Abstract: The vortex system behind an aircraft is responsible for more than half of the aircraft drag in cruise flight and sometimes more in other flight conditions. The purpose of the vortex diffuser is to intercept the wing tip vortex just aft of the wing trailing edge, diffuse the trailing vorticity and thereby achieve a reduction in drag. To do this, an airfoil-shaped device is mounted on a trailing boom situated at or near to the wing tip. The airfoil is mounted above the boom at an angle inboard of the vertical. Its height is a percentage of wing semispan as is also the mean airfoil chord.The aft-mounting feature permits greater drag reduction at high subsonic Mach number and the inboard vane cant provides significant structural relief. In addition to drag reduction by diffusing the wing tip vortex, some reduction in trailing vortex hazard is also obtained.