Series of photos showing the 'wake vortex', an air whirlpool which occurs at an aircraft's wingtip. An Ayres Thrush agricultural plane is shown flying at low level past a column of coloured smoke which shows up the normally invisible vortex. These tests, undertaken by NASA at the Wallops Flight Facility, are part of a study of chemical drift in agricultural crop dusting. Wasteful drift of chemicals beyond the target area is not only expensive but may also damage the environment. One important result of the studies was the discovery that the use of winglets, vertical extensions of the wing at either tip, cuts down the chemical drift caused by the wake vortices.