THE INVESTIGATION OF A POSSIBILITY OF INCREASING THE LIFT-TO-DRAG RATIO OF A MANEUVERABLE AIRCRAFT AT SUBSONIC SPEEDS

摘要

Presented are the results of the experimental investigation of the possibility of increasing the subsonic lift-to-drag ratio of a maneuverable aircraft with thin wing by virtue of wing mid surface deformation. The experiments were carried out in the TsAGI T-112 wind tunnel on the two research models of a maneuverable aircraft at free stream Mach number of 0.6. Studied on the first model was the effect of the whole wing mid surface deformation. The model was tested with several variants of a thin trapezoidal wing of moderate aspect ratio (AR = 4) with the same plan form and thickness distribution: one had the flat mid surface, the shape of the two others was calculated so that at the design regime (M = 0.6, C_(L des) = 0.5 and 0.8) there were no load peaks at the wing leading edge, the shape of the fourth wing was calculated with an additional constraint on the pitching moment value. It is shown that with respect to the flat mid surface wing the lift-to-drag ratio increment due to wing deformation is △L/D ≈ 4.5... 3.0, C_L = 0.6... 1.2, M= 0.6. It is also shown that the additional constraint on the pitching moment could be fulfilled practically without decreasing the lift-to-drag ratio gain. Studied on the second model was the possibility of increasing the lift-to-drag ratio by means of deflecting the leading edge flap. The model was tested with thin trapezoidal wing of medium aspect ratio (AR = 3.2) and moderate camber and twist, equipped with several variants of a leading edge flap with constant spanwise absolute chord: two smooth flaps deflected at 20 and 40 degrees, and one with sharp bend deflected at 20 degrees. It is shown that deflection of the smooth leading edge flap results in considerable increase in the lift-to-drag ratio: △L/D ≈ 3, C_L =0.7... 1.0, M= 0.6. In comparison with the LE flap with sharp bend the smooth LE flap yields appreciably greater increments in the lift-to-drag ratio: △L/D ≈7.5, C_L = 0.5... 0.9.