight of the new wings is 14 per cent. against 15-8 per cent, for the original wings. If the loading were to be kept constant so that there is a change of aspect ratio, the difference will be reduced. In the example considered the span was changed from, roughly, 77-5 to 71 ft., and the chord reduced from, roughly, 7-6 to just under 7 ft., whereas for constant loading the chord should be increased from 7-6 to 8-3 ft. The gap span ratio is assumed to remain constant (e.y.. about 0-11). As readers will remember from previous article?, this is the criterion of induced drag due to biplane effect. The weight of wings may be considered as due to a structure of two parts : (a) the '" span" structure, (b) the chord structure. The chord structure represents a much smaller proportion of wing weight and is less influenced by load factor and scale. The primary chord structure is merely represented by the drag struts and bracing, and the influence of changes in chord on spar loads, due to drag or drag compo- nents, as the latter is of opposite sign to the former, the influence of change of chord on the primary structure is small. The secondary chord structure is represented by the ribs and fabric—or rather, the effect on them of changes of 702c
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