Device for improving the aerodynamic coefficient of semi-trailers, trucks and container boxes with canvas sides

Device for improving the aerodynamic coefficient applicable to semi-trailers canvas, truck and containers boxes, including vertical-tension mechanisms arranged in alignment on both sides of the canvas covering the box of a truck, semi-trailer and container, characterized in that it comprises lamellar bodies (1-1') that cover and conceal the vertical-tension mechanisms (4) making up a smooth surface that follows the outer surface of the sides of the canvas (2), such lamellar bodies (1-1') being fixed to the canvas (2) through anchoring means.