Abstract: The device comprises at least one flap member (3) having a rear flap portion that runs in a plate plane, and a forward portion, as seen in the direction of motion (F). The forward portion (8) is connected to the object (2) in such manner that the flap portion (17) can be moved in the fluid transverse to the plate plane and between two positions which are on their respective sides of a neutral place (P). Furthermore, the device comprises an actuating means (8, 9) which allows a freely oscillating motion of the flap member (3; 61, 62), and a drive unit (6) for actuating the flap member (3; 61, 62) when the valve of an oscillation amplitude of the flap member (3; 61, 62) is less than a predetermined threshold value.

Abstract: The device comprises at least one flap member (3) having a rear flap portion that runs in a plate plane, and a forward portion, as seen in the direction of motion (F). The forward portion (8) is connected to the object (2) in such manner that the flap portion (17) can be moved in the fluid transverse to the plate plane and between two positions which are on their respective sides of a neutral place (P). Furthermore, the device comprises an actuating means (8, 9) which allows a freely oscillating motion of the flap member (3; 61, 62), and a drive unit (6) for actuating the flap member (3; 61, 62) when the valve of an oscillation amplitude of the flap member (3; 61, 62) is less than a predetermined threshold value.