Low-speed wind-tunnel tests on two thin cranked wings with 60-deg sweepback inboard

Abstract

Low-speed wind-tunnel tests have been made on two thin wings of aspect ratio 3 with 60-deg leading-edge sweep at the root. Both wings show large forward movements of the aerodynamic centre at moderate lift coefficient (CL = 0.5 to 0.7). This forward movement can be delayed to CL = 1.0 by full-span Kruger-type leading-edge flaps. The normal type of split flap with hinge-line parallel to the wing trailing edge gave a decrease in usable CL and better results were obtained with flaps with their hinge-line skewed to the wing trailing edge at a smaller angle of sweepback. With skewed split flaps and full-span nose flaps CL = 1.2 at α = 17½ deg was reached on both wings with only small movements of the aerodynamic centre. Abrupt changes in lv and nv with change of incidence occurred in the region of flow breakdown on the wing without flaps. These abrupt changes were postponed to CL > 1 by nose flaps and skewed trailing-edge flaps. Ailerons with unswept hinge-line produced greater rolling moments than ailerons with swept hinge-lines or all-moving tip ailerons. The Reynolds number of the tests was about 2.3 × 10power6 and the Mach number 0.18. Some favourable scale effects would be expected at higher R, but the general nature of the breakdown of flow will probably be similar on a full-scale aeroplane.