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Aviation History
1920
1920 - 0481.PDF
APRIL 29, 1920 upper surface is reduced in going from the centre to the tips.The spar room is increased 25 per cent., and the general performance of the section is improved by this addition,making this one of the few changes that are both structurally and aerodynamically beneficial. Adding a convex lower surface of this type gives thefollowing results :— Lift.—The maximum Lc is reduced 3 to 6 per cent. Thelift is reduced at all angles, but at 0° and 40 is quite high, 7 I I' If 1 7 ' .3 <U' Plot IS — I AI 1 CENTER OF PRESSURE T/fAVEL 50 --- 0' 4' 6' 8' 10" Um W 16' IS' 20'A*iyle o f chord to tn/ind giving a decided hump to the curve at this point. Thischaracteristic was noticed when a convex lower surface was added to the Durand 13. Section No. 50 gave an unstableburble point at 30 m.p.h., but at 40 m.p.h. gave a very flat maximum with the same value of Lc. (Plots 11 and 12.) Drag.—The drag is lowered at all angles except near theburble point, and the position of the minimum is moved to more negative angles. The minimum is lowered about 20 percent., and has a flatter curvature (Plots 11 and 12). & L/D.—The maximum L/D is reduced 1 or 2 per cent., Ptof/g. -2 2' -f* 6'. 0' 10' a' H' AS' /8' 20'Angle of chord to wrnd. few thin sections. Section No. 50 gives the higher maximum lift and the greater room for spars, but No. 53 gives the higher efficiency. •50 FIGURE 16 but the L/D at one-quarter maximum Lc is increased 10 per cent., and that at one-ninth maximum Lc 35 per cent. (Plots 13 and 14). Centre of pressure travel.—The centre of pressure travel for No. 50 is plotted in Plot 15, and shows no difference from the travel on thin sections. The Effect of Varying the Mean Thickness in a Series of Wings with Constant Tip and Centre Sections H The object of this series was the determination of the effects due to thinning the wing more or iess rapidly from the centre to the tips. Front profiles of these sections (Nos. 46, 51, 52) are shown on Fig. 17. • -, •, MAXIMUM SECTION A/0RML TO CHORD Full Size ChorJ'3' . . :^>^; Both of these sections are excellent from every point of view. They allow room for ample spars (10-in. depth on a «;-ft chord have a high maximum Lc, a maximum L/D . ... , - , ., only slightly lower than the average for thin wings, yet lift does not decrease as rapidly as the thickness for the have an L/D at low values of Lc that is only exceeded by a lift is approaching the limiting value of a fiat plate. (Plot 18.) The following facts are evident from this test:—Lift.—The lift is everywhere decreased as the section is thinned, and all the sections show a flat burble point. The have an L/ at lo values 48I
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