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Aviation History
1927
1927 - 0364.PDF
SUPPLEMENT TOFLIGHT 36 THE AIRCRAFT ENGINEER MAY 26, 1927 I.I 1.0 as O.8 t0.7 C.ft las u 0.3 O.I . aoo 1.1 1.0 0.3 0.8 %0.6 %0.5u ^0.4 0.3\ O.l\ 1 7 / T T I t iuci 11 I1 1 ill(lit Mrft 11 \j Vi V V Hi Of V 1 1 17 T- 1 1 / 7 0 * 5 ,A ^* 'o •— 6 Airfoil 11 0.7 •'O.B —i—' U i ~TTIndue 1 i 11 1 ±Jf \ -ed dr -]—~t\ 1 1 /J r/I / ' • / ^fu r l s / 7 / *—' 1' 1 -I J, T"~ y—' / i / y —^ i I ,0.3 '0.9 0.8 ? r ! 0 5 0.7 i — In 11 II 11 1 •at / / / T/ y<3»- /I _7 ,/ i i Ar 1 i' / 1/r /A 9.6 / ] fo L i L 5 X' %^ ! \ 1 — 5 —— | ' i ! ~l "^1 ' ''r- —_ s 1 1 0.6^ • |j> N • .—-^ pr j ti ' ' i V .04 .08 .IB .16 .BO .B4 .B8 .3B .36 .00 .04 .08 .12 .16 .20 .24 .28 .32 .36 .00 .04 .08 .12 .16 .20 .24 .28 .32 .36 .4$ Drag coefficient, Q, Drag coefficient, C, Drag coefficient. C» FIG. 28 FIO.30 f «•• 32 i Inc j Jj. I 7 iuced drag '• • 1 / 7j i\ I i / i /1/EL /: lU1 1 ffiv ! 1 ~3^ ] y ^ Airfoil B1 • \ a 8 ; j j ^ , i • . i i I ! yo.6 1 | i i 1 1 i . 1 ; 'i Indueed drag 1 \ ' i i I 1 / i I! i ; ; / '• \f i 7 ; /' / i / ; / ! i i 1 ' ' ' J-J I ' / ' ' ' >^"0.7 / "FTI— f~ / ___, i-O.8 I A I ' / : - 1 V 03 i ! ; / ; j j/j 1 ' / 'vsJ !/ i i i^k j I ! i i i ! 1 Induced drag / 1 i7 y; ^! : ; : i ' i V 1\ tri 1| i i _ f Airfoil 6 1 > I I | \ 0.5 \ , '••::•• y/I / ! /; j \ s s \ 1 as i _^ i 1 ] ; 0 .04 .03 .12 .16 .20 .24 .28 .32 .36 .00 .04 .08 .IB .16 .20 .24 .28 .32 .36 XX) .04 .08 .12 .16 .20 .24 .28 .32 .36 .46 Drag coefficient, Q, Drag coefficient, C, Drag coefficient, Co ri0-« FIO. 31 FIG. 33 Fig. 24. the lift coefficient less than that corresponding to the normal minimum profile drag. In the case of the thickest sections, the flow appears to break down completely. The further tests on the same aerofoils carried out in N.A.C.A. 255 include the measurements of the pressure distributions across the median section. A sketch indicating the characteristic type of the change of pressure distribution with speed is given in Fig. 26, which represents aerofoil No. 1 at an incidence of 12J at values of V Vc of 0-5 and 0-95 respectively. It will be seen that the low-pressure peak on the forward part of the upper surface is truncated at the higher speed with the result that the forward component up wind is reduced, and consequently the drag of the whole aerofoil tends to increase as the lift goes down. In other words not only is the total pressure reduced, but the type of pressure distribution is unfavourable to low drag. Some observations by means of oil and threads were made qualitatively on the type of flow. The following abstract is typical of the results obtained :— •" A change in flow begins in a fairly sudden manner in the boundary layer on the upper surface immediately behind the maximum ordinate for thin airfoils at the lower speeds, and at the trailing edge for thick airfoils at the lower speeds! At the lower speeds the change takes place at comparatively large angles, and is analogous to the well-known burble point. At the higher speeds, the change takes place at small LOWER SURFACE LEADING EDGE UPPER SURFACE 3306 Fig. 26.
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