Experimental investigation of apex fence flaps on delta wings

An exploratory wind tunnel investigation, involving pressure surveys and flow visualization, was performed to observe the flowfield effects produced by vertically deployed "apex fences" on a highly swept delta wing. The fence-generated vortices were intended to alter the upper-surface vortex patterns and associated induced pressures in such a way as to improve the lift and pitching moment characteristics of the planar delta. It was determined that relatively small apex fences, when symmetrically deployed, enhance the average suction level on the wing upper surface, which may amount to a 10% increase in the average pressure coefficient for angles of attack of 0-20 deg. Indications are that even higher suction levels may occur over the wing apex region between the fences, producing a nose-up pitching moment for longitudinal trimming (i.e., when trailing-edge flaps are used for lift increment).