Abstract: In a wing with a main wing part (1) and a drag-reducing wing grid arranged at a distal end of the main wing part, a grid includes at least two winglets (2) staggered in parallel and with an overlap (c/t) smaller than one. A zero air flow direction of the winglets (2) is, on average, matched to the zero air flow direction of the main wing part (1) and the ratio of the length of the chord (cM) of the main wing part (1) to the chord length (cW) of the wing grid is essentially the same as the correction factor Kappa according to Betz applicable for the overlap of the winglets. For this wing, the lift of the main wing part (1) and the wing grid is not only equal in the design point, but also the lift gradients of the main wing part (1) and of the wing grid are coincident. This means that the drag-reducing effect of the wing grid is maintained independent of the momentary angle of attack of the wing, without the wing grid having to be adjusted accordingly.

Abstract: In a wing with a main wing part (1) and a drag-reducing wing grid arranged at the distal end of the main wing part, the grid comprises at least two winglets (2) staggered in parallel and with an overlap (c/t) smaller than one, the zero air flow direction of the winglets (2) is on average matched to the zero air flow direction of the main wing part (1) and the ratio of the length of the chord (cM) of the main wing part (1) to the chord length (cW) of the wing grid is essentially the same as the correction factor Kappa according to Betz applicable for the overlap of the winglets. For this wing, the lift of the main wing part (1) and the wing grid is not only equal in the design point, but also the lift gradients of the main wing part (1) and of the wing grid are coincident. This means that the drag-reducing effect of the wing grid is maintained independent of the momentary angle of attack of the wing, without the wing grid having to be adjusted accordingly.

Abstract: A surface for contact with a fluid, flowing in a flow direction (A) over the surface, is provided with grooves (1) to prevent flow separations at low, local Reynolds numbers. The grooves extend between an upstream-directed, closed groove entrance and a downstream-directed, open groove exit and are inclined to the flow direction (A), at least in the vicinity of the groove entrance.