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Aviation History
1932
1932 - 0760.PDF
SUPPLEMENT TO FLIGHT 50 JULY 29, 1932 THE AIRCRAFT ENGINEER FIG. 10. IV. R. ANDREWS Maximum lift coefficients. there are other factors which govern the lift coeffi cient developed on the wings. The position and size of the body, and the gap between aileron and wing, etc., all have their effect on maximum lift. Returning to the question of KL for the mono- ^ max plane wing, Fig. 11 gives the values of lift for the sections having the maximum camber at 0.3 of the chord plotted against Km . Generally speaking, sections having the maximum camber at 0.5 of the chord give a slightly higher maxi mum lift than when the maximum camber is at 0.3 c. 1-0 O -06 H SWB0LS + -09 A X • 12 V •l5^RATI0-t •18 •21 -01 02 03 -04 05 •06 -07 •9 •a z _i •6 •5 •4. —^ cft^-- yS^S .0^^ FIG.I2. 06 08 10 12 14. 16 » -20 -22 Maximum lift coefficients for sections having their maximum camber at 0 • 3 of the chord. There are no tests to show how KT varies with the max point along the chord at which maximum camber occurs. The general shape of the KL curves is approxi mately the same, whether the maximum camber is at 0.3 or at 0.5 of the chord. As pointed out previously the sections having maxi mum camber at 0.3 c. represent most nearly the majority of aerofoils in present use. The tests carried out on aerofoils having maximum camber at 0.5 c. are, therefore, not used for want of data connecting KL with the point of maximum camber. Fig. 12 gives the results of cross plotting the curves of Fig. 11. There curves are instructive as they show that the thicker the section the less important the camber of the section becomes, so far as maximum lift is concerned. At 20 per cent, thickness the only effect of camber is to increase the value of the profile drag. On such a section the camber does not appear to move Kj, far from no-lift, as shown by Figs. 4 and 5. It is concluded that as the thickness ratio increases above a certain amount, the camber must be decreased to obtain the most efficient section, the efficiency being measured as the ratio: — KL max KD cruising The values of maximum lift obtained from Fig. 12 are somewhat higher than those obtained on monoplanes using conventional sections. The test on sections—Gott 398, B.106 and N.60 (Reference 7)—and certain full-scale results at the writer's disposal have suggested Fig. 13 as being fairly representative of the lift coefficient obtained on a full- size monoplane. FIG.I3 20 22 Maximum lift coefficients for sections having their maximum Maximum lift coefficients. Generalised curves for mono- camber at 0-3 of the chord. planes. 710 6
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