Low-speed aerodynamics of apex fences on a tailless delta configuration

Apex fences are highly swept, upper-surface spoiler-like surfaces hinged at the leading edges of a delta wing. The fences are deployed vertically to generate a strong pair of counter-rotating vortices at low angles of attack when the main-wing vortex system is weak. The intense suction induced by the fence vortices on the wing apex area creates a nose-up moment that, in conjunction with trailing-edge flaps, will enhance the trimmed-lift capability, thus reducing landing speed. Conversely, at high angles of attack, when the basic delta wing apex is highly loaded, the fences reduce the apex lift, resulting in pitch-down acceleration for a rapid return to normal flight attitude. These hypothesized characteristics of the apex fence concept were validated through low-speed tunnel experiments on a 60-deg delta wing configuration using flow visualization techniques, upper-surface pressure surveys, and balance measurements. This paper presents selected results of the investigation indicating the quantitative benefits that can be realized by the application of apex fences to tailless delta aircraft.