Boundary-layer control for high lift by suction at the leading edge of a 40 deg swept-back wing

Abstract

Wind-tunnel tests have been made on a 40 deg swept-back wing, 10 per cent thick with constant chord and an aspect ratio of 4.6. Boundary-layer control was applied along the whole leading edge, and a comparison was made between the effects of distributed suction and suction through a slot. A 45 per cent Fowler flap was used in some tests. The overall effect of the two systems was similar, giving an increase in CL max by increasing the stalling incidence and making the wing statically stable up to the stall, when there was a severe loss of lift. At R = 1.29 x 10power6, a gain in CLmax of O.5 was obtained when CQ = 0.0023 with distributed suction over the first 2.5 per cent chord, while a CQ of 0.0074 was needed to obtain the same increment with a slot (0.18 per cent chord wide at 2.5 per cent chord). A maximum value of CL max of 1.95 was obtained by both methods with flaps down at α = 25 deg. For full-scale application, the suction required for distributed suction (8.2 lb/sq in.) is much higher than for the slot, but it may be possible to reduce this by grading the porosity in a chordwise direction or by dividing the leading edge into a number of separate spanwise compartments. With the slot, the quantity required is higher but the overall power is about the same. A reduction in power may be possible in this case, by improving the shape of the slot. As a means of producing high maximum lift on swept wings, both these methods have the disadvantage of requiring variable-incidence wings, if the full gain in CL max is to be used.: Either method can be used as a means of preventing tip stalling as an alternative to nose flaps or leading-edge slots.