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Aviation History
1937
1937 - 0254.PDF
SUPPLEMENT TO FLIGHT 94d THE AIRCRAFT ENGINEER JANUARY 28, 1937 Rolling Moment Test on Tapered Wings It was necessary to test ordinary flaps as ailerons for the purpose of comparison on the tapered wing, together with the effects of opening and sealing the cut slot as well. All my experiments appear to show the tip-stalling phenomenon on the tapered wing, even at small angles of incidence such as 3 J deg , 9 deg. and then finally at 15 deg. incidence. Various arrangements were tested and a con siderable increase of lift was found with all of them. The results have been plotted in graph No. VII. The ordinary aileron curve indicates a continuous decrease in the rolling moment from the very beginning, and at 15 deg. it starts dropping so steeply that the control is reversed at 17 deg. The ordinary slot-sealed/flap curve, a.though it shows an increase in rolling moment from 5 deg. to 16 deg. owing to the flap effect, nevertheless stalls in a similar manner, and at 17 deg. there is also a reversal of control. This curve indicates a slightly earlier stall at 14 deg. owing to the flap effect. The effect of slot opening under identical conditions is indicated by the unusual upward peak in the curve from 14 deg., delaying the stall of the wing to 20 deg. It will be seen that there is an increase of about 75 per cent, at 19 deg. incidence com pared with the slot-sealed curve with flap down, and it is double that of the ordinary curve at 24 deg. As the flap was moved to the rear, the effect increased still further, which is shown by the Nazir rear flap curve. The effect of the trail flap is most interesting ; there is even a still further increase in lift af er the stall. Full Rolling Moment Comparison of Both Ailerons on Tapered Wing Graph No. VIII shows rolling moments of both ailerons of various combinations. It will be seen that the trail flap curve shows a general increase of about 37 per cent. Rolling moment coefficients of single lift ailerons. Tip chord 0.5 of centre chord ; V = 44 ft/sec. ; R = 116,000 Rolling moments of both ailerons on tapered wing. at small angles up to 16 deg. and more than double at 20 deg. Although there is a drop in the curve, it is still doubled at 24 deg. incidence, compared with the same curve. The upward peak of the single lift aileron curve is more interesting, it indicates the rolling moment due to the lift aileron after the normal stall of the wing. The amount of rolling moment due to drag aileron is also clearly seen. There is an increase of about eight times for the Nazir curve of 22 deg. incidence compared with the single lift ordinary aileron flap. The maximum rolling moment at 16 deg. is shown by the sliding type curve which indicates a steep stall at 18 deg. The one combination curve does not show as great rolling moment as the trail flap curve. Comparison of Air Flow Round the Slotted and Nazir Flaps Fig. 6 shows airflow around two flaps, namely: the slotted flap and the Nazir flap at incidences of 12 deg. and 20 deg. Figs, (a) and (b) show both wings at an angle of 12 deg. with their respective flap deflections. Figs, (c) and (d) are at 20 deg. incidence with greater flap movements on each wing. It will be clearly seen how disturbed is the region behind the slotted flap, compared with that behind Fig. 6 (b). In the case of Fig. 6 (a), when the flap is deflected at the required angle the top profile of the wing is considerably broken, resulting in the formation, of eddies owing to an unsupported flow of air at the rear. In the case of Fig. 6 (b) (the Nazir flap) it will be seen that k>r equal wing incidence the original airflow path along the top profile of the wing is unaltered (because of the trailing portion being fixed with the whole wing) Consequently the wing is in much closer touch with the air stream than
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