Abstract
A wind-tunnel study was made of the reduction of the aerodynamic drag of tractor-trailer trucks due to turning vanes used to control flow separation. A variety of vane settings and positions were investigated on the tractor and on the trailer. It was found that substantial drag reductions were obtained by employing vanes on the lower part of the front vertical edges of the tractor. Vanes mounted elsewhere had a smaller effect on the aerodynamic drag. Vane setting, turning angle and edge radius were found to be highly important.