WIND TUNNEL TESTS OF A SLOTTED FLAPPED WING SECTION FOR VARIABLE GEOMETRY SAILPLANES

Abstract

A variable geometry sailplane uses a large full span retractable flap to extend the operating flight speed range from slow flight needed for climb to high speed flight for cruise. The slotted flap wing section has advantages over the earlier chord extending type flap in that it is simpler mechanically and is better able to accommodate strong aileron control. A new slotted flap wing section designed at the University of Alberta has been tested in the low speed wind tunnel. It shows lift characteristics that will be suitable for a variable geometry sailplane, with particularly docile stall characteristics for safe handling. The extent of laminar flow on this wing section was stabilized by the use of laminar separation bubbles as a mechanism for transition. It was found experimentally that additional drag caused by these laminar separations could be reduced by the introduction of boundary layer trips just ahead of the laminar bubbles. These were effective in reducing the drag even when they were not big enough to trip the boundary layer to cause transition. Overall performance of this wing section was comparable to the FX67-VC- I70/1.36 designed by Professor Wortmann for the Sigma project.