Figure 4.5: Flow Around Corners of a Lifting Surface
At larger aspect ratios, the low becomes more two-dimensional over a larger part of the rudder surface. The low around the corners can be avoided by walls or end-plates. A rudder which almost joints the stern of the ship at the upper side of the rudder, has a considerably increased efective aspect ratio. Then, theoretically, the effective aspect ratio is twice the geometrical aspect ratio.
A fat plate has a relative large increase of the lift coefficient with the angle of attack, so a high @CL=@® value. From the lifting surfaces theory, see [Abbott and von Doenho¤, 1958], follows: