NACA-RM-L50K06

Abstract

INTRODUCTION <br>Previous experimental investigations of the effects of horizontal-tail position on the low-speed static longitudinal stability characteristics of sweptback-wing models (references 1, 2, and 3) have shown that the stability exhibited at high lift coefficients is critically dependent on the vertical location of the horizontal tail. It has been shown that the optimum tail position from the point of view of low-speed stability takes advantage of the favorable downwash gradients below the wake center line. Reference 4 shows that for two wings of 47.7^&#176; sweepback at the leading edge and aspect ratios of 5.1 and 6.0, the longitudinal instability caused by tip stall could be alleviated by the use of leading-edge devices, but, for some combinations of leading- and trailing-edge flaps, unstable variations of the pitching moment would occur prior to. the maximum lift. <br>The present investigation was conducted, there fore, to determine the longitudinal stability characteristics of the two 47.7⁰ sweptback wings in combination with a fuselage and horizontal tail and to determine the extent to which the horizontal tail is effective in overcoming the unstable variations of the pitching moment prior to the maximum lift. The tests were made at a Reynolds number of about 6.0 x 10⁶ (Mach number of 0.14). Air-stream surveys of the flow in the region of the tail were also made.