A device to alter and/or reduce the aerodynamic, base drag on and improve the stability of a bluff bodied vehicle, such as a heavy trailer with or without two aft vertically hinged doors, comprised of preformed, resilient, semi-circular airfoils permanently attached with hinges to the aft planar surface or the rear doors of the vehicle, at the vertical left and right corner edges, the horizontal top corner edge, the horizontal bottom corner edge of the vehicle, or at two or more of these positions. The airfoils self stow when the doors are opened and resume their initial shape when the doors are closed. If accidentally impacted, the airfoils deflect and then resume their initial shape. The airfoils can be fitted with compact air nozzles to blow air tangentially over their outer surfaces to enhance their effect. The device is inexpensive, lightweight and easily installed, replaced and retrofitted.