A Model Experiment on Hydrodynamic Characteristics of Biplane-type Otter Board.

A biplane-type otter board is composed of a pair of ordinary cambered otter boards with the same size and shape. To investigate and compare the hydrodynamic characteristics of a biplane and ordinary types, a series of experiments was carried out using 1:10 scale models in a circulating water tank, each having 260.4cm2 in area, with the camber of 15% of chord and aspect ratio of 3.0.The lift and drag forces, and moment were measured with a three component balance at attack angles ranging from 0° to 70°. The maximum lift coefficient was 1.68 at the gap-chord ratio of 0.91 and attack angle of 20°. The effect of stagger angle on the maximum lift coefficient was extremely small. The maximum lift coefficient of a biplane type was nearly the same as that of ordinary cambered type. Also, the range of the attack angle for the biplane type was wider within the higher level of lift coefficient than that of an ordinary type. This suggests that the former is hydrodynamically more efficient than the latter.