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Aviation History
1933
1933 - 1110.PDF
w SUPPLEMENT ro FLIGHT NOVEMBER 30, 1933 THE AIRCRAFT ENGINEER The process can now be reversed by keeping the leading-edge slope constant, as given by Table 7 and Fig. 10, the leading-edge slope being 0.264. TABLE 7 Series j y to give ; L.E. Slope ; <j> = <J> ! 0-264 T.E. Slope 0-264) 43—63 44—64 46—65 ' Y^-015 y-^0-2 004 -y-0-3= 0-0061 -149v -°114 0 0533 T=-0-178j 0009 49 Y -*- 0-25 j 0-066 -Y-^25= 0-0129 -0-264 The law to the curve is AKm0 = 00009 -0-0453 0 [for <j> = 0-264 and t = o... (8) The final combination gives (from Table 3 and equations 7 and 8) :— K«i„ = F, [Km, (calc. by R. & M. 910) + 0-0036 4, -0-04530] (9) where F, = [1 — 4-9 <2] 016 0IA 012 010 006 A Km 006 004 002 0 CONSTANT L.E. ANGLE - -264 FIG.I0 -03 -02 -01 0 TE SLOPE If, now, one considers a reflexed section having Km, = O then Km, is zero for all values of trailing-edge angle. Again, in the case of the centreline which becomes tangential to the datum line at the trailing edge, the trailing-edge angle is always zero, while Km, is finite and still proportional to camber. Between these two cases there are an infinite number of combina tions which make it impossible to represent Km, wholly in terms of trailing-edge angle. Any such curve can only apply to one shape of aerofoil. Warner's curve, while forming an excellent guide to the moment of similar aerofoils, must be used with discretion when attempting to apply it to special cases. For the present series it is found that the approxi mation for Km,, in terms of the trailing-edge angle, takes the form: — Km0= 0-34 0 (1 - 4-9 P) (10) The obvious check on the empirical correction if equation (9) would be to apply it to a refiexed section where the trailing-edge angle is of opposite signs. Choosing at random sections Nos. N.60 and N.60.R. 08 07 06 -OS •04 C3 02 •01 0 ••01 -02 -03 • FIG.II ' > .; V0 S ',(*) t |"yoF,(x)dx- 07154 [^FjMdx- 00702 / !*• k F.(x) r y»f.(x)| / / / ! 3 •! » 16 15 B 12 a II 10 09 08 Variation of No-lift Moment with Slope of Centreline of Section N.60. Calculation of No-lift Characteristics by Trailing Edge Method of R. and M. 910 This result is obtained from either Figs. 9 or 10, but both have been included to show more clearly the relative effect of leading- and trailing-edge slopes. The plotted values in Fig. 9 show that there is very little change in Km, with the leading-edge angle. This confirms Warner's conclusion that to a first approximation the Km, is a func tion of the trailing-edge angle only. For any particular shape of centreline the trailing-edge angle is proportional to camber. It has been shown also that Km, is pro portional to camber for sections similar to those at present under •discussion. For sections, it follows, therefore, that Km« is proportional to trailing-edge angle. TABIE 8 X 0 0-0125 0025 0-05 0-075 01 0 15 0-2 0-3 0-4 0-5 0-6 0-7 0-8 0-9 0-95 10 dp dx Section h(x) 2-89 2 09 1-54 1-31 1-18 1-05 10 0-99 108 1-27 1-62 231 3-98 10-6 29-2 GT * .•. k x) 8-78 610 4-13 3-225 2-67 1-96 1-5 0-87 0-41 0 -0-41 -0-87 -1-50 -2-67 -413 3/0 0-0035 0 0071 0-0130 0-0187 0-0234 0-0299 0 0348 0-0402 00411 0-0410 0-0364 0-0308 0-0222 0-0118 0-0058 0 N.60 voh(x) 0-0101 0-0148 0-0200 0-0245 0 0276 0-0314 0-0348 0 0398 0 0443 0-0521 0 0590 0-0712 0-0883 0-1230 0-1695 + 0-270 -0-115 vaMx) 0-0308 0 0432 0-0537 0-0603 0-0625 0-0585 0 0522 0 0350 0-0168 0 -0 0149 -0 0268 -0 0333 -0 0310 -0-0240 vo 0 0-0031 0 0063 0-0116 0-0166 0-0206 0-0257 0 0292 0-0318 0 0294 0 0245 0 0166 0 0077 0-0025 -0-0005 -0 0010 0 N.60 R, vohix) 0 0090 0 0132 0-0179 0-0217 0 0243 0-027 0 0202 0 0315 0 0317 0 0312 0-0269 0 0178 0-0097 -0-0064 -0 0292 +0-251 +0-0368 90/2M 0 027 0-0385 0-0480 0-0535 0-0550 0-0503 0-0437 0-0277 0-0120 0 -0-0068 —0-0067 -0-00375 +0-0016 + 0-0041 1198 /
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