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Aviation History
1921
1921 - 0132.PDF
Above : Slotted aerofoil 51A, 36 in. by 6 in. Below Slotted aerofoil 51B, 36 in. by 6 in. FEBRUARY 24, 1921 So far the tests described have been on one particular kind of section, and further experimental work has been carried out showing that similar results may be obtained with any type of section, both on what may be termed a " high speed " section, such as R.A.F./I5, or a " high lift " section, such as R.A.F./19. Fig. n shows the R.A.F./15 section—51A and 51B—the section with the slot closed and the underside gap filled up being with an R.A.F./15. There is a slight difference between the two, 51 A having the leading edge of the aft main aerofoil with a slight Phillips entry, whereas 5IB has the leading edge of the aft aerofoil on the chord line. The results are plotted in Fig. 12, showing a slight improvement in lift in favour of 51s. A comparison between the R.A.F./15 and this section with the slots open is also given on the curves. The maximum lift coefficient is increased from .52 to .84, an increase of 61 per cent., fe- Rftf 19 jtCTION THRDt iL0Ti.«i.l»0FOILN-«4^ R.A.F. 19 section. Above : Three slots, aerofoil No. 44F ; below, three slots, aerofoil No. 44L, both 36 in. by 6 in. E ;M\r a«CT|o« iai »o v.oi R.F.A. 19 section. Seven slots, aerofoil No.53J, 36 in. by 6 in. R.A.F. 19 section. Above (a) no slot ; below (6) one slot, aerofoil No. 44A, 36 in. by 6 in. F/C./6O. R.A.F. 19 section with seven slots ; aerofoil, No. 53 J, 36 in. by 6 in. Sec- tion shown at angle of maximum lift R.A.F. 19 section. Above : Two slots, aerofoil No. 44C ; below, two slots, aerofoil No. 44D, both 36 in. by 6 in. and the lift/drag ratio is higher with the slot open at all angles above 12°. The same general type of results were obtained with a thick section, such as R.A.F./19, a section of which is shown in Fig. 13 with and without the slot, this aerofoil being No. 44. As, however, the R.A.F./19 is a section of small lift/drag ratio, the results of the single slot have not been included in this Paper. An investigation of pressure distribution on the main and auxiliary aerofoils formed by the slot showed that the results obtained were of the same character as in an ordinary aero- foil, and that " burbling " would take place on the small auxiliary aerofoil when it was at its critical angle, just as an ordinary aerofoil would do without a slot. It is evident that this can be overcome by further slots extending throughout the plane, and a series of experiments were accordingly carried out with various sections, to determine the lift that would be obtained with a multiplicity of slots. In Figs. 14, 132
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