Subsonic wind-tunnel tests were conducted to determine the aerodynamic effects of leading-edge flaps deflected upward from 60- and 75-deg sweep delta wings. Leading-edge flaps of various sizes and shapes were tested at a range of flap deflection angles. It was found that inverted flaps cause a strong vortex lift at low-tomoderate angles of attack and give large increases in CL at those angles. Examination of pitching moment data reveals that the lift increases due to inverted flap use are not necessarily accompanied by the large changes in pitching moment which are associated with trailing-edge flap deployment. With a properly shaped leading-edge flap, a negative flap deflection can give substantial increases in CL with no change in longitudinal stability.
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J. MARCHMAN (1981) studied this question.